Help
Options
Question
The stratigraphic record of sedimentary rocks is fundamental for:
click to flip
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't know
Question
Sedimentology
Remaining cards (113)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
Strat/Sed Exam 1
| Question | Answer |
|---|---|
| The stratigraphic record of sedimentary rocks is fundamental for: | understanding the evolution of life, determining climate, reconstructing earth history, interpreting climate change, finding resources like fossil fuels |
| Sedimentology | study of the process of formation, transport, and deposition of sediments in continental and marine basins |
| Stratigraphy | study of rocks to determine the order and timing of events in earth history; allows us to interpret sedimentary rocks in terms of evolving environments |
| Fundamental Facies Model | a body of rock with specified characteristics that reflect the environment of deposition using lithology, texture, sedimentary structures, and fossils |
| Principle of Uniformitarianism | the laws of nature have not changed in the course of time; the present is the key to the past |
| Petroleum formation and concentration | rare event-special conditions needed; not distributed evenly in space and time |
| What are the elements of a conventional petroleum reservoir? | source beds conduit beds reservoir seal |
| Source | organic-rich rocks (usually shales); temp. and pressure conditions that results oil and gas generation |
| If oil is too deep or too hot, it becomes: | gas |
| What do conduit beds do? | connect source beds to reservoir rock; allows oil migration |
| Strat-parallel component | sand and silt layers |
| cross-strata component | faults and fractures |
| reservoir | porous and permeable rock that stores oil and gas, most commonly sandstones and carbonates |
| How to make organic-rich sediments (two factors)? | high biological productivity (upwelling area, nutrient-rich water), rapid burial without organic decay (anoxic basins) |
| Why are phytoplankton important? | key source of oil, autotrophs, stored solar energy |
| why are there no source beds in the deep ocean? | when plankton dies, it rains down on the sea floor and creatures will eat the organic matter |
| Why are source beds more common in near-coastal areas? | shallow basins are high-productivity and more likely to form oil; when plants, they use oxygen so an anoxic environment is formed |
| What kinds or organic-rich rock is formed often? | black shale |
| what is a closed basin on land? | lake |
| Algal, oil-prone kerogen is rich in what? | hydrogen |
| Woody, gas-prone kerogen is poor in what? | hydrogen |
| Oil and gas are formed by the _________ _________ of organic compounds buried in fine-grained rocks. | thermal cracking |
| (Hydrocarbon formation chart) What happens up until 30 degrees (C) | some gas is formed |
| (Hydrocarbon formation chart) What happens around 90 degrees (C) | kerogen is turned to oil |
| (Hydrocarbon formation chart) What happens around 150 degrees (C) | natural gas is formed |
| What structural feature is known for having oil | anticlines |
| Trap | 3D configuration that "pools" the oil and gas |
| Seal | rocks that prevent leakage from the trap |
| Bedload | discharge of sediments that are too heavy for turbulent action of a stream to suspend |
| exfoliation | cracks occurring on surface of larger rocks creates many superficial layers |
| Bedform | geologic feature that forms at interface of fluid and a movable bed; result of bed material being moves by fluid flow |
| Bioturbation | disturbance of sediments by living organisms |
| Principle of Superposition | oldest strata towards the bottom of a facies (unless overturned) |
| Principle of Original Horizontality | strata are horizontal when deposited; external forces may fold stratum (takes millions of years) |
| Principle of Lateral Continuity | similar rocks on opposite sides of a canyon were once connected |
| Principle of Cross-Cutting Relationships | any part of a facies with a fault running through it is older than the fault |
| Principle of Inclusions | inclusions of lower rock into upper layer is erosion of lower layer by the upper layer, which is younger; inclusions of upper rock into lower layer is the result of magma intrusion into upper layer (which is older), partially melting it |
| Principle of Faunal Succession | fossils are distributed in discrete layers; finding new types of fossils indicates being in a new layer |
| Facies | character of a rock expressed by its formation, composition, and fossil content |
| Walther's Law | sedimentary environments that start off side-by-side will end up overlapping over time due to transgressions and regressions |
| Diagenesis | chemical, physical, and biological changes that occur after sediment is deposited |
| Sedimentary Facies | bodies of sediment that are recognizably different form adjacent sediments and resulted from different depositional environments |
| Lithostratigraphy | deals with physical contrasts in lithology; reflects environment of deposition |
