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WHOI-73-28
LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY
AND PALEOLIMNOLOGY OF THE RIFT VALLEY
LAKES OF CENTRAL AFRICA
By
Robert E. Hecky and Egon T. Degens
WOODS HOLE OCEANOGRAPHIC INSTITUTION
Woods Hole, Massachusetts 02543
May 1973
TECHNICAL REPORT
Prepared for the National Science Foundation
under Grants GA-30641 and GA-35334.
Reproduction in whole or in part is permitted
for any purpose of the United States Govern
ment. In citing this manuscript in a biblio
graphy., the reference should be followed by the
phrase: UNPUBLISHED M4JVUSCRIPT.
Approved for Distribution
iohn M. Hunt, Chairman
Department of Chemistry
Late Pleistocene
Chemical
of the
Stratigraphy
Rift
Valley
-
Holocene
and Paleolimnology
Lakes of Central
Africa
Robert E. Hecky1
and
Egon T. Degens2
Woods Hole Oceanographic
Woods Hole,
Institution
Massachusetts
02543
3-Present address:
Fisheries
Research Board of Canada,
Freshwater Institute,
WINNIPEG 19, Manitoba
2Present address:
Institut
Geologisch-Pal&ontologisches
der Universitt
Hamburg, 2 HAMBURG 13, Von-Melle-Park
11.
TABLE OF CONTENTS
Page No,
2
ABSTRACT
INTRODUCTION
6
MODERN LAKES
WATER CHEMISTRY
7
LIMNOLOGY
8
Kivu
8
Tccnganyika
11
Edz1ard
13
Albert
14
Malci
15
16
GROSS STRATIGRAPHY AND CHRONOLOGY
Kivu
16
Tanganyika
21
Ediard
22
Albert
23
Malcai
24
24
LAKE KIVU SEDIMENTS
DEEP, NORTHERN BASIN
>400 m water
depth
24
Chemical Stratigraphy
24
Bios tratigraphy
40
Silicious microfossils
40
Organic matter
51
SHALLOW SOUTHERN BASINS
<100 m water depth
South Idjwi Basin Station
Bukavu Basin Station
25’
23’
56
56
58
LAKE LEVEL OSCILLATIONS AND WATER BUET
Kivu
62
Tanganyika
66
Edward
80
Albert
82
Malc&i
85
62
CONCLUSIONS
87
REFERENCES
88
-2-
ABSTRACT
The interaction
Late Pleistocene
tological
of climate
and Holocene
and limnological
and geology in Central
is examined.
Africa during
The study is based on sedimen-
work on the main lakes of the Western Branch
of the East African Rift Valley,
particularly
Lake Kivu,
Changes in
sediment chemistry, mineralogy and diatom assemblage provide a detailed
histogram of lake level oscillations...
drop in lake level
Kivu,
Fluctuations
Calculations
indicate that the
could be as high as 600 m for Tanganyika and 400 m for
in water levels.are
the means for reconstruction
climatic events in tropical Africa of the last 15,000 years.
climatic
pluvial
Bdlling,
comparison between tropical
times coincide with the prominent
AllerØd,
in equatorial
that
in Europe,
e0g0
cool and dry periods
Africa with ice ages in the Northern Hemisphere.
accompanied by corresponding
This may suggest
activities.
Paleo-
zones reveals
interstadials
Climatic Optimum, and reversely,
The African climatic
cence0
and temperate
of
sequence .of pluvials
periods
and interpluvials
of hydrothermal
that rain water exercises
activity
control
is
and quies
on hydrothermal.
-3-
INTRODUCTION
Eastern Africa
focus of intense
tectonic
dramatic topography,
in large rifted
crustal
and volcanic
Broad regional
troughs
blocks
since Miocerie times
Bishop,
activity
uplift
can be traced across the African
Cloos,
continent
which has produced a
of the Red Sea as a juvenile
has directed
rift
interest
system and its
rifts
relationship
Degens et al.,
elsewhere
buried
to the present
1971,
1939,
This pattern
oceanic
rift
and riftirig
Recent charac
with active
status
to the world-wide
have been accompanied by profuse
Active volcanoes
spreading
of the African
system of mid-ocean
in eastern
Africa
as
volcanism which has deeply
large areas of Precambrian basement under Tertiary,
and Recent lava and ash,
of rifting
for nearly 3,000 km from the
and future
Uplift
resulted
downward movement of
Zambesi River in the south to the Red Sea in the north.
terization
has been a
has concomitantly
formed by the relative
along normal faults
1963
are still
Pleistocene,
a prominent
feature
of the landscape.
The African
sections:
1
valleys
are generally
the Nyasa section,
or Gregory Rift
1965,
rift
and 4
These Rift
2
section,
the Western Rift,
the Lake Rudolf and Ethiopian
valleys
delimit
drainage basins,
lakes the size of which is partially
over the respective
grouped into four separate
areas.
the Eastern
section
Fig.
regime
a large area of the Nyasa
Kivu, Edward, and Albert
along the arcuate Western Rift valley
Holmes,
and they contain
dependent on the climatic
Lake Malawi occupies
while Lakes Tanganyika,
3
1.
are strung
out
Lakes Edward and Albert
have recently
been renamed as Lake Idi Amiri Dada and Lake Mobutu Sese Seko
respectively,
but they will be referred
to in this
paper by their
former
-.4-
names to facilitate
valleys
referring
have comparatively
are presently
tributary
regions
high rainfall
of external
Lake Malawi.
of internal
the Zafre
literature.
over their
drainage,
to three of the largest .rivers
Edward and Albert,
drainage
shrinking
between .the Eastern
lake,
and Western Rift
duct of the same large-scale
Lakes
and the Zambesi
Rift are large basins
but it has been grad
Livingstone
Victoria,
are
lakes dot the vast area.
is an exception,
last 5,000 years
The other large East African
the Nile
Lakes Kivu and Tanganyika,
Rift
and they
The lakes of these rifts
in the world,
where only small saline
for the
These two rift
catchment,
The arid Eastern Rift and Ethiopian
Lake Rudolf in the Ethiopian
ually
to the earlier
and Kendall,
occupies a gentle
valleys,
and likewise,
1968.
downwarp
it is a pro
earth movements which led to the formation
of the rifts,
The antiquity
their.geology
present
the interaction
ficant
of these rift
earth historians
of climate
to be found.
growing explosively;
poorly understood.
their
tropical
a unique.opportunity
and geology on the continents
portion of geological
longer records
basins,
time.
however, the correlative
controversy
the evidence for numerous Pleistocene
glacial
cycles
differences
a continuous
holes and seismic
presence
records
record from the continents
for maximum climatic
in the Albert
of over 1.2 km of sediments
record is
over the correlation
record so far examined has preserved.
is preferred
a signi
of the oceans is
continental
continental
setting
to examine
through
which the
To reconcile
is required
information,
Basin have demonstrated
Bishop,
between
found in the oceanic
record and the concept of only five or so major glaciations
tropical
and
Only in the oceans are substantially
Knowledge of the history
There is still
position,
such
and a
Borethe
1963; and Wong, unpublished.
-5-
Seismic profiles
tude
Table
from the other lakes show accumulations
1; Degens et al,,
stratigraphic
sections
but the aridity
Thus far,
sites
Butzer
lished.
coring techniques
12 m core recovered
and Richardson,
information
of exposed stratigraphic
Albert which covers the past
1965
unpub
of a
and descrip
see Bishop,
of a 12 m core from Lake
is also. presently
under study
This paper presents
Institution
1971 to Lake Kivu and 1972 to Lakes Kivu.
and piston
cores of varying
a 1972 expedition
of Heidelberg
cores up to 3 m in length
from each of these
to the description
Livingstone,
25,000 years
In addition
torium f1r Sedimentforschung
of gravity
1972; Richardson
in the Albert basin
have returned gravity
from 1 m to 8 m.
30,000 years
from the Woods Hole Oceanographic
in 1970 to Lake Tanganyika,
lengths
a rather
communication,
Recent expeditions
Edward and Albert
is limited
sections
in reconstructing
of the Western Rift is very
The diatom stratigraphy
Thomas Harvey, personal
the greater
record in the shallow lakes
over the past
rift
from Lake Tanganyika
1963,.. for a summary.
cores
of that
1972; Richardson
Published
record,
Rift have received
have been successful
view of the history
known,
of the modern lakes
which can be brought to these
By comparison the paleolimnology
poorly
suite
a continuous
of the sedimentary
Such efforts
et al,,
and the shallowness
Rifts,
because of the abundance of human cultural
and the accessibility
coherent
Thick
found in the Eastern and Ethiopian
of recovering
of paleohistorians
remote areas,
1973; Wongç unpublished.
the lakes of the Eastern
to the unsophisticated
tions
are also
of the climate
reduce the probability
attention
1971,
of similar magni
University
by the Labora
has recovered
a
from Lake Malawi.
the chemical stratigraphy
of representative
lakes along with the biochemical
and diatom
-6-
stratigraphy
still
of Lake Kivu.
in progress.
struction
stratigraphic
climatic
on these lakes.
logy of the present
Malawi Brooks,
depauperate
Verbeke,
various
lakes,
such as the species
1950; Fryer,
fauna in Kivu
unusual aspects
1959
is also
a miniscule
fraction
it does cover the
and shows the effects
In addition,
recon
15,000 years
lakes,
evidence will have significance
been proposed to explain
cores are
a provisional
represents
record in these
transition
the stratigraphic
data,
material
Late Glacial-Holocene
fluctuations
on the other
of these lakes for the past
Although the available
of the potential
studies
Based on the available
of the history
attempted.
Microfossil
of Pleistocene
interpretations
to theories
which have
of the biology
flocks
of
and limno-
in Tanganyika
and
and the immense methane reservoir
Degens et al,,
1973; Deuser et al,,
and
1973;
1957.
MODERN LAKES
To provide
follow,
a brief
The information
extracted
synopsis
presented
from a diverse
to the original
see
a framework for the historical
Damas, 1937; Verbeke,
for Lake Tanganyika
et al..,
in Table 1 and Table 2 and reviewed below was
literature;
Tallingff
and the interested
discussion
1963; Verbeke,
1957; for Lake Kivu
1955; Verbeke,
to
of the modern lakes is necessary.
sources for a more detailed
for Lake Albert
Kufferath,
of the limnology
reconstructions
Beauchamp, 1939; Capart,,
1971; and for Lake Ma1awi
of the various
lakes
1957; for Lake Edward:
Damas,
1957; Degens. et al.,
reader is directed
1937; Schmitz and
1973; Deuser et al,,
1952; Coulter,
Beauchamp, 1953; Eccles,
1973;
1963; Degens
1962,
WATER CHEMISTRY
The chemical
composition
Kivu, and Tanganyika
Table
magnesium values relative
that these unusual
of the area.
of lake waters
is remarkable
1
from Albert,
for the high potassium
to the other cations.
ionic
ratios
find their
The Virunga volcanic
Kilham
These rocks have K20
>
by their
Na2O, and the Ca and Mg contents
than for average crustal
material
Higazy,
These volcanic rocks are also rich
rocks
of Southwestern
ultrabasic,
and
proposes
in the volcanic
origin
between Edward and Kivu, and the Toro-Ankole field,
are characterized
1971a
which forms the drainage
field,
in the Edward basin,
Edward,
divide
Uganda
potassic
rocks.
are much higher
1954; Bell and Powell,, 1969.
in TiO2 and P2O5, and have relatively
great
abundances of Sr, Ba, Rb and Zr, which are uncommon for such ultra-
basic
rocks.
sedimentary
These facts
l97la
and Degens et al,
of these rocks by hot,
quent loss of Ca by precipitation
a straightforward
in turn,
Semliki
taries
taries
take on these
proportion
the plateaus
different
tive
to interpretations
of
composition
cf.
of salts
intense
the observed composition
arise
in
and Tanganyika will,
major tributaries,
in Edward md Kivu,
the
These tribu
of the water budget and an even
to Albert
escarpments
Malagarisi
Albert
as their
and Tanganyika.
from the Precambrian granitic
above the rift
contribution
will yield
portion
of the salts
believe that
CO2-charged ground waters with subse
characteristics
supply a considerable
deriving
1973
manner for Kivu and Edward.
and Ruzizi respectively,
greater
be important
chemistry..
Kilham
weathering
will later
and metamorphic rocks of
are more dilute
and Ruzizi
by these tributaries
Other tribu
and of a quite
in Table 1.
The rela
must be minor,
as Albert
-8-
and Tanganyika strongly
resemble Kivu and Edward in their major ion
composition,
Lake Malawi farther
the aforementioned
The volcanism,
to the south and with no connections
volcanic provinces, has a quite
unusual
petrology,
different
and hydrothermal
spring
water chemistry.
activity
so dominate the lakes in the Western Rift are less
significant
Nyasan Rift.
valley,
Hot springs
are known along the rift
with
in the
but they are
unaccompanied by active volcanism Von .Herzen and Vacquier, 1967.
lake
is much more dilute
that weathering
Rift,
in volcanic-derived
CO2,
The
suggesting perhaps
are lower because the ground waters
rates
are not enriched
than those of the Western
which
of the region
However, rainfall
is generally
higher, temperatures lower, and the lake volume smaller than Tanganyika,
and the dilution may simply reflect
composition of the waters is representative
though Talling
low,
and Talling
1965
.1973,
of fairly
The ionic
of most African waters,
do note that
According to Becky and Kilham
African lakes are indicative
times.
lower residence
the chloride
is relatively
low Cl/Na ratios
humid conditions
al
in many
in the drainage
basin,
LIMNOLOGY
Kivu
Damas
first
1937
described
Kivu which has since been studied
al,,
1973.
the unusual
in ever
increasing
Below 70 m, temperature and salinity
The density increase
produced by higher
sity decrease inherent
hydrography
salinities
with the higher temperatures
Degens et
detail
increase
just
of Lake
with depth.
offsets
resulting
the den
in a stable
-9.
thermohaline
r.’he greater
density structure,
diffusivity
to salts yields a series of convecting cells
of heat relative
Turner, 1969,
and the
increases in temperature and salinity with depth occur in a steplike
fashion.
Density differences between these cells are minute and can often
be resolved at a decimeter level
density
differential
F, Newman, unpublinthed
data,’
and the
between even surface water and water below 350 m is
not large, being on the order of .002 g/cm3 Schmitz and Kufferath,
At present,
1955.
Kivu would seem to be a delicately balanced system which has
persisted for at least the 40 years of observation,
The history of this
phenomenon over longer periods is an important consideration
present stratigraphic
of t.he
work.
MeromixiS in Kivu greatly reduces the exchange of water between
the upper 70 m of water which circulate
water of greater
depths.
The effect
at least seasonally and the anoxic
of this
lack of mixing is dramatic,
Surface waters are depLeted
as the nutrient values in Table 1 attest,
in phosphorus and nitrogen by plankton production and subsequent sinking
and decay below the thermohaloclines where regenerated nutrients are
effectively
trapped.
Silicon,
in Table 1, also increases
the other nutrient
with depth, but it gives a linear regression on Na,, indicating
well as trapping
canic
al.,
has little
and resolution
production
CO2
nutrients,
to do with the observed trends.
the deep waters also accumulate
and predominantly
biological
.origin
The loss of nutrients
the primary productivity
diatom
As
gases of vol
H2S and CE4
1973, which are held in solution .by hydrostatic pressure,
below 300 m contain two liters
that
Deuser et
waters
of gas for each liter of water,
to the deep water trap profoundly influences
of surface waters
Table
2.
Primary production
-10-
is less
than one-fourth
that of Edward and Albert,
similar
size and chemical composition,
In addition
dines,
Kivu has a seasonal
which is established
thermocline
20 m depth during the warm, rainy seasons,
ences between the epilimnion
stratification
can develop,
temperatures
tropical
as the density
Cool, dry seasons lead to full
is increased
after
is reduced by the increased
listed
in Table 2 pertain
offshore
Coulter,
by intense
in the greater
to 50 m,
plankton blooms;
the inshore waters
none of which is considered
Chaoborids
1957.
The fish
extinctions,
judging from the abundance of shells
esp. pelecypods,
in the lake,
a pelagic,
planktopha-
seem to have suffered
The planktonic
diatom flora
Various possible
unusual water chemistry,
perspective
on the limnology
recent
of species which are
for the domination by the genus Nitzschia,
is also shared by Tanganyika.
insight,
aspects which have
are absent from the lake as they are from
The molluscs,
and an historical
are often
fauna is depauperate
Tanganyika.
overturns,
The values
part of the lake.
with only 11 species,
catastrophic
of the
whereas such events are uncommon
Verbeke,
is remarkable
production
communities of the lake.
caused prior comment
no longer extant
Biological
of plankton.
The fauna and flora of Kivu have several
gous species.
a very stable
and the transparency
populations
1963,
differ
than at lower temperatures.
only to the pelagic
In Kivu as in Tanganyika
characterized
are slight,
greater
of mixing,
waters
at approx
changes at these elevated
circulation
these periods
to the deep thermohalo
Although temperature
and hypolimnion
are relatively
which are lakes of a
causes,
etc.
Hustedt,
a feature
including
1949
which
volcanism,
have been suggested,
of the lake should provide
-11-
Tanganyika
Tanganyika is divided by a shallow
500 m into two basins,
of which the southern
mum depth of 1,470 m,
It is thermally
dine
100 m.
lying at approx.
depth in both basins,
structural
sill
mean depth
is the deepest with a maxi
stratified
with a perennial
Although the thermocline
the lower limit of detectable
lies at the same
dissolved
oxygen is
200 m in the south basin of the lake and 100 m in the north,
indicating
that mixing phenomena for the basins .are somewhat different.
differences
across the seasonal
and perennial
thermoclines
thermocline
in the dry season,
to maintain
several
years.
unknown.
plete.ly
the thermal stratification
The persistence
Brooks 1950
deeper in 1895.
suggests
Beauchamp
irregularly
suggested
littoral
1939
that
cooler tributaries
introduce
waves, generated
stresses,
may account
into the epilimnion
is
the lake might mix com-.
Talling,
currents
intervals
1963
or seasonal
to .the depths.
of
have
cooling of
which would con
In offshore
of the thermocline
areas
under meteoro
for much of the mixing of hypolimnetic
Coulter,
Despite the perennial
cient to prevent any significant
constituents.
e.g.
and nocturnal
by tilting
is suffi
stood somewhat
of time when prolonged
downslope density
cooler waters
1963
over longer periods
the thermocline
Others
combined
over at least periods
believed that
over long periods
waters might yield
tinuously
waters
that
Coulter,
of stratification
of cooler climate allowed mixing.
logical
are slight,
This .minor density differential
with the enormous volumes of water to be mixed
internal
Temperature
from 2-3°C in the wet season to 0.5-1°C across the perennial
ranging
cient
thermo-
.1963,
thermocline,
mixing processes
stratification
Only those minor consitutents
are suffi
of the major chemical
subject
to biological
uptake
-12-
and release
mous store
exhibit
of nutrients
in the greater
offshore
stratification.
waters
suggesting
Alteration
is similar
an enor
populations
and others
consider
whereas the littoral
the
regions
have been done in the lake,
of the present
is even
to Kivu and the transparency
that the offshore
of the lake,
to planktonic
1963
measurements
areas are even less productive
hydrographic
greater mixing across the thermocline
ductivity
constitute
at the southern end of the lake are eutro
upweliing
No primary productivity
greater,
Coulter
to be ultra-oligotrophic,
but the diatom flora
Kivu.
which are unavailable
part of the lake.
and areas of seasonal
phic.
The deep waters
than
regime which would permit
could substantially
alter
the pro
and evidence of such might be found in the strati-
graphic record.
The Ruzizi River is the major tributary
its
chemical composition,
and most authors
The lake has been closed in historical
agree that without
the Ruzizi
ganyika would be closed and more saline
Ruzizi coincided with the blockage
drainage
The acquisition
of the formerly northward
Moore 1903
originally
ventured
work has moved the date of the Virunga event substantially
events
Brooks,
1950,
Hydrological
in the Kivu basin and the status
problem which will
find resolution
Tan-
of the
flowing
of the Virunga volcanoes
years B,P, based on the rugged appearance of the volcanoes,
Pleistocene
times,
and the Kivu drainage,
today.
in the Kivu basin by the imposition
which created Lake Kivu.
to the lake and determines
a date of 15,000
Subsequent
back into the
linkage via the Ruzizi between
of Tanganyika
in stratigraphic
is a most interesting
studies’ on the sedi
ments of the two lakes,
Biologically,
Lake Tanganyika
is exceptional
among the East
African lakes for the large number of endemic genera and species
Brooks,
-13-
Although species
1950,
the region,
especially
much more restricted.
flocks
among fish are present in other lakes of
Malawi and Victoria
at the generic
In addition
nearly all
to fish,
groups have a high degree of endemicity,
lakes.
diversification,
istry
responsible
greatly
to understanding
and temporal isolating
for the evolutionary
in lake levels
but temporal variability
are thought to have played a role.
tribute
the major faunal
which is not the case in the other
of the lake is.most
The antiquity
level they are
Stratigraphic
and water chem
studies will con
importance of geographical
the relative
mechanisms to speciation
in Tanganyika.
