Hi I need help with this geology homework it doesn’t require much the first file is the homework and the second one the article you need to complete the homework. Thanks
GEOL 311:Sed/Strat.
Homework #3: Pet Formation Paper Critique
assigned Oct. 2, 2020
due Oct. 9, 2020 before 8 am
Goal:
The goal of this homework is to start gathering information for your “pet formation” project. It will
help you start (or add to) your reference list. It will also teach you more about depositional
environments.
Assignment:
During the first week of September, you were assigned a stratigraphic formation in the United States.
For this homework assignment, do the following:
1) Find a peer-reviewed scientific article about your formation that focuses on its depositional
environment(s). A good way to search is by using Google Scholar (not regular Google). Try it
out and if you have trouble, Kathy or Maya can help. Make sure you are signed into your
mix account first; that will allow you access to papers directly from Google Scholar to WVU’s
subscriptions for journals, so you can download them for free. Never pay for a journal
article! WVU spends lots of money every year (partly through your library fees) so we can
access scholarly literature. If WVU does not have a journal you need, you can request it
online through the WVU Library interlibrary loan, or ask a WVU librarian, or email the
article’s author to request a pdf. Some excellent journals that are focused on sedimentary
geology are Journal of Sedimentary Research, Sedimentology, and Sedimentary Geology.
Others that may have good papers for you include Geology and GSA Bulletin. There are a lot
of other good journals that host sed. geology papers.
2) Once you identify a paper that seems to have good information about the depositional
environment(s) of your formation, read it carefully. Take notes. Look up words you don’t
know. Ask Kathy or Maya if you encounter concepts you don’t understand.
3) Write a critique about the paper you read. Write it in essay style (paragraphs). Include in
the first paragraph the full citation of the paper and the formation name, age, location, and
rock type(s). Include the goal of the paper and the methods used. What is the interpretation
of the depositional environment(s)? What lines of evidence led the authors to that
interpretation? Were you convinced about the depositional interpretation? Did you
identify strengths and weaknesses in the paper? What are some further studies suggested
for this formation? Was there anything else that you found interesting?
One note: We have had some classes so far on siliciclastics, but not yet on carbonates or evaporites. If
your formation is composed of carbonates and/or evaporites, I think you’ll still be able to do fine on
this assignment. Your textbook, and Maya and Kathy are resources for you.
To submit, save as YourLastName_GEOL311_Homework1 and email to Kathy and Maya.
GEOL311: Stratigraphy & Sedimentation
Fall 2020
Criteria for the recognition of siliciclastic depositional environments
main environments in which siliciclastic sediments are deposited:
marine siliciclastic environments:
clastic continental shelves
continental slopes
pelagic (deep) ocean
marginal marine siliciclastic environments:
deltas
barrier complexes (aka beaches and adjacent settings)
tidal flats
continental siliciclastic environments:
alluvial fans
meandering fluvial systems (rivers and floodplains)
lakes (aka lacustrine environments)
freshwater lakes vs. saline lakes
perennial lakes vs. ephemeral lakes
eolian environments
paleosols (ancient soils); note that soils do not get deposited; they are
developed on sediment and/or rock undergoing weathering (but
not erosion) in subaerial (exposed to air) settings
other depositional means that may involve more than one environment type:
glacial deposits
mass wasting deposits
There is variation amongst any one environment type. For example, rivers can deposit gravel, sand,
and/or mud. However, there are some characteristics that may be considered criteria for the
recognition of that environment type. For river deposits, a 3D geometry consisting of elongated
narrow ribbon shape in map view and channel shape in cross-section is considered a criteria for
their recognition. The following pages are Kathy’s notes on the characteristic criteria for identifying
the depositional environment of siliciclastic rocks. Not all of the features listed might be contained
or seen in an individual outcrop or deposit. However, we always aim to observe the most we can in
a sed. rock in order to determine the environment in which it was deposited.
