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HotE > W1 - Sediments and Sedimentary Rocks > Flashcards

W1 - Sediments and Sedimentary Rocks Flashcards

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1
Q

What type of rock is the worst to date?

A

Sedimentary, since they’re amalgamations of many types of rocks

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2
Q

What type of rock is the best to date?

A

Igneous

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3
Q

What type of rock is best to study fossils in?

A

Sedimentary, since the pressure and heat used during the creation of other rocks will destroy any fossils

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4
Q

Describe the rock cycle

A

Magma cools and solidifies to igneous rock, igneous rock weathers and erodes to sediment, sediment deposits and lithifies to sedimentary rock, sedimentary rock undergoes heat and pressure to become metamorphic rock, metamorphic rock melts to become magma

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5
Q

What are sediments?

A

Unconsolidated loose solid particles formed by:
a) weathering or erosion of pre-existing rocks on the Earth’s surface
b) chemical precipitation from solution through organic or inorganic environments

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6
Q

What are the 3 particle types?

A

1) Fragments (clasts) eroded from pre-existing rocks
2) Skeletal debris produced by organisms
3) Crystals precipitated from solution

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7
Q

What 2 factors cause sediment to become lithified?

A

1) Compaction = decrease in rock volume due to weight of overlying sediment
2) Cementation = bind grains together with cement (carbonate or silica)

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8
Q

What is the process that converts sediments into sedimentary rock?

A

Lithificaiton

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9
Q

What is diagenesis?

A

The process of changing sedimentary rocks after lithification

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10
Q

What’s an example of diagensis?

A

Limestones can be diagenetically altered by the movement of Mg-rich fluids through the rock; substitution of Mg for Ca ions in rocks produces new carbonate rock called dolostone (decrease in rock volume and formation of void spaces is called vugs)

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11
Q

How are sediments and sedimentary rock classified?

A

Composition, grain size, grain size distribution (sorting), and grain shape

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12
Q

What is the composition of a sedimentary rock?

A

Clasts (grains), matrix between grains made of very fine grained material, and cement

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13
Q

What are the 2 types of sedimentary rocks?

A

Clastic and Chemical (non-clastic)

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14
Q

What are clastic sedimentary rocks?

A

Made of fragments of pre-existing rocks or organic particles such as shells and skeletal fragments

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15
Q

What are the 2 types of clastic sedimentary rocks?

A

1) Siliciclastic (terrigenous clastic) are made of fragments of pre-existing rocks
2) Chemical/Biochemical and Carbonaceous are made of organic particles such as shells and skeletal fragments

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16
Q

How much of Earth do sediments and sedimentary rocks take up?

A

Cover 70% of Earth’s surface and comprise 5% of the volume of Earth’s crust

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17
Q

What type of rock is the crust made from?

A

Igneous rock

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18
Q

Why are sediments and sedimentary rocks important?

A

Contain most of the world’s energy resources (fossil fuels), hold most of the world’s subsurface aquifers, and contain fossils that document the history of the development of life on Earth

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19
Q

How are sedimentary rocks classified according to grain size?

A

Classified according to the size of fragments they contain using standardized scales, like the Wentworth Scale

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20
Q

What are chemical sedimentary rocks?

A

Formed by direct precipitation of minerals from solution; include ‘inorganic’ limestones and chert; commonly found in arid, tropical environments
Ex: halite and gypsum

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21
Q

What is sorting?

A

Organization according to grain size; ranges from poorly sorted (rock sizes are very different) to very well sorted (rock sizes are almost identical)

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22
Q

What does sorting tell us about the depositional process?

A

Poor sorted rocks are close to the source (proximal) and experienced little reworking
Well sorted rocks are father from the source (distal) and experienced more transport and reworking

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23
Q

What is grain shape?

A

Describes the angularity/roundness of a grain; ranges from very angular to well rounded

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24
Q

What can grain shape tell us about transport mechanisms?