Edward
Lake Edward lies
to the north of the Virunga volcanic
runoff from that area via the Ruchuru River as well
receives
George to the east via the Kazinga Channel.
is nearly identical
meters,
with that
which has important
to the seasonal thermocline,
generally
waters
Below this
depth,,
However, depths greater
efficient.
great
of Kivu and probably Tanganyika.
consists
The productivity
primarily
this must be considered
anoxic,, nutrient-rich
Consequently,
and nutrient
a eutrophic
most
regenera
of Edward is four times as
The diatom flora of the
of Nitzschia fonticola
discus dconasi of secondary importance..
which
than 80 m occupy only
side of .the basin,
tion is quite
areas
In addition
there is a feeble deep thermocline
of the basin is mixed to the bottom seasonal1y
offshore
as from Lake
The lake’s water chemistry
consequences for productivity.
a very small area on the western
as that
It
of Kivu, but its mean depth is only forty
lies between 70-80 m,
are encountered.
dam.
with Stephano
In view of the productivity,
assemblage.
-14-
The fish fauna of the lake is depauperate
northern
neighbor,
Albert.
the basin indicate
Brooks,,
1950
desiccation
stratigraphic
the fauna was more diverse
and was of Nilotic
during
origin,
the Pleistocene,
been from Lake Victoria,
Albert
Fossil-rich
when compared to its
beds exposed in
in the early Pleistocene
Extinction
is attributed
Most recent faunal invasions
and recolonization
is precluded by the cataracts
to
have
by the Nile fauna in Lake
on the Semliki
River,
Albert
Lake Albert receives
a large portion of its total
Lake Edward via the Semliki River,
in proportions
Talling
to Edward, but the nutrients
and Talling,
but impoverished
These nutrient
The major constituents
1965,
in silica,
relations
flora between the lakes,
are strikingly
Albert waters
from
are similar
different
are very rich in phosphate
whereas the opposite
may account
inflows
is true in Edward,
for the differences
as sediment assemblages
in the diatom
from Albert are domi’
nated by Stephanodiscus aslraea as opposed to the Nitzschia fonticola
in Edward.
This is consistent
S. astraea is a low silica
production
efficient
nutrient
regeneration.
in Albert,
stratification
lations
of nutrients
This stratification
inshore
waters.
ephemeral
specialist
is also high in Albert,
stratification
lived
with Kilham’s
l97lab
hypothesis
among planktonic
and .again this
diatoms.
is related
that
Primary
in part
There is no well defined seasonal
but Talling
1963
reports
a peculiar
short-
of sufficient
magnitude to allow detectable
and depletion
of oxygen in the deepest waters,
evidently
is initiated
accumu
by the sinking of cooler
Contrary to the other lakes,
stratification
to
then,
Albert achieves
it does ‘have in the cool-dry season,
the
and is most
thoroughly mixed during the warm-wet seasons,
to be warmer than offshore
when inshore waters tend
waters.
Malai’i
Malawi is the least
tioned
above,
Its nutrient
nutrients
its water chemistry
chemistry
generally
is quite
is most similar
are low in the offshore
thermocline
deeper than in Tanganyika.
than Tanganyika;
273 m, substantial
areas
This in conjunction
dominant diatoms,
The depth of detectable
and, because the average
has fallen
more saline
deep
and
oxygen 250 m
depth is only
of the lake are mixed to the sediment surface,
Beauchamp,, 1953
should mean a fairly
estimates
under
high pro
are available,
the
conditions,
to one genus.
much younger than Tanganyika,
there
The lake has a perennial
depth is much more variable
Malawi has some species flocks
most reasonable
all the
Melosira nyassensis and Stephanodiscus astraea, suggest
mesotrophic
restricted
from the other lakes,
to Tanganyika in that
Although no primary productivity
ductivity.
As men
with the apparent mobility of the thermoclines
the strong wind regime
largely
different
waters,
as in Tanganyika,, but its
is also greater
at least
studied of the lakes considered,
Brooks,
phases occurred
The lake is generally
with a Middle Pleistocene
1950,
below its outlet
among the fish,
but these are
considered
origin considered
As is the case in Tanganyika,
in modern times;
in the past.
the lake
and it is conceivable
However,
to be
that
according to Brooks
are no faunal elements as there are in Tanganyika which require
suggest such a phase,
or
-16-
GROSS STRATIGRAPHY AND CHRONOLOGY
Ki vu
The gross
stratigraphy
lS,,
and 13’ are presented
tive
of the greater
are from different
of sediment cores from stations
in Fig, 2..
These are considered
number of cores collected
depths and basins.
10, 4’,
representa
in 1971 and 1972 as they
Stations
10 and 4
Fig,
are
1
from the deep northern basin of the lake where depths exceed 400 m,
10 has three distinct
finely
loci,
units.
laminated with alternating
particularly
generally
very high,
dark brown material
is almost entirely
are carbonate,
90-95%,
The second unit is also finely
is not present.
of organic-rich
material
of pure diatomite
stratigraphic
a meter of this
alternating
volcanic
material
organic,
of this
was recovered
section
is
of the
consist
Several intervals
are also. found.
ash, terminates
section
laminated with alter
with diatomites,
cm thick
while the
The brown material
layers.
The laminations
up to several
unit,
has a gel-like
The .water content of this
dark grey and yellowish-white
upper section
At several
from 24-29 cm and .100-138 cm,, the white laminae are
The brown material
white laminations
From 0-138 cm the sediment is
dark brown and white layers,
absent and the resulting
consistency.
nating
sedimentary
Core
The third
the core at 320 cm,
at a nearby station:
Over
towards
the
bottom of the second unit,
from 260 to 320 cm,, numerous thin intercala
tions
3 cm of ash. occur in the top unit from 75 to
78 cm,
of ash occur,
The massive
Also,
ash was not encountered
from the north basin,
out rapidly.
bathymetric
Capart
suggesting
that
from Verbeke,
study of the lake,
in numerous other 5 m cores
it .is of local occurrence
1957,
identified
and pinches
as a consequence of a detailed
three sublacustrine
volcanic
-17-
cones in the north basin in the vicinity
of our station
the deepest members of a set of volcanic
cones along the northern shore
of the, lake,
which erupted underwater,
1955, 1963,
DeNaeyer,
with the activity
subsequent
sedimentation
sublacustrine
is an 8 m section.
shortening
gases on retrieval
cones.
and the fine structure
section
has essentially
10,
and core-
were along bedding
intercalations
>0.5
The
as the second unit
cm
are more frequent,
unit of core 10 is absent,.
stratigraphy
indicates
13’ and 15’ are significant
lower water levels
in the past,
and second units
of station
10 present,
because their
Station
in 86 m of water at the southern end of the main lake.
dark grey,
texturally
stiff,
and structureless,
but it terminated
crumbly texture
similar
lost on retrieval,
bottom unit,
in.a third
This unit was
except for the top 30 cm,
which were white because of a high calcium carbonate
also a thin white band at.195.
13 was
This core had the
unit which extended from 160 cm to the bottom at 421 cm,
than its
of station
Numerous gas spaces between sections.
only one unit... .It is laminated
Cores from stations
first
extent,
of the sediment was not disturbed.
in core 10, but major diatomite
The first
limited
of the section by expanding
of core were present upon opening,. but .the separations
planes
origin with
over 10 m of sediment,
past the core catcher
probably occurred,
associated
A subaerial
kilometers’ to the southeast
The corer penetrated
or extrusion
10 is probably
seems to be ruled out by their
Core 4’, from several
These are
although they are now exposed
The ash at station
of these
10.
content,
There was
The very .bottom of the core had a dry,,
to a soil.
Some of this material
may have been
Organic and water content were low throughout this
The stratigraphy
present level
suggests .that the lake stood much lower
during the deposition
of this third unit,
was probably lower than the coring site before.then,
and it
-18-
than its present
level during the deposition
of this
was probably lower than the coring site before
Station
90 m.
organic
then,
from the main lake and station
The first
35 m deep,
and structureless,
and water content
that
aragonite
The high carbonate
very
From lSO.to...260 cm the sediment has frequent
bottom of the core the sediment has a light
reveals
13’ by a
150 cm are dark brown to black,
thin laminae of calcium and magnesium carbonates,
material
and it
was in the Bukavu Basin of Lake Kivu at a depth of
l5
This basin is separated
shallow sill,
third unit,
are relatively
Below 260 cm to the
grey appearance
low,
Microscopic
needles are a primary constituent
and low organic
content suggest
and organic
examination
of the sediment,
a shallow environment
and lower water levels.
Several other cores recovered
evidence of
A core from station .9 in a depth of 338 m had the same
lower lake levels,
two upper stratigraphic
tured clay-rich
from Kivu contained
facies
units
as core 10, but it terminated
which extended from 337-357 cm,
The lower 20 cm
almost bridge the stratigraphic
gap between core 10 and 4’.
virtually
in depths greater
absent
in the present
>60%
from sediments
lake,
are restricted
that the silts
and clays derived
to depths of less
338 m suggests
than 40 m,
of station
369 cm clays
from..the rivers
Verbeke
in a clay-rich,
10 are present
of station
1957
are generally
Presence of the clay-rich
a profound drop in water level,
of water also terminates
two units
depths,
Clays are
than one hundred meters
and sediments with the clay content
to much shallower
in an unstruc
reports
restricted
sediments at
Station
.unstructured
9
1’ in 229 meters
sediment,
The top
from 0-180 cm, but from 180 cm to
become much more important,
From station
12’ in 254 m of
-19-
water a 257 m core was recovered,
present,
and this
From .150 to 190 cm a clay facies
was underlain by an .even coarser,
190-250 cm, suggesting
that
the mouth. of a larger
by at the time of deposition.
laminated and diatomaceous,
mica-rich
that
bed from
creek was very close
The bottom .7 cm of.this
which indicates
was
core were finely
a much higher lake level
had preceded the shallow water phase.
The most dramatic evidence for a much lower lake level
at station
14, where a 6 m core was taken in 310 m of water.
cm of this
core contained
stratigraphic
units
correlative
two units of station
10,
well-rounded
of metamorphic provenance,
pebbles
5,5 cm in diameter.
fragments
Below 90 cm the core consisted
the seismic profiles
tural
is a beach deposit.
Degens et al.,
Further
1973,
These sediment depths .contrast
of shell
for a
level
comes from
show that
age of 10,000 years.
These dates indicate
part
the struc
sharply with the greater
for the cores from Lake Kivu are listed
Sediment from a depth of 170 cm in station
The bottom of 10 is correlated
of core 9 by microfossil
overlying
at
found in the deep northern basin,
Radiocarbon dates
age of 6,200 years,
sorted,
of which was
support
These records
is only a thin veneer of sediments
than 0,5 km of sediments
Table 3,
of poorly
than 300 m,, which are .found mostly in the southern
there
basement,
with the upper
the largest
former lake stand at more than 300 m below the present
of the lake,
The top 90
The lack of graded bedding and the presence
suggest that this
depths of less
was found
and chemical criteria,
in
10 is assigned an
with the dated bottom
and it is assigned an
The base of core .9 has an age of 10,700 years,
a sedimentation
rate of 0,3 mm/yr for sediments
between 9 and 170 cm and 0,4 mm/yr for sediments
between 170 and 320 cm.
-20-
A date of 11,200 years B,P, was obtained
Such an age is reasonable
10 is absent,
as the distinctive
and microfossil
that there
indicate
brownish upper unit of core
and chemical data to be presented
is explained either
of the corer,
covered the brown unit,
dates
from 4’ indicate
superpenetration
by a depositional
seems most likely.
a very high sedimentation
Although the high rate
is surprising,
The
hiatus
The other
rate of 3-4 mm per
10,000 years
it is similar
rate measured on a 1 meter core from 310 m n
and Vacquier,
later
As all ‘other cores in the basin re
year, or nearly 10 times the rate for the past
10.
4’,
is no temporal overlap between cores 10 and 4’,
absence of the upper units
or superpenetration
from the top of station
at station
to the high
Lake Malawi Von Herzen
1967,
Other samples for dating were chosen in order to estimate
date of the former lowered lake levels
rise,
The dates from core l3
of the relatively
core,
i.e.,
laminated
inorganic,
for the surface
indicate
shallow water facies
sediments
sediments,
of the subsequent
very rapid deposition
at the bottom of the
13’ and .5,2 mm/yr at station
in 15’ were deposited
and the uppermost unlaminated
error
and core.l5’
1,6 mm/yr at station
sediments
and the rapidity
at 0,15 mm/yr,
An assumption of atmospheric
sizable
contribution
13’ and 15’ seem to show that
between the initiation
11,070
years B,P,
CO2 to the alkalinity
data to estimate
The
assuming no zero
for the CO2 in the modern lake may be unfounded,
we have no pertinent
15’.
at a lower rate of 2,6 mm/yr
bration
of volcanic
the
the possible
equili
as there
is a
of the lake,
error,
but
The dates
from
as much as 1,000 years may have elapsed
of predominantly
and biogenic
biogenic
sedimentation
sedimentation
over 15’
over 13’
9,725 years B,P..
-21-
This implies
until
that the Bukavu basin was separated
approximately
the Bukavu basin,
10,000 years
B,P,.. .As the Ruzizi exits the lake from
Kivu had no surface
outlet until
timing of these rising
lake levels
with dates established
on other African lakes
Kendall,
1969,
and this
in the ‘sediments
assuming that
suggests
was quite
climatic
from the main lake up
and eventual
that..the
that
after
tIme.
overflow are consistent
Butzer
et al,,
1972;
organic carbon incorporated
near equilibrium
with the atmospheric reservoir,
events in East Africa were contemporaneous.
the carbon dates are affected
The
If
by "old" carbon, then the dates given are
maximum estimates.
Tan ganyika
The stratigraphy
and radiocarbon
cores have been previously
short
presented
review will be given here.
in length
are available
the north basin,
Sedimentation
station
3.
A series
from various
and only a
cores up to 250 cm
depths in the lakes,
A core from
3, are depicted in Fig, 2,
12, and 0,4 mm/yr at
Rates which were 10 times lower are found on the sill
Both cores have two stratigraphic
laminated,
in color and the laminations
less
thick are present through both sections
quent in the southern basin core,
contain
1971,
of gravity
are about 0,5 mm/yr at station
is dark .grey in color and finely
higher
of the Tanganyika
Degens et al,,
12, and one from the south,
rates
the two basins,
lighter
chronology
sedimentation
rates
a much greater
regular,
Turbidites
in both cores,
These thrbidites
of clays,
The upper one
while the lower section
in the deep basin.
admixture
units,
between
is
up to 3 cm
but are more fre
explain
in part the
All the Tanganyika cores
principally
kaolinite
with
-22-
some illite
and chlorite,
from station
19 over the sill
stratigraphic
blue-grey
than the deep...cores
units
in 550 m.ofwater
not encountered
and’grey in color,
the present regime.
greater
two additional
These were
in.-..the deep basin cores,
dominated the clays,
combined with the absence of pyrite
in
these sediments were laid down under
suggested that
conditions,
oxidizing
recovered
and montmorillonite
The change in the clay mineralogy
these lower units
A 200 cm core
from Kivu.
which implies
a hydrography markedly different
from
A date from the bottom of core 19 gave an age of
than 28,200 years B,P.
Edward
The sediments
At station
5
laminated,
but the thickness
variable;
see
of Lake Edward varied
120 m, and station
similar
throughout
visually
laminae
diatomites
to that of station
the cores very, fine volcanic
over as much as 10 cm bands,
present,
of the light
Also discrete
but these coarser strata
finer material.
a result
These two cores
bands of coarser ash were
were not directly
associated
homogeneous brown color and still
in the deeper cores,
very organic.
to these depths brings
fine lamination
present
at greater
sufficient
with the
and had a quite
of their high pigment content,
no trace of the lamination present
At several
ash was disseminated
other cores from Edward were from depths of 80 m or less.
ing of waters
was quite
4’ in Kivu,
These two deep cores were very organic
pronounced green color,
with depth,
4, 102 m, the sediments were
numerous bands, 1-2 cm thick,. were encountered,
are strikingly
intervals
Fig. 2,
quite dramatically
The three
These showed
They were of a
Presumably
turbulence
seasonal mix
to destroy
the
depths below the more permanent deep
-23-
The role of organisms
thermocline.
but Verbeke
of less
states
1957
than 40 m,
in sediment mixing cannot be ignored,
that the benthic
A radiocarbon
fauna is restricted
to depths
date from the deepest core indicates
a
rate of 0,9 mm/yr.
sedimentation
Albert
The sediments
of Lake Albert
the other lakes considered
Fig,
are quite
2,
different
The core from station
mum depth of the lake is a nearly uniform grey sediment,
the most abundant component,
There is a slight
site.
The core from station
5 at the maxi
and clays are
color change over the length
of the core as it becomes darker towards the top,
near the base of the core yields
from those of
a sedimentation
A carbon date from
rate of 0,7 mm/yr at that
3,, water depth 47 m, is more noteworthy,
From the top to 185 cm the sediment is dark grey to black in color,
from 185 to 460 cm it is a uniform light
grey,
480 is very sandy, and the core terminates
481 cm,
T. Harvey
personal
at 660 cm in his 12 in core taken
bracket
the layer indicate
is studying
the diatoms of Albert
7,500 years B,P,
fossil
at’this
site,
at station
The shallowness
layer
His carbon dates which
Harvey
an age of
Thus, sedimentation
years B,P,
have been quite variable
Harvey also finds the rates
of this
at
assigned to 340 cm by a micro-
0.25 mm/yr from 13,000-7,500
5,
a similar
3 and has informed us that
with his well dated core.
from 7,500 to the present,
material
layer is 13,000 years old,
could be provisionally
correlation
encountered
from Albert.
that this
The sediment from 460 to
in a dry, brittle
communication
and
rates
and 0,45 mm/yr
and much lower than
in his core to be labile,
lake.and the large fetch of the wind allows mix
ing to the bottom throughout
much of the year, which results
in fairly
-24-
well .oxidized
sediments.
time may indicate,fairly
topography
of the sites
The variable
sedimentation
the different
in space and
which combine with the
strong bottom currents
to yield
rates
rates,
Malcmi
A 252 cm core from 553 m of.water
made available
similar
by G, Miller of Heidelberg,
to. those of Tanganyika in that
and diatomaceous
laminations
The sediments
are often apparent,.
especially
available
core, but the possibility
mm/yr
15 at Malawi was
appear to be
the sediment is fine and organic,
are also frequent,
for this
of station
below 143 cm,
Mica-rich
turbidites
No carbon dates are yet
of rather
high rates
in the lake is demonstrated by Von Herzen and Vacquier
3
1967,
LAKE KIVU SEDIMENTS
DEEP NORTHERN BASIN >400 in water depth
Chemical Stratigraphy
Nineteen trace metals
tuents
of the sediments,
determined
Details
in separate
reports
radiocarbon
from stations
Degens and Kulbicki,
chronology,
10 and 4’ are considered,
to give a nearly
mentary events in the northern basin
years,
of the method as well as the raw
l973ab;
1970.
The cores
their
Fe2O3,, SiO2, A12O3, CaO, MgO, and TiO2, were
by uv.spectroscopy.
data are presented
Baradat,
as well as the major chemical consti
because of
complete record of sedi
of Kivu through the past 14,000
However, as we have constructed
the chronology,
a gap between
-25-
10,000 and 11,000 years B,P.
this gap are present
supports
results,
in nearby core 9.
such an interpretation.
graphy are presented
which exhibit
stratigraphy
Fortunately,
Other evidence presented
The highlights
in Fig. 3; the distribution
large variation
we recognize
is presented.
oscillating
Mn..
,of only those
On the basis
elements
of this
in the cores,
by high but variable
chemical
The lowest
Al.and
The second unit from 710 cm to 500 cm has declin
ing Al and the Mn fluctuations
frequency..
later
of the chemical strati
five geochemical units
from 710 cm to 1,200 cm is characterized
strongly
about 700 years of
are reduced in intensity
and eventually
From 500 cm to 410 cm, Fe accompanied by Ni is prominent in
the sediment,
A similar
facies
is present
from 320-275 cm in core 10,
From 275 to 130 cm and from 90-35 cm in the latter
core the CaCO3 content
is high1 while
from 130 to 90 cm and 35-0 cm CaCO3 is again absent,
organic matter
and Pb are greatly
Spencer et al,
analysis
to interpretation,
unstructured
to a simplified
Factor analysis
were found to explain
varimax factor
just detectable
limits,
the efficacy
matrix which is more amenable
rotation
Table 3 presents
matrix for each element which was present
the identification
ments are not depicted in Fig..
behavior of the other elements,
Spencer,
data of cores 10 and 4’, and five
82% of the variance,
concentrations..
of factor
raw data which sedimentary
with orthogonal
was performed on the elemental
factors
within
yield,
elevated.
have demonstrated
for reducing the large,
analyses generally
1966
1968
and
These factor
loading
of the factors..
3, this
table will
in greater
the
than
scores permit,
Also,
as all the ele
allow insight
into the
-26-
The high loadings of A12O3, Ti02, Ga, Cr, Cu,, Zn, and V suggest
that this
linite
is the detrital
and illites
first
three
component consisting
and weathered volcanic
elements with detrital
are generally
residuals
of clays
is not surprising,
Cowgill
kao
The movement of the
ash,
minerals
of weathering
primarily
& Hutchinson,
as they
1970
and
the movement of the other four elements with this
group can be traced to
the unusual volcanic
rock sequence of the basin..
The rocks of the area
are thought
1954
atite
Higazy,
magma with crustal
istics
to have resulted
rock,
These distinctive
imparted by the volcanic process
are brought
association
lesser
mobilization
The high negative
loading
is with SiO2.
the SiO2 of factor
The positive
gical origin,
growth,
the sediments,
is certainly
factor
as both elements are essential
The negative
incorporated
relationship
but it will be shown later
carbonate deposition
As a general
factor
rule,
indicates
The
their
not detrital,
primarily
micronutrients
by diatoms,
with a biolo
for algal
with the organic matter of
between the carbonate phase
This is partially
that temporal and spatial
changed
high biological
accompanied by low carbonate deposition
2 suggests
The highest posi
is in line
mutual dilution,
have probably
though,
factor..
being contributed
and. the biogenic phases suggestsa
true,
with this
of V and Mo on this
and they are probably
factor
of Ca, Sr, and Ba on factor
As this
2 is biogenic,
loading
character
than the other metals,
that the carbonate phase is involved
loading
geochemical
and erosion process,
of Cr, Zn, Cu and V with this
by weathering
of a carbon
to the lava and ash of the area
to the sediment by the weathering
strong
tive
from the reaction
fundamentally
productivity
patterns
of
in the lake,
has probably been
to the coring sites,
and the
-27-
observed
hints
loading on factor
2 is the result,
The negative
loading
of Mn
at a manganous carbonate phase which, it will be seen, was reason
able for an early period of the lake’s history..
Factor 3 has high positive
Zn, and Cu,
The close association
ments has previously
1970,
been noted
availability
of a sulfide
factor
depositional
of these
for Fe, Ni, Co,
elements in lacustrine
determined by redox phenomena and the
3 might be characterized’as
and co-precipitation,
the redox potential
of the
environment,
almost entirely
Manganese also has a sizable
waters of this region
This is consistent
and Fyfe, 1973
Table
1
to factor
loading
4 with a very high
on this
remains in solution,
factor,
solutions
Christ
seem to show that
Mg in
while Ca is removed,
with its known chemical behavior,
magnesium bicarbonate
Experiments
and Hostetler,
aqueous Mg2+ is very unreactive
in itself
of a magnesium carbonate phase;
crystallization
crystallization
is catalyzed
may be a primary determinant
the salinity
by increasing
of the lake,
as attractive,
low although
the possibility
in Kivu,
and factor
4 would
The specificity
of factor
involving
because the loading
it must be admitted
of such compounds.
is more compatible
salinity
hypothesis
that
strength.
however,,
Thus,
of Mg deposition
Mg does not make an alternative
formation
increasing
ionic
because
Mg2+ concentration
In fact,
inhibits
with
1970; and Sayles
of its highly hydrated structure.
then reflect
sedi
1966; Cowgill and Hutchinson,
phase for precipitation
Magnesium responds
loading.
loadings
MacKereth,
Their behavior is largely
Therefore,
>0,400
or chlorite
for SiO2 and A12O3 is very
a low loading
The relatively
with a carbonate phase.
sepiolite
4 for
does not rule out
high loading of Mn
The only appreciable
negative
-28-
loading
is that
ductivity
tation
of Mo, which may result, from decreased planktonic
or at least
dilution
would be consistent
with the hypothesized
Only one element,
this
makes it difficult
by the Mg-rich phase,
Pb, has significant
to establish
shows that the Pb concentration
from 85 cm to 120 cm with lesser
carbon and pyrite
material
suggesting
Pb becomes available
above and below that,
1970
in rather
discrete
volcanic
provided by factor
through nearly 14,000 years
discussed
this period,
mica, constituted
continual
of its
In Kivu sediments
to its concentration
analysis,
it is now possible
of the north basin of Lake Kivu
history.
earlier,
Between 13,700 years
and
which, based on the
may have been as much as 300
Al203 was between 10 and 20% average
and detrital
or the
1954,
the lake stood at a much lower level
below the present level,
throughout
rock Higazy,
the hydrogeochemistry
stratigraphy
Cowgill
but they did not observe the pulsing
3 to 4 times enriched relative
gross
pulses.
which suggested
Pb is always at least
With the insight
and
studied were enriched
up to 5,800 ppm which we find.
<10 ppm in neighboring
that
But the upper unit
very high Pb content
12,500 years,
Organic
perhaps by chelation
found that the sediments they
and precipitation,
to characterize
Fig.. 3
from 0-30 cm does not show the Pb enrichment,
in lead when compared to source materials
leaching
5, and
of the factor,
or as a sulfide,
of organic-rich
and Hutchinson
on factor
low, but has extreme values
with organic.matter,,
in humic.compounds,
that
loading
are also high between 85 cm and 120 cm, suggesting
the Pb is removed either
incorporation
pulses
Either interpre
high salinity,
the identity
is generally
pro
components, especially
over 50% of the sediment by weight.
=
in
12%
kaolinite
and
Although A12O3 is
-29-
abundant,
levels
its
quite markedly,
value fluctuates
and. distances
from source rivers
reflecting
and streams to the coring site,
Lake Kivu during this period was a closed basin lake;
levels,
reflecting
Langbein,
short-term
1961,,
changing water
and astatic
and evaporation
balances of precipitation
would be expected,
The waters of a closed Lake Kivu would have been saline
alkaline;
and, except for their
distinctive
source rocks,
bicarbonate-carbonate
waters
Ca precipitates
sition
in offshore
they would have strongly
peripherally
as it enters
and alkalinity
increase
aspect
the exception
and Ca depo
Na, K, and Mg would accumulate
from the Eastern
water depth,
of Rudolf,
sediment surf ace diurnally,
tocene Kivu suggests that
water level would
The closed basin
lakes of East Africa,
level,
but the greater
with
Lake Kivu, even
had 100 m of water over the
lakes are usually mixed
prolonged
1961.
Rift Valley lakes in one signi
are shallow or even ephemeral,
The shallow
This explains
when the lake was down Langbein,
when it stood 300 m below its present
4’ coring site,
the lakes,
with time, but a fluctuating
wastage by deflation
Lake Kivu would differ
In these alkaline
is low Kilham and Hecky, in press.
Ca content of core 4’,
ficant
resembled the sodium
lakes of the Eastern Rift Valley,
areas
and
somewhat higher K and Mg derived from
the negligible
allow salt
water
oxygenated
to the
water depth of the Late Pleis
stratification
might have occurred
as it does in the deep, modern lakes,
The oscillating
stratification
Mn reflects
leads to deoxygenation
After deoxygenation,,
redox potentials
the stratification
history,
of deep waters
in productive
lakes,
in deep waters
and sediments
decline;
and, as they do, many elements become reduced and the solubility
Prolonged
of their
-30-
compounds may change,
Mn and Fe as well as many other transition
are chiefly
affected,
Mn will be reduced first
or silicate
and will enter deep waters,
to drop, Fe2+ can become available,
concentration
solubility
from its
sedimentary oxide
If the redox potential
In the alkaline,
saline
of these two reduced species would probably
with respect
pH values than deep waters
continues
Kivu,,. the
increase
to the carbonate phase was exceeded,
behavior would also be pH dependent,
metals
until
Thus their
Surface waters would have higher
and, therefore,
more CO3
available
to remove
Mn or Fe,
Kivu during this
period was a closed system,
so that
simply
changing the Mn from an oxide to carbonate would not produce ,the oscilla
tions,
Two scenarios
redistribution,
are offered which could bring about the required
One is largely
not mutually exclusive,
temporal
In the first
and one spatial,
and they are
case stratification
occurs;
diffuses
from the, sediment and accumulates
waters,
Subsequent mixing because of weakening or obliteration
stratification
would deposit
as a carbonate
The second case involves Mn2+ diffusing
across the thermocline
and precipitation,
would lead to resolution
shallow water permits
Fluctuations
record the position
Garrels
of the
of Mn2+ oxida
and MacKenzie,
from sediments,
Precipitation
mixing
in deep water
because of the lower pH, while precipitation
incorporation
water sediments become impoverished
enriched,
low pH deep
MnCO3, as the slow kinetics
tion should favor precipitation
1971.
in relatively
Mn2+
in the sediments,
in Mn while shallower
in Mn content
of the thermocline.
was above the thermocline;
In this
at the 4’ site
case deep
sediments
in this
in
are’
case would
When Mn is high, the 4’ site
and, when Mn is low, it was below the thermo-
dine,
Thermal stratification
cation
meromixis
would be much more stable
case Fe2+ and sulfide
rather
constant
at 13,500,
seems most likely,
production
throughout.this
13,200,
period,
The first
in which
In fact
showing enrichment
in the core by .a bed, almost 1 cm thick,
stratifi
and longer lived,
should have occurred,
and 12,500 years BP,
the chemical composition
as a salinity
Fe is.
only 3 times,
of these is represented
of nearly pure manganosiderite;
of this material
is not known, since our routine
5 cm spacing between samples missed this bed,
If the depth of mixing of the epilimnion
period is considered
sampling interval
mentation
level,
site
rate’,
to be more or less
then these
High water levels
and Mn-depleted
fluctuations
sediment would accumulate,
which implies that
with no significant
Mn occurred,
values
sediment,
our
there are no significant
was more persistent,
The redox potential,
to liberate
of Mn on factor
could be generated
as suggested
Subsequently
to water
levels
would
is presented
might be reconstructed,
stratification,
stratification
sufficient
Lower water
the lake may have been completely
In the discussion
loading
years
well above the 4’
This interpretation
when the lake was shallowest
content of deposited
what higher,
of Mn can be related
would place the thermocline
4, which shows how lake levels
13,500 years,
over several
low water
is on the order of 10 years because of the high sedi
bring Mn-rich sediment to the site,
Fig,
constant
during this
Prior
in
to
by the A12O3
oscillations,
mixed throughout
the lake level was some
and redistribution
however, only infrequently
of.
dropped to
Fe2+,
of the factor
4, the Mg factor,
by fluctuating
analysis
a rather
was noted,
lake levels
high positive
Such a covariance
in a closed,
alkaline,
-32-
lake
saline
Periods of Mn deposition
and higher salinities.
favor precipitation
scale,
Increasing
be particularly
high, i.e.,
dine
could alter
cient
to modify salinity
siderite
x-ray
above,
a slight
Mn deposition
contains
ionic
strength
never on a massive,
the correlation
would not have to
shift
without
ensued,
a period of generally
The A12O3 and Mn contents
increases,
ash are present,
to volcanism rather
Therefore,
detrital
this
that
even higher,
increases
than changes in lake level.
and the increases
from greater
Iron shows an appreciable
and pyrite
formation.
higher
Mn will continue
lake level
and a more stable
the more reducing conditions,
discussed
halocline.
later,
to migrate
also
suggest
a stable
Between 11,700 years
Thin laminae of
to the TiO2 peaks,
increase
in sediments
suggesting
The availability
to shallow
stratification
The fossil
thermocline
more strongly
of sulfide
metals,
while the
environments.
A
presumably engendered
diatoms in these
and 11,500,
are accom
in A12O3 are related
in the deep waters will trap Fe and other transitional
more soluble
sediment
inputs of unweathered
between 12,000 and 11,700 years B,P,,
reducing conditions
rising
No extreme fluctuations
observed correspond
higher Mn results
material.
deposited
indicating
of the deposited
High A12O3 values
panied by TiO2 values which are relatively
in Mn occur,
by
analyses,
and the iron content
volcanic
of note the the mangano
Itis
Beginning at 12,500 years B,P,,
decrease
a volume change suffi
involving
significantly.
of the thermo
in the position
on average between 50 and 80% MnCO3 as ascertained
diffraction
lake levels
should
and alkalinity
although
of magnesium carbonates,
By the models presented
lake levels
at 4’ imply falling
strata,
or possibly
Fe deposition
to be
a weak
decreased
-33-
slightly
rise,
in relation
This implies
to other components,
a less
stable
and biogenic
sedimentation
deposition
to open the lake to the south,
are inferred,
The core from station
however,, the bottom of this
interval
.greater
High lake levels,
and a stable
but
stratification
core is assigned an age of 10,000 years
of sediments deposited
in the north basin record,
at station
between 10,000 and 11,000 years B.P,
formed at the base of core 4’
to
10 begins with Fe and Ni similarly
B,P,, which leaves a gap of 1,000 years
geochemistry
was relatively
decreased,
not sufficient
high;
continued
stratification,
After 11,500 years B,P, pyrite
as detrital
and water levels
9 in the critical
resembles
high Al and low Fe,
closely
The
time
those
A lower lake level
stand is inferred,
The beginning
of CaCO3 deposition
in offshore
when the lake rose above the Ruzizi outlet,
vation than now,
decreased,
As the lake overflowed,
the HCO31 -CO32
removal of CO2 caused its precipitation.
nickel
results
and a hydrography similar
thermocline
catastrophic
by the CaCO3,,
The decrease
in iron and
The lake had open drainage
i.e,,
a deep, perennial
events occurred in the lake’s basin,
which indicates
sedimentation
but it
up to 5,000 years B,P,, when
stratification
From 5,500 to 5,000 years B,P,,
sharply,
alkalinity
as it entered,
to Edward and Tanganyika,
with no salinity
ele
where high pH values because of photosyn
thetic
from dilution
is effected
which stood at a higher
Ca was no longer removed peripherally
was mixed into the open lake,
waters
of ash,
increasing
TiO2 and A12O3 deposition
volcanic activity
At 5,000 years B,P,,
organic carbon and Pb increase,
rose
in the basin and
CaCO3 deposition
ceases while
The organic carbon emerges as the contri-
-34-
bution of other sedimentary
is reduced,
Rather,
production
In contrast,
especially
to be discussed
of terrestrial
the Pb increase
with the biostrati
organic matter was relatively
by a factor
of nearly
100 sug
a large input at that time,
CaCO3 is not being deposited
either,
The lake is presently
with CO2 Degens et al,,
have been.accomplished,
Surface waters
at the station
but the trend.is
water’
acidic with depth.
noticeably
become anoxic,
Therefore
CaCO3 particles
and incorporation
is only possible
in depths
above the first
Kivu’s
today exhibit
shoreline
surface
charged
No pH measurements on the deepest
the deep water redissolve,
Verbeke,
today,
and the deep waters
meromictic,
1973,.
10 site
have pH values between .9 and 10, but the pH drops below
7 as the waters
1957;
sediments.
halocline,
regions
The absence of carbonate
to that existing
and extremely alkaline
today,
Many areas of
pavement of CaCO3
have carbonate-rich
from 130 cm to 90 cm implies
It ,does not mean a lower lake
surface waters,
ments.. of the core from 400 cm to l200
into
falling
of CaCO3 into the sediment
a nearly continuous
and cores from shallower
meromixis similar
level
CaCO3 and diatoms,
carbon does not.mean higher productivity,
dropped
and the contribution
increased.
gests
The higher organic
planktonic
graphy,
constituents,
as the carbonate-free
cm, because.the
sedi
Al203 content
is
low.
The warm, saline,
to hydrothermal
springs
became significantly
sediments
deep waters of.the
Degens et al,,
stronger
present
1973,
5,000 years B,P,
are a good marker of spring activity,
years indicate
that the springs were present
lake are attributed
and this
spring
activity
High Pb values for the,
and peaks ,prior
to 5,000
but on a reduced scale,
-35-
The Pb derives
from intense
leaching
ash by warm, ground waters
charged with volcanic
should enrich the lake waters in all
of the metals and their
of the metal-rich
differ
are split
phase,
and it contained metals which were either
were not incorporated
their
highest loadings
on factor
with the detrital
more resistant
part of a widely recognized
of metals
Spencer
1968
conditions,
which migrates
covariant
together
time,
quite
Pb exists
different
virtually
behavior
alone in the last
hydrothermal
metals
increased,
ment.
The removal was effected
process
Pb was the first
sedimentation.
precipitated
spheres
sulfide
and failure
by sequestration
Degens et al.
to form sphalerite
to find these
dominate after
indicating
a
the input of all
the
to be removed and added to the sedi
"1 micron in diameter
which covered the sphere.
factor,
activity,
with organic material
1972
for Zn in Lake Kivu, but with a different
fied resinous
under.oxid.izing
from the other metals,
With the increased
and subsequent
suite
In Kivu the oxides and heavy metal carbonates
predominate prior to 11,500 years B,P., while the sulfides
that
Zn,
3 while Zn and Cu also had significant
This represents
and reducing
to leach
Fe, Ni, and Co had
factor,
loadings,,
et al,,
The first
into the lake sediments,
loadings on this
fate
Factor analysis
among three factors,
contained those metals which were associated
Cu, and Cr had their highest
This leaching
markedly.
factor
ing or, if leached,
lavas and
but the geochemical
the metals,
sedimentation
showed that the heavy metals
CO2
volcanic
describe
result,
They identi
which chelated
crystallites
a similar
Zn and
5 to 50
in size
These spheres were found in the water column,
spheres in the sediment suggested that
were buoyant and were being lost
to the lake,
they
Such is not the case with
-36-
the chelated
lake.
Pb,, however, and it is rapidly
Cowgill and Hutchinson
similarly
during weathering
petrologic
provenance
lavas and ash.
to soils
similar
was
observed,
in Kivu indicates
above mechanism rather
being
sedimented,
entry to the
in a basin which has a
to Kivu, i,e,,
Both Zn and Pb were greatly
after
Zn and Pb behaved very
found that
and sedimentation
and rock; no difference
weathering
factor
1970
deposited
abundantpotassic
enriched
in mobilization
alkalic
in sediments relative
between Zn and Pb during
The high loading of Zn on the detrital
that
it is being lost from the basin by the
than being totally
deposited
in the lake,
but it is being removed in a manner similar
Pb is
to that of
Zn.
The abs’ence of Fe and other metals
Zn from the sphalerite
organic
not,
resins
no organic
as sulfides
specific,
reasons,
chelator
excluding
coordinate
was present
or in shallow waters
metabolic
free energy;
demonstrates
as oxides.
at depth,
sulfide
in surface
production
waters,
that plankton production
thermal pulses;
the
These metals
for which
Precipitation
of sulfide
of these metals
by sulfate-
as a hydrogen acceptor in
They are dependent on organic matter as a source of
and, thus,
organic production
that
would have to be removed in deep waters
These organisms use sulfate
oxidation,
1972
with.
those metals which could
properly.
in deep waters would depend on the production
reducing bacteria.
associated
spheres suggested to Degens et al,
were highly
for structural
frequently
this
in turn
in deep water will be tied to
Evidence to be presented
sharply fell
during these hydro
should also have affected
The magnitude of this
decrease
9,000 years B.P,, CaCO3 rose from nearly
later
microbial
can be estimated
activity
in Fig. 3,
At
0 to 30% of the sediment by dry
-37-
weight,
This necessarily
approximately
this
amount,,
one-third
i,e,,
decreased
to maintain
also decreased
at this
5,000 years H.P.,
at least
supply of metals,
migrated
a one-third
production
been destroyed,
hydrothermal
sufficient
salts
of cooling
The therinohaline
unless
surface
constant,
of heat and salt
i,e,,
1957
and aridity
Assuming
to the
hotter waters
leach
then the maintenance
is dependent
source of denser water must exist,
If the lake became closed,
waters and/or
could lead to a breakdown,
thermal density decreases,
diluted
stratification
in the Kivu system are
or concentrating
Hutchinson,
waters must be constantly
as coolness
or out the Ruzizi River,
contribution
is relatively
to offset
a sublacustrine
as they
years B,P, and which occurs today had
the deep waters
of crenogenic meromixis
i
to meet the greater
The deep waters were no longer acid because
that the relative
waters
production’
to the deep waters
The density changes involved
and a combination
heuristically
in a major
4,000 years H.P., CaCO3 was again being deposited
from 5,000-4,000
or diluting
in sulfide
did not increase
were more efficient,
which was present
increase
Diatoms
to the organic matter.
in the deep north basin.
mixing processes
CaCO3 disap
As Fe did not rise by 5% at
reduction
to shallow oxygenated sediments
Approximately
heating
and the only relative
and these metals were lost
they could coordinate
small,
At 5,000 years H.P.,
by organic carbon,
Sulfide
Iron did decrease by
but there was no response by the Fe,
time,
component is registered
had occurred,
a zero sum.
from 15% to 10%.
peared from the sediments,
the other major components by
all
on two processes:
and ii
surface
by runoff and loss at the effluent,
surface waters would become more saline;
are correlated
in the African climate,
and,
surface
-38-
cooling might be expected
also,
breakdown of the convecting
Such a state
water cells
The depth of the well-mixed
hilated,
would grow from above in a gradual
extended over many years,
process
catastrophic,
near
atmospheric
equilibrium
cells,
If the
the mixing of the immense reserves
into the surface
that Kivu was without
of CaCO3 deposition,
and saline
layer
are anni
waters need not be
as it was prior
a surface
outlet
during this
Despite the fact that the lake was closed
to 9,000 years B,P,,
Ca was deposited
deep north basin because the source of Ca was the sublacustrine
not surface
activity,
of
Evidence from other cores and lakes will be presented
below, which indicates
interval
as density differences
cascade of collapsing
gases and heavy metals
hydrothermal
of events would lead to a
in the
springs,,
runoff as was the case previous to the onset of spring
The occurrence of high Pb concentration
CaCO3 deposition
means that the hydrothermal
within the period
springs
of
simply changed in
water chemistry.
