Quiz 2: Black Shales, Evaporites & Limestones PDF
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University of Guyana
2023
University of Guyana
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Summary
This document is a past paper from the University of Guyana, GEM 3114, covering topics such as black shales, evaporites (including gypsum and anhydrite), and carbonate rocks. Questions cover topics like chemical compositions, formation processes, and fossil contributions in different geological settings. The quiz is from 2023.
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1: (a) What is a "black shale"? \(b) How is "oil shale" different from "black shale"? \(c) How does sulfur, in the form of pyrite, commonly come to be present in black shale and in oil shale? \(d) What is a "maceral" (compared to a mineral)? List the 3 main groups of macerals found in kerogen. \...
1: (a) What is a "black shale"? \(b) How is "oil shale" different from "black shale"? \(c) How does sulfur, in the form of pyrite, commonly come to be present in black shale and in oil shale? \(d) What is a "maceral" (compared to a mineral)? List the 3 main groups of macerals found in kerogen. \(e) What is the key difference between "humic" kerogen and "sapropelic" kerogen? 2: (a) Why are evaporites considered "chemical sediments"? \(b) What is the sequence of precipitates you could expect from fully evaporated seawater? \(c) Where does gypsum form in a sabkha? \(d) What is the chemical difference between gypsum and anhydrite? \(e) Why did thick Aptian salt get deposited offshore southeast Brazil (as in the oil-rich Santos Basin)? 3: (a) What is the chemical formula for calcite? Why are calcite and aragonite considered different minerals when they have the same chemical formula? b\) What is the chemical difference between "calcite" and "dolomite"? \(c) Why are most carbonate rocks bioclastic? \(d) What is a "skeletal" carbonate clast? \(e) What is the difference between "micrite" and "sparite"? 4: (a) Which types of carbonate sediment would you expect to find in a "back reef" lagoonal platform? \(b) Which types of carbonate sediment would you expect to find in a "fore reef" environment? \(c) How do coral polyps precipitate calcite (or aragonite) from seawater to make reefs? \(d) What is the main different between modern day reefs and geologically older reefs created by rudists, stromatoporoids and the algae which form mud mounds? \(e) Why do sponges contain "spicules"? What are they made of? 5: (a) What is a non-skeletal allochem? \(b) How do ooids form -- you can use the Bahamas as an example? \(c) What are "pellets" and what simply distinguishes them from "ooids"? \(d) What are "coccolithophores" and what did they house themselves in that made the Cretaceous chalk deposits? \(e) How do the sizes of coccolithophores and typical foraminifera compare (in Cretaceous times)?
