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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 43 (1959)

Issue: 10. (October)

First Page: 2521

Last Page: 2521

Title: Petrology of Anacacho Limestone of Southwest Texas: ABSTRACT

Author(s): Lee L. Harvill

Article Type: Meeting abstract

Abstract:

The Anacacho limestone, noted for its high asphalt content, is exposed in scattered outcrops west of San Antonio, from western Bexar County to eastern Kinney County. It occupies the stratigraphic position of the Taylor group in the Upper Cretaceous. The formation consists predominantly of organic fragmental limestone, containing only traces of terrigenous material.

The Anacacho is locally abundant in asphalt. A previous investigator concluded that this was deposited with the limestone, and argued from this example that liquid petroleum generally originated in the reservoirs where it now is found. However, the present writer's petrographic study shows that the bituminous material Previous HitinvadedTop the limestone, then shrank by loss of volatile constituents. This is based especially on the following evidence.

1. The pore space in the limestone is overwhelmingly of secondary origin; no truly primary porosity could be demonstrated.

2. The contact of asphaltic with asphalt-free rock cuts across the bedding.

3. The asphalt does not completely fill the pore space of the rock but forms a coating on the limestone particles.

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Copyright 1997 American Association of Petroleum Geologists