The above results
if mixing was propagated
and/or hotter
water,
sharply with what would happen
would contrast
from below by the injection
These circumstances
substances
equilibrium.
of the deep waters could be introduced
case
rapidly
into the
consequences for the biota,
no. evidence in the stratigraphic
record
the fossil
record,
the biota
coincides
stratification
for a situation
whether such short-term
This evidence will be discussed
later,
this,
but
events could be resolved
with the onset of intense
than the termination
There is
like
What evidence there is for conditions
rather
cells
In this
surface waters with catastrophic
it is questionable
saline
would lead to convecting
growing from below and not in atmospheric
toxic
of less
hydrothermal
deleterious
activity
of the thermohaline
in
to
and
structure,
-39-
Events similar
to those that happened at 5,000 years B,P,
occurred
again at 1,200 years H.P.
High TiO2, A12O3, and Mn content
volcanic
ash are found in sediments
immediately underlying
depleted
sediments,
suggesting
The Fe and Ni subsequently
that the productivity
duction was not as drastically
similarity
of surface
spring activity
relationship
between volcanism
in both cases,
may be involved
also,
The strong
As the water of these
Degens et al,,
namely climatically
1973,
climatic
determined
availability
of water for deep percolation
through the porous lavas and ash of the
Virunga system might regulate
the volcanic
with hot magma, would be transformed
changes could fracture
release
or dislodge
of volcanic ejecta
system are undersaturated
fore,
supplies
The water,
confining
Holmes,
critical
volume
overburden and allow the
The latest
with water
by mixing
to this
lavas from the Virunga
1965, p. 1024;
and, there
system,
The chemical stratigiaphy
of the deep, northern basin of Kivu
the following
about the lake history:
i
below its
activity,
to steam, and the consequent
and lava,
water may be especially
pro
seems to imply a causative
and spring activity,
springs has been shown to be meteoric
processes
and hence sulfide
waters
ash followed by evidence of increased
i.e.,
hydrothermal
CaCO3-
more rapidly,
by the second event,
affected
of the two events,
increase
Pb-rich,
from
information
Prior to 12,500 years Lake Kivu stood as much as 300 m
present level;
the lake necessarily
was closed and more saline
and alkaline;
ii
water;
Station
4’ site
was under at least
and, judging from the fluctuating
depth of the perennial
thermoclines
marked the depth of the thermocline
one hundred meters of
Mn deposition
in the modern lakes,
at 4’ and the
it may have
through much of that time;
-40-
iii
thermocline
at 12,500 years B,P, water
levels
moved well above the 4’ site
was some volcanic
but not quite
formation
dropped sharply
there
around 10,700 years H.P.
to the low level it occupied prior
the lake achieved the elevation
v
increased;
in the area around 12,000 years H.P.;
activity
the lake level
iv
the deep waters
and sharpened;
and sediment became more reducing and pyrite
the
began to rise;
to 12,500 years H.P.;
of the Ruzizi outlet
9,500
years B,P, and began to freshen;
vi
at 5,000 years H.P. hydrothermal
dramatically
following
complex hydrography
or coinciding
similar
spring
with increased
to that extant
activity
increased
volcanic activity;
a
in the lake today was estab
lished;
vii
terated,
the thermohaline
probably
viii
density
by the lake level
a wetter
hydrothermal
and volcanic
thermohaline
structure
structure
falling
obli
was subsequently
below the Ruzizi outlet;
and
climate reopened the lake and another pulse of
activity
1,200 years H.P. reestablished
which has persisted
the
up to the present.
Bios tratigraphy
Siliceous micro fossils.
of the north basin cores,
analyses
Characterization
10 and 4’, is based on siliceous
for both cores and synoptic
hexosainines
for core 10,
of the biostratigraphy
determination
Diatom frustules
of amino acids and
are by far the most abundant
microfossils
in cores from all of the Rift Valley lakes,
preservation
vary from lake to lake and within
basin of Kivu preservation
is excellent
microfossil
Fig.
lakes,
3,
States
of
but in the north
Very few species
-41-
attain
relative
abundances greater
shore planktonic
variability
populations
is greatly
in large,
reduced relative
of the diatom stratigraphy
information
derived
of this
lakes;
to more temperate
as hydrographic
lakes.
paper,
Analyses
only a brief outline
from diatom analyses will be necessary,
of the diatom stratigraphy
presentation
deep tropical
in of f-
of other Kivu cores and the other lakes is still
For the purposes
in progress,
than 5%, as might be.expected
of the
A more detailed
will be given when all
the work on
Kivu is completed,
From the bottom of core 4’ to 130 cm in core 10, only 3 species
comprise well over 90% of the flora
Stephanodiscus astraea v, minutuja
Grun,,
at any sample level,
Katz,
and iVitzschia spiculum Hustedt,
These three are
Grun,, IVitzschia fonticola
mong the other diatoms only
Nitzschia acicularis W. Smith achieves abundances over 5% for short periods
of time,
Transmission
in Figs.
5-7,
stratification
electronmicrographs
Comparative availability
of nutrients
of the water column appear to control
tivity
of these species,
from
1
Understanding
the distribution
between
relationships
4
the behavior of the species within
conclusions
the relative
produc
ecology has been achieved
2
core,
simple
in lakes,
and sinking rates,
the present
elsewhere
and
An elaboration
Hecky and Kilham,
in prep,,
are given here in order to interpret
of the diatom species
through time in the north basin,
Stephanodiscus astraea is a low silica
tonic diatom species.
and, indirectly,
of nutrients
species productivity
of the argument will be presented
are presented
in the modern lakes,
distribution
3
and only the general
of their
of the species
models of the three-dimensional
the distribution
of carbon replicas
Kilham l97lab
states
specialist
that
among plank
it only becomes promi
-42-
nent in the plankton of lakes as dissolved
below 1 mg/l,
In Lake Albert,
silica
which has very low silica
S. astraea dominates the microfossil
phorus,
sediments,
In Lake Edward, where dissolved
N, fonticola predominates,
much higher,
Nitzschia species to the virtual
25:1
N, spiculuni Figs.
nutrients
phosphorus
5 and 6
are extremely
is nearly vanishing
in surface waters
Surficial
sediments of Lake
thin
long,
thin morphology results
to volume ratios,
of the nutrient-depleted
euphotic
and maximize the surface
area available
the situation
constituent
blue-green
of the phytoplankton
algae
slower sinking
esp,
The
area
can be achieved,
Contrary to
diatoms are not the most prominent
in Kivu and Tanganyika today,
rates or self-motility
and other
dominate,
reduce phosphorus
yet dissolved
level,
in the north basin surface waters,
Rather,
algal groups with
This is especially
studied,
sion on Na through all depths.
pro
of sinking out
uptake.
in Kivu, which has been most extensively
unaffected
The low nutrient
and high surface
for nutrient
Lyngbya sp, in Kivu
to a negligible
under nutrient
and can be seen in Table 2,
zone before reproduction
in Edward ‘and Albert,
These
on photoplankton
reduce the probability
All
while dissolved
production
in slow sinking rates
These attributes
morphology,
Table 1.
for other diatom species.
which was remarked on earlier
to width ratio
of this
in .Kivu surface waters
which are unsuitable
is
of other species.
Tanganyika waters,
supply in Kivu and Tanganyika has a marked effect
ductivity,
length
exclusion
long, thin Nitzschia appear to be able to sustain
conditions
from surficial
silica
is quite representative
low in offshore
f all
and high phos
assemblages
Tanganyika and modern Lake Kivu contain long,
>
concentrations
Biological
silica
clear
processes
is virtually
as Si gives a linear
regres
Diatoms must account for only a small
-43-
of the primary productivity
proportion
when 5, astraea is prominent,
greater
and the
accomplished is due solely to the Nitzschia spp.
diatom production
versely,
in the north basin today,
proportion
diatoms are accounting
of primary production
as dissolved
Con,
for a much
Si is driven very
low,
In tropical
for surface waters
drainage basin,
lakes two quantitatively
can be identified.
The salt
derived from the weathering
fallout
dissolved
from the water
of tributaries
is primarily
and nitrogen
as rich
from regeneration
are efficiently
Silicate
SiO2,
In contrast,
will be poor in silica.
regenerated
Runoff from
constituents,
in dissolved
rocks
will yield
and weathering
SiO2 and HCO31 as the most prominent
derived
from the
of nutrients
Hecky and Kilham, 1973,
in the Kivu basin,
present
sources
of rocks except in arid regions where atmos
the basin can be characterized
nutrients
contribution
becomes important
are exclusively
nutrient
One, is surface runoff
and the other is regeneration
column and sediments,
pheric
significant
Phosphorus
from plankton detritus,
yielding
the very low turnover times for these elements which are often measured
in lakes
Rigler,
1964,
judging from the vast
eration
however, is only slowly released,
accumulations
of SiO2 can probably
time scale,
inately
Silica,
of diatomites
be considered
Thus water masses receiving
from regeneration
processes
in these lakes,
negligible
their
and
regen
on an ecological
nutrient
content predom
will be comparatively
rich in P and
N but poor in Si,
The relative
runoff and Si-poor
and stratification,
contribution
deep water,
Generally
of these two types of water,
will be determined primarily
speaking,
Si-rich
by lake size
as lake area and volume increase,
-44-
replacement times increase
and the nutrient
runoff to the lake decreases
the lakes,
production
of large tropical
extent
lakes,
as that
diatoms with silica
to low silica
of regenerated
nutrients
mixing processes,
periods
In such lakes,
of their
areas
is’ possible
proportional
dine,
i.e..
This difference
interfaces
systems, but
in aquatic
only eddy diffusion
differential
in conjunction
seasonal variation
depends on
occurs in deep water,
across more
is significant
order approximation,
to the density
for most
mixing will be inversely
across a thermocline
with meteorological
in temperature,
winds,
in turn,
gives
an indication
rainfall,
etc,,
This depth
area constituting
exhibit
surface waters,
which is mixed completely most of the year,
Edward, which is likewise
less
thoroughly
circulated
than 10% of its
a hi’gh productivity,
will
of the amount of deep, nutrient-
rich water which will be mixed into the nutrient-poor
Lake Albert,
or halo
stresses,
determine the depth range or mobility of the thermocline,
range,
attuned
The availability
across very stable
and chemoclines
As a first
1973
surface waters
as much of the regeneration
thermoclines
area.
et al.,
should predominate.
in all the lakes under consideration
or less stable
of time.
Guillard
to the euphotic
in upwelling
the productivity
Therefore,
independent of
A continuum from molecular diffusion
to advection
tends to remove peri
and is relatively
uptake kinetics
concentrations
enter
of the ocean, depends to a large
processes;
inputs over significant
of surface
Where tributaries
and this
from weathering.
on regeneration
tributary
proportionally,
can be intense,
the nutrients
pherally
contribution
total
and they do,
and Lake
except for a small
surface area,
Productivity
should
should also
-45-
be reasonably
Table
2.
high in Malawi,
as its
The deep thermocline
of Kivu have been nearly
is fairly
deep thermocline
of Tanganyika and the thermohaloclines
stationary
over the periods
of observation,
thus mixing and productivity
are low,
shallow
will engender fluctuations
seasonal thermocline
Formation and obliteration
value determined by mixing across the perennial
With the above considerations
abundances for the period
A12O3 content
the presence
the waters
are relatively
near-shore
conditions
relatively
less
what higher water levels
The mobile thermocline
tively
efficient
water
levels
rich
in Si,
or at least
stratification
This indicates
of land-derived
Mn reflects,
and N. spiculum increased.
interpretation,
that
N, fonticola subsequently becomes
of low Si nutrient-rich
of deep water to the phytoplankton
As the
time indicates
and a nearby tributary
and reduced influence
and more stable
agree with this
at this
and S. astraca increases,
regeneration
is prominent,
value in the core and low lake levels
which the fluctuating
years H.P., N, fonticola
around a low mean
in mind, the changes in diatom
of N, fonticola
are implied,
abundant,
of the
from 13,700 years H,P, to 5,000 years H,P, can
is near its highest
are indicated,
and
thermocline,
At 13,700 years B,P,, N, fonticola
be interpreted.
mobile
rising
contribution
The low Al203 and Mn
These elements subsequently
S. astraea returns to dominance, reflecting
rela
Around 13,000
This suggests
as the relative
is reduced,
nutrients,
permits
water,
some
lower lake levels
rise,
and
and better
circulation,
Again at 12,000 years H,P,, N, spiculurn became prominent,
rather
stable
stratification,
Geochemically
the stabler
made the deep water and sediments more reducing,
implying
stratification
and Fe-deposition
as
-46-
pyrite
and organic carbon
deposition
sedimentary constituents.
evidence
for volcanism
subiacustrine
water at depth.
activity
relative
of these
during this
period
saline
and the introduction
surface
resulting
layer of water overlying
sharp,
stable
would be favored.
thermocline
of climatic
cooler,
Prolonged.intervals
of a relatively
saltier
warm,
water,
The
and N, spiculum
endured for nearly two hundred years
as stratification
B,P,, N, fonticola
became less
High water levels
and a fairly
increased
stable
Increased pyrite
deposition
deep thermocline
and high runoff is similarly
and became diluted
subsequently
in abundance,
N, spiculum,
recognized
as the temperature
waters
increases.
a strongly
stable
becaue
thermocline
only the availability
production
are suggested,
reducing hypolimnion,
implied
A
as the lake opened
to be replaced by N, fonticola
a general
and the thermocline
and density
differential
is becoming more
of surface
of the phytoplankton
and deep
result,
between S. astraea and N, fonticola
of Si, and do not necessarily
and
warming trend in the
Reduced mixing and lower productivity
shifts
to S.
relative
From 9,000 years to 5,000 years B,P,,
This reflects
world-wide,
stable
be emphasized that
implies
at 9,000 years.
S, astraea declines
the total
is a climatic
change or reduced volcanic activity,
At 11,500 years
climate
spring
through this
would reduce mixing,
These conditions
before N, spiculum declined
astraea,
of saline
‘lake was being freshened,
of warm, wet years might favor the establishment
with the
could indicate
However, Pb is low, and equally plausible
and a closed,
dilute
to the other
conditions
The climate was becoming warmer and moister
causation,
time,
The association
high Ti02
volcanic
increased
It must
reflect
imply any changes in
or even of the diatoms,
Gross
-47-
productivity
will be set by the supply of P and N, which will be utilized
by non-siliceous
algae as well as diatoms.
A relative
increase
spiculum, however, does imply, under the model presented,
phytoplankton
production
Hydrothermal
ture approximately
has decreased
activity
established
overall
low mixing rates,
density struc
a thermohaline
5,000 years H,P,,, and the consequences
were rapid and extreme,
for diatoms
At a sediment depth .of 130 cm in core 10, there
is a sharp contact both in lithology
5 mm, the sediment changes
yellowish
In the space of
and biofacies,
from a carbonate-rich,
ment, dark greenish grey in color,
and diatomite,
as it reflects
that
finely
laminated
to olive
in color,
dark brown in color,
and finally
material,
The diatoms
change from Nitzschia spiculum in the first
with a gel-like
of Nitzschia such as N, palea Kitz,
absolute
abundances,
siliceous
scales
Saedeleer
identified
fossil.
scales
Fig.
6,
Even more striking
as diatoms.are
consistency,
unit to purely
This assemblage
of short,
is not nearly
siliceous
Fig.
6,
as extreme as it was in the first
algal
de
but the elimination
the past
event.
of
5,000 years
Among non
species of the green algal genera Tetraedron and
Cosmarium are prominent in these brown layers,
fiable
Stokes
become the most abundant micro-
species which are abundant throughout
microfossils,
and minute,
wide Nitzschia and Paraphysomonas
recurs within each brown layer
the long, thin
are the changes in
Paraphysomonas vestita
by R. W. Norris
short
W. Smith and
scarce in the brown unit,
of the chrysophyte,
ash
to an organic,
Stephanodiscus astraea v, minutula in the second, to relatively
N. accomodata Hustedt
sedi
to a thin layer of fine volcanic
unlaminated
and, wide species
in N,
remains is quite
but incidence
of identi
low compared to the other sedimentary units.
-48-
The brown units
phytoplankton
are interpreted
productivity.
Planktonic
Many of the species present,
for an epiphytic
substrates
planktonic
as nutrient
as periods
e,g,,
occupying benthic
motile,
colorless
reduced
diatoms were virtually
eliminated,
N, palea, have a demonstrated
existence
habitats
1956
Gessner,
and/or energy sources.
species
of greatly
in Kivu,
phagotroph which ingests
and using organic
Hustedt
found these
1949
Paraphysomonas vestita is a
and small algae
bacteria
The emergence of these
and Leedale,
1961,
microfossils
in the sediment may simply be due to the elimination
more.numerous producers,,
i.e.,
counting
400 diatoms
restriction
suggests
of this
that
flourished
at each level
they are remnants of a distinctive
techniques
them; but the
and the Parccphysomonas
phytoplankton
which
at the time,
By the models discussed
stable
would not reveal
of the
throughout
the standard enumeration
element to the Nitzschia spp,
Manton
as the most prominent
species
these elements are ubiquitous
the core, but at abundances so low that
ability
density
stratified
rapid onset of this
and led to a constant
implies
the lake sufficiently
activity
that the hydro
to trap CO2 and dissolve
such low productivity
displaced
of an extremely
reduced mixing and extremely
As the chemical stratigraphy
calcium carbonate at .that time,
the pre-existing
is expected,
The
deep water upwards
advection of water low in Si but rich in N and P
into the surface waters,
Production
discus astraea was deposited,
between the cool,
was intense
and the layer of Stephano-
As the warm, saline
basin and rose near the surface,
established
the establishment
interf ace could lead to greatly
low productivity.
thermal activity
earlier,
a sharp density
dilute
water filled
difference
the deep
would be
surface water from runoff and the
-49-
water,
hydrothermal
The exact depth of this
mined by the relative
stable
two-layer
the result,
inputs
would be deter
interface
of the two water sources,
Initially
system may have been present with very low productivity
Diatoms, because of their
sinking habit,
again in the low nutrient
environment,
of an epiphytic
would survive by attaching
existence
buoyant algae such as blue-greens,
would be selected
Only those diatom species capable
flagellates,
tc
resources,
as a great .proportion
will be tied up in dissolved
perhaps
on microalgae,
e.g,,
unable to ingest the larger
previously
water,
from below,
of biogenic heating
liferation
and greater
increased,
conditions,
two-layer
This species would be
conditions,
system, warm salty water under cool,
system proliferated
because of the heating
may have been significantly
layers
mixing resulted,
surface waters,
the salinity
and euplanktonic
bacteria
Deuser
reduced density
diatoms reappeared.
et al,,
differences
As the hydrothermal
and productivity
augmented because
relationships
between layers,
of the surface
waters
Under the low nutrient
the long, thin Nitzschia were expected
The ecological
Pro
1973,
water mixed into the
Fig.
was joined by N, bacata and N, mediocris as new elements
plankton,
feeding
The Tetraedron and Cosmariwn would not be
by fermentative
of multiple
in the system
diatoms which dominated the phytoplankton
a multi-layer
This heating
The
to utilize
pm would be present,
with the proposed oligotrophic
From the initial
dilute
10-20
more
we have found up to 50 mg
small flagellates,
and subsequently.
inconsistent
ability
of’ the nutrients
organic material;
The small P. vestita
C per liter,
larger,
and green algae,
Nitzschia spp. would also be favored because of their
organic
a
of these three
7,
N, spiculuin
in the diatom
is unclear,
as
-50-
little
is known about any of them, but they all
morphology,
occupation
of planktonic
of all other diatom species,
determine whether this
lutionary
niches left
greatest
relative
or absent,
which should indicate
to
of new species or evo
of immigration
N, mediocris and
within the lake,
have their
vacant by the exclusion
record is insufficient
The available
is a result
diversification
the long, thin
of Nitzschia spp, of this morphology probably
Proliferation
represents
do exhibit
N, bacata
abundances in the core where CaCO3 is low
that stratification
was most stable
character,
N. spiculum has a maximum for the past
5,000 years at approximately
2,000 years B,P,, while CaCO3 was being
of a thermohaline
deposited
and perhaps
only a deep thermocline
and
was present.
Another new element in the diatom plankton was a Chaetoceros sp.
Fig,
7,
This genus is rarely
typically
tinental
marine,
All previous
recorded from inland waters,
reports
of significant
waters have been from lakes much more saline
Lake Kivu, where we have found it in surficial
1958,
Its
abundance through
imately 4,000 years B,P,
higher salinities
Its presence
in the modern lake may reflect
conditions
negative
as salinity
interaction
indicating
that
eliminated
during
stratification,
is probably
combined with low nutrient
adaptation
abundance in con
than the present
sediments
the past 5,000 years
cf,
Anderson,
in Kivu peaked
related
conditions,
by a strain
changed slowly over time,
as it is
approx
to somewhat
Its persistence
to the more dilute
It exhibits
a very strong
with the stubby Nitzschja spp, of the brown layers,
it,, as all the plariktonic
the ultra-oligotrophic
species of diatoms,
periods
of extremely
is virtually
stable
-51-
Although the lake has experience&notable
because of climatic
and volcanic
to varying nutrient
the Chaetoceros sp.
can be interpreted
diatom stratigraphy
is entirely
in reconstructing
portions
in part
tools,
of the lacustrine
conditions
conditions
of salinity
alone,
witness
the modern lake,
The chemical
waters,
on quite
surface waters,
which are caused by lake level
diatoms
can yield
by species shifts,
and biological
to.changes
fluctuations
information
as seen above,
evidence can full
reflects
of surface’water
in the deep
of CaCO3 in the deep waters
diatoms yield information
and respond principally
different
stratigraphy
but the imprint
the dissolution
In contrast,
The
Together they provide
as they yield evidence
in the surface
Only
with the chemical stratigraphy
of the lake,
environment.
the
regimes.
can and will be strongly modified by conditions
water and burial
tion,
in.terms
consistent
the paleolimnology
powerful paleoecological
changes in hydrography,
related
diatom flora has responded primarily
changes in salinity
primarily
in nutrient
and ‘stratification.
on relative
biological
Only by integration
understanding
of
on
chemistry
In addi
productivity
of the chemical
of the paleoenvironment
be achieved.,
Organic matter,
in core 10 and’throughout
organic
carbon is rather
core 4’
Fig.
