Abstract: Carbonate Diagenesis and Facies Distribution of Anacacho Limestone Associated with Late Cretaceous Volcano, Dimmit County, Texas

Pamela E. Luttrell

Late Cretaceous volcanic activity resulted in the growth of cones which form an arcuate trend in south-central Texas. These cones ultimately grew to sea level and served as nuclei for shallow-water carbonate deposits known as the Anacacho Limestone. Excellent hydrocarbon accumulations have been found associated with the limestones of many of these volcanoes. Core and electric logs from the carbonate rocks of one such volcano were studied to determine the distribution of facies and origin of porosity.

Shoal-water carbonate rocks, ranging from grainstones to wackestones in texture, were deposited near the cone with sporadic interruptions by pyroclastic lapilli tuff deposition. Away from the cone, open-shelf planktonic foraminifer-bearing calcareous mudstones were deposited in deeper water. These terrigenous sediments ultimately filled the basin and covered the volcanic complex.

Porosity in the Anacacho Limestone is mostly in the packestone facies; it consists both of primary interparticle porosity and secondary leached vugs. Later diagenesis resulted in partial reduction of both porosity types by blocky calcite cementation and pressure solution.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA