--> Abstract: Stratiform Dolomitization In Pennsylvanian Bioherms Of The Western Orogrande Basin, Nm, by G. S. Soreghan, R. A. Furley, and M. H. Engel; #90928 (1999).

Datapages, Inc.Print this page

SOREGHAN, GERILYN S., ROGER A. FURLEY, and MICHAEL H. ENGEL
University of Oklahoma, Norman, OK

Abstract: Stratiform Dolomitization in Pennsylvanian Bioherms of the Western Orogrande Basin, NM

Upper Pennsylvanian phylloid algal mounds of the western Orogrande Basin (NM) consist of high-frequency cycles (sequences) bounded by surfaces of paleo-subaerial exposure. Stratiform dolomitization affects cycles throughout mound complexes, but is most extensive in mound-flank positions.

Preliminary petrographic and geochemical analyses suggest that dolomitization was early, but underwent significant late-stage modification. Dolomite typically increases in abundance upward through a cycle, and consists of both aphanocrystalline (predominant), and medium- to coarse-grained (subordinate) phases. Dolomite is pervasive in facies exhibiting evidence for restriction and peritidal deposition (e.g. peloids, algae, fenestrae, intraclasts, gypsum). Replacive dolomite is calcic (52-57 mole% CaCO3), Sr-rich (400-1600 ppm), and Fe-poor. Coarsely crystalline dolomite averages 51 mole % CaCO3, is relatively Sr-poor (250 ppm) and Fe-rich. d18O values of both calcites and dolomites (whole-rock powders) are depleted relative to Pennsylvanian marine calcite cements, suggesting post-depositional modification. On average, however, d18O and d13C values of dolomites are significantly enriched relative to calcites.

These observations suggest: (1) penecontemporaneous dolomitization of peritidal facies associated with evaporative conditions, and (2) later neomorphism and pore-lining cementation during burial. Early dolomitization significantly influenced porosity-permeability attributes, and could induce compartmentalization in productive analogs.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas