Stratigraphic Patterns, Sedimentology and Diagenesis of Capitan Backreef Strata, Permian, Guadalupe Mnts, New Mexico

MUTTI, MARIA, University of Milan, Milan, Italy, and TONI SIMO, University of Wisconsin--Madison, Madison, WI

Capitan backreef strata, Yates Formation, are characterized by six cycles, each with a lower siliciclastic and an upper carbonate unit. The factors controlling the deposition of these packages remain controversial. Traditional sedimentary and stratigraphic approaches

have been integrated with diagenetic events to understand the main controls on the genesis of these cycles.

Cycles are bounded by sharp and erosive surfaces on the backreef strata. Basinward these surfaces become concordant and disappear within massive Capitan. The lower siliciclastic units lap over the unconformity and are interpreted as a transgressive deposit. The upper carbonate units are transitional to the sandstones and are interpreted as transgressive to regressive subtidal to supratidal deposits.

Syndepositional and syn-unconformity diagenetic features are: (1) marine calcite or aragonite cementation, (2) dissolution of metastable mineral phases, and (3) dolomitization (both replacive and primary precipitate). Geochemistry of dolomites is consistent with evaporation-concentrated and slightly reducing marine waters. Meteoric calcite cements were not found associated with the subaerial exposure surfaces at cycle tops in shelf strata. Arid climate probably prevented the establishment of stable freshwater lenses. Postdepositional diagenesis includes meteoric and shallow burial calcite cements, dissolution vugs, kaolinite, and vadose calcite cements.

Combination of sedimentologic and diagenetic studies of Guadalupe Mountains outcrops suggests that sea level fluctuations probably were responsible for the deposition of cyclic strata and syndepositional diagenetic features. Relative sea level falls exposed parts of the shelf driving dolomitizing fluids through shelf strata. Relative sea level rises flooded the shelf and deposited subtidal to intertidal siliciclastic and carbonate rocks.

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