EAES 101: Global Environmental Change Spring 2018 B) Use the following field not

Question

EAES 101: Global Environmental Change Spring 2018 B) Use the following field notes from a stop at a rock outcrop to determine the most plausible paleo-environment for each sedimentary rock bed described. Additionally, provide a phrase or two justifying your paleo-environmental interpretation. (7 points) (hint: list your paleo-environments interpretations vertically with the environment for the bottom-most bed at the bottom of the list and your paleo-environmental interpretation for the top-most bed at the at the top) - the base of the outcrop is dark mudstone, which is finely laminated and there are directly above the mudstone bed is a bed of limestone with some fossils present occasionally imprints of marine sea shells directly above the limestone bed is a sandstone bed with ripple structures best interpreted as wave ripples - above the sandstone bed is a coal bed - the top-most bed in the outcrop is another limestone bed, but this one is somewhat sand C) The above sequence of sedimentary rock bed can be interpreted as a series of sea level rises and/or falls. Discuss what local sea-level was doing at the time of deposition of these sedimentary beds. Also, identify periods of transgression and periods of regression. (3 points)

Explanation / Answer

B-The finely laminated mudstone is indicated of a very calm environment with a continuous supply of very fine sediments. The imprints of the seashells are indicative of the presence of marine organisms. Therefore the paleo-environment may be a deep marine environment.

The bed of limestone indicates a decrease in the water depth of deposition. The presence of fossil indicates that there must have been under deeper water columns before. This can be carbonate platform paleoenvironment.

The sandstone beds are now indicative of a more energy-rich environment and also of smaller transportation distances. The presence of the wave ripple marks is evidence that the deposition of the sediments took above the wave base. The paleoenvironment may be a coastal one.

The presence of the coal bed is clear evidence of a marshy environment where the organic matters were deposited.

The sandy limestone bed may be evidence of mixed fluvio- marine control on the sediment deposition.This may have been deposited in a platform interior environment.

C.

The sequence starts with a marine sediment bed and is followed by progressively shallower water sediments until the deposition of the last limestone bed. The swallowing down of the water can be attributed to the regression of the sea. As the sea regresses the water level is continuously decreased and the deposition environment becomes progressively shallower. After the deposition of the coal bed, we can see that the depositional environment change to a deeper one which points out that the sea level has started to rise again and that the sea is transgressing. Therefore the period o regression includes all the periods of deposition excepting that of the sandy-limestone bed deposition which was deposited during transgression.

Potential depositional

environment

i. produces effervescence when treated with acid.

ii)composed of CaCO3

continental margin platforms

reefs

deep marine

i) grain size below .0625 millimetres

ii) finely laminated

tidal flat

marine slope/rise

deep marine

i) composed mainly of sand-sized (0.0625 to 2 mm) particles

ii)composed of quartz and feldspars mainly

beach

marine shelf/platform

tidal flat

delta

lake

glacier - outwash

desert dune

stream - channel

i) composed of organic matter

ii) there is no grains.

swamp

delta

Rock Category Observation

Potential depositional

environment

Limestone Biochemical

i. produces effervescence when treated with acid.

ii)composed of CaCO3

continental margin platforms

reefs

deep marine

Mudstone Clastic

i) grain size below .0625 millimetres

ii) finely laminated

tidal flat

marine slope/rise

deep marine

Sandstone Clastic

i) composed mainly of sand-sized (0.0625 to 2 mm) particles

ii)composed of quartz and feldspars mainly

beach

marine shelf/platform

tidal flat

delta

lake

glacier - outwash

desert dune

stream - channel

Coal Oraganic

i) composed of organic matter

ii) there is no grains.

swamp

delta

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.