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208_Lect02_color - Sedimentary environments 1 Fluvial 2...

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Unformatted text preview: Sedimentary environments 1. Fluvial 2. Eolian 3. Glacial 4. Lacustrine 5. Shallow marine 6. Deep marine Can you see them in this image? You will learn all these and more in detail in Sed -Strat. Here in Sed we want the basics … A definition to start: • Sedimentary Facies: – Assemblage of fossils, sediment characteristics (structures) and rock types (sediments) indicative of a particular local environment. – examples: flood plane, stream channel, dune, beach, etc. • Sedimentary Environment = Assemblage of sedimentary facies – E.g. Alluvial fan, braided stream, meandering stream, reef, etc. ON board: Walther’s Law, Transgression-Regression 1 First: Fluvial Environments • Fluvial refers to River systems • Alluvium is the sediment deposited from fluvial systems • This is an Alluvial Fan: notice the channels, convex fan shape Braided Stream: anastomosing channels separated by gravel and sand bars What do you suppose this looks like in cross-section? 2 A braided estuary? Environmental disaster Meandering stream: Bars, levees, channel and flood plain deposits Might this be the cross-section of a fluvial system? 3 Deltas: what do you suppose these look like in cross-section? 4 Aeolian Environments & Deposits Aeolian = wind blown These include Desert and Glacial settings Dunes! What do they look like in cross-section? Hmm… How does that cross-bedding form? How form? Note: forms in streams too 5 Desert pavement caused by deflation Loess deposits: Massive, well sorted, frosted silt deposits. Origin: wind blown silt from glacial outwash plain (or dust from dessert). Glacial Environments • Till (unstratified, poorly sorted with fine matrix) delivered to terminus and deposited by melting Ice. • Drift = fluvio-glacial deposits, often stratified, in drumlins, eskers, etc. • Moraine: till deposited on margins and base of glacier 6 Glacial settings: Moraines Till p.s. Don ’t go into the field looking like this 7 Lacustrine (lake) Environments Varves = annual cycles of sedimentation 8 Playa Lake (restricted basin, arid environment) Shallow Marine Environments Estuaries and Lagoons 9 Beaches and barrier islands (too much here to go into now) Tidal Flats: clay, silt and fine sand dominated Carbonate Shelf 10 Atolls Deep Marine 11 Turbidites = submarine avalanche deposits. Source on shelf, avalanche down canyon onto rise Turbidites and Turbidity Currents • Avalanche from shelf to rise out onto abyssal plain. • Often triggered by Earthquake or by melting methane ice – Methane ice is produced by methanogenic bacteria and decomposition of organic mater – Under pressure and cold T, methane ice is stable Turbidity current 1 Turbidity current 2 Videos of Turbidity Currents 12 Pelagic sediment: oozes (e.g., diatoms and forams) Pelagic sediment: clays 13 • So, what happens to facies laterally and over time? • On the board: – Walther’s Law – TransgressionRegression – Cyclothem 14 Cyclothems = large scale sedimentary cycles caused by long-period, cyclic migrations of environment Transgression-regression cartoon 15 ...
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