General Geology Lab #4: Sedimentary Rocks and Environments

Transcription

1 Name General Geology Lab #4: Sedimentary Rocks and Environments Please identify the following group of sedimentary rocks. Please determine whether they clastic, biogenic or chemical. Also, answer the sample specific questions. Depositional environment refers to the following: river (fluvial), shallow marine, deep marine, beach, slope (or landslide), reefs, evaporative environment, etc. NOTE: SAMPLES CAN BE VIEWED IN ANY ORDER. Sample 1A, 1B and 1C 1) You have three different grades of coal (listed below). List the correct sample number beside each of the grades: Lignite Bituminous Anthracite 2) In what environment does the organic matter found in coal accumulate? 3) What type of organic matter dominates coal (i.e. plant vs. animal vs. microorganisms)? Pressure and temperature cause chemical and physical alterations to organic matter during burial. These changes result in higher-grade coals that burn cleaner and at higher temperature than low-grade coal. The principle elements in organic molecules are carbon, oxygen and hydrogen. From lignite to anthracite, which element(s) increase in relative concentration and which element(s) decrease in relative concentration (write either increase or decrease next to the three elements): Carbon Oxygen Hydrogen

2 Sample 2A, 2B, and 2C 2A Identify the predominant mineral in this rock: 2B 2C Identify the predominant mineral in this rock: 4) Rate the samples 2A, 2B, and 2C from based on sorting (well-sorted to poorly-sorted): Near the sourceland, sandstones contain a lot of incompletely weathered minerals and rock fragments. As sand is transported (via rivers and wind), the more easily-weathered mafic minerals transform into other materials, such as clays and ions in solution, leaving behind more and more quartz (the most resilient common igneous mineral). Because of this process, sedimentologists often discuss sandstones in terms of maturity: immature sandstones have undergone limited weathering and transport, whereas mature sandstones have been highly weathered. 5) Which rock is most mature and which is least mature? Support your answer (mineralogy, sorting).

3 Sample 3A 6) Why is this rock black (meaning what component of the rock is making it black)? 7) What is the depositional environment of this rock? Where did it most likely form? Sample 3B 8) What is the depositional environment of this rock? Where did it most likely form? Sample 3C 9) What is the depositional environment of this rock? Where did it most likely form? 10) Looking at samples 3A, 3B and 3C, list the rocks in order of the energy of the depositional environment (meaning fast-flowing vs. slow-flowing water)?

4 Sample 4 11) What is the depositional environment of this rock? Where did it most likely form? Sample 5 12) What is the depositional environment of this rock? Where did it most likely form? Sample 6 What is the main mineral in this rock (note fracture patterns) 13) What is the depositional environment of this rock? Where did it most likely form? Sample 7 14) What is the depositional environment of this rock? Where did it most likely form?

5 Read the description (below) of shell symmetry between bivalves (a common class in the phylum Mollusca during the Cenozoic Era that includes clams, oysters, and mussels) and brachiopods (a phylum of shell-producing invertebrates that were very common during the Paleozoic Era 543 to 251 million years ago and considerably less common today). 15) Are these fossils brachiopods or bivalves? Why? 16) Based on the fossil assemblage is the rock Paleozoic or Cenozoic in age? 17) Which sample is older (geologically), sample 5 or sample 7?

6 Sample 8 Mineralogy (main mineral) 18) How did the concentric rings form? 19) What is the depositional environment of this rock? Where did it most likely form? Sample 9 Main Mineral (Try scratching it with your fingernail) 20) What is the depositional environment of this rock? Where did it most likely form?