A

Better rounding indicates more transport and reworking

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25
How does sediment move?
Transported by water, wind, or ice; travels in fluids as a suspended load, bedload, or dissolved load
26
What is a bedload?
Grains move in continuous or intermittent contact with the bed; exhibit a rolling or jumping motion; happens to coarse grained sediment (fine sands and upwards)
27
What is a suspended load?
Sediment is carried in fluid without coming into contact with the bed; happens to fine-grained sediment like silt and clay; sediments are deposited under low conditions
28
What is a dissolved load?
Sediment is dissolved within fluid; can alter density of fluid
29
What are bedforms?
Topographical features on the bed; develop as current velocities and grain size change
30
What are the 3 types of bedforms and in what conditions do they form under?
1) Plane bed - formed in very low or high velocities 2) Ripples - form in low velocities 3) Dunes - form in moderate velocities
31
What are sedimentary structures?
Same type of bedforms stacked and preserved
32
What type of sedimentary structure does each bedform make?
1) Flat bed = horizontal lamination 2) Ripples = ripple X-lamination 3) Dunes = cross bedding
33
What are asymmetrical ripples?
Form by unidirectional currents (in rives, sand dunes); steeply dipping ripple foresets dip in the direction of current movement
34
What are symmetrical ripples?
Form below waves from oscillatory currents
35
What are orbits in reference to waves?
Orbits describe the circular motion of water molecules below the waves; become smaller with depth
36
What is the wave base?
Depth at which water movement is negligible - fairweather refers to average daily wave base and storm refers to storm wave base
37
What are hummocky and swaley cross-stratified sands (HCS and SCS)?
Formed under storm waves in water depths of 10-30m (shallowish)
38
What are sediment gravity flows?
Density driven currents triggered by slumping or failure of a slope
39
What are debris flows?
Poorly sorted gravity flow; seen in many aqueous environemnts
40
What are turbidites?
Instantaneous gravity flow of graded beds (well sorted bed - fine to coarse from top to bottom); can be coarse-grained, medium-grained, and fine-grained; caused by the falling of loose sediment and slope instability of continental shelf in subcutaneous setting; results in sediment deposit
41
What is an important turbidite?
Grand Banks, NFL earthquate and turbidity currents in 1929 were recorded by cable breaks in sea floor (as connection was lost, could estimate how big it would have to be), with flow velocity measuring 15-60km/h
42
What does a turbidity current deposit look like?
Bouma sequence (character changes as you move from proximal to distal): A division = massive B division = laminated C division = rippled D division = laminated E division = massive silt/clay Sole marks on base
43
What are facies?
A body of sediment or rock with particular characteristics that distinguish it from other rock bodies; "the sum aspect, appearance and characteristic of a sedimentary rock or sediment which are used to distinguish it from adjacent units from which the origin and environment of deposition may be understood
44
Why are facies important?
Help us obtain paleoenvironmental information from sediments/sedimentary rocks through their interpretation according to depositional process
45
What paleoenvironmental information can we obtain from facies?
Use individual facies to discern depositional process (ex: sediment gravity flow, traction current) Use genetically related groups of facies to discern depositional environment, including the place and climate (ex: coastline, lagoon, rive, glacier, reef)
46
What is a facies association?
Group of facies genetically related (same formation for how it originated) to one another; have same environmental significance
47
What is Walther's Law?
Only those facies and facies areas can be superimposed (stacked on top of) primarily which can be observed beside each other at the present time; if facies exist alongside each other, they can occur on top of each other; explains how the vertical stacking of facies relates to environments that were laterally connected in the past
48
How does Walther's Law relate to sea level change?
Stacking of facies vertically is often associated with sea level change
49
What are transgression and regression?
Transgression = shoreline moves landward; relative sea level rise Regression = shoreline moves seaward; relative sea level lowering
