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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 9. (September)

First Page: 1429

Last Page: 1430

Title: Local Carbonate Production on a Terrigenous Shelf: ABSTRACT

Author(s): R. Rezak

Article Type: Meeting abstract

Abstract:

During the past 10 years, the Department of Oceanography at Texas A&M University has been involved in investigating reefs and banks on the Texas-Louisiana outer continental shelf. Studies were conducted on the geologic structure, sediment distribution, biology, and water and sediment dynamics at over 30 reefs and banks. Because of the influence of the Mississippi River and other streams, the dominant sediments in this part of the Gulf of Mexico are terrigenous sands and muds. Uplift of the sea floor caused by salt diapirism exposes bed rock that serves as a substrate for colonization by calcareous organisms.

Sediment facies and biologic zones at the Flower Garden Banks are closely related. The presence of a bathymetric high influences the direction and velocity of bottom currents. Factors that control sediment facies are biologic components and depth of the nepheloid layer (turbid water). Factors that control biologic zonation are the nature of the substrate, the water depth, and the depth of the nepheloid layer.

No land-derived sediment (silt and clay) are present above a depth of 75 m. Studies of the physical characteristics of the water column indicate

End_Page 1429------------------------------

that the nepheloid layer rarely rises to depths of 75 m. The 80-m depth contour marks a major boundary between biologic communities. That depth separates the turbid water fauna below from the clear water fauna and flora above.

The east and west Flower Garden Banks serve as modern analogs of Tertiary reefs, such as the Oligocene reef at Damon Mound, Brazoria County, Texas. The sediment facies are similar, even to the muddy Porites gravels and Heterostegina sands that were deposited under an Oligocene nepheloid layer.

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