Download 5.1 INTRODUCTION The structure of sedimentary rocks are those

CHAP'l'EJ{ 5
SEVIMENTARY .STRUC'l'URE;;
-----
5.1
-r-
INTRODUCTION
--------
The
structure
of
sedimentary
rocks
are
features that are studied best in the outcrops.
those
'l'hese are
formed from materials of varied composition and are product_"_
"~-
of
physical, chemical
and
biological
in
present
Certain
processes.
'
processes
are
common
day
environments,
but
combination of processes, often with particular directional
properties · ""ari3, diagnostic of specific environments.
study
the
of
sedimentary
sedimentary
structures
environment or
are helpful
facies
in
'l'he
to understand
which
the
rocks
were deposited .
.Sedimentary
and
secondary
structures
classes.
are
Primary
divided
into primary
structures
generated in a sediment auring or shortly after
Whichresul t mainly from physical processes.
are
those
deposit~o~
'l'he secondary
s<·dimentary
after
structures
sedimentation.
are
those
which
formed
sometimes
They result from essentially
chemical
processes.
'rhe
classification
of
structures
sedimentary
present in the study area are as follows :
SEDIMENTARY STRUCTURES
5.2
5.3 Secondary
Primary
I
~---------L--------~-;
Inorganic
Organic
5.2.1 Bedding
5.2.2 Desiccation
cracks
5.2.3 Stromatolites 5.3.1 Karstification
5.3.2 Stylolites
5.3.3.Calcite veins
5.2
PRIMARY SEDIMENTARY STRUCTURE
INORGANIC
5.2.1
BEDDING
The
rock
universal
is
their
primary
bedding
or
structure
sedimentary
of
stratification.
Bedding
or
stratification expressed by rock units of general tabular or
lenticular
unity
arranged
form
that have some
(Pettijohn,
1984).
in layers or strata.
lithologic
Most
or
sedimentary
structural
rocks
According to Payne (1942)
are
a
stratum is an individual layer of 1 em. thickness or
~reater
and is separated from strata above and below by a discrete
lamina
is
similar to stratum but is less than l em in thickness.
A
in
change
lithology
or
a
physical
bed is a rock unit composed of
Individual
essentially
bed is
constant
several
observed
conditions by uniform processes
Bed
contacts
non-deposition
represent
or
strata
laminae.
biological
and
or sequence of processes.
conditions
changes
erosion.
or
to be. deposited under
chemical
physical
A
break.
The
~reater
part
of
to
calcium
carbonate in the limestones, results from the activities of
organisms which precipitate it as part of their metabolic
processes.
':
Village
and
Jhen]hri:
of
Lithofacies-A and village Boria of Lithofacies-C show small
exposure
of
well
laminated
structure
calcareous shales respectively.
with
1-2°
dip
towards
north
in
limestone
and
The beds are horizontal or
east.
In
Nandini
Mines
of
Lithofacies-B small patches of well laminated limestones are
observed
(Plate
22 B
)
.
Other
than
the
field
area
bedding and cross beddings are shown in Haipur sandstone and
shale at Kumhari,
5.2.2
Khapri, Rawan and Siltara (Wadhwa, 1976) •
DESICCATION CRACKS/SHRINKAGE CRACKS
calcareous
or
compaction
and
Desiccation
argillaceous
muds
water
of
produce
a
filled
system
of
shrinkage cracks, which in their typical development, form a
network
shapes.
and
divide
surface
into
irregular
polygonal
If these fissures remain open while the surface is
being buried and
rock,
the
persist
after
sediment
has
hardened
to
they constitute a characteristic indicator of the top
surface.
If the plates of mud-cracked layer are subJected
to fragmentation followed by some erosion and transportation
before burial,
they
will be rounded
to
some
extent.
If
deposited with variable orientation they constitute one type
of intraformational conglomerate or breccia.
This structure
is not characteristic of top or bottom of beds
In
Lithofacies
limestone at village
A
and
Jhen]hiri
&
C
small
exposures
of
Boria show characteristic
cracks
desiccation
respectively
(Plate.~
22 A
pebbles
formed
in
are
conglome.rate
intraformatinal
and
LJesiccation
)•
the
upper
tidal
cracks
and
and
mud
supratidal
zones (; .Flugel, 1982).
ORGANIC SEDIMEN'rAEY STRUCTURE
5.2.4 .,
STROMATOLITES :
Stromatolites
are
organosedimentary
structures
produced by the carbonate precipitating and sediment binding
&
activities of blue/green algae.
The Raipur limestones show an abundant growth of
The
stromatolites.
referring
'I'hey
to
term
laminated
was
coined
structures
occur
in
rocks
from
predominant
in
rocks
older
of
than
environment
palaeogeographical
and
have been made based
On
the other hand
is
many workers,
origin.
Recent,
Ordovician
al~al
and
but
most
stromatolites as
apparent
palaeo-ecological
upon algal
to
( 1908)
n!
The potential usefulness of
of
Kalkowski
problematic
Precambrian
predominant in ijpper Precambrian.
indicator
by
and
many
reconstructions
stromatolite
assemblages.
specially from the USSR,
claim
that
the
evolutionary
various
forms
phenomenon
biostratigraphic
assemblages.
reflect
time
controlled
and
have
attempted
correlations
based
upon
present
study
stromatolitic
make
some
usefulness
as
stratigraphic markers and as environmental indicators.
The
specific
The
regional
attempts
towards
contribution
their
to
associated sedimentary structures have also been useful
deducing
the
palaeoenvironmental
condition
in
during
sedimentation of Raipur limestone of Raipur Group.
In the present area of study,
reported as concretions by King
described their morphology.
have
reported
Nandini
the
(M.P.),
whilst
Chandra
stromatolites~
from
Ghosh
(1965),
&
Shah
&
were .earlier
(1885), sen (1966), briefly
Vishwanathaiya & Shastri (1973)
presence
phosphorites.
they
of
algal
studying
Bhattacharya
Raipur
limestone
Schnitzer
stromatolit~g,'·
the
occurrence
(1973)
at
(1971),
studied
at
of
the
Mandir
Hasaud.
WadhWa-'
(1976),
Jairaman & Banerjee (1984), N (Jha) ChatterJee et al (1990),
Moitra A.K.
(1986), Murti (1978) described their occurrence
in the Raipur Group.
Kreuzer et al (1977) carried out the
geochronological studies of Chandarpur Sandstone.
CLASSIFICATION & DESCRIPTION OF STROMATOLITES
The
groups
stromatolit~s.
on the
basis
of
are here divided into different
their
morphological
shape and ornamentation of the columns,
etc.
as
(1969).
suggested
by
The coluinnar
identified belong
Raaben
features
types of branching
& Semikhatov
(1969JA Cloud
stromatolites
to Colonnella
like
of Raipur
and l:laicalia
limestones
9roups.
The
domal non-branching stromatolites are identified as Nucleela
Komar
(1966).
The
various
forms
identiFied are described
below along with field sketches and photographs
Group - Colonnella Komar 1966
Form - Colonnella co1umnaris
(Plate 19A Fig.l7A to E)
SHAPE AND MODE OF OCCURENCE
Columnar form, columns being 4 to 8 ems. long and
2 to 4 ems. wide,
planes.
developing perpendicular to the bedding
'
T,e laminae shows different degree of
convexities.
The columns are arranged close to each other ( 1 to 2 ems.
apart).
The
gap
is
filled
filling calcite (fenestral).
almost equal.
60 percent.
with
carbonate
mud
and
void
The spacing between columns is
The density of the colony varies from 40 to
MICIWLAMI NATIONS
Laminae exhibit banded microstructure of alternate
dark and light coloured ones 600 ,urn to 2000 ;Urn thick.
darker
laminae ane relatively thin and composed of micrite
and microdolospari te grains,
while the light coloured ones
are made of micrite and micro-sparite grains.
are
The
smooth
and
resulting
continuous
microstructure (Plate
Microlaminae
banded
into
,.,. '
21 B),
COMPARISON
The
group
form
Colonnella
columnar is
Burzyan
Riphean)
1960).
Baicalia
well
(1966)
Komar
Korolzuk
Series
of
compares
(1960).
(Lower Riphean)
Southern
Urals
with
and
the
non-branching
form
Masloviella
Such
forms
and
Avzyan
(Keller
et
are
al,
known
from
Series
(Middle
19 60;
Kry lov,
In the Raipur limestone these are associated with
baicalica
associations
has
which
been
is
very
reported
significant.
from
Jammu
Similar
Limestone
(Raha, 1984) and from Gangolihat Uolomites (Pant, 1985).
LOCALITY
Village
JhenJhiri
(Lithofacies
A)
and
Nandini
Mines (Lithofacies B)
Group - Nucleela Komar, 1966
Form -
Nucleella Fm. Komar, 1966
(Plate lY B)(Fig.l7F)
SHAPE AND MODE OF OCCURRENCE
Leaf
hemispheroids
smooth.
like
are
solitary
5-7
ems.
hemispheroidal
in
diameter,
forms.
margins
The
being
The growth laminae show, higher convexities at the
base and becoming almost flat at
the top.
The density is
40% to 60%.
MICROLAMINATIONS
The laminae are composed
grey micrite and microdolospari te
of
alternate
thin dark
( 1500 ;urn) and relatively
thick (1500 to 2000;uml light coloured microsparite grains.
The nature of contact between these layers is sharp (Plate
COMPARISON
'rhese
depressed
forms
were
reported
Collenia symmetrica Fenton & Fenton (1937).
very little
known
to develop
Semikhatov
ll976J
in quiet
noted
subtidal
that
such
conditions.
forms
as
Such forms have
However,
significance.
strati~raphic
earlier
have
they are
Krylov
lon\:1
&
range
extending from Aphebian to Riphean.
LOCALITY
Nandini mines of (Lithofacies B), associated with
Colonnella columnaris
Group - Baicalia Krylov 1963
Form - Baicalia baicalica Maslov
(Plate 20 A,B)
(Fig. 17 G,H,I)
SHAPE AND MODE OF OCCURRENCB
Colonies
characteristic
are
slightly
dichotomous
oblique
branching.
to
The
bedding with
are
branches/ club
shaped, constricted at base and widening upward.
is seen at angle of 20-30° .
is 50-70%.
Branching
The density of colonial growth
The transverse section
are more
or
less
oval
shaped.
'l'he
maryinal
areas
places bumps are also seen.
are
hiyhly
irreyular and
Tun~ussids
Unlike
at
there are no
horizonal tuberous branchiny in these forms.
MICROLAMINATIONS
The thickness of dark and light laminae is 200;um
to 600 ;Um, which is very much less,
forms of Raipur stromatolites.
as compared
The dark lamina
to other
is made up
of micrite, while light coloured is of microsparite.
The
contact between the two laminae is gradational.
COMPARISON .
These
forms
show
similarities
with
Tun~ussids
broadly but the columns are sparsely widening and horizonal
tuberous
branchiny
demonstrated
by
the
~s
absent.
present
'l'he
forms
other
is
that
distin::tion
these
are
wall-less while Tungussids are walled forms, and form tube
like
structure.
In
USSR
l:laicalia
baicalica
is
characteristic of Middle Riphean sometimes extendiny up to
Upper Riphean.
These forms
are
very much
similar
to the
Baicalia baicalica (Valdiya, 1969; Pant, 1985) recorded from
Ganyolihat Dolomites..,
Valdiya
( 1989)
compares
these forms
•a:
,.....----~~
z
a
~
z
a
z
::J
0
c::
<(
~
(,J'l
w
z
0
f-
(,J'l
w
~
...J
with Tunyussida ot bhander and as such Kaipur limestone can
be assigned an Upper Middle Riphean to Upper !\ivhean age·
However, the peculiar association of baicalia baicalica with
Colonnella
columnaris
being
siynificant
and
sugyests
a
Middle Riphean age.
LOCALITY
Nandini
mines
l~ithofacies
and
b)
near
village
Chikhli (Lithofacies AJ 20 Km SW of Nandini.
PALAEOENVI!WNBEN'I'
Considerable doubt
variations
in
morphology
controlled
biologically
environment.
control
of
of
or
still persists as
different
are
a
In Russian literature
the
stromatolities
morphological
is
predominant,
to whether
stromatolitles
function
of
are
physical
the concept of biotic
feature
and
of
the
Precarnbraian
influence
of
ecological factors on gross shape of hiphean stromatolites
is
under estimated
(Serebryakov
&
Semikhatov
sometimes practically denied (Raaben 1969).
1974)
and
98
However, any conclusion concerning either physical
environment can only be broad and tentative till the specific
effects
more
of these factors on the stromatolite morphology
properly
understood.
stromatolite
analogy
study
of
have
ancient
The
been
environmental
developed
stromatolitic
are
aspects
largely
of
through
recent
forms
with
algal
stromatolites
stromatolites.
The
identified
flat
different
of
in the present study indicate
environment.
consists
type
of
marine
intertidal
tidal
environment
The main part of the
the intertidal zone which
passes
subtidal zone and shoreward to supratidal zone.
water
intertidal
environment 1s
also
seawards
The
supported
water
the
shallow
associated
with
the Raipur Limestones in the Raipur area (Wadhwa, 1976)
and
mud
structures in the Raipur Sandstones,
shallow
by
occurence of ripple marks, current bedding and other
to
cracks
Raipur
J
intraformational
limestone
Separately,
(near
Boria
flat
pebble
village)
conglomerate
(Lithofacies
it has been shown that the depositional site
1n
C).
of
these limestones trends NE-SW.
The
predominantly
are
stromatolites
of
Raipur
composed of columnar type.
Limestones
These
are
structures
suggestive of a local exposed intertidal environment
to
99
•ed
protec~;intertidal
'l'his view can be
mud flat environment.
supported by the presence of mudcracks and intraformational
flat pebble conglomerate such as seen near Boria, north east
of Nandini.
Additional detailed studies may enable a further
sub-divisions
into
subenvironments
and
also
lead to
the
delineation of the strand line.
AGE
Several
workers
classification of
Precambrian
stromatolite assemblages.
attempted
had
formations
Notable
is the
stratigraphic
on
basis
of
sub-division
of
Riphean (Late Proterozoic) of USSR into three
Lower
(1650-1350
m.y.);
Middle
(950-650 m.y.) by Raaben (1969).
the
sub-divisions~
(1350-950 m.y.)
and Upper
It is remarkable that this
zonation is in good agreement with palaeontological evidence
being supported by absolute age data.
The stromatolite assemblage of Raipur
thus
comprises
Nucleella,
predominantly
Baicalia
baicalica
of
etc.
Colonnella
(suggestive
Limestones
columnaris,
of
Middle
JVU
HiEJhean
the
1350-950 m.y.).
absence
of
This age is further
Group
Kussie11a
and
conf.jrmed by
Jurusania
which
if
present would have indicated Lower Riphean (1650-1350 m.y.).
Therefore,
all these forms can tentatively be
assigned
to
Middle Riphean.
5.3
SECONDARY SEDIMENTARY STRUCTURES
5, 3 ,1'
KARS'riFICA'l'ION
Karst
is
the
cavernous limestones were
province
!
--~-
in
Yugoslavia,
where
identified and studied for
the first time for its unique morphology and, thus, the term
Karstification has become classic and universal application
for cavernous limestones of all
stratigraphical
itself.
two
horizons
and
shades,
has
composition and of
become
the
sujbect
by
Karst can be viewed as an open system composed of
clearly
subsystems
integrated
operating
upon
hydrological
the
karstic
and
geochemical
rocks.
Karst
landforms are the product of the interplay of processes in
these linked subsystems.
The !<;arstic system can be grouped into t110 zones
erosional and depositional, according to its origin. In the
101
erosional zone, there is net removal of the Karstic rock, by
dissolution, same redeposition of eroded rocks occurs in the
zone mostly in the form of precipitates.
Erosional karstic
features are common than depositional features.
Erosional
Karstic
features
are developed in the
Raipur limestones at various localities in the present area
of
study.
Deorjhal.,
karsts
Some
by
surface).
them are Durg-Dhamdha road at Pitora,
Nandini-Kundini
found
(covered
of
here
can
sub-soil);
Both the
etc
be
and
karstic
(Plate25, 26). The
classified
bare
karst
as
type
sub-soil
(exposed
of
Karst
on
the
feature are characteristic of
limestone terrain.
The
solution
planes may be regular
(bleby cavities).
cavities
( clints)
running
along
horizontal
or may have irregular form
Vertical solution openings are termed as
grikes (Plates 25 B ) •
Styloli t.es·; are thin zones of discontinuity within
rocks.
They
generally
consist
projections with intervening
of
conical
depression.
to
column~r
These structures
102
in
size
from
contact
·sutured
microscopic
(microstylolites) up to stylolites• several meters in lengt
They
are
pressure-solution.
contact
between
generally
regarded
as
the
result
o
This involves solution around points o
mineral
grains
I weight of overburden) •
Since
in
response
certain
to
pressur
minerals
are
mor
susceptible to pressure solution than others, various burial
are
depths
necessary
stylolitisation.
for
supplying
in
order
to
produce
a
strong
Pressure·solution is an important process
carbonate
for
the
formation
of
carbonate
cements.
Stylolites are very common in Raipur limestones of
study area.
They are generally parallel to bedding planes-
.'im(i cut perpendicular
exposures
at
to stromatolitic limestones.
Jhenjhiri
(Lithofacies
A)
and
Small
Biroda
(Lithofacies B) show this structure very clearly (Plates24B)
5. 3. 3•
CALCITE VEINS
Many
filled
veins
l~mestone
and
display various systems of calcite
veinlets.
Experimentally
deformed
103
carbonate rocks indicate that the mechanical behaviour and
the
origin
of
fracture
is
controlled
sparite, micrite and dolomite.
micrite
are
limestones.
relatively
In
pure
by
the
amount
of
Limestone with more than 50%
strong
as
compared
dolomites
or
dolomitic
strength and ductility depend on the texture •
to
sparry
limestones
In the study
area micrite limestones show very few calcite filled veins.
But these are very common in dolomitic limestones of Nandini
mines
which are more brittle
and fractured
(Plate 23B ) •
The width of veins range from a fraction of 2 to 30 em : and
are
filled
with
rhombohedral
crystals!Plate 27A).
and
scalenohedral
calcite
PLA~l'E
5
6
7
8
9
10
11
12
13
14
15
16
A : Colonnella columnaris Komar, showing vertical
stalked hemispheroids perpendicular to bedding
planes. Intercolumnar area is filled with
carbonate mud. Locality : Nandini Mines
( Lithofacies-B) •
B : Nucleella Fm. Komar showing solitary
hemispheroids. Locality : Nandini Mines
( Lithofacies-B) •
19
PLA'l'E 20
A & B : Baicalia baicalica showing conspicuous
branching the columns being constrained near the
branching .
Locality : Black stone quarry (Nandini Mines)
(Lithofacies-B).
PLATE 21
..........
A : Photomicrograph showing microlaminations
of Nucleella Fm Komar.
Bar scale
200
~
B : Photomicrograph showing microlamination
of Colonnella columnaris.
PLATE 22
;
A : Desiccation Cracks in shaly
limestone
Locality : Boria N.E. of Nandini (Lithofacies-C)
B : Bedded micrite showing alternate dark and
light coloured bengs.
Locality : Nandini Mines (Lithofacies-B).
PLATE 24
A : Stromatolite bearing limestone (1ithofacies-A)
showing polygonal mud-cracks on the outcrop.
Locality : Village Jhenjhri.
B : Stylolite traversing parallel to bedding plane
Locality : Village Jhenjhri (Lithofacies-A).
PLATE 25
A : Karstification on Raipur limestone. Stylolites
are clearly observed.
Locality : Deorjhal (~ithofacies-B).
B : Karstic rock showing grikes (Horizontal) and
clints (vertical openings) •
Locality : Deorjhal (ldthofacies-B)
PLA'l'E 26
A : Karstification produced by solution action
on Raipur limestone.
Locality : Deorjhal (~ithofacies-B)
B : Karst topography.
Locality - Pitora (~ithofacies-B)
PLATE 27
A : Calcite vein traversing Parallel to joints.
Locality : Dhamdha bridge (Lithofacies-A).
B : Thickness of soil cover Raipur limestone.
Locality : Dhamdha Bridge (~thofacies-A)