1
clastic continental shelves
diagnostic criteria:
silt and fine sand
mostly quartz and clay minerals
some shell fragments
may contain some carbonates (mixed with the siliciclastics) in tropics and subtropics
glauconite (green clay mineral)
hummocky cross-bedding (storm deposits)
graded beds (storm deposits)
burrows
marine fossils
continental slopes
diagnostic criteria:
silt and fine sand
mostly quartz and clay minerals
soft sediment deformation (especially convolute laminations and convolute beds)
vertical repetition of turbidity current deposits (turbidites)
turbidite (aka Bouma sequence)
small-scale climbing ripple cross-bedding
laminations
graded beds
erosional base
pelagic deposits (deep ocean)
diagnostic criteria:
mud
clay minerals and/or chert
fish scales and deep marine fossils (including pelagic microfossils)
few, if any sed. structures
black, dark green, dark gray colors
2
deltas
are influenced by sediment input, wave energy, and tidal energy
are formed where a river empties into a ocean, sea, or lake
associated with fluvial meandering deposits and with shallow marine sediments
diagnostic criteria:
wedge-shaped geometry
thick (10’s – 1000’s of meters)
great lateral area (10’s – 1000’s of square kilometers)
wide range of grain sizes, from mud – coarse sand
commonly contain some coal and other organic matter
ripple marks, ripple cross-bedding
burrows
shells, plant fossils (mixture of marine and continental fossils)
soft-sediment deformation
How do deltas differ from fluvial deposits? Mostly a scale difference (deltas are thicker and more
laterally extensive)
barrier complexes (beaches)
are different than tidal flats in that beaches have small tidal range and greater wave energy
diagnostic criteria:
low-angle herringbone cross-bedding
sands and some silts
mostly quartz, some heavy minerals (ex. magnetite, garnet)
interference ripples (including ladder ripples)
planar beds
long-thin geometric shape
burrows
diverse fossils (mostly shells)
commonly yellow, tan, pale gray, pale orange, pink colors
closely associated with intertidal, deltaic, and/or shallow marine deposits
tidal flats
tidal flats have a wide tidal range, so daily wetting and drying; only strong wave action during a
storm
form mostly at low-relief passive margins
usually little, if any, vegetation
tidal channels cross tidal flats
diagnostic criteria:
tidal bundles (alternating laminations of mud and fine sand)
flaser and lenticular bedding
mudcracks and conglomerates composed of ripped-up mudchips (called intraclasts)
small-scale ripple marks and cross-bedding
limited, low diversity fossils (gastropods are common in Phanerozoic tidal flats)
some burrows
some stromatolites and algal laminations (but more common in Precambrian)
3
alluvial fan
cone-shaped (triangular) deposits coming off mountains
processes active here are gravity deposits (especially grain flows) and distributory, ephemeral
streams and flash floods)
diagnostic criteria:
gravel, coarse sand
lots of lithic grains
poorly-sorted
many angular grains
can be very thick
reverse-graded beds (coarsest grains at top of bed)
some cross-bedding
no fossils
meandering fluvial systems (rivers)
diagnostic criteria of rivers:
ribbon geometry in map view, channel shape in cross-section
graded beds
mostly sands, muds, some gravel
ripples, cross-bedding
planar beds
flute casts, tool marks
plant fossils (including wood)
land vertebrates
fish fossils
freshwater mollusks (gastropods, bivalves)
associated with floodplains
diagnostic criteria of floodplains:
muds
planar laminations
mudcracks
raindrop imprints
climbing ripple cross-bedding
nonmarine fossils
associated with paleosols
4
lacustrine deposits (lakes)
there are a diversity of lakes; they can be deep or shallow; they can be perennial or ephemeral; they
can be freshwater or saline; therefore, there are a range of lake deposits
lakes are sensitive to climate and seasonality
lakes are sometimes found in regions of tectonic depressions
diagnostic criteria for freshwater lakes:
muds, fine sands
planar laminations (often are varves, alternating mud and fine sand laminations)
some convolute laminations
nonmarine fossils (including ostracodes, nonmarine fish, pollen, plant fossils, algae, bivalves,
gastropods)
organic material (so black or dark gray color)
small ripple marks, wave ripple cross-bedding, and mudcracks at/near shorelines
sometimes, stromatolites (more common in Precambrian and early Paleozoic)
in deep lakes, thin turbidites (see continental slope deposits for cross-sectional sketch)
associated with paleosols and other continental deposits (eolian, fluvial) on all sides
diagnostic criteria for saline lakes:
evaporite minerals (halite, gypsum, etc.), carbonate minerals, and/or siliciclastic mud
few fossils
little organic matter
planar laminations or thin beds of crystals
small-scale ripple marks
mudcracks common, but not necessary
eolian (wind) deposits
“eolian” is American spelling; Brits spell it “aeolian”
commonly sand
diagnostic criteria:
commonly, bimodal grain size distribution (two main grain sizes)
very well-sorted
well-rounded, highly spherical grains
commonly ~95% composed of one mineral (commonly quartz)
frosted or pitted grain surfaces
some grains may be coated thinly with Fe-oxide minerals, giving an orange color
some large-scale, high-angle, tangential tabular and tangential wedge cross-bedding
some low-angle cross-bedding (typically planar tabular)
some thick laminations with reverse grading of bimodal sand
rare vertebrate fossils
root casts
insect burrows
commonly, yellow, tan, orange, white colors
associated with other continental deposits (mainly alluvial fans and saline lakes)
5
paleosols
are ancient soils
are not technically deposited, but are formed on other deposits that are exposed subaerially
for a long time without erosion and with organic material (usually plants stabilize it,
anchoring it in place)
can be made of siliciclastic sed or carbonate seds
most soils eventually erode away and are not preserved in rock record
sensitive to climate
indicate land surface of the past and mark unconformity
diagnostic criteria:
mud, rare sand
lots of cracks (mudcracks, circumgranular cracks, sheet cracks, crazed plane cracks)
root traces
peds
some burrows
various colors (red, purple, blue, green, black, brown, gray)
are relatively thin deposits (typically less than ~2-5 m)
6