Evaluation of the Allochthonous Model for the Formation of Waulsortian Mud Mounds in the Sacramento Mountains, South-Central New Mexico

Geovanni Romero, New Mexico State University, Department of Geological Sciences, Las Cruces, NM,  [email protected]

Despite their high potential and quality as hydrocarbon reservoirs, Waulsortian mud-mounds remain a poorly understood Mississippian carbonate facies.  The mounds consist of mudstone cores surrounded by halos of crinoid-bryozoan debris which offer high porosity.  Although the mechanism of mound formation is still controversial, two end-member hypotheses are proposed: (1) biohermal buildup and (2) allochthonous sedimentologic buildup. Although organisms present in mounds are documented, there is no consistent evidence for organic carbonate mud binding or precipitation.  In the allochthonous model the mound core to flank facies juxtaposition is created by gravitational slide, glide and flow processes.  These processes are associated with a detachment surface and other predictable structural features such as extensional structural regimes in up-dip areas, contractional in the down-dip areas and a zone of translation of blocks connecting the up- and down-dip regions.  Systematic evaluation of the presence or absence of these predicted features has not been performed in areas containing Waulsortian mud-mounds exposures.  The goal of this research is to test the allochthonous model by conducting a detailed structural characterization of the Mississippian units in the Sacramento Mountains.  Understanding of the mechanism mud-mound formation is critical to prediction of mound trends and facies distribution for exploration and production models.  In the study of reefs, Waulsortian mounds represent an important evolutionary link following the late-Devonian decline of the stromatoporoid and tabulate coral reefs and the raise of the Pennsylvanian/Permian phylloid algal reefs.  If the mounds are predominantly built by resedimentation processes this evolutionary model will need to be reevaluated.