historical geology we’re learning about the history of the earth.
question is, how can we do that?
already discussed this question somehow, and got to the fact, that we would use
Geologic Principles, and fossils, to put together he puzzle.
we have to learn to listen to the stories of ancient environments, climate
and paleogeography (paleolatitude, paleoaltitude).
the remaining question is how are we going to make the rocks, and the fossils to
talk, to tell us their own stories.
we do that, we have to know about the present day environments, to be able to
use the great idea of uniformitarianizm.
the Hypsometric curve of the earth, which represents the surface of the earth.
living things relate to their environment is called ecological niche. For a
specimen its environment has to give food, and particular physical, and chemical
conditions. Some specimens have much broader niche than others. Every specimen
is restricted in its natural occurrence by certain environmental conditions.
all of the specimens have to share their environments, and frequently have to
compete for food and living space.
of several species living together are called ecological
these communities the eating habitat is depend on the food chains or food web in
the given environment.
organisms of a community and the physical environment they occupy called ecosystem. The animals of an ecosystem are called: FAUNA
and the plants are called FLORA.
Diversity is used to describe the number of species that live
together in an ecological system. It is nothing else than the account of the
number of different specimens
distribution and abundance of organism on a board geographic scale are studied
within the field known as biogeography.
most important limiting factor is temperature. Some to polar, some to
equatorial. More species are adopted to tropical regions than to polar areas.
limiting factors are land barriers for aquatic forms or water barriers to
fauna and flora of the continents. Today sea-level is lower than during most of
the geologic time, and the world has a steep temperature gradient between the
poles and the equator. Climatic
conditions have a very important influence on the distribution of organisms on
remarkable how closely the distribution of terrestrial vegetation corresponds to
the geographic pattern of climates. This correspondence, coupled with the fact
that plants are dominant producers for food web, thus strongly effect the
distribution and abundance of animals.
temp:18-20°C (64-68°F) or higher, and usually found at latitudes within 20°.
Lots of different kind of plants and animals.
The rocks in such a climate environment are chemically weathered. The
soil zone well developed, rich in nutrients.
20-30° latitude the tropical desert zone occur. Ex. Sahara. Much less
diversities. Big temperature different during a day. A few
plants, therefore just a few animals. Max 10 inches of rain/year. The
sediment here only physically weathered, mostly sand transported by winds.
also can occur in other latitude, such as mountain shadow (Arizona) or far away
from the ocean (Gobi)
enough for grass and scattered trees, but not enough for dense forest. They are
positioned between wetland and deserts usually. (Great Plain). They are famous
about the large amount of relatively large animals; bosons, antelopes, zebras,
and chemical weathering common, well developed soil.
contrast, from rain forest, Savannah. Today two icecaps exist. One on
Antarctica, the other one on Greenland. In ancient times, where there were no
continents on the poles, there were no existing icecap on the earth. If there is
no icecap, it is easy to imagine, that there is no temperature contrast either.
In these cases the climate is much more equal on earth.
life on the ice caps are very scattered, almost no plants, and just a few animal
can survive the very cold climate there.
weathering, no soil.
layer of the soil beneath is frozen even during the summer. In these conditions
water is rare. Here the plants are low, and they do not need too much water.
mosses, sedges, lichens and low growing trees. North America-Eurasia,
small diversity animal life.
physical, and chemical weathering, poorly developed soil, mostly from grass.
are located next to the tundra. Pine trees. In this zone the summers are very
soil, chemical and physical weathering, good soils.
replaces the evergreen forests. Among some pine trees these are characterized by
maple oak trees. Ground animals are more diverse in temperate forest, than in
evergreen forests. Birds are especially well presented,
developed soil zones.
summer and wet winter. They mostly lie about 40° from the equator.
Mediterranean see). In these areas chaparral vegetation is common which consist
of plants with waxy leaves, that retain water during dry summer. Lots of animals
Why climate is so important to interpret rocks and
plants are so sensitive of environmental changes, the fossil plants are such
good climate indicators. Geologists are often using fossil plants in climate
example Cycads, are today living in warm climate, and bec. Of uniformitarianizm,
we think that they also lived in warm climate during geologic times. Therefore
their distribution would help to draw climate boundaries of the past. Reptiles,
the cold-blooded animals also suggest warm climate.
basins are the area for most of the sedimentation throughout the earth history..
This is the place where the sediments and the fossils have more chance to be
between 0-10km. Most of the seafloor lies between 3-6 km below sea level.
extension of a continent. The edge of the shelf is called shelf break.
the sea margins barrier islands are
frequent, because the longshore current, and the wind. Behind barrier islands
there are lagoons bays, or marshes.
These marshes are populated by plants and animals especially in warmer
latitudes. Peat, coal formation is
frequent, especially on mid latitudes.
the sea occupies the land area as well, it is called epicontinental sea. Today
any of those exists, but in ancient time they were very common.
of the continental shelf is the continental
base of the continental slope there is now continental crust, but oceanic.
rise: seaward of
the continental slope
plain: below the
upper layer of the ocean where the light can penetrate is called PHOTIC zone. There are sea animals and plants for which photic zone
is the only place to live. The depth of photic zone is about 100-200 m, which is
about the same distance seaward as the shelf break.
life the hardest conditions exist in the near land zones. Here depending on the
climate the chemical and temperature conditions are frequently changing, so
there is no diverse biota. Also close to the land because of the waves biotas
have to survive high energy conditions.
deeper sea conditions are more stable.
that are floating in the water are called PLANKTON.
Phytoplankton: plantlike organism (photosynthesis).
on the phytoplankton are floating animals ZOOPLANKTON.
Some of the animals in the plankton are able to swim, however most of the just
drifting with the flow.
moving, swimming in the water are called NEKTON.
and nekton together is called pelagic
living on the floor are called Benthos. The
seafloor itself is the substrata.
distribution of marine life depend on:
temperature of the sea water
Corals are restricted to the tropical latitudes.
of the sea water
salt content of natural water is called salinity.
water is normally contains 35 parts of salt per thousand parts of water.
of lower Salinity is called brackish
of higher salinity is called hypersaline
also a limiting factor
ex.At the shoreline which is very high energy environment, just certain type of
plants and animals can live
difficulty of living in water of low salinity is a major reason, that the
diversity of life in freshwater is very low.
the loose sediment forming on the top of the rocks by weathering.
we learned in physical geology, that soil in humid climate is Al, Fe rich mostly
clay mineral (Pedalfer) and on arid climate it always contains carbonate (Pedocal).
The tropical soil, which has no SIO2
in it is called laterite.
we recognize ancient soils?
it is difficult, because diagenetic alteration.
most of the time roots, animal burrows are diagnostic features. To recognize
ancient soil horizons is important, because it tells us, that the rocks below
the soil were exposed to air.
the percentage of lake sediments is not too big in sedimentary rocks, however
they are very important to recognize. Most of the time to separate lake
sediments from marine can be done by the fossils!!!!!!!
freshwater animals are very different from marine (plants also).
are usually also very close to other terrestrial environments such as river.
recognize glacial environments is very important for paleoclimatology studies.
easy to recognize the areas which were once occupied by glaciers. As glaciers
move they erode the rocks. They live characteristic U shape valleys, and
sediments. The sediment of the glaciers are usually the mixture of boulders,
pebbles, to mud (UNSORTED) is easy to recognize. This material is called TILL. Sediment particles in till will never be rounded. Lithified
till is called tillite. In lakes farther from the glaciers fine grained sediment
accumulate called varves. Each coarse
layer forms during summer, when meltwater carry sand into lake. During winter,
when everything is frozen, just very few organic rich mud would deposit in this
lakes from suspension.
like in humid environment. The most important feature of arid environment is
carbonate precipitation+the presence of evaporites (gypsum, anhydrite, rock-salt (halite).
presence of mudcracks are important signs for alternating wet/dry season. Dry
Valley a good modern example.
sand in sand dunes are piled up by wind, therefore it is well sorted, all the
grains are well rounded. The sand dunes are always cross bedded.
prevailing wind direction is changing the cross beds are angular, called trough
environment always indicates arid climate. (If it was humid, soil would form,
and dunes would become stabile).
of alluvial fans form at the feet of the mountains and steep hills in both arid
and humid regions. This sediment is usually unsorted and grains are angular.
Alluvial fan has characteristic delta shape like delta.
forms just below the alluvial fan. It has a complex network of channels and
islands. The bars between the channels are filled up by coarse grained, hardly
channel sedimentation is cross bedded.
channels of the stream migrates. Point bar, cut bank..Natural levee,
sorted, well rounded sediment, mostly clay, and q-sand
the delta sediment becomes finer grained, lots of clay accumulates. The
sediments in the delta frequently influenced by marine processes, such as waves
and tides. When a river enters into a large body of water the flow slows down,
and sedimentation happens.
has some characteristic parts: Prodelta, delta front and delta plain.
of the sedimentation delta builds toward the ocean:Progradation.
the progradation happens the earlier prodelta will be overlied by deltafront,
and than delta plain.
Deltas are very important places to find bec. of the clay the channels are good
closed reservoars for everything.)
islands and lagoons
flat, talus, back reef lagoons
(ancient atolls are also good reservoars).(bomba)
platforms (inter, supra, subtidal)
slopes and turbidite
sediments (deep sea sediments)
interpretation and historical geology
of environmental significance
Geometry: three dimensional shape of rocks
a. detrital grainsize (energy level)
b. Carbonates-sedimentary facies with characteristic grain types (grainsize also show energy level).
a. macrofossils as rock builders (reef)
b.Macro-micro fossils as environment indicators
c.Trace fossils (sign of specific environments)
a. ripple marks
b. cross beds