12% C on a dry weight basis,
in core 10, organic.carbon
through the upper section
cm,
with an average
rises
below 130 cm
Values range from 1.5% to
around 7,5%,
Above 130 cm
sharply to 16% and remains over 12%
except for the interval
Changes in sedimentary
simply interpretable
3,.
constant
between 90 cm and 30
organic carbon in the north basin are not
in terms of productivity,
Much of the pattern
can
-52-
be accounted
mentary
for by the varying
constituents,
example,
i.e,,
diatoms,
at 130 cm, organic
tion of Fig.
3 shows that
contributions
CaCO3
‘
i...
of ‘the ‘other principal
and detrital
carbon increases.from.
the detrital
minerals
above, planktonic
plankton production
represented
strongly
reducing and more conducive
as a salinity
can easily
stratification
account
sitating
an increase
organic
carbon yields
productivity
in productivity.
to be’greatly
This couldbe
that
In this
production
in glucose. from terrigenous
had a distinctive
associated
relative
to an allochthonous
fell,
to other sediments,
source which would
origin.
organic
with relatively
The enrichment
contribution
component remained
which created a relative
cellulose,
sugars,
was too high
low planktonic
Itis
present during .deposition
pattern.of
in the brown
They found the
However, galactose
case the land-derived
and.phytoplankton
are usually
of the
thatplanktonic
the sugars
a.terrigenous
with the hypothesized
the unusual phytoplankton
layers
in glucose
as reflecting
all the material
is compatible
enrichment
suggests
from.,other strata.
large amounts of cellulose,
layer.
constant,
carbon withoutneces
characterization
characterized
enriched
interpreted
to attribute
to this
of organic material
fell
brown.layers
in glucose
phyto
These events taken together
In ‘fact,
and compared them with sugars
contribute
‘
in organic
which also
Mopper and Degens ‘1972
layers
or vanish,
The deep waters became more
was established,
information
and total
for preservation
for the dramaticrise
by Al203
all decrease
diatoms ‘became scarce,
probably also fell.
For
5% to 15%, but inspec
TiO2, CaCO3 and Fe2O3, the other major components,
As discussed
minerals0
sedi
also possible
of these brown
but brown organic.sediments
high allochthonous
contributions
-53.-
Hutchinson,
plankton production.
probably
Earlier
deep water,
Reducing
sediments
activity
otherwise,
The very fact that
the lowered activity
of the sulfate-reducing
these sediments
bacteria,
As a substrate,
organic matter which had already been subjected
degradation
in soils
teria
as plankton
Separation
all
productivity
record,
activity
of intense
from nutritional
activity
does reduce.phytoplankton
metals
to eliminate
ganic’ sediment constituents,
a rising
trends
through
concentration
the cores,
initiated
changing diagenetic
conditions
and the thermocline
becoming sharper,
in the hypolimnion,
would be expected.
created by inor
no
amino acids demonstrated
may reflect
in the deep water,
Better preservation
and contin
in part
The climate
which leads to stronger
Hexosamines increase
strati
production
amino acids exhibited
but total
This rise
from
is reduced.
at 260 cm 8,500 years H.P.
uing to the surface of the core.
conditions
the variability
The individual
activity.
are given for core 10
Amino acid and hexosamine concentrations
recognizable
bac
density
the stronger
and the input of toxic
in Fig. 8 on a carbon basis
hydrothermal
ones is not possible
but it is clear that
imposed by spring
even when spring
for the sulfate-reducing
the evidence is compatible with very low
during periods
of toxic effects
the stratigraphic
fication
to bacterial
detritus,
In conclusion,
phytoplankton
black because
are brown reflects
terrigenous
would not be suitable
the Fe and
would have been removed
are characteristically
of FeS precipitation,
was
sulfate-reduction
of these sediments;
from the hydrothermal
with a low phyto-
is consistent
it was noted that
less during deposition
other heavy metals
in.the
This likewise
1957, p. 882,
the
is warming
reducing
of organic material
even more sharply
at 260 cm, but
-54-
they subsequently
tinue to fall
contribute
towards the surface,
biomass produced,
of amino acids,
information
neglecting
bacteria
affected
effects
rapidly
are more conducive
therefore,
Degens and Hecky, 1973,
as ammonification
by heterotrophic
in oxidized sediments while reducing conditions
to preservation.
Chitinous
particles
relative
activity.
mental to zooplankton
plankton,
Better preservation
to amino acids in deep
in two ways,
The first
into surface
The second would be indirect,
eliminate
and change in algal
some zooplankters.
activity
as stratification
species
composition
caused a drop
sufficient
In modern Lake Kivu calanoid
at all
seasons,
dant only after
seasonal mixing when productivity
cladocerans
as the
waters could poison the zoo-
zooplankters
In Edward and Albert,
could be detri
would be direct,
the predominant
1957,
AA:HA ratio
of amino acids would account
but the hydrothermal
of heavy metals
in productivity
appear to be
across the contact which marks the onset of strong
for the change in part,
introduction
can yield
Mopper and Degens, 1972,
threefold
hydrothermal
source
Diagenesis will
In Lake Kivu sediments the amino acid:hexosamine
increases
considerations,
community through time,
as hexosamines are enriched
ocean sediments
By trophic
will be the most prominent
of the plankton
for amino acids,
proceeds
and bacteria
but we concur with Kemp
of these two components,
on the balance
be most critical
cell walls,
algal proteins
A ratio
diagenetic
sediments,
insects
chitin will be more abundant and more resis
to breakdown than bacterial
i.e.,
less
‘that
sharply at 130 cm and con
Zooplankton,
hexosamines to lacustrine
and Mudrochova 1972
tant
off and then decrease
level
to
copepods are
while cladocerans
is highest
are abun
Verbeke,
and copepods are abundant
-55-.
throughout the year,
phytoplankton
although their
be that one or all
of these
.L.J.
acteristics
may explain
of diatom frustules
population
than one-half
in the percentage
to benthic
that
of breakage
zooplankton
analyses
view of the present
to either
toxic
that
LJ_
L11.L
a shift
in
organisms,
decreased
substances
are broken.
only those
frustule.
Prepara
and thus breakage was not
rapid
agitation.
as the entire
of zooplankton
Therefore
the
The decrease
an overall
in the
or a reduction
the breakage
of zooplankton
Breakage
core is finely
of zooplankton.
have been done on’the core,
distribution
Helow
by counting
can be explained by either
element producing
in the
changed,
bottom fauna be absent,
decrease in the feeding activity
cladocerans
eJ.LL
an entire
for’samples,
breakage must be due only to the activity
that
__....___--
LiL
indicates
which does include
which requires
microfaunal
for cladocerans
the Nitsschia spiculum frustules
were identical
cannot be attributed
specific
iL.A
depicted in Fig, 8 were generated
due to sample handling,
laminated,
are necessary
occurred when the AA:HA ratio
which were greater
tion techniques
._1..__.
and it may
why clad.ocerans have never been found offshore
130 cm nearly 50% of all
frustules
phytoplankton,
Lake Tanganyika.
Observation
The frequencies
lakes have high productivity,
characteristics
-.--
ultraoligotrophic
numbers wax and wane with
and a diatom-dominated
4-,-.
.,
zooplankton
The latter
productivity.
high standing crops,
relative
during feeding,
No
but it is tempting,
in the lakes,
in
to conclude
in the Kivu about 5,000 years ago as a response
from hydrothermal
quantity
and nature of food sources,
particles
>15 pm more effectively
activities
Large cladocerans
or a change in the
harvest
than small zooplankton
large
Hrooks,
1969,
-56--
Most of the diatoms
a reduction
of this
study would qualify
in diatom production
to explain
of Kivu,
As there are no planktivorous
the paucity
of cladocerans
by predation,
lakes
would not be a factor,
If conditions
as they did 5,000 years H.P.,
of trophic
status,
duction is markedly increased,
degree,
These circumstances.
is available
from that
in much better
phytoplankton
pro
to a lesser
in the AA:HA ratio,
was highest based on the diatom evidence
Only one analysis
and the AA:HA ratio
As the lake was
time,
circulation
high ratio
of amino acids.
increase
algal
lake phase of 13,000 years H.P.
vertical
this
reducing,
saline
zooplankton
as an indicator
is that
would lead to an increase
In the Kivu core, productivity
in the shallow,
could serve
of eutrophication
while
reduction
do not change markedly in a core
the AA:HA ratio
A characteristic
plankton
commonly observed in temperate
which i
of preservation
in the offshore
fish in Lake Kivu today,
of large zooplankters
1969,
and
5,000 years H,?, might be sufficient
in itself
Brooks,
as large particles,
In this
production
at that
time,
cannot be attributed
case the high ratio
and eutrophic
is 20,
and deep waters
to better
reflects
less
preservation
extremely high
conditions.
SHALLOW SOUTHERN BASINS <100 m water depth
South Idjwi Basin Station
At the southern
13’
end of the main lake,
there
is a shallow,
like basin which has a maximum depth of 220 in, and deep sills
separate
the deeper water of this
main lake,
basin from direct
The 421 cm core from station
a soil horizon which developed
l3
in 86
shelf
at 180 m
exchange with the
in
of water ended in
during the low lake stand,
A radiocarbon
-57-
date near the bottom indicates
at 12,130 years B,?.
that
lacustrine
This correlates
average
sedimentation
the core
Fig,
geochemistry
9
from this
elemental
10,
conditions,
a gradual
material
that the same five factors
at station
on the detrital
lowering of the lake after
in
in the core are given in
factor
1
deep water
by downcutting
are
13’ as were operating
followed by the return
This is explained
as indicated
factor
a relatively
years and 5,000 years B,?,,
of
with the deep water record,
indicates
distribution
as it indicates
a much lower
The chemical stratigraphy
Factor scores for each level
The loading
instructive,
analysis
1.6
should reveal the shallow water hydro-
which was correlative
the north basin,
Fig,
site
rate,
and this would be consistent
After 11,000 years B,?,
rate is observed,
Varimax factor
controlling
A high sedimentation
up to 11,000 years B,?,,
with a near shore environment,
was initiated
well with the high stand hypothe
sized from evidence in the north bas’in,
mm/yr, was indicated
sedimentation
is especially
stand between 10,000
to somewhat shallower
at the Ruzizi which created
it opened,
The deposition
of detrital
by the Ti02 and Al203 content was very high initially,
No diatoms were observed in the sediments below 330 cm, which also suggests
a very rapid rate of deposition,
The negative
loading
of over most of the core on factor
that
deposition
of CaCO3 was high relative
this
correlates
well with events of this
basin.
2 means
to diatom sedimentation,
time period
in the northern
The very high values for Ca at 11,000 years H.P. support
hypothesis
that
in the closed
lower values prior to that
tributions,
lake Ca was removed peripherally,
represent
dilution
and
the
The
by the high detrital
Mn has maxima with the Ca, confirming the precipitation
con
of
-58-
a manganous carbonate
Fig,
9
does not increase,
deep water during this
of the core,
it
at least
Mn is relatively
time,
weakly reducing
thermocline
conditions
most of the Mn present
phase,
Negative
and a sulfide
independently
is in the detrital
in the
of A12O3 and TiO2, suggesting
was over the site
were common,
shown in
high in the lowest portion
The subsequent period of low deposition
the seasonal
during this
as it was being removed’ as a sulfide
but it oscillates
is authigenic.
Fe2O3 not
in shallow water environments.
suggests
at this
time,
that
and
In the upper region of the core,
The lake was dilute
phase.
and MnCO3 would not be expected.
loadings
facies
on factor
3 are also low over most of the core,
was never abundant at this
by the behavior of Ni
Fig,
loaded through the core,
9.
The Mg factor
indicating
site;
this
is likewise
is demonstrated
negatively
that the lake waters over this
site
have always been dilute.
The increase
reflects
trapped
of Pb deposition
the initiation
factor
of hydrothermal
5
activity.
at 5,000 years
H.P.
Not all the Pb was
in the deep waters of the north basin by organic chelation
precipitation,
but the amounts incorporated
in the shallow-water
‘ments are much lower than in the north basin sediments.
of the sediments
reconstruction
at station
of the
Bukavu Basin Station
Ruzizi River,
sill,
sedi
The geochemistry
13’ does not appear to conflict
with the
lake based on the north basin record,
15’
The Hukavu Basin is isolated
by a shallow
and
approximately
the only outlet,
30
exits
from the main lake and station
in
deep at its maximum depth,
from the southern
13’
The
end of this basin,
-59-
The stratigraphic
record in the Hukavu Basin should be the best
for the opening of the lake and the existence
ysis again implicates
scores
ical
the same factors
a light
grey color;
>5 mm/yr.
the latter
core,
often
The highlights
saline
waters
during this
of higher lake levels
deposition
fell
at this
an evaporating
site because the Ca-source
land
a saline
but it was probably not as saline
of salinity,
initial
until
alkalinity
sedimentary
Carbonate
was farther
as that was also
as the smaller
would remain high and Ca-removal would
above the present
at the coring site
freshened.
not due to overflow
deep lake would have existed prior
deposition
in itself,
the lake was considerably
in
The first
in the Hukavu Basin prior to connection.
decrease was perhaps
in the Kivu area 100
pan.
Connection with the main lake
dilute
body of water which existed
with the main
is about 10,000 years H.P.
the waters
with
The gross stratigraphy
the coring site.
would not significantly
body of water,
rapid deposi-
The lake was below
If it were connected
away and/or the waters were more dilute,
was
for 70% of the dry weight.
approximating
indication
be peripheral
of the chem
for most of the sediments,
covered the site,
time,
shallower conditions
Regardless
and factor
from 290 cm to the bottom,
accounting
60 m of water would overlay
suggests
cores,
suggested extremely
Clays and CaCO3 account
Shallow and alkaline
lake,
of this
and carbon dating
predominating,
the Ruzizi outlet
10,
Factor anal
are depicted in Fig, 11,
The lowest portion
tion,
as for the other
for each sample are given in Fig,
stratigraphy
of an outlet,
evidence
at the Ruzizi,
lake level
to overflow,
allowed relative
Therefore
suggest
that
The decrease
increases
the
Terraces
a rather
in CaCO3
in all
the other
components, such as A12O3, TiO2, and Ni in the detrital
phase,
-60-
and Mo and organic
carbon in the biogenic phase,
due solely to the decrease
depth increased,
concentration
of carbonate
sedimentation
A very strong negative
and the detrital
These increases
correlation
and biogenic
at site
Throughout the lower portion
as a carbonate
or oxide,
shallow water stage.
phases is evident from Fig, 11,
it rises
quite
alkaline,
sharply,
At approximately
and for several
though Ca-deposition
become diluted,
conditions
indicating
and Ca-deposition
A similar
suggest
slight
These sediments
served,
completely
during
circulated,
lake level
was
The low Mn
Mn-deposition,
in the record,
rates
are ob
as the river downcut its outlet
From 5,000 years H.P. the basin has been
the sediments were not sufficiently
reduction,
This means that
the main lake must have been below the sill
water depths greater
the same time,
and MnO2 remained in the deep sediment,
the high lake stage,
to allow sulfate
the lake had
of Ca-deposition
and slow accumulation
resulted
and lowered the lake level,
was very low, even
and decreased
marks the highest
conditions
it begins to decrease
This means that
change in the nature
are not diatomites,
Oxidizing
were still
was a consequence of photosynthesis
reducing conditions
and the low Mn interval
in the
conditions
hundred years Mn deposition
recorded in the north basin at approximately
values
that
9,600 years B.?,,
achieved high values,
in offshore waters,
were possible
in CaO is recorded in Mn, and
decrease
again when CaO does also,
than the other ele
of the core it is probably present
as oxidizing
The initial
as water
between the CaO
The Mn as usual appears to behave differently
ments,
are
than 130
in
during
Even
reduced
the deep thermocline
separating
the high stand.
the basins
in
at
-61-
Trace metals
and freshening
alkaline,
in the carbonate
of the lake,
saline
phase likewise
In the aragonite
deposited
Sr and Ba are very high,
phase,
record the opening
in the shallow,
They drop sharply
Mn does as a response to a change in the nature of carbonate
tion.
As Ca-deposition
changed from being purely
mediated by algal photosynthesis,
aragonite
personal
to calcite,
communication,
the crystal
lattice,
ited, once again,
deposition
activity
hydrocalcite
increased
a return
the correlation
line of evidence that
implicates
served changes is an attempt
years B,?.
This material
The attempt
atmospheric,
Further
futile.
Stoffers,
began to be depos
as hydrothermal
and made deposition
Lead also increases
at the same
with the north basin,
the springs
Another
as the cause of the ob-
to date sedimentary
organic carbon between
gave an anomolously old date of 9,460 ± 240
This was the only attempt made to date sediments deposited
‘after the hydrothermal
lake,
to inorganic processes
impossible.
changed from
This change in carbonate
the input of Ca and alkalinity
substantiating
115-170 cm.
aragonite
and the Ba and Sr increase,
represents
P.
to being
change excluded Sr and Ha from
At 5,000 years H.P.,
in the deep north basin
time,
and protodolomite
The structural
sedimenta
inorganic
the carbonate mineralogy
when
springs
determined
the water composition
confirms that the carbon from the springs
and only partial
dating of sediments
As a result,
equilibration
of the
is not
with the atmosphere
occurs.
deposited
in the past
5,000 years would be
age assignments
during this
interval
are only
approximate.
There is a pronounced maximum in Mg at a depth of 60 cm.
its peak Mg is nearly equal in concentration
to Ca, suggesting
At
that
-62-
authigenic
dolomite may be present,
must imply a substantial
increase
For reasons discussed
in salinity,
The lake dropped below
the Ruzizi,
and may have had only an intermittent
main lake,
Such a connection
evaporative
directly
1967,
concentration
to high magnesium calcite
Liebermann,
dried out during
The shift
from aragonite
and dolomite once again excluded Sr and Ba
from the carbonate phase.
This Mg maximum is correlative
CaCO3-rich sediments
deposited
in the north basin.
The decline
Ruzizi outlet,
ion ratios
actually
did it overflow.
but neither
to
to dolomite precipitation
might be favorable
There is no evidence that the basin
this interval,
from Kivu which
The waters when subjected
because of the unusual
from solution
connection with the
allowed recharge of waters
were already low in Ca and high in Mg.
this
earlier,
between 3,500 years and 1,200 years H.P.
The consequences
overflow will be discussed
with the
in Mg is attributed
to regaining
the
for Tanganyika of the intermittent
later.
LAKE LEVEL OSCILLATIONS AND WATER BUDGET
Kivu
The radiocarbon-dated
logy of lake levels
are considered
i
cores
Table
to be established,
4
allow an absolute
The most reliable
chrono
datum points
to be:
The thick
beach deposit
level the lake recorded
at station
in the time interval
ii
the clay facies
iii
the initiation
at station
14 which marks the lowest
sampled;
9;
of sedimentation
at station
13’;
-63-
the first
iv
decline
the terraces
v
hiatus
correlate
at -310 has not been directly
is thought to have occurred,
The clay facies
in station
This implies that
10,000 years B,?.
dated as a depo
but it is thought to reasonably
age of 13,700
bedding.
as much as 250 m,
and there
over 90% of the assemblages,
that the age is too young,
no source
of "fossil"
carbon.
1959.
The only possible
Precipitation
the lake surface would reduce the residence
to incorporation
and. Walton,
1959.
to be reasonably
discussed, earlier,
of volcanic C02, the
and this
error
anions
so there was
could arise
all
except
from
in the closed lake
of Ca and
invasion
across
time,
All our 14C analyses
fraction
will be much less
of old carbon than will the carbonates
Therefore,
accurate
and it is
There is no reason to assume
rock exposed in the basin,
‘were performed on organic carbon,
or graded
from the atmosphere by weathering
time for the HC031 -CO32
and Walton,
extends
astraea constitutes
is not a turbidite,
Prior to the injection
There is no carbonate
a long residence
Broecker
This deposit
of the water was derived
reactions,
The clay facies
and Stephanodiscus
of a shallow water environment.
alkalinity
between 11,000 and
is no evidence of coarser material
Diatoms are abundant,
indicative
9 has a date of 10,670 years H,?,,
the lake dropped significantly
by perhaps
over 30 cm of depth,
15’; and
the time not sampled by cores 10 and
which means it was deposited during
subject
at station
with the bottom of core 4’, which has a carbon-dated
years B.?.
