Abstract: Pennsylvanian Carbonate and Siliciclastic Depositional Patterns and Sequences Across Sacramento Shelf, New Mexico

John C. Van Wagoner

The Gobbler Formation (Morrowan? through Desmoinesian) of the northern Sacramento Mountains, New Mexico, records the contemporaneous deposition of carbonate and siliciclastic sediment across a narrow shelf between the Pedernal uplift on the east and the Orogrande basin on the west. Carbonate parts of the shelf consist predominantly of shoaling-upward carbonate cycles which begin at the base with deeper water spiculitic mudstones, pass upward through normal marine-shelf packstones, and are capped with bioclastic grainstones. Siliciclastic sediments are preserved in symmetric and asymmetric cycles recording progradation, aggradation, and abandonment of fluvial-deltaic environments. A northwest-trending topographic depression, the Alamo trough, provided a pathway down which iliciclastic sediment moved toward the Orogrande basin. The high margins of the trough were sufficiently restricted from siliciclastic influx to permit deposition of nearly pure carbonate sediment.

Five depositional episodes compose the Desmoinesian of the study area starting in the lower Desmoinesian with (1) deposition of deeper water spiculitic mudstones during a sea-level rise followed by (2) widespread delta progradation and reduced carbonate deposition, (3) deposition of shoaling-upward carbonate cycles, (4) deposition of interfingering carbonate and deltaic sediments, and (5) deposition of carbonate bank and cycle sequences at the top of the Desmoinesian. These facies patterns were controlled by relative sea-level rises and structural movements associated with the Pedernal uplift.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma