Abstract

Lower Mississippian carbonate mud-rich bioherms, generally referred to as Waulsortian mounds, are commonly associated with low-paleolatitude carbonate ramp settings and have recently been recognized as important hydrocarbon reservoirs. The factors controlling localization of Waulsortian mounds have heretofore been poorly understood. Stratal relations exposed in the Alamogordo Member of the Lake Valley Formation in the Sacramento Mountains of New Mexico illustrate the effects of tectonism on carbonate sedimentation prior to, during, and after mound growth. They indicate that mound initiation and localization were strongly controlled by tectonically generated, intraramp, sea-floor topography. These observations bear strongly on understanding the controls on localization and growth of mud mounds in general. Stratal geometries observed in the underlying Andrecito Member indicate that this topography was modified by erosional and depositional processes prior to mound initiation. Mounds formed on the surfaces and margins of the intraramp topography as the result of aggradational, in situ accumulation of biogenic sediment. Differences in growth geometry of stratal units within individual mounds and differences between mounds are correlated with position of the mound on the ramp and the deformation occurring immediately prior to mound growth. It is probable that local tectonism continued during mound growth, and that local differences in the amount of relative uplift resulted in different amounts of space for growth of individual mounds, and thus determined differences in mound size and geometry.

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