Tuesday, April 5, 2011

Article of the Week

Schlee, John. 1973. Atlantic Continental Shelf and Slope of the United States -- Sediment Texture of the Northeastern Part. Geological Survey Professional Paper 529-L. U.S. Department of the Interior, Geological Survey. 64 pp. plus plates.

I've read this one a couple of times, but it's been awhile. It's an important paper, the foundation of the geologic model for the shelf of the eastern seaboard. It's very well written and serves as a good reminder of some geological basics and how geologists use substrate data (plus seismic and core data). Note that many of the maps and diagrams are on Plates that are addenda to this document. I do not know if they are available online.

The main conclusions:
1. The sediment on the shelf is a result of Holocene and Pleistocene deposition and reworking. There is a lack of sediment influx on the shelf now.
2. Evidence of glacial deposits provides further support for continental glaciation.
3. There are basic populations of sediment types on the shelf: clay-fine silt, sand, and gravel.
4. Grouping of cumulative size curves show five main types which can be associated with various transport, deposition, and reworking processes.
a) log normal distributions of excellent, moderate, and poor sorting -- associated with transport and deposition by bottom currents, grain-by-grain settling, and ice.
b) polymodal sand and gravel -- deposition as glacial outwash with later reworking by tidal- and storm-generated bottom currents
c) skewed sandy silt -- mixing of sand and silt by gravity settling and tractive bottom currents.
5. Subbottom studies show that sediment can change markedly with depth and exhibits variation across the shelf.

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