12 Depositional Sedimentary Environments Lab

Lab 12 Sed. Dep. Env. Answer Pages Study the sedimentary environments in the images below and answer the questions associated with the images. Write your answers on the blanks provided at the end of the lab.

Answer the questions in the blanks provided on the following pages to make it easier. Figure A. Death Valley National Park, CA 1. What are the prominent depositional features formed at the mouths

of the canyon? 2. Describe the textural characteristics of the sediment forming the

features named above. 2. What other non-marine features could exist on the flat terrain in front

of the range?

Figure B. Navajo Sandstone in Zion NP, UT

3. What type of bedding does this represent?

4. Was this sandstone deposited in a non-marine (terrestrial)

or marine environment?

5. Was the sandstone deposited by fluvial or aeolian processes?

Figure C. Bedding surface from Capital Reef, UT

6. What type of markings are present?

7. Assuming the rock is marine in origin, what do these

markings indicate about the depth of water in which in the sediment was deposited?

Figure D. Cracked surface in Alaska 8. What type of markings are present? 9. Assuming the rock is marine in origin, what do these

markings indicate about the depth of water in which in the sediment was deposited?

Source: Shutterstock

Source: Shutterstock

Source: Shutterstock

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Figure E. Conglomerate in Chiang Rai, Thailand 10. What type of grain shape and particle sorting

are shown here? 11. What is a possible depositional environment?

Give reasons for your interpretation. Figure F. Sandstone Zion NP, Utah 12. What type of bedding is present? 13. Was this sandstone deposited in a nonmarine

(terrestrial) or marine environment? Was the sandstone deposited by fluvial or aeolian processes? If in water, in shallow or deep water? Explain how you know.

Figure G. Breccia, Lake Mead, Nevada 14. Describe particle color, texture, and sorting? 15. What was the depositional environment

responsible for creating this rock?

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Name: ___________________________________

Lab 7: Sedimentary Environments (macro scale) Record your answers to the questions about the images above here:

Figure A

1 __________________________________________________________

2 __________________________________________________________

3 __________________________________________________________

Figure B

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6 __________________________________________________________

Figure C

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8 __________________________________________________________

Figure D

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10 __________________________________________________________

Figure E

11 __________________________________________________________

12 __________________________________________________________

Figure F

13 __________________________________________________________

14 __________________________________________________________

Figure G

15 __________________________________________________________

16. __________________________________________________________

General Questions

16. What general rock and rock feature would indicate a long duration of deposition in an arid environment? __________________________________________________________________________________

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17. What type of environment would a breccia with dark grey and/or purple rock fragments likely be from? __________________________________________________________________________________

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18. What is the probable depositional setting and source of a pure white quartz sandstone?

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19. What do bidirectional ripples indicate about the depositional environment of a rock? __________________________________________________________________________________

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20. What would the sedimentary environment be for oolitic sediments?

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21. How would the sediments differ from a playa lake to that of a freshwater lake?

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22. List three environments that ripples can form in:

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23. List two ways cross bedding can occur:

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24. How does a conglomerate form? Is there more than one way? If so how?

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Laboratory 12: Sedimentary Depositional Environments (Macro Scale) Objective:

To understand the large sale features that are observed in sedimentary environments and the role they play in understanding depositional environment.

Materials Needed: Images of various sedimentary environments provided by instructor Paleogeography is the study of what an environment was like during a certain time in the past. Paleogeography takes biostratigraphy one step further in reconstructing the earth's history. By examining a set of rocks in several different locations, all representing the same age, we can begin to reconstruct the ancient environment by using the rock type and fossil content. The rock samples can be collected over a large or small lateral area, and the locations and shapes of landmasses and seas can be deduced by knowing which types of rocks and fossils are expected to be found in particular environments. An environment of deposition is the sum of all physical, geographic, climatic, ecological, and chemical parameters that affect the composition of the sediment. Many factors must be considered when deciding on the environment of deposition, including lithology, fossil abundance, and fossil assemblage.

