Cyclic Carbonate Sedimentation in Horquilla Formation, Southwestern New Mexico

Bertrand Gramont, D. B. Johnson

The Virgilian (Upper Pennsylvanian) part of the Horquilla formation is exposed on the west and north faces of Big Hatchet Peak, Hidalgo County, New Mexico. Previous studies indicate that this limestone sequence (100 m thick) is composed principally of wackestones that were deposited in the quiet waters of an open-marine outer shelf.

A unit of Virgilian age was chosen for lateral study. Biotic constituents and their high diversities suggest that deposition of the unit occurred under normal marine conditions. Decreased abundance of stenohaline organisms toward the top of the unit is interpreted to indicate shallowing during deposition. Packstones under the unit were deposited near wave base. Wackestones of the unit were deposited below wave base in quiet waters of the outer shelf. Overlying laminated wackestones and crinoidal packstones were deposited in deeper waters, well below wave base.

This facies distribution suggests that the unit was deposited between two major deepening phases or transgressive events. Lower and upper bedding surfaces of the unit mark abrupt changes to deeper facies. The deposition of the unit could have been governed by a pattern of relative changes in sea level similar to those regulating sedimentation of punctuated aggradational cycles. The Virgilian part of the Horquilla formation thus could be composed of a stack of shallowing-upward units where numerous relative rises and falls of sea level could have governed cyclic sedimentation.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.