Print this pageTectonic Controls on Carbonate Mound Growth, Orogrande Basin, New Mexico
SOREGHAN, GERILYN S., and KATHERINE A. GILES
Phylloid algal mound complexes of the eastern and western Orogrande basin developed coevally (early-middle Virgilian), but exhibit contrasting facies and geometric attributes. Western Orogrande mound complexes comprise thick (100 m) stacks of biohermal growth cycles and display strongly aggradational geometric trends. Dolomitization is widespread in this system and preferentially affects evaporitic peritidal and pedogenically modified facies located in intermound regions. These dolomitized facies display reservoir-grade (up to 20%) porosities, which contrast with the tight (<2%) mound-core facies. Mound complexes of the well-studied eastern Orogrande margin also compromise multiple cycles of biohermal growth events, but these successions are comparably thin (30 m), and predominantly progradational. Further, the dolomitized facies that characterize the western Orogrande mounds do not occur in the eastern mound complexes.
Given that the western and eastern mound complexes formed coevally, fluctuations in climate, eustasy, and sedimentation rate influenced both mound systems equally. Therefore, differences in facies and geometric trends relate to tectonically induced accommodation variations between the sites. Significant topographic relief created during lowstand exposure of the western Orogrande mounds created highly restricted conditions in intermound regions. Transgressive dolomitizing brines penetrated intermound facies creating secondary enhancement of porosity. The progradational geometry of the eastern Orogrande mound system apparently precluded generation of these depositional and diagenetic conditions.
This example is important because (1) the link between stratigraphic product and process can be narrowed to a tectonic cause, and (2) tectonically induced variations in accommodation space significantly influenced the reservoir (and therefore economic) attributes of the mound system.