Transcript Stratigraphic Principles

SOURCES of ROCK and
FOSSIL DATA
• SURFACE DATA:
Equipment:
- Measuring Tools
- Collecting Tools
- Recording Equipment
• SUBSURFACE DATA:
- Core Logging
SOURCES of GEOPHYSICAL
DATA
• Remote Sensing
• Geophysical Well Logs
- S.P.
- Resistivity
- Induction
- Dipmeter
- Radioactivity
- Sonic
- Caliper
- Temperature
• Reflection Seismic Survey
• Gravity
• Magnetic
Lithostratigraphic Units
Member A
Formation A
Member B
Member C
Group A
Member D
Formation B
Member E
Member F
Formation C
Member G
Member H
Member I
Member J
Supergroup
Formation D
Member K
Member L
Member M
Member N
Group B
Formation E
Member O
Member P
Member Q
Member R
Formation F
Member S
Member T
Supergroup
|
Group
|
Formation
|
Member
|
Bed
• Lithostratigraphy is a sub-discipline of
stratigraphy, the geological science
associated with the study of strata or
rock layers. Major focuses include
geochronology, comparative geology,
and petrology. In general a stratum will
be primarily igneous or sedimentary
relating to how the rock was formed.
Sedimentary layers are laid down by
deposition of sediment associated with
weathering processes, decaying organic
matters (biogenic) or through chemical
precipitation. These layers are
distinguishable as having many fossils
and are important for the study of
biostratigraphy.
Igneous layers are either plutonic or
volcanic in character depending upon
the cooling rate of the rock. These
layers are generally devoid of fossils
and represent intrusions and volcanic
activity that occurred over the geologic
history of the area.
• A lithostratigraphic unit conforms to the
law of superposition, which state that in
any succession of strata, not disturbed
or overturned since deposition, younger
rocks lies above older rocks. The law of
horizontal continuity states that a set of
bed extends and can be traceable over
a large area.
• Lithostratigraphic units are recognized
and defined on the basis of observable
rock characteristics. The descriptions of
strata based on physical appearance
define facies. Lithostratigraphic units
are only defined by lithic characteristics,
and not by age.
• Stratotype : A designated type of unit
consisting of accessible rocks that
contain clear-cut characteristics that are
characteristic for a particular
lithostratigraphic unit.
Lithosome: Masses of rock of essentially
uniform character and having
interchanging relationships with
adjacent masses of different lithology.
E.g.: Shale lithosome, limestone
lithosome…
Lithostratigraphic
Example:
Grand Canyon
Principles (Laws) of Stratigraphy
Principle of…
• Original Horizontality
• Superposition
• Lateral Continuity
• Cross Cutting
Relationships
• Inclusions
• Faunal Succession
Walther’s Law
Nicholas Steno
1. Principle of Original Horizontality
A stratigraphic
section of
Ordovician rock
exposed in central
Tennessee, USA.
The sediments
composing these
rocks were formed
in an ocean and
deposited in
horizontal layers.
2. Principle of Superposition
Youngest Strata
Oldest Strata
Stratigraphic column
on north shore of
Isfjorden, Svalbard,
Norway. Since there
is no overturning,
the rock at the
bottom is older than
the rock on the top
by the Principle of
Superposition.
3. Principle of Lateral Continuity
Lateral Continuity
4. Principle of Cross Cutting
Relationships
5. Principle of Inclusions
Stratigraphic Relationship
• Two types of contact: Conformable and
Unconformable.
• Conformable: Unbroken deposition, no
break or hiatus (break or interruption in
the continuity of the geological record).
The surface strata resulting is called a
conformity.
• Two types of contact between
conformable strata: Abrupt contacts
(Directly separate beds of distinctly
different lithology, minor depositional
break, called Diastems) Gradational
contact (Gradual change in deposition,
mixing zone).
Unconformable: Period of erosion/nondeposition. The surface stratum
resulting is called an unconformity.
Four types of unconformity
• Angular unconformity Younger
sediment lies upon an eroded surface of
tilted or folded older rocks. The older
rock dips at a different angle than the
younger.
• Disconformity The contact between
younger and older beds is marked by
visible, irregular erosional surfaces.
Paleosol might develop right above the
disconformity surface because of the
non-deposition setting.
• Paraconformity The bedding plans
below and above the unconformity are
parallel. A time gap is present but there
is no erosion, just a non-deposition
period.
• Nonconformity Relatively young
sediments are deposited right above
older Igneous or metamorphic rocks.
Disconformity
with the Lower
Cretaceous
Edwards
Formation
overlying a Lower
Permian
limestone; hiatus
is about 165
million years;
Texas.
Boundaries:
Conformable Bed Contacts
Gradational
Sharp
Boundaries:
Unconformities
Gaps in Rock = Gaps in Time
Types of Unconformities:
Nonconformity
Nonconformity - Grand Canyon
Using Inclusions to Recognize a
Nonconformity
• Fragments of a rock unit (xenolith meaning foreign
rock) which are included in another (host) rock unit
must be older than the host rock. This may occur in
sedimentary environments, where pieces of preexisting rock can be ripped up and included in
younger sediments. Alternatively, when igneous
rocks are intruded, fragments of the country rock may
be incorporated into the intrustion.*
Types of Unconformities:
Angular Unconformity
Formation of an Angular Unconformity
Angular Unconformity in the
Grand Canyon
The Angular
Unconformity
at Siccar
Point,
Scotland
Source: Edward A. Hay, De Anza College, Cupertino, CA
Types of Unconformities:
Disconformity
Formation of a Disconformity
Walther’s Law
Johannes
Walther
(1860-1937)
Concept of
Sedimentary Facies
Depositional Environments
Facies
Sedimentary Facies refers to all of the characteristics
of a particular rock unit.
The characteristics of the rock unit come from the
depositional environment.
Sedimentary Depositional Environment
describes the combination of physical,
chemical and biological processes
associated with the deposition of a
particular type of sediment and,
therefore, the rock types that will be
formed after lithification, if the sediment
is preserved in the rock record
Types of depositional
environment
Continental
• Alluvial
• Aeolian
• Fluvial
• Lacustrine
Continental
• ALLUVIAL- Alluvium (from the Latin,
alluvius, from alluere, "to wash against")
is loose, unconsolidated (not cemented
together into a solid rock), soil or
sediments, eroded, deposited, and
reshaped by water in some form in a
non-marine setting.
Continental
Alluvium is typically made up of a
variety of materials, including fine
particles of silt and clay and larger
particles of sand and gravel. When this
loose alluvial material is deposited or
cemented into a lithological unit, or
lithified, it would be called an alluvial
deposit.
• The term "alluvium" is not typically used
in situations where the formation of the
sediment can clearly be attributed to
another geologic process that is well
described. This includes (but is not
limited to): lake sediments (lacustrine),
river sediments (fluvial), or glaciallyderived sediments (glacial till).
• Most, if not all, alluvium is very young
(Quaternary in age), and is often
referred to as "cover" because of the
fact that these sediments obscure the
underlying bedrock. Most sedimentary
material that fills a basin ("basin fill")
that is not lithified is typically lumped
together in the term alluvial.
• Alluvium can contain valuable ores such
as gold and platinum and a wide variety
of gemstones. Such concentrations of
valuable ores is termed a placer
deposit.
Section of alluvium at
the Blue Ribbon Mine in
Alaska
Outcrop of Enon
Conglomerate
formed by Alluvial
deposits in the
Gamtoos Valley,
Eastern Cape,
South Africa
An alluvial fan is a fan-shaped deposit
formed where a fast flowing stream
flattens, slows, and spreads typically at
the exit of a canyon onto a flatter plain.
A convergence of neighboring alluvial
fans into a single apron of deposits
against a slope is called a bajada, or
compound alluvial fan.
A vast alluvial fan
blossoms across the
desolate landscape
between the Kunlun
and Altun mountain
ranges that form the
southern border of
the Taklamakan
Desert in Xinjiang.
Alluvial fan in
the French
Pyrenees
Continental
• EOLIAN - processes pertain to the
activity of the winds and more
specifically, to the winds' ability to
shape the surface of the Earth and
other planets. Winds may erode,
transport, and deposit materials, and
are effective agents in regions with
sparse vegetation and a large supply of
unconsolidated sediments.
• Although water is much more powerful
than wind, aeolian processes are
important in arid environments such as
deserts.
• The term is derived from the name of
the Greek god, Æolus, the keeper of the
winds.
Particles are transported by
winds through:
• suspension
• saltation
• creep.
Crossbedding of
sandstone near Mt.
Carmel road, Zion
Canyon, indicating
wind action and
sand dune formation
prior to formation of
rock.
• FLUVIAL is used to refer to the
processes associated with rivers and
streams and the deposits and landforms
created by them.
Channel pattern
• Straight river, which are found in the
most tectonically incised/active areas.
This is more of a hypothetical endmember, and are not often found in
nature. Straight-type channels can be
found at alluvial fans.
• Meandering rivers which form a sinuous
path in a usually low-gradient plain
toward the end of a fluvial system.
• Braided rivers, which form in
(tectonically active) areas that have a
larger sedimentary load than the
discharge of the river and a high
gradient.
• Anastomosed River is a rare case of a
relatively straight, complicated vertical
sequence of river deposits with banks
held together by dense vegetation.
• Lacustrine -lake (from Latin laus) is a
terrain feature, a body of liquid on the
surface of a world that is localized to the
bottom of basin (another type of
landform or terrain feature; that is, it is
not global) and moves slowly if it moves
at all. Another definition is, a body of
fresh or salt water of considerable size
that is surrounded by land
On Earth, a body of water is considered a
lake when it is inland, not part of the
ocean, is larger and deeper than a
pond, and is fed by a river.
• Natural lakes on Earth are generally
found in mountainous areas, rift zones,
and areas with ongoing or recent
glaciation. Other lakes are found along
the courses of mature rivers. In some
parts of the world, there are many lakes
because of chaotic drainage patterns
left over from the last Ice Age.
• All lakes are temporary over geologic
time scales, as they will slowly fill in with
sediments or spill out of the basin
containing them.
Transitional
• Deltaic
• Tidal
• Lagoonal
• Beach
• A delta is a landform that is created at
the mouth of a river where that river
flows into an ocean, sea, lake, reservoir,
flat arid area, or another river. Deltas
are formed from the deposition of the
sediment carried by the river as the flow
leaves the mouth of the river. Over long
periods of time, this deposition builds
the characteristic geographic pattern of
a river delta.
• Herodotus the great historian coined the
term delta for the Nile River delta
because the sediment deposited at its
mouth had the shape of the upper-case
Greek letter Delta: Δ.
Types of Delta:
– River-dominated deltas
– Wave-dominated deltas
– Tide-dominated delta
• River-dominated delta, such as the
Mississippi River Delta, usually take on
a multi-lobed shape that results from
repeated sequences of channel
occupation, offshore deposition, and
channel avulsion.
• When a single channel is occupied for a
long period of time, its deposits extend
the channel far offshore, and causes the
delta to resemble a bird's foot; the term
“digitate delta" is sometimes used as
well. These deltas are often
characterized by a main channel that
divides itself into several distributary
channels.
• Wave dominated deltas, wave erosion
controls the shape of the delta, although
deposition still outweighs the amount of
erosion and the delta is able to advance
into the sea. Deltas of this form, such as
the Nile Delta, tend to have a
characteristic Greek-capital-delta shape
.
The Ganges-Brahmaputra River delta in
India and Bangladesh is a massive tidedominated delta. It is one of the most
fertile regions in the world.
Tidal deltas behave differently from riverand wave-dominated deltas, which tend
to have a few main distributaries. Once
a wave- or river- distributary silts up, it is
abandoned, and a new channel forms
elsewhere.
In a tidal delta, new distributaries are
formed during times when there's a lot
of water around - such as floods or
storm surges. These distributaries
slowly silt up at a pretty constant rate
until they fizzle out.
Tides are the rise and fall of sea levels
caused by the combined effects of the
rotation of the Earth and the
gravitational forces exerted by the Moon
and the Sun. The tides occur with a
period of approximately 12 and a half
hours and are influenced by the shape
of the near-shore bottom
• Erosion is also an important control in
tide dominated deltas, such as the
Ganges Delta, which may be mainly
submarine, with prominent sand bars
and ridges. This tends to produce a
"dendritic" structure. Tidal deltas
behave differently from river- and wavedominated deltas, which tend to have a
few main distributaries.
Lagoon is a body of comparatively
shallow salt or brackish water separated
from the deeper sea by a shallow or
exposed barrier beach, sandbank of
marine origin, coral reef, or similar
feature. Thus, the enclosed body of
water behind a barrier reef or barrier
islands or enclosed by an atoll reef is
called a lagoon.
This application of lagoon in English dates
from 1769. It adapted and extended the
sense of the Venetian laguna
Beach is a geological landform along the
shoreline of a body of water. It usually
consists of loose particles which are
often composed of rock, such as sand,
gravel, pebbles, or cobbles. The
particles of which the beach is
composed can sometimes instead have
biological origins, such as shell
fragments or coralline algae fragments.
Marine
• Shallow water marine
• Deepwater marine
• Reef
Others
• Evaporite
• Glacial
Marine Transgression = Sea Level Rise
Marine Regression = Sea Level Fall
Walther’s Law
Sedimentary environments that started out side-by-side
will end up overlapping one another over time due to
transgressions and regressions.
Facies
Limestone
Reef
Shale
Siltstone
Lagoon Near Shore
Environment
Sandstone
Beach
Marine Trangression
Walther’s Law
Marine Regression
“The sea goes in, the sea goes out.”
Correlation
A
Regression
Transgression
B
C
Example of Correlation
Colorado Plateau Correlation
Colorado Plateau Correlation
6. Principle of Faunal Succession
Sketch by Baron Cuvier (1769-1832)
William
“Strata” Smith
6. Principle of Faunal Succession
" . . . each stratum contained organized fossils peculiar
to itself, and might, in cases otherwise doubtful, be
recognized and discriminated from others like it, but in a
different part of the series, by examination of them."
Biostratigraphy
Superzone - Biozones - Subzones
Defined by first and
last appearance of
index fossils and/or
fossil assemblages
Chronostratigraphy
and the
Development of the
Geologic Time Scale
Geologic Time Scale
Eon
Geologic
Time
Scale
Era
Period
Age (Myrs)
Quaternary
C
e
n
o
z
o
i
c
P
h
a
n
e
r
o
z
o
i
c
1.8
Neogene
5.3
23.8
Tertiary
33.6
Paleocene
54.8
65
M
e
s
o
z
o
i
c
Cretaceous
144
Jurassic
Triassic
Permian
P
a
l
e
o
z
o
i
c
Pennsylvanian
Mississippian
Devonian
Silurian
Ordivician
Cambrian
P
r
e
c
a
m
b
r
i
a
n
0.01
206
248
290
323
354
417
443
490
543
Proterozoic
2500
Archean
3800
Hadean
Age of the Earth 4600 Myrs (4.6 Byrs)
Source: Geological Society of America (1999)
Epoch
Holocene
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
Relative Dating of Rocks
Using Stratigraphic Principles
Example 2 of Relative Time
Orbit w/o eccentricity
Orbit w/ eccentricity