I. NONMARINE (CONTINENTAL) Most non-marine environments are typically the sites of erosion or non- deposition, although a small percentage of deposits may be preserved. A. Aqueous- 1. Fluvial (streams and rivers)-

(a) Floodplain- Sandstone, siltstone and shale with some conglomerate and coal, moderate sorting, moderately quartz-rich; horizontal laminations, asymmetric (current) ripple marks, animal tracks and trails, mud cracks, raindrop impressions; plant debris and tree fossils; irregular and thin sheet shape. (b) Channel-Sandstone and conglomerate, moderately sorted and quartz-rich; cross-bedding, current ripple marks, scour of channel surfaces; may contain plant debris, non-marine (aqueous and terrestrial) fossils; irregular lenticular to sinuous shape, closely associated with floodplain deposits.

2. Paludal (Marsh or Swamp) - fine-grained deposits (siltstone, shale, coal) with dark color and high organic content; thin horizontal laminations or massive (no visible sedimentary structures); abundant plant fossils; irregular lens to sheet shape. 3. Lacustrine (lake) - fine-grained shale and some limestone; varve (alternating thin, light and dark layers) clay common; possible freshwater fossils (ex. snails); irregular lens to sheet shape

B. Terrestrial (subaerial)- 1. Desert-

(a) Aeolian dune- fine-to medium-grained sandstone with excellent rounding and sorting; large- scale cross-bedding common; fossils rare; extensive sheet-like or “blanket” shape. (b) Alluvial fan- poorly sorted arkosic sandstone and conglomerate, abundant feldspar and mica; cross-bedding, massive bedding, inverse and normally graded beds; fossils rare to absent; thick fan-or wedge-shaped deposits.

2. Glacial- poorly sorted massive sandstone and conglomerate containing angular particles striated pebbles, large pebbles and boulders, variable mineralogy; massive or crude horizontal laminations; fossils absent; irregular shape and patchy distribution.

II. TRANSITIONAL (MARGINAL MARINE)

A. Delta- A complex grouping of environments including channels, floodplains, swamps, bays, etc. Deposits range from sandstone to siltstone and shale, and generally became finer-grained outward from the shoreline; cross-bedding, horizontal laminations, current ripple marks and animal burrows are common in some parts; fossils generally rare but may include locally abundant plant stems and roots and rare marine; delta complexes are generally fan or wedge shaped.

B. Barrier Island/Lagoon-

1. Barrier Island- are mostly high energy deposits consisting of well-sorted and rounded quartz rich sandstone. Grain size decreases systematically in a seaward direction; large-scale cross-bedding; current and symmetrical (wave) ripple marks, horizontal laminations and animal burrows common; fragmented marine fossils may be present; sand body shape is narrow and elongate parallel to the shoreline and a lagoon is typically present between the barrier and the mainland. 2. Lagoon- lower energy environment dominated by fine-grained sandstone, siltstone, and shale; horizontal laminations, ripple marks, and animal burrows, tracks and trails are common; carbonate lagoons contain abundant and diverse marine fossils; shape is characteristically elongate parallel to shore, and a barrier island is typically present immediately offshore from the lagoon.

C. Littoral (between mean high and low tides)-

1. Beach - high energy environment dominated by medium- to course- grained sandstone, well- sorted and rounded; horizontal laminations, low-angle cross-bedding, wave ripple marks are most abundant; fossils are rare and typically broken into fragments; sand body is elongate in shape and trends parallel to shore. 2. Tidal flat – so named due to the tide coming in and receding in this relatively flat region. It will have inter-bedded sandstone, siltstone and shale, with grain size increasing in a seaward direction; cross-bedding (some large-scale), wave and current ripple marks, mud cracks, scour or channel surfaces, and animal burrows, tracks and trails are common; fossils (marine) are rare to abundant; wedge to irregular sheet shape.

III. OPEN MARINE

A. Pelagic- These environments are within the ocean water mass; thus, they don’t have characteristic features preserved in the geologic record. Organisms which live in these environments fall to the ocean bottom upon death and become part of the record of one of the benthic environments listed: 1. Neritic-depth to sea-floor less than 200 meters 2. Oceanic- depth to sea-floor greater than 200 meters

B. Benthic (bottom environments) 1. Shallow marine (Shelf) - sandstone, siltstone, limestone and shale interbedded, sandstone composed predominantly of quartz but with some marine fossil fragments; cross- bedding (some large-scale), ripple marks, and marine burrows, tracks and trails common; marine fossils locally abundant; widespread sheet-like or blanket shape. Water depths are typically less than 200 m.

2. Carbonate Reef/Platform- Unbedded, very fossiliferous with large and small scale, very course grained sediment. Abundant, often large, organisms attached to the sea-floor, high energy environment. 3. Deep Ocean- shale, fine-grained limestone and/or sandstone; graded bedding produce by turbidity currents; large fossils rare; microfossils may be abundant; sheet to fan-like shape.

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The following charts summarize the previous discussion

ALLUVIAL FAN FLUVIAL (river) LACUSTRINE

(lake) AEOLIAN DESERT

(dunes) PALUDAL (swamp)

ROCK TYPE breccia, conglomerate, arkose

conglomerate, sandstone, siltstone, shale

siltstone, shale, limestone, evaporites

quartz arenite, (sandstone) gypsum

peat, coal, siltstone, black shale

composition terrigenous terrigenous terrigenous, carbonates,

evaporites terrigenous or evaporite terrigenous

color brown or red brown or red black, brown, grey, green,

red yellow, red, tan, white black, gray or brown

grain size clay to gravel clay, silt, sand, gravel,

fining upward clay, silt, sand (coursening

upward) sand clay to silt

grain shape angular angular to rounded ---- rounded or polished ----

sorting poor variable variable good variable

inorganic sedimentary

structures cross bed and graded bed

assymmetrical ripples, crossbedding, graded

beds, tool marks

symmetrical ripples, lamination, cross beds,

graded beds, mud cracks, raindrops

crossbedding laminated to massive

organic or biogenic

structures ---- tracks, trails, burrows

tracks, trails, burrows, rare stromatolites

tracks and trails root marks, burrows

fossils ---- rare freshwater shells,

bones, plants fragments freshwater shells, fish, bones, plant fragmetns

---- plant fossils, freshwater

shells, bone, fish

Continental- Sedimentary Depositional Envirnonments

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DELTA BARRIER BEACH LAGOON TIDAL FLAT

ROCK TYPE sandstone, siltstone, shale, coal

quartz arenite, coquina siltsone, shale, limestone, oolitic limestone, gypsum

siltstone, shale, calcilutitie, dolostone or gypsum

composition terrigenous, some organic terrigenous or carbonate terrigenous, carbonate or

evaporite terrigenous, carbonate or

evaporite

color brown, black, grey, green, red

what to tan dark grey to black or brown grey, brown, tan

grain size clay to sand (coursening upward)

sand clay to silt clay to silt

grain shape ---- rounded to angular ---- ----

sorting variable good poor variable

inorganic sedimentary

structures

cross bedding, graded bedding

cross bedding, symmetrical ripples

lamination, ripples cross bedding

lamination, mudcracks, ripples, cross bedding

organic or biogenic

structures trails, burrows tracks, trails, burrows trails, burrows

stromatolites, trails, tracks, burrows

fossils plant fragments, shells marine shells marine shells marine shells

Transitional- Sedimentary Depositional Envirnonments

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REEF CONTINENTAL

SHELF CONTINENTAL

SLOPE AND RISE ABYSSAL PLAIN

ROCK TYPE fossiliferous limestone sandstone, shale, siltstone,

fossiliferous limestone, oolitic limestone

litharenite (grewacke), siltstone and shale, limestone

shale, chert, micrite, chalk, diatomite

composition carbonate terrigenous or carbonate terrigenous or carbonate terrigenous or carbonate

color grey to white grey, brown, tan, green grey, green, brown black, white, red

grain size variable frameworks, few to no grains

clay, silt, sand, gravel clay to snad clay

grain shape ---- ---- ---- ----

sorting ---- poor to good poor good

inorganic sedimentary

structures ---- lamination, cross bedding

graded bedding, cross bedding, lamination, flute

marks, tool marks (turbitdites) lamination

organic or biogenic

structures ---- trails, burrows trails, burrows trails, burrows

fossils coral, marine shells marine shells, sharks teeth marine shells, rare plant

fragments marine shells (mostly

microscopic)

Marine- Sedimentary Depositional Envirnonments