Question

Gaining Insight into Depositional Environments of Sedimentary Rocks

Name: ________ Course:____________
Section:_______ Date:_____________
Sedimentary structures, fossils, cements, and other features of sedimentary rocks provide insight into the environment in which the sediment was deposited.
Match each of the features in the left-hand column to an aspect of the depositional environment listed in the right-hand column by placing the corresponding letter in the proper blank.
Rock and/or feature of the rock
(a) poorly sorted arkose
(b) contains fossils of intact coral
(c) red mudstone containing dinosaur footprints
(d) black shale containing some pyrite crystals
(e) sandstone containing symmetrical ripples
(f) cross-bedded sandstone
(g) contains > 50% carbon and fossil leaves
(h) contains large, rounded pebbles and cobbles (contains fossils of feathers G very angular grains
Aspect of the depositional environment
1. deposited in a desert dune or in a current
2. formed from sediments accumulated in a swamp
3. deposited in very quiet (stagnant) water
4. deposited in an anoxic marine setting
5. deposited by a swiftly moving stream
6. formed from warm-water, shallow marine reef
7. has not undergone a lot of transport immature,
8. deposited close to the source
9. formed from terrestrial mud (riverbank deposits)
10. deposited on a beach

Answer 1

(a): 7. and 8.

(b): 6.

(c): 9.

(d): 4.

(e): 10

(f): 1.

(g): 2.

(h): 5. and 3.

Step-by-step explanation:

Sedimentary rocks are rocks generated from pre-existing rocks and/or once-living organisms. Arkose is a type of sandstone rich in feldspar (at least 25% of this mineral). Moreover, a rock containing coral fossils indicates that its depositional environment was located in warm tropical reef waters. Mudstone is a kind of sedimentary rock composed of clay (in this case, sediments continued to be deposited above the dinosaur footprints). The black shales are fine-grained sedimentary rocks composed of a mixture of clay (in this case, the pyrite crystals are used as an indicator of low oxygen). Symmetrical ripple marks in the sandstone indicate a marine environment where water motion was dominated by wave oscillations. Cross-bedding is a common structure of sedimentary rocks that form during deposition on inclined surfaces of bedforms (e.g., ripples and dunes). Sediment deposition in swamps is usually heavily vegetated and therefore they are rich in organic matter, while deeper swamp sediments are generally anoxic. Finally, cobblestones are naturally occurring cobble-sized stones formed from the flow of water and gathered from stream beds, while pebblestones are formed when water bodies hit the giant rocks in the rivers and lakes.