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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 942

Last Page: 942

Title: Organic Matter Characteristics Near Shelf-Slope Boundary: ABSTRACT

Author(s): R. W. Jones, G. J. Demaison

Article Type: Meeting abstract


The organic characteristics of the sediments deposited near the shelf-slope break depend on the organic facies, which then depend upon the types of organic matter available at the deposition site and its early diagenetic history. The amount of land-derived organic matter generally decreases away from the shoreline, although high percentages of land-derived organic matter can be deposited on slopes, particularly when close to large rivers.

A primary control on the organic facies present at the shelf-slope boundary is the depth at which the oxygen minimum zone impinges on the water-sediment interface. Currently, the oxygen minimum zone in the world's oceans intersects the continental margins mostly on the upper slope, and it is there that the best potential source rocks now being deposited preferentially exist. The oxygen minimum zone locally reaches onto the shelf, most noticeably in areas of upwelling as in offshore southwest Africa.

In the past, owing to such factors as climate change and different current patterns, the oxygen minimum layer has transgressed well onto the shelves on a regional basis. Such events have resulted in the deposition of the source rocks of much of the world's oil as transgressive shelf deposits.

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Copyright 1997 American Association of Petroleum Geologists