4’.
deposition
which surround the lake,
The beach deposit
sitional
in aragonite
Hroécker
the dates on the cores are considered
for the one from station
15’ which was
-64-
The initiation
years H.P.,
of sedimentation
at which time the lake level
appears unlikely
record at station
to tell
and the mineralogy
It may have before
12,400 years H.P.
sediments
and sloping
The terrace
Olson and Hroecker,
and is likely
was a fossil
too old,
site,
and this,
13
combined
would favor erosion
at +100 m has been dated at
1959,
but the date is on shell
A date of 9,500 years H,P, seems more
This date is likely
as the higher terrace,
reasonable.
from a beach at the present
A date of 14,000 years H.P. suggested to them this
beach.
same factor
to be in error by nearly the
and an age of 11,000 years would be
This would coincide with the high stand prior
at 10,500 years.
If the lake stood that high,
connected with the Bukavu Basin,
in
so it is not
as this high stand probably marked the opening of the lake.
level of the lake.
100
The
exposure of station
duration,
Olson and Broecker also dated shell material
in level
15’,
it sank down at 10,500 years B.?,
The low stand was of short
than soil development.
appropriate,
changed at station
evidence of the subaerial
with the unconsolidated
material
However, it
in,
if the lake overflowed into the Hukavu Basin prior to
There is no noticeable
rather
exceeded -86
15’ extends only to 10,200 years B,P,,
10,000 years B,?,
at that time,
13’ occurred at 12,130
that the lake overflowed before 9,500 years B,P,, when
carbonate deposition
possible
at station
but the Ruzizi outlet
to the drop
then it was
was still
nearly
above the lake,
The only unequivocal
evidence for lower stands
H.P. are the Mg-rich sediments
not extreme,
probable,
and an intermittent
The sill
in station
15’,
since 9,500 years
The drop in level was
connection with the main lake appears
is at -30 in, so a drop of much more than 30
have been only temporary.
in
would
-65-
The reconstruction
of lake levels
is presented
it is compared to a record of lake level
for Lake Victoria.
because of its
more detail.
A rather
but the Kivu record,
to 12,000 years H,?,,
Butzer
are slight
Victoria being a shallow saucer,
would be more comparable.
exists,
1969
exhibits
for a low stand in Victoria between
at that time
This is a result
12, where
inferred by Kendall
but the closed basin lakes
changes in Victoria
changes in Kivu,
lake level
rate prior
There is no clear evidence
record lower levels
The level
good, correlation
high sedimentation
2,000 and 3,000 years B,?.,
valley
changes
in Fig.
et al.,
in the Eastern Rift
1972; Hecky, 1971,
compared with the tremendous
with
of the morphometry of the basins,
and Kivu a deep cup.
The hydrologic
parameters
changes in Kivu will be discussed
later
The volume changes
which permit
in connection
these
with
Lake Tanganyika.
Aside from the firm datum points
core suggests
somewhat higher levels
and 13,000 years H.P. on the basis
geochemistry.
tive
The prominent
discussed
above,
at approximately
of the fossil
the station
12,000 years B.?,
diatoms and sediment
12,000 years H,P. event is probably
with the "BØlling" interstadial
followed would then correlate
of Europe.
interstadial.
which station
the "Younger Dryas",
is not identified
in the European chronology,
the Camp Century ice core
lations with approximately
These oscillations
the Holocene,
Dansgaard
et al.,
and the
The very low lake
succeeding high lake with the "Aller$d"
opening of the lake would initiate
correla
The lower lake which
with the "Older Dryas" stadial,
9 records would represent
4’
and the
The 13,000 year event
but o8 fluctuations
1971
in
reveal minor oscil
a 940-year period which precede
will be termed "Kivu Oscillations",
the BØlling,
because the Lake
-66-
Kivu record presents
the most complete and readily
the late ?leistocene
yet available
great detail
nearly
that
climatic
in tropical
correlated
Africa.
history
It confirms
of
in
events between the equator and the poles were
synchronous through the past
14,000 years,
Tangcmyika
The cores
available
The oldest sediments
19
separating
recovered
The sedimentation
low, and the possibility
are rare in the core,
suggesting
rates
of a hiatus
and one of these was chosen for detailed
resolution
for the chemical history
diatom stratigraphy.
The recovered
station
Station
15 which was radiocarbon
an age of 4,000 years,
presented
in Fig.
13.
performed,
and abundant fossil
to gain better
analysis
and is readily
dated,
with the
In addition,
dating,
correlated
in
of water,
with nearby
The bottom of the core is assigned
of the chemical stratigraphy
the core from station
organic carbon,
are
2 in the south
and CaCO3 analyses
This core was somewhat longer and older and covers over 6,000
years.
The CaCO3 stratigraphy
in Fig.
15, where it is compared to that
is .given in Fig.
The Ti02 and A12O3 content
of the core.
variation,
or non-deposition,
and to allow correlation
The highlights
basin also had radiocarbon
seems likely.
12 is in the north basin in 1,200
core is 195 cm long,
station
implied for this
dissolution
The cores from the deep basin have much higher rates
diatoms,
cores,
are in a core taken from the sill
the two basins.
core are extremely
Microfossils
from Tanganyika are short gravity
14 and the organic
of stations
carbon
15 and 19,
are nearly uniform over the length
The A12O3 concentrations
presented
in Fig,
as they are given on an expanded scale;
13 show some
but the variability
-67-
reflects
primarily
diatoms,
organic
the sedimentation
of the other components,
carbon, and carbonates.
to have been stable
Likewise,
for the Mn system.
that the hydrogeochemistry
4,000 years.
sharp rise
higher
very low concentrations,
High Ca-deposition
which they fell
than those prior
similar
sharply
to 3,000 years
was recorded in the recent past.
strates
Only CaO concentrations
H,?.
while Ca-deposition
very low organic
The ionic
was noted above,
1952; Coulter,
one-half
Fig.
abrupt.
the salts
thermal activity
Ca-deposition
an appropriate
delivered
in Tanganyika are rel.ated
e.g.,
period,
15
Heauchamp,
the Ruzizi accounted
but
do have
1939; Capart,
for up to
We have seen that
of enforced hydro
which began in Kivu 5,000 years B.P.
in Tanganyika;
about
from Kivu and Tanganyika
investigators
that
Fig.
river is the result
delay which reflects
Organic
1971.
to the lake annually.
of the present
demon
increased more than 1,000 years
of surface waters
have suggested
14
from much lower levels
Degens et al.,
and most previous
1963
the high salinity
and, salts
similarity
for
Another sharp increase
cores which cover longer periods
carbon contents
is a rather
to rates which were still
The record in the north does not extend over this
other correlatable
in the past
rates were maintained
changes, but they are somewhat less
4,500 years H.P.,
show
approximately
The south basin core
carbon in the south basin core,increased
later.
there
at 130 cm which extends 30 cm, representing
time, after
appear
invariant
of the lake has changed markedly
From initially
600 years of deposition.
a short
conditions
Lead is relatively
except for a pronounced peak at 95 cm,
especially
The’ increases
in
to the events in Kivu, but with
the large residence
times of water
it would take nearly 1,000 years
for the
-68-
tributaries
of Tanganyika
evaporation
losses,
to renew the volume of the lake,
The Ruzizi is more saline
and hence it flows downslope on entering
on surface waters.
effect
Only after
across the thermocline.
Thus the initial
of the lake become affected
input
source
with the deep water
homogenization
become noticeable
becomes a broad diffuse
than Tanganyika waters,
the lake without immediate
will any pulse in salts
Ruzizi
neglecting
in surface waters by mixing
point
the
thermocline
nearly synchronously
the
source of salts
and wide areas
well after
the initial
increases.
In Fig.
14 the CaCO3 content of station
with the Tanganyika
records.
basin of Kivu occurred
10 in Kivu is juxtaposed
The maximum in deposition
during an interval
in the north
when the lake was closed.
the Kivu basin is the primary source of the calcium in Tanganyika
postulated,
after
then a hiatus
a sufficient
lag as a lower deposition
seems consistent
increase
in CaCO3 deposition
salinity
with the available
concentration,
changes.
source of the Ca.
in Tanganyika.
Further
as the tremendous volume of the lake buffers
The correspondence
thermal activity
indicts
as the mechanisms
different,
of the effect
on Tanganyika of the hydro
from analyses of interstitial
of a core from station
Kivu water as the
of the maxima in Ca-deposition
in Kivu and the climatically-induced
the Ruzizi is obtained
waters
are quite
confirmation
The
in Tanganyika 2,000 years ago cannot be due
The peak in Pb concentration
the increases
Such a
CaCO3 stratigraphy,
2,000 years H,P, in Kivu and Tanganyika is fortuitous,
eliciting
as
in the overflow from Kivu would be reflected
sequence
to evaporative
If
2 have been analyzed
intermittency
waters.
of’
The pore
Greene and Jones,
-69-
1970,
and the results
salinity
are given in Fig.
of the lake over the past
ions which are most sensitive
disproportionately
other inflows
dramatic,
and a second interval
similar
pattern
an interval
of increase
without
although slowly,
salts
as Na does,
of the Ruzizi and the Malagaris;
That Mg and
only emphasizes that
by calculations
presented
later,
cations
in Table 1.
of the lake is still
cf,
It appears
increasing,
which indicate
tribu
and this
that more
enter the lake via the Ruzizi than leave the lake via the Lukuga.
As the lake is not in equilibrium,
have little
meaning.
In general
calculations
of salt
it is concluded
that
primary
source of salts
flowing
into the lake between approximately
B.?,
the Ruzizi,
are the primary source for these
from Fig. 16 that the salinity
is supported
of the lake would
of the Virunga, which is the second largest
tary to Lake Tanganyika,
the chemistry
the period
for
As Tanganyika must become
continue
rocks of the volcanoes
A
is seen for Na, but the pause so evident
the salinity
through
pat
concentra
to the surface,
closed when the Ruzizi is not flowing,
K do not increase
and
a similar
of constant
extending
Mg and K is only a change in slope in Na,
to increase,
The two
on the Na and Ca would be less
Both Mg and K exhibit
of increase,
of increase
is demonstrated.
carry large amounts of these cations,
Ca is buffered with a solid phase,
tion,
in the
in Ruzizi waters when compared to
The effect
as the other rivers
an interval
increase
to events in Kivu are K and Mg, which are
to Tanganyika,
i.e.,
A general
5,000 years
over-represented
tern,
16.
This chronology
constructed
to the lake,
and that
residence
the Ruzizi
times
is the
Lake Kivu was not over
4,000 years and 1,000 years
for the Ruzizi at Tanganyika agrees, well with that
for the river
at its
source,
-70-
The initiation
the salinity
of the Ruzizi River,
the deep waters
shows.
of hydrothermal
of Tanganyika,
activity
which began to increase
as the stratigraphy
The immense volume of the deep waters
very slowly.
As the increases
Kivu, mixing processes
in the Kivu basin increased
of interstitial
allowed salinity
were slow, unlike
generally
the salinity
water
to change
the situation
kept pace and no persistent
in Lake
chemocline
developed.
The Ruzizi River is also cooler than the surface waters
Heauchamp,
1939
The increased
and nearly isothermal
salinity
of the Ruzizi
the cool water plume to greater
libration,
reduced,
The thermocline
As previously
,
Nitzschia sp.
detail,
relative
it
with the deep waters
after
depths
of the lake,
5,000 years H.P. would carry
and reduce somewhat thermal equi-
would be sharpened and mixing and productivity
discussed,
such conditions
Although the diatom stratigraphy
is clear that
would favor long,
is not complete
prior to 5,000 years H.P. in the north basin the
In the south basin S, astraea remains prominent
microfossil
assemblage up to the present,
the south,
The depth of detectable
Degens et al.,
1971.
of seasonally
account
for these differences,
material.
immediately
distance
south winds
Coulter,
from surface
i,e,,
1963
in the
mixing in
and the
presumably
stratification
would lead
of organic
waters would not begin until
in surface waters,
deep water salinity
at 5,000 years B,P,, organic
astraea
in the south
and better preservation
Ca began to increase
of these events,
better
from the Ruzizi,
A more stable
reducing conditions
CaCO3 precipitation
the Ruzizi-derived
succession
strong
indicating
02 is also greater
The greater
effects
to more strongly
thin
in any
abundance of Nitzschia spp. was lower and Stephanodiscus
was present.
of
The temporal
beginning to increase
carbon increasing
at 4,000 years
-71-
B,?.,
and CaCO3 precipitation
buffering
beginning
yika are closely.linked,
separated
from the former,
Tanganyika,
In view of this,
lake.
hydrology may allow insight
Hydrological
reconstructions
basin geology as it affects
In open lakes,
of the latter
require
runoff,
changes are subdued,
proportional
to surface
area,
An increase
will cause lakes to rise until
increased
surface
a reduction
it is possible
generate the lake levels
given in Langbein
within
observed,
primarily
estimates
Theeuws
The only discharge
of
rainfall
and run
from the
Thus, when Kivu was closed
most probable
climates
the hydrological
parameters
to
relations
data.
evaporation,
for the Lake Kivu basin
of the Kivu basin are given in
abstracted
newly generated
for rainfall,
1920,
lakes,
1961,
These were partially
represent
in discharge
and lower inputs will lead to
following
and the Lake Tanganyika basin exclusive
tially
knowledge
In closed-basin
in inputs
limits,
Morphometric and hydrological
Table 5.
from the,
which will be directly
area and lake level,
to reconstruct,
detailed
losses by evaporation
area equal the inputs;
in surface
into that of Lake
and lake morphometry.
response is mediated by changes in lake level,
water from a closed basin is by evaporation,
of Lake,
for that period
response to changes is reflected
while water level
cannot be
a reconstruction
although we do not have a record
of climate,
off
the
has shown that Lake Kivu and Lake Tangan-
and that the history
Kivu’s late ‘Pleistocene
rates
reflects
to change which the immense size of the lake engenders,
The above discussion
latter
at 2,000 years,
from various
sources
For Lake Tanganyika,
and inflow to the lakes
which appear to agree fairly
and par
hydrological
are those of
well with subsequent measure-
-72-
ments
1952,
Capart,
Morphometric data are based on the map of Capart
and Hutchinson
1949
1957;
lated using 900 mm as the average
of the Lake Kivu drainage
volume of inflows
Verbeke
1957.
and dividing
50% larger
were estimated
rate,
Data for the past
than previously
function
trough-like
Figs.
city,
morphology
to some fractional
relation,
believed,
equations
17, 18,
A
Tanganyika basins
Hutchinson,
Langbein,
in
Volume
area is propor
1961,
any significant
of Kivu, which dictates
the volume
are double and one-half
Rainfall
and rapid infiltration
i.e.,
For simpli
assume a linear
error
The basin slope,
The runoff coefficients
exclusive
is
for Kivu
interest
coefficients,
In most lakes,
lakes,
to the north of the basin effectively
For Tanganyika,
discharge
rates
Of special
these two parameters
change in area,
1957, p. 230.
is steep,
flow over a
in both lakes because of their
A
V°’40’75
relating
ganyika is nearly double that
nearly twice as much.
from Amenage
that
Evaporation
1961.
of area
as it will for other
a given proportional
indicate
and runoff
but this will not introduce
Tanganyika,
relief
10 years
from
power of volume, because most lakes have a
cross-section,
Langbein’s
value into the total
which was obtained
from a graph in Langbein
V. is a nearly linear
curvilinear
over the basin exclusive
des Chutes de Mururu, which monitors
Table 5 are the basin slope parameter
tional
this
is calcu
The data for Kivu are abstracted
except for discharge
dam on the Ruzizi,
nearly
area,
annual rainfall
less the Ruzizi,
ment Hydro-Electrique
The runoff coefficient
p. 168.
for Kivu and
AV/iA, for Tan
that to accomplish
depth
must decrease
for the Kivu basin and the
the world average
respectively
is quite ,high in the Kivu basin,
into the porous lavas and ash
,reduce evapotranspiration
of the Kivu basin,
losses.
much of the basin area is
-73-
in the semiarid plateau
are extreme,
region of Central
The water budgets
Tanzania,
lower than those of Heauchamp 1939,
which are often cited because he
the mean depth of Lake Tanganyika.
are estimated
salt
losses
and storage times,
are not completely
valid,
as the lakes
in Table 6
Also given
As mentioned earlier,
via the Lukuga outlet.
the interstitial
these
are probably not in any long-term
It can be seen that the Kivu basin is currently
twice as much Na and over three
storage
time are much
for refill
overestimated
equilibrium,
losses
for the two lakes based on the data in
The estimates
Table 5 are given in Table 6,
and evaporative
contributing
times as much K to Tanganyika as is lost
These values
water stratigraphy,
support
the interpretation
Both water and salts
given to
have long
times in Tanganyika and can be expected to respond slowly to
changes in input,
From Tables 5 and 6 it can be seen that
18% of the tributary
the Lukuga using
waters,
either
and its
the Ruzizi accounts for
volume discharge
Theeuw’s estimates
{l920} or Capart’s
Thus, loss of the Kivu overflow will be sufficient
to become closed,
Within the past
The question of interest
and what possible
l952},
to cause Tanganyika
14,000 years this has happened twice,
is how far did the level
effects
from Kivu exceeds
did it.have
of Tanganyika
drop,
on the biota of the lakes,
When Lake Kivu stood at -300 m, the lake had an area of 948
Fig.
19
and the tributary
is possible
bein
1961
2
With these values it
to generate a family of curves giving possible
of mean annual temperature
sufficient
area was 6,192
to maintain
and mean annual precipitation
combinations
,which will be
a lake at a given level by using graphs in Lang
and assuming different
runoff values.
Two sets
of curves
-74-
20,
are given in Fig.
a closed lake at the modern level,
maintain
ditions
One set gives the combination
which would maintain
conditions
tions.
it is necessary
Schumm 1965
to precipitation
gives a family of curves
This indicates
sity have on runoff.
arid climate,
the effect
that
determines
highly variable
a selection
it can
than
poro
Temperature
glacial
1967
the depression
is less likely
lower temperatures.
Flint
calculated
firn line.
1959
Mt.. Kenya and 7°C for Mt. Kilimanjaro
to be
and the probable
the elevation
of the
of 4°C under modern precipitation
of.the
by
or precipi
that
maxima in the Ruwenzori and determined
in mean temperature
one-
during the late Pleistocene
changes in Africa
Osmaston
i.e.,
With a curve selected
over wide areas than precipitation,
line during
polation
A value of 0,20,
of mean annual temperature
the other parameter,
have been estimated,
require
From this
would be lower under a more.
should be reasonable.
magnitude of temperature
would explain
mean annual runoff
but it would probably not approach the value for Tanganyika,
runoff coefficient,
decrease
relating
condi
topography and substratum
The runoff coefficient
half the modern value,
firn
of possible
is nearly 50% greater
0.08, because of these unique basin factors.
tation
set those con
of "most likely"
for numerous basins,
coefficient
just to
From these, sets
to pick a combination
be seen that the modern runoff
expected,
and the other
a lake at -300 m.
and temperature
sufficient
under similar
of these values to lower elevations
conditions
Drier conditions
calculated
requires
a
would
a value of 5°C for
assumptions,
Extra
an assumption
about
the lapse rate.
A temperature
decrease
of 3°C in the Kivu basin in the
late Pleistocene
should be conservative.
For a mean annual temperature
of 17°C, only 70 cm/yr annual precipitation
would be required
to maintain
-75-
the lake at -300 m,
coefficient
higher,
If the temperature
then even less
annual precipitation
nearly
the Kivu basin,
and Coetzee
conditions
Pleistocene,
Africa,
summarize evidence
extrapolation
areas is reasonable.
i
Rainfall
fell
resulting
of
changes of similar magnitude,
for the African
Zinderen,
Bakker
climate of the Late
were cooler and drier
all over
of changes from the Kivu basin to nearby
are:
to 60 cm/yr over the greatest
of the modern value,
the runoff coefficient
lead to overestimation
was
exclusive
can be estimated,
conditions
Assumptions
which is two-thirds
ii
exhibited
of Tanganyika
and conclude that
so that
Present
time.
in the Tanganyika basin,
which was closed,
1972
would be adequate.
is 130 cm/yr, which shows that precipitation
then the probable level
basin,
rainfall
half the ,modern value at that
If climatic
were lower and/or the runoff
part
90 cm/yr;
was the modern value
of tributary
inflows
of the
this
should
and underestimation
of
volume changes in the lake;
iii
iv
temperature
mean annual temperature
net.annual
evaporation
was 114 cm/yr
the following
where iV is the volume change,
no
I-EA1
I the volume of inflows,
=
0
then
‘
i.e.,
can be evaluated:
and A the lake area at equilibrium.
A1
and
1961.
with these .conditions,
equation
=
evaporation,
for the assumed precipitation
from Langbein,
For the lake at equilibrium
volume changes,
was 21°C cf. modern 24°C; and
=
7,550
When
E the net annual
-76-
This area can be converted to a depth by means of Fig,
relates
area and volume to depth.
lake was lowered by over 600
be sufficient
to split
in
The above conditions
imply that the
during the Late Pleistocene,
the lake into separate
basins.
which would
The relatively
large lowering of the lake is imposed by the high basin slope,
requires
area.