50
How does glaciation affect sea level change?
Global sea levels lower during glaciation events (water is trapped in ice on land); referred to as glacio-eustatic (loading and unloading of ice) sea level lowering
51
How do changes in the sea floor affect sea level change?
Sea floor spreading rates have an effect: Slow spreading has cool crust and causes low elevation Fast spreading has hot bulging crust and causes high elevation, displacing water onto land Tectonic movements and mountain building also have an effect
52
What are carbonate sediments?
Created through biological activity; mostly composed of skeletal fragments of carbonate secreting organisms, where grains are bioclasts that may be surrounded by mud
53
What are some of the types of carbonate sediments?
Limestone = >50% calcite or aragonite, largely precipitated by organisms as shells or skeletons Dolostone = >50% dolomite Chalk = very fine grained
54
What are carbonate sediments important?
Compose 20-25% of the sedimentary rock records; hosts 50% of hydrocarbons worldwide and 20% in NA; limestone is often used in construction
55
What are bioclasts?
Clastic sediments made from skeletal fragments or shells
56
Why is paleontology important in classifying carbonate depositional systems?
Most carbonate producers have changed over time; carbonates are born, not made; need to understand conditions in which organisms lived (similar currently extant species can help determine environment of past extinct species)
57
What is the major carbonate sediment-producer of the Cenozoic (current) era
Coral
58
What are the types of carbonate sediments?
1) Muds = made from disaggregated skeletons 2) Allochems = recognizable grains 3) Chert (flint) =
59
What are the types of allochem carbonate sediments?
1) Skeletal particles (coquina) = >= 2mm 2) Ooids (coated grains) = spherical coated grains <2mm in diameter; make the rock oolite 3) Stromatolites (coated grains) = formed by photosynthetic cyanobacteria and algae; 4) Peloids = silt to sand sized mudballs; round to pellet-shaped; mostly originate as fecal pellets (ex: shrimp) 5) Intraclasts = ripped=up clasts, typically mud; form from very different sudden depositions
60
How are stromatolite laminations formed?
By vertical growth of bacterial filaments in daylight that traps grains and horizontal growth in night that binds layers of sediment
61
How are carbonates classified?
Based on matrix (sediment) content
62
What are the 4 classifications of carbonates?
1) Grainstone = grains are touching with no mud 2) Packstone = grains are touching with little mud 3) Wackestone = sediment is mud with >10% grains 4) Mudstone = sediment is mud with <10% grains (ex: limestone)
63
Where are carbonates produced?
Modern reefs are important producers; highest productivity in reef and shallow platform (always underwater)
64
What conditions are necessary for carbonate growth?
Modern growth window is narrow: need warm, clear, agitated water with plenty of sunlight on the equator Past growth window is probably the same Carbonates are good climate indicators
65
What is chert (flint)?
Inorganic precipitation; microscopic siliceous fossils; often occur as 'nodule' within limestone or dolostone
66
What are evaporites?
Evaporation of sea water
67
What does a reef environment look like?
Look at picture for answer
68
How have reef builders changed/stayed the same over time?
Growth patterns are similar for corals, sponges, and stromatolites (example of convergent evolution through time as different reef builders adapted to the same conditions) As extinctions wipe out reef builders, different phyla have developed very similar morphologies to thrive in similar conditions to previous reef builders Reef zonation is similar regardless of type of organism (uniformity of conditions through time results in analogous evolution)
69
How are fossils created?
Through the exchange of original soft tissue substance with mineral matter 1) Shells are buried and preserved unaltered for <100 my 2) Shells undergo permineralization = cavities fill with silica, calcium carbonate, iron Fossils can also be preserved as molds, imprints, casts in resin
70
What is ammolite?
Organic gemstone; can form ammonite fossils that are iridescent
71
What are trace fossils?
Fossils preserved as tracks, trails, burrows, borings
72
What is ichnology?
Study of trace fossils
73
What is bioturbation?
Process of disturbing sediment

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