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Constraints on the Diagenetic History of the Capitan Shelf Margin (Upper Permian) from Previous HitMagneticNext Hit and Diagenetic Studies

DARKE, GILLIAN, Shell Gapsa, Buenos Aires, Argentina

Assemblages of Previous HitmagneticNext Hit minerals in sedimentary rocks are of depositional or diagenetic origin. Previous HitMagneticNext Hit, diagenetic, and outcrop studies in rocks from the Capitan shelf margin (U. Permian), West Texas and New Mexico, show that the diagenetic history of these rocks was dominated by anhydrite cementation until uplift from Tertiary times onwards and that the Previous HitmagneticNext Hit minerals are of diagenetic origin.

Diagenetic studies, including petrographic, cathodoluminescence and electron microprobe analysis, show that the diagenetic history can be divided into three main phases: (1) Pre-burial--cementation by calcium carbonate contemporary with deposition followed by anhydrite cementation and dolomitization. These processes prevented much compaction in the back reef, reef, and upper foreslope facies. (2) Burial--continued cementation and replacement of some carbonate by anhydrite; accompanied by dolomitization, the development of dolomite overgrowth cements, and minor kaolinite formation. (3) Uplift--minor calcitization of anhydrite accompanied by kaolinite formation; followed by dissolution of anhydrite, brecciation and fracturing, and the precipitation of calcite spar cements.

The mineralogy of Previous HitmagneticNext Hit particles and the age of remanence acquisition was deduced from thermal and alternating field demagnetization, despite the low Previous HitmagneticNext Hit mineral content of most samples. Pyrrhotite acquired remanence at around 190 Ma and from around 45 Ma to recent times. The formation of the oxides, hematite and geothite, from the oxidation of preexisting sulfides and by authigenic processes accompanied the dissolution of anhydrite and the precipitation of the calcite spar cements.

These results shed new light on the diagenetic history of the Capitan shelf margin and illustrate the value of Previous HitmagneticNext Hit studies of sedimentary rocks when Previous HitmagneticTop data are integrated with accompanying diagenetic studies.


AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)