--> Abstract: Comparison of Diagenetic Cements in the Backreef Setting of the Permian Capitan Formation in Dark Canyon, New Mexico, by Jenna Donatelli and Dana Ulmer-Scholle; #90181 (2013)

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Comparison of Diagenetic Cements in the Backreef Setting of the Permian Capitan Formation in Dark Canyon, New Mexico

Jenna Donatelli and Dana Ulmer-Scholle
New Mexico Institute of Mining and Technology

The Capitan Reef in southeastern New Mexico and southwest Texas has been extensively studied for decades. However, a petrographic and isotopic comparison of the diagenetic events has never been made. The back-reef Tansill and Yates formations, as well as the Capitan Massive reef facies, are well exposed in Dark Canyon, making it an optimal study site. Two research cores, each approximately 400 feet deep, were drilled by Amoco on the north side of Dark Canyon. These provide a window into the shallow subsurface for study of diagenetic features within the Tansill and Upper Yates formations, and Capitan Massive facies.

Thin sections throughout both cores have been made and extensive petrographic analysis has been done. The originally aragonitic and high magnesian calcite cements are inferred to have formed syndepositionally. Since then, the aragonitic cement has been neomorphosed or paramorphically inverted into calcite. There were at least two episodes of dolomitization. The dolomitization could have occurred during and after the syndepositional formation of deformation features, such as fractures and faults. The earlier dolomite is fabric preserving. It also rims and/or replaces fossils. The later dolomite is not fabric preserving. It replaces originally aragonitic material, as well as what is inferred to have been high magnesian calcite. The timing of the dolomite that rims voids has not yet been determined. The latest diagenetic cement is coarse grained, sparry calcite cement that fills void space, and has been inferred to be replacive of evaporites. This cement is inferred to have occurred during uplift and exposure of the Capitan Formation.

Isotope data for the late calcites currently at the surface have been collected and interpreted (Alan and Matthews 1982, Given and Lohmann 1985 and 1986). Isotopic studies on the dolomites in the back-reef have yet to be conducted. Comparing the isotope data from each diagenetic event could help constrain the chemistries of the fluids that diagenetically altered the backreef facies of the Capitan Formation and how they changed over time. This could lead to more information on the paleohydrology of the system, which is important in understanding oil migration patterns on the shelf.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013