Unformatted text preview: Sedimentary
5. Shallow marine
6. Deep marine
Can you see them in
You will learn all these
and more in detail
in Sed -Strat. Here
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?
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
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
Source on shelf,
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
– 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
• On the board:
– Walther’s Law
– Cyclothem 14 Cyclothems = large scale sedimentary cycles caused
by long-period, cyclic migrations of environment Transgression-regression cartoon 15 ...
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- Spring '11
- Sediment, sedimentary facies, turbidity currents, flood plain deposits