| Biostratigraphy | based on fossil evidence of rock layers and changing fossils pattern, not rock; correlate different layers of rock with similar fossils |
| Chronostratigraphy | studies layers that were deposited at the same time; can deal with two different environments being present in the same layer |
| Angular unconformity | when a group of rocks has been tilted and eroded, with younger rocks being deposited on top |
| Disconformity | erosional surfaces between two layers of the same sedimentary rock |
| Nonconformity | bedded rocks on an eroded surface of crystalline rocks |
| What processes control vertical succession of facies in marginal marine environments? | transgressions and regressions |
| What is the relationship between lithostratigraphy and chronostratigraphy? | use lithostratigraphy to identify different depositional environments within the same layer |
| What is the importance of Siccar Point? | formed with the first and second orogeny of the Appalachian mountains (same rock and layer), but they're separated by an ocean |
| What is the relationship between Tapeats sandstone, Bright Angel Shale, and Muav Limestone? | marine transgression (fiining upwards) |
| What is stratigraphy? | study of the origin, relationship, and extent of strata |
| What basins form at divergent plate boundaries? | Rift Basins and triple junctions |
| What basins form at convergent plate boundaries? | convergent plate margins (forearc basins and retroarc basins) |
| What basins form at transform plate boundaries? | transform basins |
| What sedimentary facies are associated with rift basins? | alluvial fans, braided streams, lacustrine, evaporites, and playa lakes |
| What sedimentary facies are associated with triple junction basins? | braided stream and meandering river |
| What sedimentary facies are associated with convergent plate margins? | retroarc– immature clastic sediment and components from continent; braided stream proximal to arc, meandering stream distal to arc forearc– turbidites, rivers, and some delta facies |
| What sedimentary facies are associated with transform basins? | anoxic environments with basin plains, slopes, and shelf edges |
| What two mechanisms cause basins to subsidize? | rapid increase of weight/pressure on an area (sediment deposition or water) and thinning crust (magma doming) |
| What basins are most likely to be a source for oil? | shallow sea basins |
| Why is quartz the most common siliciclastic mineral in sedimentary rocks? | it's resistant to weathering |
| Why are the cliff rocks in Zion National Park red? | iron staining |
| Hydroloysis | leaching of minerals out of a rock by percolating water; makes mineral seem to "disappear" from the rock without a trace |
| What factors control texture of clastic sediments? | grain size and interrelationship between grains |
| Why are there no clays on the moon and abundant clays on Mars? | no water on the Moon, but there once was liquid water on Mars |
| Sedimentary rocks consist of what three general classes of material? | 1. clastic 2. organic 3. chemcial |
| What are the three parts making up an alluvial fan? | 1. proximal fan 2. mid-fan 3. distal fan |
| What sedimentary structure indicates an alluvial fan? | multiple layers of sediment with coarsening upward sequence (progradation) |
| What is the difference between the conglomerates of an alluvial fan and a braided stream? | alluvial fan conglomerates have a lot more sand in them (less sorting) |
| What is an alluvial fan? | large accumulation of sediments that are sorted with large clasts and poor sorting towards the throat of the fan, and smaller, somewhat-sorted clasts towards the distal fan |
| What are the main components of an alluvial fan | feeder (throat) and the fan |
| What are the primary mechanisms of transport in an alluvial fan? | debris flow, sheet flow, and stream flow |
| Debris Flow | water-laden mass of fragmented rock that rushes down the throat of a fan (very hazardous) |
| Sheet Flow | shallow water not confined to stream beds that spread out across a large distance (mid-fan area) |
| Stream Flow | occurs across the surface of an alluvial fan, carrying lighter material like sands in braided streams (distal fan area) |
| Discuss the role of tectonic activity in the development of alluvial fans: | alluvial fans most common in foreland basins |
| What are the principle mechanisms of weathering? | mechanical and chemical weathering |
| What role does climate play in weathering? | rainfall and temperature play the biggest roles in weathering cold climates have more mechanical weathering (more extremes in temperature) warm climates have more chemical weathering taking place (less mechanical) |
| Does basalt or granite weather quicker? Why? | basalt weathers quicker because its minerals are less stable and quartz is more resistant to weathering |
| How does physical erosion change the rate of chemical erosion? | physical erosion speeds up chemical erosion |
| How does surface area affect chemical erosion? | increase in surface area increases chemical erosion |
| How does weathering influence crustal composition? | weathering destroys unstable minerals and those least resistant to weathering, leaving mostly quartz leftover |
| What factors influence rate of weathering? | rainfall and temperature |
| What role does weathering play in the rock cycle? | helps to recycle rocks and form new sedimentary rocks through transportation, deposition, and lithification |
| What are some of the products of weathering? | mud and quartz |
| What is the difference between laminar and turbulent flow? | laminar flow is quiet, slow-moving water turbulent flow is fast, erratic-moving water |
| What are varved sediments? | seasonal variation in lake deposits; dark, anoxic sediments deposited during winter and light sediments consisting of gypsum and anhydrides deposited during summer |
| What is normal grading? | large sediments towards the bottom that fines upwards; indicated high energy that slowly dies down |
| What is reverse grading? | small sediments towards the bottom that coarsens upwards; indicated events where energy starts off slow and builds up, then stops suddenly (debris flow) |
| What is imbrication? | as a current flows in a single direction, long axis of a boulder is flipped so that they are all oriented in the direction of the current |
| What is a geopetal feature? | caused by sediments with fossilized ammonites where their shells fill with sediment, leaving a small opening in their innermost chambers; calcite crystallizes in the openings on the side of the shell facing upwards you can always tell which way is up |
| What is the difference between tabular and trough cross-stratification? | tabular– formed by migration of larg, asymmetrical, straight-crested ripples; forms rectangular layers of crossbeds trough–formed by dune migration; forms crescent-shaped lenses of crossbeds |
| What is the difference between ripples and dunes? | Dunes are larger than ripples (same internal structure) |
| What processes form sedimentary structures, and what can we learn from them? | currents from wind or water can form sedimentary structures we can learn about what type of environment sediments were deposited in, what time of year it may have been, energy in the environment, etc. |
| What factors influence ripple morphology? | size of grains and velocity of the current |
| What are antidunes? | result from rare events where fast-moving water causes dunes to form along steep slopes against the direction of flow |
| How are wave ripples formed? | forwards and backwards motion of water depositing and eroding sediments from both sides of a ripple |
| How are braided stream sediments determine provenance? | are clasts arkosic or lithic? |
| Define a braided stream: | shallow stream with many interlocking channels separated by gravel bars; channels switch often |
| Discuss the primary process the leads to the formation of braided streams: | large bedload that is easily erodable creates a shallow stream that gets clogged easily but can also form new channels quickly |
| Explain the role of sediment transport in shaping morphology of braided streams: | Saltation is the main transport that occurs in braided streams boulders are rolled over and crash into other rocks, causing a bouncing and rolling cascade |
| Explain the types of sediment commonly found in braided streams and their sizes: | clast-supported conglomerates and very coarse sands |
| How do braided streams contribute to the formation of alluvial fans? | carry finer sediments towards the distal fan |
| What is the difference between glacial tillite and alluvial fan deposits? | tillite– no sorting or rounding at all alluvial fan– specific coarsening-up pattern |
| Why is marine sedimentary record better than the terrestrial record to determine the frequency of glacial advance and retreats? | glaciers destroy any terrestrial record of glaciers, but can't rip up the sea floor |
| what causes the advance and retreat of glaciers? | periods of high and low summer insolation (Milankovitch Theory) smaller angle of tilt– weaker summer insolation bigger angle of tilt– stronger summer insolation |
| What is continental evidence of glaciers? | giant U-shaped valleys with mountains that have been cut in half (Half Dome) polished bedrock with striations eskers drumlins and kames lateral moraines medial moraines terminal moraines |
| What are the two major types of glacier? | Alpine– elevation dependent; smaller latitudes reduces amount of area glacier can cover Continental– found at high latitudes; ice sheets that span thousands of km; only found in Antarctica and Greenland |
| Why do you find varved sediments in glacial lakes? | seasonal deposit of sediments from icebergs breaking off of glaciers |
| What is an outwash plain? | plain where meltwater melts to lower latitudes, carrying gravelly material and finer sediments; generally well-sorted |
| Describe the sediments found in a glacial lake: | mostly silt and clay with small layers of light sand; often contain dropstones |
| Describe the sediments found in glacio-marine environments | till deposited proximal to glacier; silt and clay deposited distal to glacier due to waves and currents producing grain-size sorting; dropstones common |
Created by:
monika.angner