KIRKLAND, BRENDA L., University of Texas at Austin, Department of Geological Sciences, Austin, TX; and CLYDE H. MOORE, Jr., Louisiana State University, Department of Geology and Geophysics, Baton Rouge, LA

ABSTRACT: Radiaxial Calcite in the Permian Capitan Formation, Guadalupe Mountains, New Mexico: A Possible Indicator of Sea Level Rise

The Massive Member (reef facies) of the Capitan Formation in the Guadalupe Mountains of Texas and New Mexico contains a distinct sequence of marine cements. The first marine cement--aragonite interlaminated with the binding red alga Archaeolithoporella--formed contemporaneously with reef growth. Subsequent precipitation consisted of large volumes of botryoidal cement followed by precipitation of a smaller volume of radiaxial calcite. In one sample from the deepest zone of the middle Capitan reef, radiaxial calcite crystals terminate with a thin rim of dolomite crystals.

This sequence of marine diagenesis (aragonite, radiaxial calcite, dolomite) reflects a fundamental change in the saturation state of the pore waters. Comparison to the modem suggests that this change resulted from a relative rise in sea level and a corresponding rise in the calcite and aragonite lysoclines. At Enewetak Atoll, aragonitic marine cements form at the oceansurface. Below the aragonite lysocline, radiaxial calcite-virtually identical to Capitan radiaxial calcite-precipitates from marine water flowing into the platform in response to thermal convection. Below the calcite lysocline, dolomite forms in marine water.

Evidence for net-sea level rise during Capitan deposition (approximately 600 m of Capitan aggradation) and evidence for possible thermal convective flow of basinal water into the shelf (radiaxial calcite in back-reef sediment and increased radiaxial calcite in the lower portion of the section) substantiate this hypothesis.

Petrographic investigation of marine diagenesis may place useful constraints on sequence stratigraphic interpretations.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.