ABSTRACT

During the past ten years, the Department of Oceanography at Texas A&M University has been involved in an investigation of 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 are terrigenous sands and muds. Uplift of the seafloor caused by salt diapirism exposes bedrock which serves as a substrate for colonization by calcareous organisms.

Sediment facies and biological 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 biological components and the depth of the nepheloid layer (turbid water). Factors that control the biological zonation are the nature of the substrate, water depth, and the depth of the nepheloid layer.

There is no land-derived sediment (silt and clay) above a depth of 75 meters. Studies of the physical characteristics of the water column indicate that the nepheloid layer rarely rises to depths of 75 meters. The 80 meter depth contour marks a major boundary between biological 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 very similar, even to the muddy Porites gravels and Heterostegina sands that were deposited under an Oligocene nepheloid layer.