Gerilyn S. Soreghan¹, Michael H. Engel², Roger A. Furley¹, Katherine A. Giles³
(1) University of Oklahoma, Norman, OK
(2) The University of Oklahoma, Norman, OK
(3) New Mexico State University, Las Cruces, NM

Abstract: Tectonic controls on early dolomite in Pennsylvanian algal mounds of the western Orogrande basin, New Mexico

Pennsylvanian algal bioherms of the western Orogrande basin (New Mexico) consist of high-frequency sequences exhibiting partial to pervasive dolomitization. Dolomitization is stratiform, preferentially affecting strata proximal to sequence boundaries, particularly in off-mound and mound-flank positions. Detailed field, petrographic, and geochemical analyses reveal both facies-selective (FS) and non facies-selective (NFS) replacive dolomite, and several burial-stage dolomite cements.

FS dolomitization occurred penecontemporaneous with peritidal deposition at each glacioeustatic fall and lowstand. NFS dolomitization occurred early post-depositional, by reflux of "mesosaline" seawater during the early to middle stages of each glacioeustatic transgression. Extensive Virgilian gypsum deposition in the Orogrande basin documents pronounced lowstand basin restriction. Early transgressive waters were therefore saline; glacioeustatic and tidal pumping, and brine density, drove early dolomitization.

The presence of early dolomite in the western Orogrande basin, and the concomitant absence in mound and mound-related strata of the eastern Orogrande basin, reflects the asymmetry of the system. The western shelf was low relief, with an archipelago of high-relief mounds. This configuration favored lowstand peritidal conditions and local extreme restriction. In contrast, the eastern shelf was high relief, and relatively elevated. This configuration precluded development of extensive tidal flats, and allowed inundation only at late transgressive to highstand stages, by normal-marine waters. Development of both peritidal and transgressive reflux dolomitization was therefore restricted to the western basin.

Recognition of the link between diagenesis and tectonic setting in this system bears on construction of deterministic reservoir models in productive analogs, since dolomitization and porosity development positively covary in this system.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana