rocks are really important in Historical Geology, because they have lots of
information about the environment they formed in. They give very important key
to the puzzle of earth history.
of sedimentary rocks
of a rock is not always meaningful, however sometimes especially in sedimentary
rocks it can give useful information about the depositional environment.
or dark color
color means the presence of organic carbon, and iron. The fact that organics
could be still in there means that there was no oxygen around to destroy it.
Usually this color is characteristic to deep water, quiet bottom environment.
Organic decay in such an environment is related to anaerobic bacteria. In this
environment Fe will have 2 charge FeO, and pyrite and hydrogen sulfur would
accumulate. Bed smell......(Source rock for oil)
or light color
iron in near surface environment where lots of oxygen is around, will have
three charge Fe2O3 (hematite) RED or light color is characteristic. Organic
decay in such an environment is complete, no any black left.
of why is most of the soil around your house is reddish?)
size, shape and arrangement of mineral and rock grains in a rock constitutes its
Grains Larger particles
Matrix Finer particles
Cement Chemical precipitates
The larger the grains, the higher the energy of the transporting material.
the grain size distribution we can determine the sorting of the sediment.
The edges of particles
How closely the grain approaches the shape of a sphere
features in the sediments that are forming during sedimentation or shortly after
sedimentation and before lithification. These are extremely useful.
of drying mud and clay
an arrangement of sedimentary beds, in which one set of layers is inclined
relative to the others.
beds, in which each beds has the coarsest grains at the bottom.
along the bedding surfaces
of sedimentary rocks
OR DETRITAL SEDIMENTARY
Goes by grain size
is very important, and can give us information about the source area (geology of the source area)
-Amount of transport,
-distance of transportation
talk about this in detail in the lab.
AND BIOCHEMICAL SEDIMENTARY ROCKS
branch of geology that is concerned with the composition, origin, age
relationships and aerial extent of layered or stratified rocks. Stratification
may occur in any of the major rock groups, however all the sedimentary rocks are
bounding surface separating one layer of strata from another is called Bedding
plane can be
rock gradually changes into an other)
Sharp (below and above rocks are different) meaning rapid
changes in sedimentation, environment, or it could mean that some time is
missing from the succession.
sedimentary layers are undeformed, than correct relative ages easy to determine
by the position in the rock sequences. However if strata have been deformed,
relative age determination is more difficult.
the time however geologic structures help to solve the geologic problems (ripple
marks, root traces etc.).
more difficult to find relative age solution
with igneous contacts, geologists are looking for signs such as baking.
of course use the other principles also; we have already learned such as Principle
of Crosscutting, Principle of original horizontality, principle of lateral
continuity, Principle of inclusion,
principle is about time breake or missing time. (we call it HIATUS, meaning
during this time there was no rock layer preserved)
of erosion or nondeposition between younger and older beds, that are parallel to
surface on tilted or folded strata over which younger strata have been deposited
of regional extent may change laterally from one to an other.
surface cut into metamorphic or igneous rocks and is covered by sedimentary
most basic local unit of stratigraphy is the formation.
series of strata that originated through the same formative process.
thinnest observable rock layer. Formation would contain lots of stratum.
chosen to define a formation are:
composition of mineral grains
thickness and geometry of stratification
six together is referred as lithology of the formation.
Realtionships - facies
formulated the principle of the lateral continuity, in which he stated, that
sediment layers will extend in each
direction untill they terminate.
Edge of depositional basin
or eroded away
termination may also occur when a rock unit becams very thin until it pinches ou
Intertonguing occurs, when a unit splits laterally into thinner units each of
which pinches out. This occurs when different depositional processes are
operating in adjacent areas.
change in rock type
environment in a sedimentary basin produces a body of sediment which can be
characterized by a distinctive set of physical, chemical and biological
attributes. The body of sediment is called sedimentary facies.
is the advance of
the sea over the land, when sea level rises with respect to the continent.
(shrinkage of the continent) This will produce a continuous shift of
environments and their sedimentary products landward. This means, that shallow
water sediments will be overlied by deeper water sediments. On the other hand
individual rock units become younger in a landward direction. These sediments
are time-transgressive meaning that their ages vary from places to place. These
are all together are so called transgressive facies pattern.
is the opposite, when there is a retreat of the sea from the land, when sea
level falls with respect to the continent. In the sediments depositing during
retreating sea we can see a regressive facies pattern.
enlargement of land (more fluvial, lake wind deposits)
Finished by erosional unconformity
seaward shift of facies through time
one locality sediments tend to be coarsening upward.
100 years ago a german geologist Johannes Walter
studied the relationship of modern facies to their environment.He noted
that environments shift position thorough time, The same facies following one
another in a vertical sequence (which does not have time break) will also
replace one another laterally. Most of the time it is easier to work with
walter’s low from the vertical successoin, than in horisontal, because of the
the repetition of facies or sequence of facies, in other word the repetition of
of transgression and regressions
are different scales of sea level changes, causing these transgressive -
-Longterm sea-level ~100 million years
Ice age/nonglacial time
-Mediumterm sealevel changes
These are related to plate tectonic movements
-Short term sea level changes
Climate changes caused by gravitational movement between the planets
(high frequency sea level changes 100, 40, 20 ky cycles)
Just for the local basins
are the remnants or traces of prehistoric life, that have been preserved in the
are important in global correlation
give information on the depositional environment
Provide information about evolution
original structure and composition)
--- Mammuth in Berezovka
that has been changed structurally, chemically or both
principle of fossil succession:
to this principle fossil assamblages succeded one another through time in a
regular and determinable order.
unique to a limited thickness of strata. It has to be widespreaded
geographically. (free floating larval stage of marine animals)They are very
important in correlation (Ammonites).
interval of strata characterized by disticnt index fossil. (Typical time
duration is 0.5-2 million years.
relative time scale
the development of the relative time scale geologists through lots of fighting
made up a composite geologic column, which is the relative time scale.
with both rocks and time the terminology includes two fundamentally different
kind of units:
defined by its content
Units defined by geologic time
Units defined by their content:
Lithostratigraphic unit (Defined by the physical char. of the rocks)
Formation (mappable rock unit, basic lithostratigraphic unit)
on fossil content
Units defined by geologic time
System (fundamental unit)
are based on stratotype
from the best locality of the certain system.
of all you guys have to learn the ERA<
PERIOD< EPOCH (pg.94).
is the process demonstrate equivalency.
ex.Correlation of lithostratigraphic units is the recognition of similar
use the presence of KEY beds (lava flow)
companies, water comp. ---well cuttings, well logs give wonderful information
about underlying lithologies.
(extremly useful )