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The AAPG/Datapages Combined Publications Database

Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 20, No. 7, March 1978. Pages 3-3.

Abstract: Shale Diapirism and Compaction of Abnormally Pressured Shales in South Texas


Richard S. Previous HitBishopNext Hit

Both salt and shale diapirs of the Gulf Coast basin occur in similar tectonic settings and seemingly have formed by the same mechanism. Despite their similarity, however, salt and shale diapirs differ significantly in size, abundance, geographic distribution, and in their capability to trap hydrocarbons. Although diapirism generally is described as an intrusive process whereby less dense material (usually salt) rises into more dense overburden owing to buoyancy, shale diapirs in the Gulf Coast do not behave as predicted by buoyancy theory. Shale density, inversions occur in large areas of both South Louisiana and South Texas, yet subsurface piercement shale diapirs occur only in South Texas. Explaining this anomalous behavior has required the integration of field data and the use of a loading Previous HitmodelNext Hit of diapirism, a Previous HitmodelNext Hit of the compaction of thick shales, and a numerical simulation of compaction history in South Texas.

Interpretation of the results is that two South Texas shale diapirs, La Ward and Sheriff, formed primarily by extrusion and subsequent burial, rather than by intrusion. In general, rapid deposition of a sandy overburden on thick, montmorillonitic shale is the condition most conducive to forming shale density inversions.

A theoretical simulation of the South Texas shale-compaction history, combined with a loading Previous HitmodelNext Hit of diapirism, provides the basis to explain this general Previous HitmodelTop of shale-diapir emplacement.

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