Lecture 1 - Sediment and Sedimentary Rocks Flashcards
(122 cards)
1
Q
what rocks are best for learning history
A
sedimentary rocks
2
Q
what rocks are best for dating
A
igneous
3
Q
metamorphic to extrusive igneous rocks
A
melting, magma, lava, consolidation
4
Q
metamorphic to intrusive igneous rocks
A
melting, magma, crystallization
5
Q
rocks to sediments
A
uplift and exposure, weathering, transportation, deposition
6
Q
sediments to sedimentary rocks
A
lithification
7
Q
ANY rock to metamorphic rock
A
metamorphism
8
Q
what are sediments
A
loose solid particles formed by weathering or erosion of pre-existing rocks on the Earth’s surface, or by chemical precipitation from solution through organic or inorganic environments
9
Q
unconsolidated sediment
A
sediment that is loosely arranged or unstratified and whose particles are not cemented together
10
Q
3 types of particles
A
fragments (clasts) (eroded from pre-existing debris), skeletal debris (produced by organisms), crystals (precipitated by solution)
11
Q
lithification process
A
compaction and cementation. the process that converts loose sediment into sedimentary rock
12
Q
compaction
A
decrease in rock volume due to weight of overlying sediment
13
Q
cementation
A
bind grains together with cement
14
Q
common cementation molecules
A
carbonate (CaCO3) and silica (SiO2)
15
Q
diagenesis
A
process of changing sedimentary rocks after lithification is termed
16
Q
how can limestone go through diagenesis
A
the movement of MG-rich fluids through the rock. Mg substitutes for Ca ions in the rock to produce a carbonate rock called dolostone. The decreased rock volume forms vugs.
CaCO3 + Mg –> CaMg(CO3)2
17
Q
vugs
A
voids of spaces in a rock
18
Q
clastic sedimentary rocks
A
made from fragments of pre-existing rocks or organic particles such as shells and skeletal fragments (bioclastic)
19
Q
siliciclastic (terrigenous clastic)
A
made from fragments of pre-existing rocks
20
Q
what are chemical/biochemical and carbonaceous sediments made of
A
made from organic particles such as shells and skeletal fragments
21
Q
what percentage of the earths surface is covered by sediments and sedimentary rocks
A
70%
22
Q
what percentage of the volume of the earths crust is sediments and sedimentary rocks
A
5%
23
Q
what are some interesting parts about sedimentary rocks
A
- contain most of the worlds energy resources (fossil fuels)
- hold most of the worlds subsurface aquifers
- contain fossils that documents the history of the development of the earth
24
Q
how are sediments and sedimentary rocks classified
A
clastic vs non-clastic
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how are clastic sedimentary rocks classified
grain size, grain size distribution, grain shape
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grain size
classification according to the grain size of the fragments they contain using a standardized scale like the Wentworth scale
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what does the sediment gravel become
conglomerate
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what does the sediment sand become
sandstone
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what does the sediment silt become
siltstone
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what does the sediment clay become
shale
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chemical (non-clastic) sedimentary rocks
formed by direct precipitation of minerals from solution. commonly form in arid, tropical environments. "inorganic" limestones and cherts evaporite deposits.
ex. halite, gypsum
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grain size distribution
sorting - organization according to grain size.
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what can grain size distribution tell you
tell us the degree of transport and reworking such as wave action
very well-sorted will be far from the source with reworking and poorly sorted is close to the source with little reworking
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grain shape
angularity/roundness of a rock
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what can grain shape tell you
tell you about transport mechanisms. better rounding indicated more transport and reworking. ranges from very angular to well-rounded
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how does sediment move
transported by water, wind, or ice as suspended load, bedload, or dissolved load
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bedload
grains move in continuous or intermittent contact with the bed. rolling or jumping. coarse grained sediment
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traction
rolling or dragging of grains in a bedload.
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saltation
bounding or jumping of grains in a bedload. repeatedly picked up and dropped.
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suspended load
sediment carried in fluid without coming in contact with the bed. fine-grained sediment. deposited under low energy conditions
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coarse-grained sediment
gravel and sand
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fine-grained sediment
silt and clay
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bedforms
topographic features on the bed. different bedforms develop as current velocities change, but can also depend on grain size. can be conserved in the rock record.
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very low flow velocity bedform
plane bed
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low flow velocity bedform
ripples
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moderate flow velocity bedform
dunes
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high flow velocity bedform
plane bed
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what are flat bed bedforms preserved as
horizontal lamination
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what are ripple bedforms preserved as
ripple X-lamination
50
what are dune bedforms preserved as
cross bedding
51
what does oscillating current result in
symmetrical ripples, with equal slopes on either side
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what does unidirectional current result in
asymmetrical ripples, with a gentler slope on thewindward and steeper slopes on the leeward face
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windward face angle
10-12 degrees
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leeward face angle
33-34 degrees
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wave base
depth at which water movement is negligible. is 1/2 wavelength. water molecules have circular orbits below waves that get smaller with depth
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fairweather wave base
depth beneath average daily waves
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storm wave base
depth beneath storm waves
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hummocky and swaley cross-stratified sands
formed under storm waves with water depths of 10-30m. indicate storm activity
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sediment gravity flows
density-driven currents of sediment downward that are triggered by slumping or failure of a slope
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grain size distribution of debris flows
poorly sorted
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sediment gravity flow of turbidites
turbidities become graded beds with more fine sediment upwards. this can be seen by looking at the x-axis of logs to see the decreasing pattern in grain size with decreasing depth. as size increases you see how the bigger grains settle to the bottom.
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graded beds
change in grain or clast size from bottom to top of the bed
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sediment gravity flow example
grand banks NFL earthquake and turbidity currents. the current could be recorded by when what cables broke on the sea floor
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turbidity current deposits
Normally graded beds are coarse at the base and fine at the top. Bouma sequence predicts distribution, there are sole marks on base, and the change in character is from proximal to distal. only happens in subaqueous settings
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Bouma sequence
A division - massive
B division - laminated
C division - rippled
D division - laminated
E division - massive silt/clay
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facies
a body of sediment or rock with a particular characteristic that distinguishes it from other rock bodies. it is descriptive and not interpretive, and the result gives the process of the event.
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how is paleoenvironmental information obtained from sediments and sedimentary rocks
interpretation of facies types according to depositional process to tell you about depositional environment
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depositional process
looking at individual facies. ex. sediment gravity flow, traction current, etc.
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depositional environment of facies
place and climate. looking at genetically related groups of facies. ex. coastline, lagoon, river, glacier, reef
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facies associations
groups of facies genetically related to one another. have some environmental significance. ex. shoreface sandstones and lagoonal deposits
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what is needed to determine a depositional environment
facies associations
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walthers law
facies sequences observed vertically are also found laterally. we see rocks in vertical sequence that were deposited beside each other at the same time
"Only those facies and facies areas can be superimposed primarily which can be observed beside each other at the present time" explains how the vertical stacking of facies relates to environments that were laterally connected in the past. environments change through the horizontal transition. there is a coarsening upward sequence, where deposits at the bottom are muddy bottom sets that transition to silty/sandy forests into delta front sands. it shows a sequence of migration of shoreline - shallowing upwards in a transition from one to the next.
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what is the vertical stacking of facies associated with
sea level change
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transgression
shoreline moves landward as relative sea levels rise.
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regression
shoreline moves seaward as relative sea levels lower. erosion of exposed surfaces can come with this.
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how does glaciation affect sea level change
global sea levels lower during glacial events. known as glacio-eustatic sea level lowering. ice leads to lower sea levels
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how does changes in sea floor spreading rates affect sea level
slow-spreading has a cool crust and low elevation, so no rises in sea level
fast spreading has a hot crust, high elevation, and displaces water onto land - transgression.
tectonic movements that lead to mountain building can also shift water nearby to the lower elevation area.
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how are carbonate sediments created
biological activity. carbonates are born not made, and the sediment producers change over time
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what percent of the sedimentary rock record is carbonate sediment
20-25%
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what percent of the worlds hydrocarbons are in carbonate sediments
50%
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what percent of N.A's hydrocarbons are in carbonate sediments
20%
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what hydrocarbon is often used in construction
Limestone CaCO3
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what percent is limestone
> 50% calcite/aragonite
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what percent is dolostone
> 50% dolomite
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what is chalk composed of
it is veryfine grained and mostly composed of skeletal fragments of CaCO3 organisms. the grains are bioclasts and may be surrounded by mud matrix. it is a kind of mudstone
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how is paleontology used for carbonate sediments
it is important in classifying the carbonate depositional systems to understand the conditions in which organisms live
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what are limestones largely precipitated by
organisms like shells or skeletons
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how is carbonate sand and mud produced
disaggregated skeletons
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allochems
recognizable grains
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why are lime muds not usually shales
they don't yield clay minerals
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examples of carbonate allochems
- skeletal particles
- ooids (coated grains)
- stromatolites (coated grains)
- peloids
- intraclasts
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what rock do ooids make
oolite
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what are ooids
spherical coated grains <2mm in diameter
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how are stromatolites formed
formed by the photosynthetic cyanobacteria algae. the lamination formed by the vertical growth of bacterial filaments in daylight traps grains and horizontal growth at night that binds layers of sediment
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what are peloids
silt to sand-sized mudballs, round to pellet-shaped, mostly originate as fecal pellets from shrimp (450/day) and other lifeforms
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what are intraclasts
ripped-up clast that is typically mud
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how are carbonates classified
based on matrix content
- contains mud or lacks mud
- mud-supported or grain-supported
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what carbonate is identified as grains supporting one another and contains no mud
grainstone
99
what carbonate is identified as grains supporting one another and contains mud
packstone
100
what carbonate is identified as mud supported with less than 10 percent grains
mudstone
100
what carbonate is identified as mud supported with more than 10 percent grains
wackestone
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what is the current big producer of carbonate
modern reefs. it is most productive in the reef and shallow platform
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subtidal factory
always underwater, reefs and lagoons
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intertidal
between tides, beach and tidal flats
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supratidal
above high tide, wet: algal marsh and arid: sabkha
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where do evaporites occur in tidal environments
the arid Sabkha area
106
what conditions needed for coral reef growth
warm, clear, agitated water with plenty of sunlight. neat the equator. carbonates are good climate indicators as it was probably the same in the past
107
temperature range for reefs
best between 25 and 29, but has to fall between 18 and 36
108
what is chert
inorganic precipitation, microscopic siliceous fossils. it often occurs as 'nodules' within limestone or dolostone
109
evaporites
evaporation of sea water, resulting in sediments such as halite, gypsum, and anhydrite
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where is lime-mud and sand made
lagoons
111
where is reef sediment made
at the reef front
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how wide is the lagoon
0.1 - 2 km
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how wide is the reef core (reef front)
50 m
114
how wide is the forereef slope
0.1-1km
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what can be said about the growth patters of reef builders
they are similar for corals, sponges, and stromatolites, which is an example of convergent evolution. zonation is also similar between builders
116
how are fossils created
- shells burried and preserved unaltered for <100 millions years. cavities are filled with silica, calcium carbonate, or iron, replacing any original substance with mineral matter and any soft tissues by carbon.
- they can be preserved as molds, imprints, and casts in resin.
- tracks, trails, burrows and borings preserved
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ichnology
study of trace fossils
118
bioturbation
process of disturbing sediment
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two types of fossils
trace fossils and body fossils
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trace fossils
tracks, trails, burrows and borings preserved
121
body fossils
remains of living things (bones). often these remains have undergone some alteration process
