Midterm 1 Flashcards
Define Geology
Geology is a complex, integrated system of related parts, components, or subsystems
What are the principle subsystems of the earth?
– Atmosphere – Biosphere – Hydrosphere – Lithosphere – Mantle – Core
Explain historical geology?
Historical geology is concerned with the origin and evolution of Earth’s continents, oceans, atmosphere, and life
What is a theory?
In science, a theory is NOT a hunch or guess, but a reliable explanation supported by a large amount of evidence.
e.g. plate tectonics is a theory
How is a theory derived?
from the scientific method, which involves:
–gathering and analyzing facts
–formulating hypotheses to explain the phenomenon
–testing the hypotheses
–and finally proposing a theory.
–Science makes no claim about the existence or nonexistence of the supernatural.
What is a hypothesis?
a tentative explanation
What is a scientific theory?
theory is a testable explanation for some natural phenomenon, that is supported by a large body of evidence
Outline how the universe was formed
• The “Big Bang” theory of how the universe formed is broadly accepted
• Massive explosion 13.7 Ga forms all the universe’s known matter and energy
—even space and time
• Immediately after, universe expanded with incomprehensible speed from its pebble-size origin to astronomical scope
• Expansion has continued, but much more slowly, over the ensuing Ga
What is earth’s place in the solar system?
–Earth condensed as a solid body from the solar nebula about 4.6 billion years ago.
–Soon after internal heat differentiated the Earth into a layered planet.
Explain how earth is a dynamic and evolving planet?
- Earth has continuously changed during its 4.6 billion year existence as a result of interactions between its various subsystems and cycles.
- Size, shape and distribution of continents and ocean basins have changed.
- Composition of the atmosphere has evolved.
What are the concentric layers of the earth?
–Crust
–Mantle
–Core
Describe the composition of the earth’s core
The core consists of:
–a small, solid inner region
–a larger, liquid outer portion
• Composed of iron and a small amount of nickel
Describe the composition of the earth’s mantle
• The Mantle –Surrounds the core and is divided into:
• a solid lower mantle.
• a partially molten asthenosphere that overall behaves plastically and flows slowly.
• a solid upper mantle.
–Composed primarily of peridotite, a rock made of the mineral olivine (and it’s high density polymorphs).
Describe the composition of the earth’s crust
• The Crust –Outermost layer •Thick Continental ≤80km • Thin Oceanic ≤10km • Asthenosphere –Surrounds the lower mantle. –Behaves plastically and slowly flows. –Partial melting in the asthenosphere generates magma (molten rock) that rises to the Earth’s surface. • The Lithosphere –The solid outer layer of the Earth. –The crust and the upper most mantle.
Explain the theory of plate tectonics
The lithosphere is composed of rigid plates that diverge, converge, or move sideways past one another over the asthenosphere.
–Plate Boundaries
• Earthquakes and volcanoes occur at the boundaries
Explain the importance of plate tectonic theory in relation to earth systems
–Plate tectonic theory is a unifying explanation for many geologic features and events, helping us understand the composition and internal processes of Earth on a global scale.
Explain the theory of organic evolution
- that all living things are related.
- descent, with modification, from organisms living in the past.
- Charles Darwin proposed that the mechanism of natural selection results in survival to reproductive age of organisms best suited to their environment.
- Fossils, the remains of once-living organisms, provide evidence for evolution and a history of life before humans.
Explain geologic time
–The immensity of geologic time is central to understanding the evolution of the Earth and its life.
–Earth goes through long cycles.
–The geologic time scale is the calendar that geologists use to date past events in Earth’s history.
What is uniformitariamism?
Is the main tenet of geology.
– This principle states that the laws of nature have remained unchanged through time and that the processes observed today also operated in the past, though possibly at different rates.
– Therefore, to understand and interpret geologic events from evidence preserved in rocks, geologists must first understand present-day processes in rocks.
Why is the study of historical geology important?
• Understanding how the Earth’s systems work will help ensure the survival of humanity.
• It will help us to understand how our actions affect the delicate balance between these systems.
• Example: Global Climate Change
–Increasing global temperatures over the past decades.
–Increasing temperatures result from greenhouse gas emissions from the utilization of fossil fuels.
–Analyzing mean global temperature changes during the last 130 years and over geologic time.
