Cenozoic Carbonate Buildups
During Late Oligocene time, marine waters transgressed the coastal plain of southern United States and coral reefs grew on topographically high features. In Texas and Louisiana, where salt dome mounds were commonly covered by coral growth, a large reef formed over three neighboring salt domes: Nash, Boling, and Damon Mound. A caprock limestone quarry on the flank of Damon Mound exposes a well-preserved fault block of Heterosteqina Zone, Anahuac Formation, coralline limestone. The outcrop consists of a complete shallowing-upward cycle of a coral reef and exhibits a great variety of fossils and lithofacies. Two-inch cores were taken to ascertain the thickness of Pleistocene alluvial sediment overburden above the caprock limestone; cores penetrating two coral reef limestone fault blocks are described in this report.
The cores reveal a sequence of reef growth identical to that exposed in the outcrop: coralliferous lime wackestone/packstone interbedded with shelf terrigenous mudstone, shallowing upward to a more massive and mud-free coralliferous lime packstone/grainstone, to a thin interval of reef core coralgal lime boundstone, and finally into a shoaling high-energy fossiliferous lime grainstone. This reef sequence is similar to that of other Oligocene reefs in the Caribbean and Central America; some of the coral species, however, are different.
Figures & Tables
Carbonate buildups have long been a focus of intense geological study. An underlying reason is the importance of carbonate buildups as significant hydrocarbon reservoirs. This core workshop is intended to provide a “hands on” look at the subsurface geologic record created by carbonate buildups with emphasis on lithofacies, stratigraphy of buildups and their surrounding deposits, geometry, “reef”-building and sediment-producing organisms, and diagenesis and porosity evolution