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Lithostratigraphy
Chapter 15
Until this moment we have examined how
sedimentary rocks are formed, and we have
attempted to infer ancient depositional
environments.
Now we will integrate information and
inferences from outcrop evidence into a larger
context.
Lithostratigraphy
• The rock record is preserved and exposed
only in certain places and is full of gaps.
• The limited exposures of outcrops on the
surface means that many deposits are not
any more connected.
• To reconstruct the geologic history we must
ask how these outcrops and environments
are related in space and times.
Era
Período
Cuaternario
Cenozoica
Mesozoica
Paleozoica
Precámbrico
Terciario
Cretáceo
Jurásico
Triásico
Pérmico
Carbonifero
Devónico
Silúrico
Ordovicience
Cámbrico
Proterozoico
Arqueozoico
Época Edad
Holoceno
Pleistoceno
0.01
1.6
Plioceno
MIoceno
Oligoceno
Eoceno
Paleoceno
5
23
35
56
65
145
210
245
290
360
410
440
505
545
2500
3800
195 my
•
Facies
Layer cake geology- in the 1700s and early
1800s, catastrophist geologist thought that the
rock had been laid down in uniform sheets over
the whole world during Noah’s Flood.
• Uniformitarianism- compares today’s sediments
with rocks (ancient deposits).
– Many sedimentary rocks are deposited
simultaneously in different areas, and no single rock
type is deposited over a very wide area at one time.
Nicolas Steno
• Noclas Steno coined the term faices for the
entire aspect of a part of earth’s surface
during a certain interval.
• Facies “aspect” or “appearance”
• Amanz Gressly:
– Used the terms facies as lateral changes in the
appearance of a rock unit.
– Facies- the sum of lithological and
paleontological characteristics of a deposit in a
given place.
Facies, lithofacies, biofacies, fluvial facies
etc.
Walther’s law of correlation of
facies
• “Facies that occur in conformable vertical
successions of strata also occur in laterally
adjacent environments”
Transgression and Regression
Transgression and regression
• Transgression- Facies show a transgressive pattern
when the sediments supply is overwhelmed by a
relative rise in sea level, or when the land subsides
tectonically.
• Regression- facies show a regressive pattern
when the shoreline moves seaward due to an
excess sediment supply from the land
(progradation), when the land is tectonically
uplifted and the sea retreats, or when there is a
relative lowering of the sea level.
Pinch-outs
Intertonguing
relationship between
Cambrian bright
Angel shale and
Muav Limestone in
western gran
Canyon
Asymmetry of transgressive and
regressive cycles
Transgressive facies are
fining-upward sequences. This
are rare in the stratigraphic
record.
Coarsening-upward,
regressive sequences are more
abundant
A-traditional symmetrical
model of regression and
transgression.
B-stages of deposition of
shoreline deposits showing
reworking and apparent rapid
transgression. Event the basal
transgression is formed by
small regressive wedges.
• Diastems- small-scale, obscure
unconformities in the stratigraphic record.
Unconformities
•
•
•
•
Angular unconformity
Nonconformity
Disconformity
Paraconformity
Angular unconformity
• Between tilted and undeformed sediments
Nonconformity
• Between crystalline rocks (igneous or
metamorphic) and sedimentary rocks.
Disconformity
• Between two parallel bodies of sediments,
but with some evidence of an erosional gap
between them, such as a channel or other
erosional surface.
Paraconformity
(obscure unconformity)
• The sediments are parallel but there is no
direct physical evidence of erosion; the
unconformity is detected by determining the
ages of the existing units.
Changing character of unconformities over distance if the
younger unit laps across different types of bedrock.
Lacuna- large time gap in the rock record composed of time
intervals when strata were never deposited,
Hiatus- when strata were removed after deposition
(degradational vacuity).
Geologic
Instantaneous
Events
How we establish time equivalence
in the stratigraphic record?
Time markers
Time Markers
• Time Marker are widespread, distinctive,
and geologically instantaneous.
• Generally, events that were separated by
years to tens of years can not be separated
in the stratigraphic record and therefore
considered instantaneous with respect to
geologic time.
Time Markers
• The primary tool for inferring time
relationships in the geologic time is
biostratigraphy. In the absent of fossil a
number of rocks can be considered to be
form instantaneously.
– Volcanic deposits of a single event such as ash
layers and their diagenetically altered
equivalents, bentonites
Bentonites
• Ash deposit flow in a matter of hours to
days and cover a wide area.
• If ash deposit can be correlated or event
dated, they provide unique time planes.
• The use of ash layers to mark geologic time
is called Tephrachronology
(tephrastratigraphy)
Tephrachronology
• In areas of frequent volcanic activity,
tephrachronology can be a powerful tool.
• It requires detailed petrographic analysis of
the ash and its geochemical fingerprinting
by comparing the amount of trace elements
that are present.
Ash deposits
• Long Valley Caldera in California erupted
about 740,000 years ago and spread an ash
cloud that extended 2000 km with
pyroclastic deposits up to 125 m thick near
the source and several centimeters 1500 km
away (Bishop Tuff). It is used to correlate
Pleistocene deposits.
Bentonites
This outcrop is exposed in a rock quarry in Chalfant Valley about
25 km southwest of Long Valley Caldera. The two main units of
the Bishop Tuff deposit are visible here: (1) the lower 5 m of the
section consists of the pumice that fell to the ground (airfall
pumice) downwind from the eruption; and (2) the upper 5-6 m of
the section consists of the basal part of the pyroclastic flows that
swept at hurricane speed away from the eruption. The thin dark
"layers" just below the contact between the units are stains from
an ancient groundwater table (manganese oxide stains).
Tektites
• Tektites are glassy spherules that are
thought to have been scattered around the
Earth by the impacts of meteorites.
• If a series of tekties layers can be clearly
identified as derived from the same event,
the layers are useful time markers.
Tektites
Impact events

tektites
Catastrophic Uniformitarism
Derek Ager (1981)- against the “myth of
continuous sedimentation”
Areas of continuous sedimentation also have
very low rates of accumulation. It will take
200 years to cover a sea urchin in the
Cretaceous chalks.
Ager
• Even classic sections have obvious and
obscure unconformities.
• A lot of holes tied together with string (with
sediment).
• Gentle continuous rain of sediment only in
the deep floor. Even there currents and
disolution produces unconfomities.
Ager
• In shallow marine deposits most of
deposition occur during storms events.
• “episodic sedimentation”
Correlation
• Correlation is the process of demostrating
the equivalence or correspondence of
geographically separated parts of a geologic
unit.
• The equivalency of lithologic units without
time implication.
• “by walking it out”
• by tracing it on a map or cross section.
Correlation
• Outcrops are seldom extensive enough.
• Some units have distinctive diagnostic
features that make then easy to recognize in
different outcrops.
• Sometimes the sequence itself can be
correlated.
• Stratigraphic cutoff- a facies change can cause
one lithology to change gradually into another.
• Intertonguing.
Time correlation
• Layer cake geology vs. time
Time transgressive
• Transgressive Cambrian marine sediments.
• Diachronism- a
mat forming in
the surface
today, but its
lateral
equivalent
buried beneath
the sabkha.
The Nature of• the
Control
Transgresive-Regresive
packages bouended by
unconformities make up
the sedimentary record of
most basins on cratons
and continental margins.
• Major unconformities
divide the stratigraphic
record of every continent
into discrete package,
which Sloss and others,
called Sequences
Sloss diagram of the
time-stratigraphic
relationships of
unconformity-bounded
sequence in North
America. Dark areas
represent large gaps in
the stratigraphic
record, which become
smaller toward the
continental margins.
Light areas represent
stratas. These
sequences has also
been recognized in
other continents.
Figure 8. Supercontinent
cycles since the Late
Precambrian. Each long-term
(400 - 600 million year
duration) cycle begins and
ends with the formation of a
Pangean supercontinent. The
rifting, drifting, and
subsequent subduction and
assembly of continental blocks
builds planetary-scale
mountain belts (shown in
orange and blue on the Jurassic
reconstruction, above), drives
long-term (first- and secondorder) changes of sea level,
and sets up the formation of
shallow equatorial (Tethyan)
seaways and continental
shelves. Many of these
shelves ultimately become the
depositional site for highlyorganic rich sediments. (data
from Worsley et al., 1984;
Nance et al., 1988; and
Veevers, 1990)
Figure 9. Temporal relationship between global first-order megasequences (B), second-order supersequence sets
(C), eustatic sea level (D), orogenic cycles (E), and tectonic phases of the supercontinent cycles (F). All cycles
and boundaries are referenced to the standard geologic time scale (A).
Figure A-F. Paleogeographic "snapshots" of the Phanerozoic supercontinent cycles, encompassing the PanAfrican, Caledonian, Hercynian, Cimmerian, and Alpine-Himalayan orogenies.
(source: R. Blakey, NAU; http://vishnu.glg.nau.edu/rcb/globaltext.html)
PAN AFRICAN OROGENIC CYCLE (Late)
Fischer (1981, 1984) recognizes long-term cycles of global climate and suggests a link between global
tectonics, sea level, climate and the development of biologic communities. He identifies the long-term
oscillatory cycles of two end-member global climatic states (Figure; cold “icehouse” vs. warm
“greenhouse”), linking these to cycles of mantle convection, eustatic sea level, and to environmental
stresses in organic communities. Icehouse climatic states (Late Precambrian, latest Ordovician, PermoCarboniferous, and Neogene-Recent) are characterized by the presence of large polar and high-latitude
continental ice sheets, strong latitudinal temperature gradients. During icehouse phases the world
oceans are marked by relatively low mean temperatures but are highly oxygenated due in part to more
active convection cells. In contrast, greenhouse climatic states (Ordovician-Devonian, JurassicPaleogene) are characterized by a lack of large polar and high-latitude continental ice sheets and relative
weak latitudinal temperature gradients. During greenhouse phases the world oceans have relatively high
mean temperatures and sluggish ocean circulation, resulting in poorly oxygenated conditions.
CALEDONIAN OROGENIC CYCLE
HERCYNIAN OROGENIC CYCLE (Early)
CIMMERIAN OROGENIC CYCLE
ALPINE OROGENIC CYCLE (Early)
ALPINE OROGENIC CYCLE