111-22 - GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111 Lecture Note Series Sedimentary Environments 5: Deep Marine Environments Lecture Goals A) Deep versus shallow marine environments (submarine fans) B) turbidites and greywacke C) chalk Reference: Press et al., 2004, Chapter 7; Grotzinger et al., 2007, Chapter 5; GY 111 Lab manual Chapter 3 A) Deep versus shallow marine environments Last time we outlined deposition on continental shelves (or shelves for short). Recall that the sediment deposited on shelves is highly variable. Near shorelines, it is usually siliciclastic in composition because of the proximity to beaches, deltas and rivers. Further offshore, you might run into bioclastic sediment that is the product of biologically-influenced chemical sedimentation. If the calcite and aragonite that comprises these sedimentary deposits are largely the result of “beasties” (i.e., shells, skeletons etc), those rocks are called bioclastic. If the sediment is sand- sized and if it is in the form of ooids (a product of tropical sedimentation), that rock is called an oolitic limestone. So now we turn our attention to deeper water environments. Recall this diagram: Deep water depositional environments are those where sediment accumulated in water deeper than about 200 m (e.g., off the edge of the shelf). Some sediment is deposited on the slope as underwater landslides originating from the shelf break (usually as a mixed sandstone-boulder breccia), but most of the action takes place at the bottom of the slope on the abyssal plain: 5000 m
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GY 111 Lecture Notes D. Haywick (2007-08) 2 The previous sketch should look vaguely familiar to you (I hope it does, you saw something like it in a lecture not that long ago). Sedimentation at the base of the slope tends to be concentrated into fan-like deposits at the mouths of submarine canyons that were carved into the shelf during times of low sea level (e.g., 18,000 years ago). Like alluvial fans, these deposits are fan-shaped and can be enormous (100's of km
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111-22 - GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111...

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