‘
relatively
great volume reductions
The drop is nearly twice that
only one-half
that of Tanganyika.
changes Kendall estimated
investigators
Valley
Hutzer
et al.,
Lake level
interpreted
of light
depressions
greater
hard,
bottom,
1949
returns
several
lakes in the Eastern
reported
as indicative
Rift
that
echo sounding
of alternating
echoes were observed.
diffuse
He hypothesized
of denser
At depths
echoes,
He
layers
In depths of less than 150 m the bottom
and no multiple
had allowed the deposition
than now possible.
than the
of this magnitude have been postulated
than 850 m only a single
appeared,
greater
and the higher lake levels
in closed-basin
Capart
and dense sediments,
a very soft
It is drastically
between 150 m and 850 m recorded multiple
these multiple
was relatively
a change in surface
1972,
before for Lake Tanganyika.
in soft.sediments
which
in Kivu, which has a basin slope
for Victoria
have identified
to effect
21, which
trace
was recorded,
that oscillations
sediments
less than 550
in
In depths
indicating
of lake level
at depths much greater
as many as eight
traces
while at depths between 550 and 850 m only two appeared.
Support for such lowerings was also found by the identification
drowned river
courses extending down to 550
Livingstone
1965
recovered
a 10.74
of many
in.
in
core from 440
in
of water
at the southern end of the lake in an area where his echosounder recorded
-77-
one multiple
echo in the neighborhood
the
fathometer
cient range to reach bottom at the sampling
no soil horizons
being quite
cm yielded
A radiocarbon
Livingstone
ash layers,
found
one
date for the ash at approximately
an age of 11,690 years H.P.
Extrapolation
575
of the inferred
rate to the bottom of the core suggested an age of 22,000
sedimentation
years H.P.
locality,
in his core, but he did find several
thick,
did not have suff i
On the basis
for why the traces
even at his site
of this,
Livingstone
would only be found in depths
the volcanic
no explanation
of less than 850
valleys
in,
remote,
source must have been quite
however, that the sublacustrine
didsuggest,
could offer
for
He
might have been
eroded by density currents,
Our hydrological
and therefore,
either
reconstructions
our estimations
explanations
of his results
tation
in Kivu suggests
rates
would disagree
are grossly
are possible.
rate for the past 11,000 years to the previously
is extremely rich in diatoms,
lake levels
productive
by the magnitude
upwelling
minimum.
Therefore,
site,
with sedimen
of the sedimentation
deposited
of sediment ages,
that Capart and we suggest would. bring the
1963
as lake levels
at the south end of the
rose after
reaching
Livingstone’s
the possibility
their
the bottom of his core may be younger than supposed
multiple
The ash layer
echo, but the congruity
with those of Capart is a supposition
least,
core
A lowering of
and may not record the events of the lowest lake stands.
may explain
sediments
Livingstone’s
as were the Kivu cores,
system Coulter,
lake near Livingstone’s
in error or alternative
Our experience
that extrapolation
could lead to gross overestimates
with Livingstone;
which Livingstone
of much lower levels
of that return
admits,
At the
during the Late Pleistocene
-78-
is revived by the demonstration
of such levels
levels
keep viable
ration
of the lake into two basins would allow allopatric
account
explain the very low sedimentation
as a depositional
probable
qualified.
of the vegetation.
are implied,
1949
Little
evidence
in
result
from a level of
that
is assumed that
the Ruzizi discharge
to -75
lower,
accumulated
discovered
as Capart
in to overflow at the
Fig.
21,
If it
without loss,
nearly
to cause Tanganyika to overflow,
When first
A,D., at which time its
are assumed
even lower levels
longer times would be required
blocked,
even if no
in,
in lake level,
2,200 km3 be added to the lake
700 years would be required
let was completely
about
the very thin sediment cover at depths
Lukuga requires
flow at the Lukuga,
19 on the
is available
If changes in precipitation
from the last decline
To recover
lake was certainly
to
that loss of the Ruzizi
of Tanganyika to fall
It may well be that
suggested.
As the
to effect
level
fell
century have been insufficient
over
in 1854 A.D,, the Lukuga out
and the lake did not overflow until
about the modern level prevailed.
junction
at station
for the loss of the Kivu overflow,
of less than 150
speciation
The lower lake stand
rate
It can be stated
changes are assumed,
to be responsible
and sepa
as the pollen data becomes complicated by cultural
alone would cause the level
climatic
lake lowerings
loss of the Kivu drainage between 4,000 and 1,000
is less easily
temperatures,
alteration
These lower lake
hiatus or even erosion by wave action.
The more recent
years B,?.
that multiple
flocks in the lake,
for the endemic species
would also
sill
the hypothesis
in Kivu,
1878
markedly before minor oscillations
Climatic
oscillations
to close the basin again,
of the past
This in con
with the long response time of the lake suggests that
1878
-79-
A.D. marked the first
overflow
at the Lukuga since approximately
4,000
years B,?.
In view of the high probability
of internal
tion.
drainage,
the salinity
The "thalassine"
as an adaptation
to previously
lake receives
even before
the hydrothermal
a disproportionate
are relatively
and salinity
of all
120 mg/i.
Tanganyika
amount of salts
soluble,
to the lake,
During arid periods
Under the climatic
assumptions
lake’s volume, 6,000 kin3, was only one-third
occurred,
and salinity
of the present
lake
would give a salinity
Harvey,
basin lakes
Hutzer
which means that
be generated
fore,
it
through
available
At -600 m, the
high,
communication
concentration
from correlation
periods,
with
and the Eastern Rift closedof 4,2 g/l would
Lower values are more likely,
is clear that Tanganyika has not been more than slightly
in pluviai
loss
Assuming a salinity
a threefold
a maximum salinity
began,
its more recent.history.
18,800
If the lake is assumed to have been
1972,
before dilution
approxi
the present volume,
which appears reasonable
et al.,
to the Mala
which placed Lake
at 0.2 mg/l/yr.
which is unusually
personal
the composition
would be imposed if no salt
would increase
closed for 15,000 years,
Lake Albert
in salinity
of 1,2 g/l,
and
as the rocks in
incoming waters were probably similar
increase
1950.
began the Kivu drainage probably
at -600 m, inflows were 8,3 km3/yr,
A threefold
Brooks,
from the Ruzizi,
mately 1 x 1012 g/yr of salt was added to the lake.
km3.
ques
in the lake has been explained
50% of its salts
activity
and periods
of the lake comesinto
much more saline waters
perhaps
the drainage
garasi
stability
aspect of the biota
The present
supplied
of lower lake levels
There
brackish
As long as the moist Kivu drainage is
a saline
Lake Tanganyika is not possible,
-80-
Truly saline
periods
must antedate
and the Virunga event.
the acquisition
The seismic
of the Kivu drainage
work in Lake Kivu puts this well.
back into the Pleistocene.
Ec,ard
A chemical stratigraphy
based on a.core
from station
for the past
6,000 years in Lake Edward,
4, is presented
in Fig.
22.
The detrital
components, TiO2 and A12O3, covary and reach maxima during
where fine ash was noted in the gross stratigraphy.
layers,
deposition
deposition
of detrital
material
has been prominent
throughout
field
the time represented
activity
water chemistry
in the Virunga field
while numerous explosion
and these may have supplied the ash.
well with the hydrothermal
years H,P,, an interval
1,200 years B,?,
spring
indicating
a different
indicating
that hydrothermal
possible
source.
that the radiocarbon
C02, and it may be slightly
concentrations
fore,
have similar
in a similar
fashion,
As this
field,
in Kivu, with peaks at 5,600
and greater
activity
since
the ash, perhaps
core begins with a Pb peak,
may already have commenced, it
date for this
core includes
Nickel also demonstrates
the Ni to any particular
is
some volcanic
of high ?b and ash concentrations;
to attribute
lava flows,
the Toro-Ankole
case the Pb precedes
too old,
during periods
it is difficult
activity
activity
to the
The Pb maxima appear to correspond
of reduced activity,
In the latter
by the
has been copious
are present.in
craters
Ash
The Virunga volcanoes
to the east and, southeast
volcanic rocks and would affect
The most recent
Aside from the ash
appears to be invariant.
core, but the exact source is.uncertain.
south and the Toro-Ankole
intervals
maximum
there
facies,
-81-
Diatoms comprise the bulk of the dry sediments,
material,
as might,be
Mo values
are indicative
values
contrasts
strongly
of detrital
with the conditions
runoff and springs
and never stratified
contributed
In Edward it is possible
on productivity,
Calcium carbonate
of any component in the core,
approximately
to dilution
200 years B,?,,
by ash.
creased dramatically
of the core.
bution
of the copious
the basin,
previously,
to the lake
efficient
springs
mixing.
effect.
were injected under
was the result.
the most marked changes in depo
A significant
increase
and subsequent decreases
In the very recent.past,
occurred
can be attributed
Ca-deposition
again in
to 43% and 54% CaCO3 by dry weight at the surface
requires
a much greater
Ca contri
The Ca is probably derived
from surficial
weathering
This tremendous increase
to the lake,
In Edward the
had a positive
and low productivity
demonstrates
The high
The shallower mean depth also
that volcanic activity
it,
Low
and hydrothermal
of Kivu.
and relatively
In Kivu the hydrothermal
the lake and stratified
The high
components.
peripherally
it with a chemocline.
allows mixing to the sediment surface
lake,
nature of the sediment,
of Edward through this period of volcanic
nutrient-rich
sition
highly productive
of the biogenic
for Mo mark higher deposition
productivity
activity
expected in this
along with organic
amounts of fresh ash which have recently
been added to
This would imply that the lake is somewhat more saline
Manganese appears to covary with CaCO3 with slight
at 2,000 years H,P, and quite
Again, increased
inputs
seem to.be involved,
to Lake Kivu,. where increased
increased deposition
sharp increases
than
increases
at the top of the core,
The situation
supply by subsurface
is analogous
weathering
of Ca and Mn in shallow waters,
led to
In Lake Edward
-82-.
such sediments
need not be restricted
lake is not strongly
stratified
to shallow waters,
and the salts
because the
are added peripherally
to surface waters,
Albert
Lake Albert is downstream from Lake Edward, and the connecting
Semliki River accounts
Talling,
1963,
stratigraphies
for a large proportion
and thus a close correspondence
reduced in Lake Albert,
and the diatoms are highly
sediments,
significant,
Oxidizing
conditions
fauna to efficiently
quence,
the Lake Albert stratigraphy
tions
in the inorganic
The chemical
presented
in Figs.
the lake,
58
in,
than at station
this
alogy,
feldspar
organic materials,
allows
a clearer
23 and 24,
of two cores
Station
Sedimentation
tates
an active
As a conse
insight
into varia
from Lake Albert are
5 is,from
the maximum depth of
have been higher at that
3, where a much longer record is available.
layer,
The core from station
This layer is underlain
U, Hriegel,
have been identified
station
Station
enriched in
by X-ray miner
and mixed with sands of high quartz
personal
edly marks a lower stand in Lake Albert
communication,
correlative
3
3 terminated
Ca, Sr, Mg, and Mn are all
and dolomite and calcite
content
all depths permit
may be
phases,
stratigrphy
carbonate-rich
layer,
fragmented and dissolution
regenerate
is somewhat closer to shore also,
in a dry,
components are
carbon is low throughout Albert
through
benthic
However, the sediments
as the biogenic
Organic
to the lake
between the chemical
of the two lakes might be expected.
of the two lakes are quite different,
greatly
of the inflows
and
This layer undoubt
with that
of Kivu.,
-83-
The’ detail
for this
as desiccation
period which Lake Kivu supplies
caused one or more hiatuses,
However, the occurrence
then,
Dating of this
make ‘the age assignments
core is by correlation,
imprecise.
Dilute
from the very low rates of CaCO3 deposition,
constituent
station
5 cores indicate.
of fluctuations
centrations
indicate
in Mn concentration
tepresent
oxidizing
Eh’.s sufficiently
was seen.on
reducing.
through this period,
low to liberate
Fe; therefore,
throughout
that a manganese carbonate phase,was
At 5,000 years B,?,
as did all
At station
5 the increases
of carbonate
carbonate
this period,
are gradual,
The Mg content
of this may be inthe
richer
does rise,
clays,
In both cores
after
increase.
with the highest concentrations
3 the increase
in
higher values than those inthe
This high carbonate
from the earlier
The waters were ionically
and it is unlikely
of the lake changed,
At station
and CaCO3 achieves
years H,?, does’differ
No effect
was only weakly
and organic carbon content
near the top of the core,
is abrupt,
The high con
involved,.
dry layer at the bottom of the core.
saline.
interface
the hydrogeochemistry
and the carbonate
is evidence
Mn from the sediment..
the other lakes in the Western Rift valley,
Pb shows a peak,
as both the
whereas the low concentrations
the sediment-water
The lake was dilute
are implied
Clays are by far the most,
In both cores there
conditions,
hiatuses
followed,
conditions
up to 5,000 years H.P.,
prominent, sedimentary
3 and station
and possible
Much higher lake levels
and the lake overflowed at the Albert Nile,
of
the lake did not open
a secondary CaCO3 and Mn at 400 cm may imply that
until
is not evidenthere,
layer at 5,000
one in that Mg does not increase,
5,000 years H,?, but not highly
but it levels
The clay facies
off at around 3%,
in Albert differs
from
Much
-84-
that in Kivu and Edward, as montmorillonite
nearly one-half
the clay by weight.
more Mg than the kaolinite
lakes,
is present
The montmorillonite
and illites
in station
5, but this
3 contrasts
rates
precipitation
is mediated by algal photosynthesis
the water.
nearshore,
fore,
as nutrient
the hihest
shore waters
eventually
rates
and the nearshore position
In large African
Ca-deposition
1969.
exceed that
different
constant
there,
There
near-
5 does
sedimentation
the chronology,
3, while station
vastly
5 yields ‘a nearly
rate.
5,000 years H.P.
significantly
As the absolute
in the station
contribution
carbon probably reflects
increased
from the Virunga hydrothermal
the Toro-Ankole field
increasing
productivity
made the sediments
noted earlier
productivity,
center
by a factor
slightly
ceased after
3, and it is true
rise in organic
Greater nutrient’inputs
eutrophication
of two.
reducing,
for station
of fresh ash in
of the lake,
perhaps
The higher organic content
and the Mn fluctuations
5,000 years B.?.
24 obscures it somewhat.
this
and the weathering
caused a natural
3 core after
of the clays is thought
to have remained the same while CaCO3 increased,
Fig.
is measured
of station
3, so that differing
at station
Organic carbon rises
station
The CaCO3
driving up the pH of
are greatest
As we have reconstructed
rates ..are evident
3.
would be expected in shallower,
of station
are also involved,
by different
of station
The CaCO3 content
with
noticeably
lakes the highest productivity’
input and regeneration
Kendall,
in the other
is best explained
sedimentation
for
incorporates
which predominate
The sharp peak in CaCO3 in station
the gradual rise
and accounts
This is quite
which were
clear
for
5,, although the expanded scale of
The effect
of the hydrothermal
waters
on
-85-
the productivity
recovered
of.Lake Edward was not noticeable,
sediments which predated
the lake was quite productive
increased nutrient
source of salts
graphic
record
ficantly
station
input.
.
the onset of spring
previously
The Semliki
and nutrients
5 core may demonstrate
on the phytopiankton
and/or
and was not as sensitive
to the lake,
5,000 years ago.
activity
to
is thought to be the primary
suggests that nutrient
increased
as we may not have
so that
"overflow"
the Albert
from Lake Edward signi
Diatom analysis
the effect
strati-
of the Albert
of the natural
eutrophication
of the lake.
Malcaii
Lake Malawi has no hydrological
Rift valley
and could not be directly
Virunga hydrothermal
for the past
part of the same rifting
phenomenon,
scale.
gesting
in the Nyasan rift,
center
of the initiation
to see
If they have,
it
is not a localized
of rifting
activity
of the sediment is pre
25.
activity
are quite variable,
observed.
of
However, Malawi is
the opportunity
The chemical analysis
The presence of several
hydrothermal
5,000 years,
and it offers
but merely an expression
in Fig.
by the events in the
that the Virunga hydrothermal
on a much greater
sented
system,
events have occurred
becomes probable
affected
with the Western
center which have dominated hydrogeochemistry
the lakes of that rift
if similar
connection
is present
Pb peaks in the sediments
in the basin.
The detrital
as would be expected from the frequent
Mn and Fe2O3 have maxima together
an oxidized phase,
suggests
that
elements
turbidites
between 40 and 80 cm, sug
but at other core intervals
they do not covary,
-86-.
implying reducing
concentrations,
indicate
conditions,
carbon and CaCO3 achieve maximum
while Pb is high between 120 and 150 cm, which may
hydrothermal
that
Organic
activity
supplied
increasing
productivity.
that time,
which could be caused by relatively
or greater
input of allochthonous
earlier.
Alternatively
atures,
more Ca and nutrients,
However, the C:N ratio
reaches
a maximum at
lower algal.production
organic material,
the high C:N might. indicate
and more rapid deamination
thereby
as was discussed,
warmer bottom temper
of amino compounds as suggested
by
Mopper and Degens 1972.
Radiocarbon dates of a nearby core, Von Herzen and Vacquier,
1967
slight
give an age of about 2,000 years for the topmost
but consistent
sediments of this
same extent,
order of 3
increase
core have been "contaminated"
the figures
in
would translate
per thousand years.
of the lithological
similarity
imply that core 15 collected
1,000 years
noticeable
old.
in this
about.1,200
in age with depth.
years
Assuming that
the
by dead carbon to the
to sedimentation
rates
in the
This rate is not unreasonable
to Kivu core 4’,
by the Heidelberg
We tentatively
that
is less
the hydrothermal
to the last
It is conceivable
in view
These high rates would
expedition
conclude that
core corresponds
ago.
sediment and a
Kivu event,
correlations
thermal events recorded in older East African rift
than
activity
which started
of hydro
lake sediments reveal
a synchronous pattern.
There is already
activity
sufficient
to allow a hypothesis
African and Red Sea rift
are considered
of related
system.
proposed for mid-ocean ridges,
evidence of periodic
rifting
activity
hydrothermal
all
along the
Such behavior would be similar
where rifting
complementary processes.
and hydrothermal
to that
activity
CONCLUSIONS
The stratigraphic
Africa provide insight
determining
times,
for five rift
into the interplay
the hydrogeochemistry
andHolocene
saline,
records
of climate
lakes
of the lakes during Late Pleistocene
The Late Pleistocene
which marked the transition
warmer and wetter Holocene appear.to
temperate
cooling
European record
is indicated,
lakes were closed and more
from this
be. readily
with aridity
occurring
Climatic
period into the
correlated
and ice cores from Greenland.
much higher modern precipitation
in Central
and geology in
as a cooler and much more arid climate prevailed,
oscillations
saline
valley
with the
Worldwide
in continental
as evaporation
areas with
from a cooler
and more
ocean was reduced,
Volcanic and hydrothermal
Virunga volcanic
region
5,000 years H,P,
water bearing the unmistakable
Virunga rocks now dictates
Rift valley
lakes.
activity
Similar
increased
The copious
chemical "fingerprint"
the chemical composition
hydrothermal
Nyasan Rift at the same time, possibly
sharply
activity
supply of.saline
of the distinctive
of all the Western
may have begun in the
marking a renewal of rifting
activity.
Water may be a necessary
prerequisite
processes,
.and the African
sequence of pluvials
climatic
may have caused corresponding
geological
record.
periods
in the
of activity
for volcanic
and rifting
and interpluvials
and quiescence
in the
-88-
A CX1VOWLEDGMENTS
We thank Drs, Peter
Scientifiques
vateur
en Afrique Centrale
Coordinateur,
logistics
support
discussions
de Virunga
during the expeditions,
de Recherches
Von der Hecke Conser-
for valuable
advice
The study has profited
B. N. Price,
by the National
and
from
S. Honjo, G, Muller,
Science
Foundation
GA-3064l and GA-35334.
Contribution
tion,
Parc National
it was supported
Institut
and Jean Pierre
with Drs, D, A, Livingstone,
and G. Kulbicki;
under grants
and Irene Kunkel
No,
3092
Woods Hole, Massachusetts
of the Woods Hole Oceanographic
02543
Institu
U.S.A.,
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LIST OF FIGURES
Fig. 1
Location map of Lakes Malawi,
Albert,
showing core sites
stations
2
discussed
in present work,
occupied in 1972 are marked with prime
distinguish
Fig.
Kivu, Edward and
Tanganyika,
e.g.,
Kivu
4’
to
them from the 1971 sites,
Gross stratigraphy
and sedimentological
description
of sample
material,
Fig.
3
Chemical
stratigraphy
Basin,
Only those elements
in concentration
of Kivu stations
Kulbicki,
on all
elements has
in the form of a Technical
Report
Degens .and
1973.
A complete
use in the reconstruction
file
The upper 4 m of the profile
10, and the lower.8
in
from station
4’,
about
Fig.
4
4’.
Nearby station
700 years of this
Distribution
9
shifted
direction
bridges
gap.
deposited
between 13,700 and 11,000 years H.P.
manganese values go on account
contents
10 and the top of
shown in graph
of manganese in Kivu sediments
the time interval
deposited
not
are from station
There is a hiatus of
about 1,000 years between the base of station
station
Deep Northern
are shown which show wide ranges
and are of particular
of the paleoenvironment.
been published
10 and 4’
of manganosiderite,
in shallow water environments.
are explained by oscillations
the area of inanganosidenite
of the present
core site,
during
High
which is
Fluctuations
in Mn
of the thermocline
deposition
which
away or in the
High water stands
are
Fig. 4
cont.
indicated
by the emergence of sulfides
assemblages.
Mineral facies
oscillations
was ca,
300
approximately
at -100
thermocline
the high water mark stood
The fluctuations
in.
diatom
The water depth at low stand
lower than today;
before 12,300 years B,?.
tions"
and reconstructed
are indicated.
in
and specific
are referred
Degens and Hecky,
1973;
in water level
to as "Kivu Oscilla
they exhibit
one major high
between 12.9 and 13,100 years H.P.
Fig.
5
Dominant diatoms of Lake Kivu sediments deposited
5,000 years H.P.
prior
to
2 micron scale,
Stephccnodiscus astrea
Nitzschia fonticola
a-c
d,g,h
Nitzschia spiculum e
ZVitzschia acicularis
Fig. 6
f
Dominant diatoms and a crysophyte
in .brown layers
2 micron
scale.
lVitzschia accomodata a
Nitzschia sp.
b
Nitzschia palea c
Nitzschia bacata d,g
Nitzschia subcommunis e
Paraphysomonas vestita
Fig. 7
Dominant diatoms
years H,?.
f,g
of Lake Kivu sediments
2 micron scale
Chaetoceros sp.
a,b,g
IVitzschia spiculum f
deposited
since 5,000
Nitzschia bacata c
Fig. 7
cont.
Nitzschia mediocris
Fig,
8
Distribution
carbon,
of amino acids
AA/HA ratios
d,e
A-A, hexosamines
and percentages
The AA/HA ratios,
contents
to organic
are expressed
relative
of Kivu station
Chemical stratigraphy
Fig. 10
Factor scores of Kivu stations
Basin
and b
13 and 15
Fig.
11
Chemical stratigraphy
Fig,
12
Reconstruction
Chemical stratigraphy
Fig. 14
CaCO3 stratigraphy
Fig. 15
Organic
15
Interstitial
19
Lake Kivu:
South
.
Mg/g C.
Idjwi Basin.
Deep Northern
Idjwi and Bukavu Basin,
of Tanganyika
15
Bukavu Basin.
12
Northern
Basin,
in Tanganyika sediments from stations
sill,
water analyses
linear
station
of Kivu and Tanganyika sediments.
Central
Greene and Jones,
Fig, 17
A-A and HA
carbon
10 ,and 4’
of Kivu Station
carbon content
North,
South
a
13
of
of lake level in Kivu for the last 15,000 years,
Fig, 13
16
of broken frustules
Nitzschia sp, in Kivu core 10.
Fig, 9
Fig.
HA, organic
and 2
South,
Lake Tanganyika,
station
2; after
1970.
volume/area
function
indicating
trough
like morphology.
Fig. 18
Lake Tanganyika:
like morphology.
linear
volume/area
function
indicating
trough-
Fig,
19
Lake Kivu:
Fig.
20
Runoff coefficient:
relationship
evaporation
A
volume/area/depth
for Kivu
relationships.
between precipitation
and Tanganyika
values for modern precipitation
B.
and evaporation.
Fig. 21
Lake Tanganyika:
Fig, 22
Chemical stratigraphy
of Edward station
5.
Fig.
23
Chemical
stratigraphy
of Albert
station
3,
Fig.
24
Chemical stratigraphy
of Albert
station
5.
Fig.
25
Chemical stratigraphy
of Malawi station
15
expedition,
1972.
Indicated
volume/area/depth
relationships.
Heidelberg
and
are
r’
C
00
0
,J
0
J
0’
0
C
0
a,0
0
C
________
ftJi
1}HLftH1
I
C
C
E
-o
C
Cl
0
C
0
U
C
C
N
C-
C,
I
IHHIflfl
II’III
uui
1 u ii
i
U;:
U
-
C
>
‘H
I
N
°I
J]Jwo
H rfliIHO
.5
-
*C
C
U
C
C
2
-
0
-
o
N
0
0
If
0
O
C
C
>
o
OD
0.-
C
0
°
-
‘5>
.E
-
>
5
00
0
[III
JoF oIl
.g’1
I.C
N
C":
0
0
I
‘I
‘
I
6
z
H
0
C
C
0
C
0
1
0
0
0
E
I
‘
C’J
I
N
,
I
io
I
‘0
Cl
C’
C
0
C
0
ioHo
i
C,
0
-o
C
C
>,
0
0
>,
-
I
Age
C’
-I
C’
0
0
C
0
c-
0
0
Co
0
C
C
I
CD
o
Depth
m
J
0
CD
>1
1
Mn
[ppm]
Therrnoc//ne [-Icke] level f
[high]
Depth
[low
f
14
0
1
L
0/
JO
400
[mb
r 0/
[mq/g C]
1
‘°
10 20 30
[xlO3yr]
1
‘3
2
3
0
Orq. C
AA HA x io---
AA/HA
N//zsc/i/c sp,
Ratio
broken frust.
200 400
100 300
1
2
3
10 20 30
50010001500
25 50 75
10 20 30
A1203
Mn
Ni
CaO
ppm
ppm
%
lyrs. B.P
Lx io
3
5
8
11
12
Pb
ppm
hO2
%
0I
10
Factor Scores
-2
+2 -2
0
+2 -2
Age
0
+2 -2
0
+2
years
I.
B.P.
x103
-3
-5.
-7
-9
-
10
volcanic ash layer
-
11
-
11.5
-
12
-
12.5
-
13
-
13.5
-
13.7
St. 4
3
Factor
4
5
Factor Scores
-2
0+2
-2
0
Age
+2 -2
St. 13
-2
-3
-4
-6
St.15
-8
-9
-
1
2
Fcc/or
10
q,o’c
CC-
Q
0
0
C
cn
E
0
0
0
C
E.
añ
[m]
5
10
15
+100
1972 level
-100
-200
-300
+20
+10
1972 level
-10
-20
water
level
14C Age
[years B.P
L
xiO3
‘17
r
yrs.8.P
[x iO
TK2
20 23
300 500 800
20
50 80
Mn
Pb
CaO
ppm
ppm
0/
/0
O
CaCO3
B
4
IYearslO
Lx 10 3J
b
2
‘S
b
4
South
North
K/vu
Tan qanyika
[o,t]
Organ/c Carbon
[Years
[
B.P.1jO
x103
2
3
q3
4
7
8
[%}
r..
ci0
a
a
E
0
0
D
z
0
IC
0
0
c’J
0
c’J
0
0
D
C-
0
0
0
0
0
CJ
E
0
q,daü
0
0
c’J
___
[km
2]
2000-
LA
v=3.0
4
1500
-
1000
-
Kivu
500
0
I
0
100
200
300
Volume
400
500
[km
3]
Ikm2
Lx
IO
3.
zA
-1.5
2Q
L
Tangany/ka
1-
0
I
I
0
Volume
I
2 Ikm1
L x1o4j
[km2]
2000
q*
1000
0
100
300
200
Depth
400
[cm]
180
4
.3
[cm]
.1
.2
180
.4
-
.3
.2
-
I:.
160
160
140
140-
120
120
L,j
-
+
100
Modern Precipitation
and Evaporation
q-
zj,
100
80
80
A
60
I
I
I
I
20
40
60
80
I
100
60
I
I
I
120
140
160
Mean Annual Preci/tat/on
40
-
0
I
I
I
I
I
20
40
60
80
100
Mean Annua/ Precioi/a
[km2
[xio
0
200
400
600
800
Depth
1000
1200
14
H
C
CO °
0
0
0
C
-
0
0
c’J
9ñt’
r’--’--l
E
L
C
-
J
0
i
0
-
0
Q
Q
0
r4
0
0
0
0
J
C
0.
G
0
C.
0
c’J
C
r0
c..J
cJ
C
C’.j
C
LI
Q
0
C
iC
C
I
c’J
tfl
r
t9L5t/
r
0
o_
40 50
60
18 20 22
1500
2500
234
200 300 400
246
[yrs.B.P1 0
[x103
]
q
Pb
ppm
Al2 03
Mn
ppm
MgO
Sr
ppm
CaCO3
0/
/0
O
22
.2 .5
.8
3 4.5
6
[cm]
2
Pb
ppm
T102
%
41203
0I
to
Mn
ppm
Fe203
0/
/0
Mo
ppm
CaCO
01
Organic C
0/
/0
Table 1
Chemicà Compo1tionQf Lake and River Waters from Central Africa
Na
K
Ca
Mg
SO4
Cl
ECO2
SI
P
35
in mole/Kg
mg/i
Tanganyika1 St. 3; surface
66.3
34.2
8.2
41.5
21
3.4
5.64
0.034.
Tanganyika1 St. 3; 1460 m
663
328
52
410
23
25
638
8.8
166
Kivu1 St.4; surface
121 6
97 4
4 8
87
55
23 8
12 5
6.5
26
Kivu1 St. 4. 100
in
192 0
145 0
64 0
147
mt
25 0
29 3
11.9
601
Kivu1 St. 4; 200 m
244 6
178 8
83 1
132
mt
166 4
42 0
12.0
1046
1
Klvu1 St. 4; 350 in
465 2
315 2
110 9
344
nt
21 0
133 0
29.6
1702
7
Klvu1 St. 4; 440
487 4
338 0
112 6
417
mt
220 0
121 0
34.3
1754
9
U70
1002
46
88
Ruzizi River at Tanganyika2
948
630
84
670
238
Plalagarisi River at Tanganyika2
164
24
129
91
155
in
Ruzizi River near Bukavu
*
nd**nd
131
0.045
178
1O46
9.0
n.d.
21
155
22.4
n.d
65
18
Lake Edward3
HO
90
12 4
47 8
36
43
9 85
Lake Albert3
91
65
9 8
32 1
33
36 5
7 33
Lake Malawi3
2
19.8
4.7
55
2.36k
1from
mt.
Degens et al., 197
.jnterference
6.4
2from Beauchamp, 1939
**
n.d.
=
not determined
4.3
0.4-0,9
Li
35.2
12O-15O
n.d
from Tailing and Tailing, 1965
determined on supernatant after setting
Table 2
Tabulation of Limnological Data
ALBERT1
EDWARD1
KIVU
TANGAN
6,800
25
58
140
2,325
40
117
90
2,055
240
485
583
34,
28.5-29
27.4-28.2
26.8-27.2
25.2-26
24.0-24.5
23.0-23.5
26
24
WET SEASON
DRY SEASON
DEPTH OF THERMOCLINE m
26.6-27.2
26.6
25.0-25.2
24.7-24.8
22,56
23
23
WET SEASON
DRY SEASON
RANGE
OXYGEN:MAXIMUM DEPTH LIMIT
MIXING SEASONS
TRANSPARENCY m SECCHI DISK
PRODUCTIVITY NET rng 02 m2hr’
DIATOMS
Astatic
Astatic
Astatic
58
15-20
40-50
25-30
80-117
20_306
Dec.-Aug.
2-6
Mar.-Apr.; July-Aug.
Feb.-Mar.; June-July
1.4-3
1UOO
Ntz4c.h..ô’i.
3.5-6.0
2308
AREA
2
MEAN DEPTH m
MAXIMUM DEPTH m
VOLUME Kni3
TEMPERATURE EPILIMNION °C
WET SEASON
DRY SEASON
TEMPERATURE i-iYPOLIMNION °c
1OOO7
SphznodLw
ct6-t-’LaQuJ.
2Capart,1952 3Coulter, 1963
7Calculated from Tailing, 1965
22.8
50
10
50
10
Ju
10
Un
40-50
20
70
1VLtz4c.hi.a 4po.
.
OJ1,tLcO&L
NLtz4 chia o p.
‘Verbeke, 1957
1,
18,
StephctnodL cs
dama
4Beauchamp, 1953
8Calculated from Degens et al., 1973
5Hutchinson, 1957
NL
Table 3
Varimax
Factor
Matrix
of Kivu Sediments
ELEMENT
FACT. 1
FACT. 4
FACT.
Vanadium
0.701
0.505
0.293
-0.018
-0.007
0
Molybdenum
0.029
0.641
0.391
-0.451
0.295
0
Lead
0.157
0.212
0.142
-0.086
0.882
0
Zinc
0.706
0.261
0.467
0.003
0.282
0
Copper
0.751
0.180
0.415
0.029
0.228
O
Chromium
0.827
-0.225
-0.012
0.097
0.161
0
Nickel
0.217
-0.299
0.724
-0.003
0.352
0
Cobalt
0.387
-0.303
0.679
-0.015
0.022
0
-0.222
-0.922
0.154
0.045
0.049
0
Baryum
0.114
-0.821
0.175
0.022
-0.119
0
Gallium
0.829
0.179
0.223
-0.116
-0.032
0
Manganese
0.260
-0.511
-0.003
0.437
-0.240
0
Fe203
0.197
0.379
0.809
0.041
-0.041
0
Si02
0.218
0.775
0.313
-0.106
0.143
0
A1203
0.945
0.164
0.058
0.005
0.011
0
CaO
-0.295
-0.900
-0.011
0.164
-0.026
0
MgO
0.044
-0.148
0.044
0.951
-0.017
0
TiO
0.878
0.007
0.186
0.177
-0.034
0
28.44
24.80
14.05
7.80
6.93
53.24
67.29
75.09
82.03
Strontium
FACT.
2
FACI. 3
No. of Samples: 381
% Variance
% Accumulated Variance
28.44
5
COM
Table 4
Radiocarbon Dates of East African Rift Sediments
f
Locality
Core
Sample depth cm
Lake Kivu
9
10
330-350
160-180
0- 84
195-230
350-400
10,670 ± 280
6,200 ± 215
11,200 ± 165
665-700
7428OO
170-210
168-205
340-382
115-170
190-250
425-480
13,150
13,560
11,950
11,070
12,130
9,460
9,725
10,170
41
13’
15’
Lake Tanganyika
3
120-140
235-255
85-105
175-195
10- 30
180-200
15
19
yr B.P.
12,300 ± 330
12,650 ± *l9P
±
±
±
±
±
±
±
±
330
165
250
160
170
240
165
140
3,670 ± 120
6,350 ± 160
1,925 ± 100
3,750 ± 105
1,300 ± 95
>28,200
Lake Edward
5
460-505
5,665 ± 100
Lake Albert
3
5
140-180
450-495
2,660 ± 90
6,910 ± 115
Lake Malawi
NY_19*
0- 8
46- 53
2,400 ± 200
2,540 ±140
2,670 ± 200
86- 94
Lake Green
LV1
Nyamuragira
volcano
N745
15O m above
Kivu water *level
*Von Herzen and Vacquier, 1967
Charcoal in
lava flow
13,300 ± 1150
515 ± 120
Table 5
Morphometric and Hydrological Parameters
for Lakes Kivu and Tanganyika
Kivu
Area:
Depth:
Km2
Ab
=
catchnient
A1
=
lake less islands
2,060
32,600
At
=
tributary area
5,080
198,400
7
=
mean
240
570
485
1 ,470
583
18,880
m
Zmax
Volume:
V
Basin slope
Discharge:
Km3
=
Runoff:
Volume
Km3/yr
over A1
cm/yr
3.2
cm/yr
0.66
2.7
160
53
130
90
volume on A1
Km3/yr
2.7
29
volume on At
Km3/yr
6.6
180
coefficient r
0.4
volume
2.7
Km3/yr
over A1
Air Temperature;
Evaporation:
0.33-0.4
V/tA1
Precipitation: rate P
7,140
Tanganyikaexclusive
of Kivu
231,000
cm/yr
134
°C
gross rate Eg
volume loss
19.5
cm/yr
Km3/yr
net rate EnEg-P
net volume
106
Km3/yr
2.1
cm/yr
-24
-0.5
0.08
14
44
24
135
44
45
15
Table 6
Calculations on Water and Salt Budgets
of Lakes Kivu and Tanganyika
Kivu
Tanganyika
Water
Volume
Precipitation + Runoff
Residence time for water
Runoff
Refill time runoff alone
km3
km3/yr
yr
km3/yr
yr
517
18,800
5.3
110
44.0
430
2.7
190
18
1,000
Salts
Total Na1
Na + loss at effluent
kg
kg/yr
13 x 1010
3.7 x 10 8
12 x
io11
1.7 x 10
8*
Storage time**
yr
350***
Total
kg
9.5 x 1010
6.3 x iO
kg/yr
3.2 x i08
9.2 x
K loss at effluent
Storage time
yr
300
7,000
6,800
*Based on calculated Lukuga discharge of 2.7 km3/yr and composition of
river identical to that of lake.
**Storage time assuming losses of salt to sediment and evaporation are
negligible.
***Storage time for whole lake; multiple water layers of Kivu will have
their own storage times.
Woods Hale Oceanographic Institution
WHOI-73-28
-------
LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY NW
PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA.
By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures
and 6 tab’es. May 1973. National Science Grants GA-30641
and GA-35334.
Woods Hole Oceanographic Institution
WHOI-73-28
The interaction of climate and geology in Central
Africa durthy Late Pleistocene and Holocene is examined.
Pileoclimatic comparison between tropical and temperate
zones reveals that p1uva1 times coincide with the
prominent interstadials n Europe, and reversely, cool
and dry periods in equatorial Africa with ice ages n
the Northern Hemisphere.
1.
Paleocliniatology
2.
Cheniçal Stratigraphy
3.
Rift Vafley Lakes
4.
Centra’ Africa
I.
Hecky, Robert E.
II.
LATE PLEISTOCENE-HOLOCENE CHEMICAL STP.ATIGRAPHY AND
PALE0LIrIN0L0GY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA.
By Robert E. Hecky and Egon T. Degens. 114 pages, 20 figures
and 6 tables. May 1973. National Science Grants GA-30641
and GA-35334.
The interaction of climate and geology in Central
Africa during Late Pleistocene and Holocene is examined.
Paleoclimatic comparison between tropical and temperate
zones reveals that pluvial times coincide with the
prominent interstadials in Europe, and reversely,- cool
and dry periods in equatorial Africa with Ice ages in
the Northern Hemisphere.
Degens, Egon 1.
III. GA-30641
IV.
GA-35334
This card is UNCLASSIFIED
I I
--
Woods Hole Oceanographic Institution
WHOI-73-28
I
.
1.
Paleocliniatology
I
2.
Chemical Stratigraphy
LATE PLEISTOCNE-HOLOCENE CHEMICAL STRATIGRAPI-IY AND
PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA.
By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures
and 6 tables. May 1973. National Science Grants GA-30641
and GA-35334.
I
zones reveals that pluvial times coincide with the
prominent interstadials in Europe, and reverse’y, cool
Ij
I
The interaction of climate and geology in Central
Africa during Late Pleistocene and Ilolocene is examined.
Paleoclimatic comparison between tropical and temperate
and dry periods in equatorial Africa with ice ages in
Woods Hole Oceanographic Institution
WHOI-73-28
I
I
3.
Rift Valley Lakes
4.
Central Africa
I
I
I
Hecky, Robert E.
I
Degens, Egon 1.
GA-3o64l
the Northern Hemisphere.
IV.
GA-35334
I
This card is UNCLASSIFIED
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LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY AND
PALEOLIMOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA.
By Robert E. Hecky and Egon 1. Degens. 114 pages, 20 figures
and 6 tables. May 1973. National Science Grants GA-30641
and GA-35334.
The interaction of cflmate and geology in Central
Africa during Late Pleistocene and Holocene is examined.
Paleocliniatic comparison between tropical and temperate
zones reveals that pluvial times coincide with the
prominent interstadials in Europe, and reversely,- cool
and dry periods in equatorial Africa with ice ages in
the Northern Hemisphere.
BLOGRApHIC DATA
SHEET
2
L Report No.
3. Recipient’s Accession No.
-
4. Title and Subtitle
7.
5. Report Date
May 1973
LATE PLEISTOCENE-HOLOCENE CHEMICAL STRATIGRAPHY AND
PALEOLIMNOLOGY OF THE RIFT VALLEY LAKES OF CENTRAL AFRICA
6
Authors
8. Performing Organization Rept.
No.
Robert E. Hecky and Egon T. Degens
.
WHOI-73-28
9. Performing Organization Name and Address
10. Project/Task/Work Unit No.
Woods Hole Oceanographic Institution
Woods Hole, Massachusetts 02543
fl. Contract/Grant No.
NSF GA-30641
12.
Sponsoring Organization Name and Address
-
National Science Foundation GA-30641 and GA-35334
13. Type of Report & Period
Covered
echnical Sept 69
Sept 72
U.
.
15. Supplementary Notes
6.
GA-35334
-
Abstracts
The interaction of climate and geology in Central Africa during Late Pleistocene
Paleoclimatic comparison between tropical and temperate
zones reveals that pluvial times coincide with the prominent interstadials in Europe,
and reversely, cool and dry periods in equatorial Africa with ice ages in the Northern
Hemisphere.
and Holocene is examined.
7. Key Words and Document Analysis.
1.
F’a1eoc1imatology
2.
3.
Chemical Stratigraphy
Rift Valley Lakes
Central Africa
4.
l7a.
Descriptors
17b. Identifiers/Open-Ended Terms
17c. COSATI Field/Group
18.
Availability Statement
FORM
NTIS-35
REV.
3-72
THES FORM
MAY BE REPRODUCED