Print this pageAbstract: Origin of Isolated Reefs and Shelf Edges in Midland Basin, Subsidence versus Sedimentation Phenomenon
A hypothesis to account for the origin of carbonate depositional topography, including shelf edges and isolated reefs, is modeled after a part of the Pennsylvanian "isolated reef trend" of the Midland basin, Texas. The hypothesis demonstrates that shelf edges and isolated reefs are interdependent and that such features develop without benefit of preexisting sea-floor topography. Carbonate-shelf edges and isolated reefs can in fact form on a planar surface through the interaction of sedimentation and subsidence rates. Local structural displacement and/or underlying structural hinging is not a prerequisite to either the inception or the location of the features.
The carbonate-shelf edge will develop on the rotationally subsiding limb of a "starved basin," assuming that various conditions necessary for carbonate deposition are favorable. It will develop along that part of the basin limb that is subsiding at a rate equal to the average maximum rate of carbonate deposition. Its inception occurs when the prescribed zone becomes submergent. Once established, the shelf edge greatly enhances carbonate deposition over that previously attainable by causing upwelling of nutrient-laden currents and by creating a zone of high energy and rapid oxidation. Isolated reefs, which represent the new optimum rate of carbonate deposition, will form on the shelf edge if the shelf edge founders. Foundering may be caused either by an increase in the rate of subsiden e or by a decrease in the general rate of carbonate deposition.
AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana