Allochthonous Model for the Generation of Lower Mississippian Waulsortian Mounds and Implications for Prediction of Facies Geometry and Distribution

Katherine A. Giles

Waulsortian mounds are currently interpreted as in situ, deep-water, biohermal buildups based on the slope depositional setting of encasing strata, mounded or conical geometry, and apparent "core" and "flank" facies relationship. Mound features inconsistent with this interpretation are: the complete lack of evidence of an organism capable of producing a biohermal buildup, dominance of well-bedded, transported sediment (debris flows and turbidites) within the core and flank facies, slump folds at the base of the mounds, presence of clastic injection dikes into the base of some mounds, and the abrupt contact between core and flanking strata. An alternative model for generation of Waulsortian mounds that is consistent with the above listed features entail buildup of the moun s by downslope movement and progressive accumulation of resedimented material. In this model, massive slope failure of rapidly accumulated sediment in an upper ramp or slope environment lead to downslope translation and internal deformation of semi-coherent, glide blocks and slump masses. Translation ceased at zones of decreased slope gradient where the translated masses were subsequently onlaped by associated resedimented material such as debris flows, grain flows, and turbidites. The result is a geometrically distinctive, mounded, carbonate facies assemblage consisting of a central slump mass (core) sometimes surrounded by bedded, resedimented facies that dip away from the slump mass (flanks).

The predicted geometry and distribution of Waulsortian facies generated by gravity-driven sedimentary processes (allochthonous model) would be markedly different from those generated by in situ biohermal growth. The two models would entail very different exploration and production strategies.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995