Abstract: Architecture and Sequential Development of a Mississippian Carbonate Platform as Exemplified by the Sacramento Mountains, New Mexico

Dave Hunt

Mississippian strata are semi-continuously exposed over 25 km along the western escarpment of the Sacramento Mountains. These exposures and a series of canyons cut perpendicular to the range front afford an excellent three-dimensional view of the sequential development of a carbonate ramp. The platform initiated on a low angle, southerly dipping and segmented slope, the segment boundaries of which were tectonically controlled. Each segment of the slope is characterized by Waulsortian buildups of comparable size and geometry.

Platform architecture is composed of two mutually compensating sequences. The lower sequence thins down dip, contains Waulsortian-type mounds, and two grain-rich progradational wedges. In contrast, the upper sequence is a mud-dominated slope-front fill which thins northward and subdued the palaeobathymetry of its precursor. The two sequences are separated by a major sequence boundary associated with erosion of a major slope break, deposition of a distinctive package of bioclastic sands, exposure of the platform and formation of local, compactionally enhanced unconformities.

In the lower wedge, tectonism in the northernmost part of the platform preceded the initiation of Waulsortian-type buildups and formed a subtle topography which controlled their location. The buildups exaggerated this topography, and in turn their size, position and orientation controlled the location and geometry of the two progradational wedges of the lower sequence. These laterally stacked grain-dominated wedges have a lobate external form, and this reflects the focusing of currents by the mounds. Within the sequences, alternations between grain-rich and mud-rich packages reflect both changes of environment and relative sea level.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994