Define mineral
A mineral is: –Naturally occurring –Inorganic –Crystalline solid –Characteristic physical properties –Specific chemical composition.
Define rock
–Rocks are composed of one or more minerals or other solid substances, such as volcanic glass or organics in coal.
Describe the ferromagnesian silicates of minerals
- silicate minerals that contain iron, magnesium, or both.
–Dense and usually dark in color.
Describe the non-ferromagnesian silicates of minerals
- lack iron and magnesium.
–May contain aluminum, calcium, potassium and/or sodium.
– Often light colored.
Describe the carbonate group of minerals
–All carbonate minerals have carbonate (CO³)-² as in calcite (CaCO³) and dolomite (CaMg[CO³]²). –Carbonate minerals are mostly found in the sedimentary rocks limestone and dolostone.
–Carbonates are derived from the shells and hard parts of marine organisms or are precipitated from seawater as evaporites.
Describe the sulfate group of minerals
–All sulfate minerals have the sulfate radical (SO4-²) as in gypsum (CaSO4•2H2O).
–Sulfate minerals are common in deserts, forming from evaporation of water.
Explain the process of the rock cycle
- Uplift and exposure of rocks
- Weathering of rocks to sediments
- Sediment transport and deposition
- Burial of sediments and lithification
- Metamorphism
- Melting to form magma
- Crystallization of magma
- Consolidation
- Volcanic eruptions
Describe sedimentary rocks and explain how they are formed
- Uplift and exposure of rocks
- Weathering of rocks to sediments
- Sediment transport and deposition
- Burial of sediments and lithification
- Metamorphism
- Melting to form magma
- Crystallization of magma
- Consolidation
- Volcanic eruptions
What are the different particle sizes of sedimentary rocks?
–Gravel (>2 mm)
–Sand (1/16-2 mm)
–Silt (1/256 - 1/16 mm)
–Clay (<1/256 mm), Mud is silt and/or clay.
How are sedimentary rocks transported?
–Running water - most effective –Glaciers –Wind –Waves
Where are sedimentary rocks deposited?
–Steam channels
–Beaches
–Seafloors, etc.
Define lithification
–Conversion of unconsolidated sediment to sedimentary rock
–Burial of sediments
–Compaction
- pressure from burial
What are the three classes of sedimentary rocks?
- detrital clastic
- detrital sedimentary rocks
- chemical sedimentary rocks
Describe the sedimentary class - detrital clastic
• Composed of detritus (clasts in sediments) –Chemical/Biochemical
• Precipitation from water
• Biochemical - precipitation by organisms
• Crystalline and/or clastic textures
Composition of Detrital Clastic Rocks
– Quartz, feldspars, clays, and rock fragments are the most common constituents in
detrital sedimentary rocks.
– Composition of detrital
sedimentary rocks depends mostly on the composition of the source rocks in the area
from which their sediment was derived (the source area).
Describe the sedimentary class - detrital sedimentary rocks
• Gravels cement into conglomerates (rounded clasts) and breccias (angular clasts).
• Sands into quartz sandstones and arkoses.
Mudrocks - siltstones, mudstones and claystones.
• Shales - fissile mudstones, which split along closely spaced parallel planes.
Describe the sedimentary class - chemical sedimentary rocks
• Carbonate rocks - limestones and dolostones.
• Evaporites - rock salt and rock gypsum, precipitate from evaporating seawater.
• Chert - spherical masses of silica.
• Coal - biochemical, buried and compressed peat (plants).
– Limestone and dolostone are the most common.
– Carbonates are mostly deposited in warm, shallow seas where the shells of
organisms can accumulate
– Evaporites, such as rock salt and rock gypsum, mostly form from evaporating
seawater
What are the processes in lithification?
- Compaction
- packing sediment grains through burial
- reduces volume by 40%
- involves desiccation which is the loss of water from pore spaces resulting from compaction/evaporation - Cementation
- minerals precipitate from sediment pore fluids to bind together grains
- most common cements = calcite and quartz
What are igneous rocks?
- magma is molten rock below the Earth’s surface
- magma solidifies into plutonic or intrusive igneous rocks
- magma erupts as either lava or pyroclastics materials
- lava and pyroclastic materials cool to form volcanic or extrusive igneous rocks
What are the textures in igneous rocks
- phaneritic (coarse-grained) slower cooling
- aphanitic (fine grained) rapid cooling
- very rapid cooling - glassy,obsidian
- porphyritic - phaneritic phenocrysts in aphanitic groundmass, a porphyry
- vesicular - a lot of cavities (vesicles)
What are the different classifications of igneous rocks based on chemistry
- ultramafic
- mafic (ferromagnesian minerals dominant)
- intermediate
- felsic (nonferromagnesum minerals dominant)
What are the different classifications of igneous rocks based on texture
- tuff - composed of volcanic ash
- welded tuff - hot volcanic ash fused together
- lapilli - consolidation of larger pyroclastic materials (2-64mm)
- volcanic breccia - blocks (angular) and bombs (smooth)
- obsidian
- pumice - vesicular volcanic glass
- scoria - vesicular, less glassy than pumice
What are metamorphic rocks?
- igneous and sedimentary rocks that are altered without melting
- metamorphism (the change) can be compositional in which new minerals form or textural when minerals become aligned
What causes metamorphism?
- heat (plutons and lava flows, deep burial)
- pressure (deep burial and differential pressure
- fluid activity (water and other liquids and gases)
What are the different types of metamorphism?
- contact metamorphism (plutons)
- regional metamorphism (plate boundaries continent-continent; oceanic- continent)
- dynamic metamorphism (rocks adjacent to faults)
What are the classification of metamorphic rocks?
- foliated (pressure causes platy and elongated minerals to align)
- non-foliated (low pressure contact metamorphci rocks; rocks without platy or elongated minerals)
List different types of foliated metamorphic rocks
- slate
- phyllite
- schist
- gneiss
- amphibolite
- migmatite
List different types of nonfoliated metamorphic rocks
- marble
- quartz
- greenstone
- hornfels
- anthracite
How does plate tectonics relate to the rock cycle?
- Earth’s heat contributes to melting and
metamorphism.
• Plate tectonics responsible for rock cycle.
• Sediment along continental margins buried
and lithified.
• Convergent plate boundaries result in
mountain building, metamorphism and
igneous activity.
• Mountains erode and produce sediments.
Why are sedimentary rocks important?
– They preserve evidence of ancient surface processes of their depositional environments, such as running water and glaciations. – Most fossils occur in them, which tell us about the history and evolution of life. Fossils are also important in relative dating. - They contain valuable resources, such as: oil and natural gas, coal, sand and gravel, gypsum, quartz, phosphate, banded iron formation
What are the different sedimentary rock properties observed in field observations?
- textures
- measuring
thickness and lateral extent - noting the composition and any
fossils - recording relationships with other rocks
What lab investigations can be performed on sedimentary rocks?
microscopic
examinations, fossil
identification, and chemical
analyses.
How do geologists use the principle of uniformitariansim?
to interpret the depositional environments of sedimentary rocks. Modern depositional environments often provide important insights into ancient environments.
What are the textures in detrital sedimentary rocks?
Texture refers to the size, size distribution, shape and
arrangement of
clasts in detrital sedimentary rocks.
– Grain size in detrital rocks provides information on transport conditions
and deposition.
– The transport of gravels requires glaciers or rapidly flowing water.
– Muds are deposited in low-energy environments.
In terms of texture in detrital sedimentary rocks what is rounding?
– Rounding refers to the removal of sharp edges and corners from
clasts through abrasion.
– Gravels tend to round very quickly as the particles collide during
transport.
– Sand grains round with considerable transport.
– Muds that are suspended in water are usually not well-rounded
In terms of texture in detrital sedimentary rocks what is sorting?
Sorting refers to the size variation of clasts in sediments or
sedimentary rocks.
– Well-sorted rocks have particles that are about the same size.
– Poorly sorted rocks have a wide range of particle sizes.
– Wind-deposited sands tend to be well-sorted, whereas glaciers carry
almost anything supplied to them and tills are poorly sorted
What are the different sedimentary structures?
– Larger scale features than textures. – Often form during deposition or shortly afterwards. – Important in interpreting depositional environments 1. laminations 2. beds 3. cross-bedding 4. ripple marks 5. mud cracks
What is the difference between laminations and beds?
Layers less than 1 cm thick are laminations. Thicker layers
are beds.
– Laminations are most common in mudrocks, but also occur
in sandstones and limestones.
– Limestones, sandstones, conglomerates may be bedded.
– Bedding planes separate beds.
What is a graded bedding?
- a layer with an upward decrease in grain size.
– In a mixture of sediment and water with waning currents, the largest and heaviest particles settle first and the smallest
particles settle last.
– Graded bedding deposited by waning floods and turbidity
currents on seafloors.
– Turbidity currents are avalanches on the ocean floor.
Describe cross-bedding in sedimentary structures
Cross-bedding - deposition of sand where individual
beds are deposited at an angle to the surface upon which they accumulate.
– Cross-bedding occurs in desert and beach sand dunes, shallow marine
deposits and stream beds.
– Cross-bedding in
sandstones indicate the direction of flow of ancient currents
Describe ripple marks in sedimentary structures
Ripple marks are small scale alternating ridges and troughs on bedding planes, especially in sand. – Current ripple marks form from unidirectional winds or flowing water in streams. They are asymmetric with a steep downstream/down wind slope. – Wave-formed ripple marks tend to be symmetrical from waves swashing back and forth.
Describe mud cracks in sedimentary structures
– Mud cracks are polygonal forms resulting from the drying and shrinking of clay-rich sediments.
– Mud cracks form in alternating wet and dry
environments, such as a lakeshore, river
floodplain or mud exposed at low tide on a seashore
What is the geometry of sedimentary rocks?
Refers to the three-dimensional shape of a
sedimentary rock body.
– May be useful in environmental analyses.
– Must be used with caution:
• Many depositional environments produce similar geometries
• Erosion, deformation and sediment compaction during lithification may distort the geometries.
Explain sheet geometry in sedimentary rocks
Rocks from marine transgressions (rising sea level) and
regressions (falling sea level) have a sheet geometry.
• These rocks are far larger in length and width than thickness.
• The origin of the ‘Principle of lateral continuity’ because most preserved sedimentary rocks are marine in nature
Explain elongate or shoestring geometry of sedimentary rocks
Deposited in stream channels and barrier islands
Describe deltas in relation to geometry of sedimentary rocks
• Lens-shaped geometry in profile • Lobate geometry from above - Coarse sediment deposited first, close to river mouth (Foreset beds) – Silt and clay transported farther then deposited (Bottomset beds) – Horizontal beds deposited on top of foreset beds during floods (Topset beds)
Why are fossils important when studying sedimentary rocks?
– When found, they are important for determining depositional environments.
– Was the organism buried where it lived (autochthonous) or was
it transported to its burial location (allochthonous)?
ie. Coral reefs buried in place.
ie. Dinosaur carcasses often washed downstream or out to sea.
– What kind of habitat did the organisms originally occupy?
ie. Corals live in warm and shallow marine waters.
Why are microfossils important when studying sedimentary rocks?
• Found in small samples, including well cuttings in petroleum exploration. • If not transported, may be good environmental indicators. • Sometimes used as guide fossils in relative dating
What are depositional environments?
• Depositional environments are locations where sediments accumulate. • Physical, chemical and biological processes operate to yield distinctive sediments. • Three main categories: – Continental – Transitional – Marine
Describe continental depositional environments in water systems
– Lakes, streams, deserts, and areas covered
by and adjacent to glaciers.
– Fluvial - streams and rivers can be:
• Braided: gravels and sands are dominant
• Meandering: sands and muds, cross-bedding may have:
– Shoestring geometry
– Point bar deposits
Describe continental depositional environments in deserts
Deserts • Dunes: cross-bedding • Alluvial fans: stream deposits • Playa lakes: muds and evaporites • Fossils, if present, are terrestrial plants and animals
Describe continental depositional environments in glaciers
Glacial
• Tills - poorly sorted, mostly found in moraines
• Outwash - sand and gravel, braided streams
• Striations on outcrops
• Varves - annual sediment accumulations in glacial lakes
• Dropstones from icebergs in lakes, seas and oceans
Describe transitional depositional environments in marine processes
Deltas
• Marine Deltas - fluvial deposits modified by marine processes, such as waves and tides. Deltas may
also occur in large lakes.
• Deposits may contain petroleum.
• Progradation - deltas build by depositing bottomset, foreset and topset beds.
• Terrestrial fossils in topsets and marine or lake fossils in bottomsets.
• Fluvial-dominated: Mississippi River
• Tide-dominated: Ganges-Brahmaputra River
• Wave-dominated: Nile River
Describe transitional depositional environments in barrier islands
- Offshore along marine coastlines.
- Separated from land by a lagoon.
- Sand-rich deposits.
- Subenvironments include: beach sands, dune sands, lagoonal muds.
- Typically require wide continental shelves, microto meso-tidal ranges, ample sediment supply and stable to increasing sea level
Describe transitional depositional environments in tidal flats
- Along many coastlines.
- Covered with seawater at high tide.
- Exposed at low tide.
- May prograde seaward and produce distinctive herring-bone cross-beds, which consist of sets of cross-beds dipping in opposite directions.
Describe marine depositional environments in the continental shelf
• Gently sloping area adjacent to continent.
• High-energy near-shore affected by waves and
tidal currents with cross-bedded sands, waveformed
ripple marks, bioturbation and fossils.
• Low-energy farther off shore - mud and marine
fossils.
• At the edge of the continental shelf, turbidity
currents transport sediments through submarine
canyons to form submarine fans on the continental
slope and rise
Describe marine depositional environments in the deep seafloor
• Mostly covered by pelagic clay and ooze.
• Major sources of sediment include: wind-blown
dust, volcanic ash and ooze (shells of
microorganisms).
• Mid-oceanic ridges.
• Iceberg dropstones in high latitudes
What are characteristics of carbonate marine environments
–Limestones and dolostones. – Dolostones - limestones altered by magnesium fluids during diagenesis & lithification. – Micrite - limey mud. – Some cross-bedding and ripple marks. – Mud cracks possible in micrite. – Some carbonates form in lakes. – Most form in warm, shallow seas.
What are examples of high energy carbonate environments?
• Barriers, such as reefs.
• Reefs include corals, mollusks and sponges.
• Ooids - spherical carbonate grains that lithify to
oolitic limestone.
• Micrite with marine fossils and bioturbation in
lagoons.
What are evaporite depositional environments
– Mostly rock salt and rock gypsum. – Some deposited in playa lakes. – Most extensive deposits form in evaporating restricted seas in arid environments
What is paleogeography?
• Paleogeography involves reconstructing
the past geography of areas and regions.
• Plate tectonics provides the locations of continents over geologic time.
• Rocks and fossils indicate depositional
environments.
• Multiple maps of an area at different
times can illustrate marine transgressions
and regressions.
What is stratigraphy?
Stratigraphy is the branch of geology
concerned mostly with the composition,
origin, age relationships, and geographic
extent of layered, or stratified, rocks.
• Stratigraphy mostly deals with
sedimentary rocks because almost all of
them are stratified.
• Geologists determine both the vertical and
lateral relationships of stratified rocks.
What are the key principles of relative dating
relative dating tells us the relative sequence of events • Principle of Superposition • Principle of Original Horizontality • Principle of Lateral Continuity • Principle of Cross-Cutting Relationships • Principle of Inclusions • Unconformities • Fossils
What is the difference between relative dating and absolute dating?
relative dating tells us the relative sequence of events while absolute dating tells us exactly when a rock is formed
What are vertical stratigraphic relationships?
– In vertical successions of sedimentary rocks,
bedding planes separate individual strata from
one another or strata vertically grade from
one rock type to another.
– Rocks below and above a bedding plane vary in composition, texture, and/or color, which result from a rapid change in sedimentation or
perhaps a period of nondeposition and
erosion followed by renewed deposition.
What information can be learned from the Principle of Superposition?
used to determine the
relative ages of undeformed overlying and underlying sedimentary layers
- If the layers have been deformed by faulting
or folding, relative dating becomes more
difficult. Other sedimentary structures or
fossils can help to resolve relative dating
relationships.
What is the Principle of Inclusions?
The Principle of Inclusions is another
method to determine relative ages
between rocks.
• The principle states that inclusions or rock
fragments within a rock are older than the
host rock.
What are unconformities?
are surfaces of erosion
and/or nondeposition within sedimentary
rocks.
Describe depositions within conformable strata
more or less continuous. • Unconformities are surfaces of erosion and/or nondeposition within sedimentary rocks. • Erosion and/or nondeposition may have lasted for millions of years. • A hiatus is an interval of geologic time not represented by strata
