Abstract: Newly Discovered Pennsylvanian Channel, Big Hatchet Mountains, Southwestern New Mexico

David J. Sivils, A. E. Tony D'Agostino, Robert Nail

Field checking for the forth-coming geological state map of New Mexico in southwestern New Mexico lead to the discovery of an undescribed Pennsylvanian channel located on the eastern flank of the range. Although it is somewhat poorly exposed the channel trends southwesterly. The lower boundary is erosional and is marked by a change from dolomitic lime mudstones to a coarse-grained cobble conglomerate. Clasts in the basal conglomerate are dominantly composed of limestone pebbles and cobbles derived from the underlying carbonates intermixed with quartz clasts. The channel fill fines-upward to a grained, pebbly quartz sandstone culminating in a horizontally laminated medium to fine-grained quartz sandstones and quartz siltstones. The channel is overlain by a lime mudstone/wa kestone marine carbonate.

The channel ranges in thickness from 12 m near the center thinning northward to 0 m. The channel is traceable to the south to a point where it is truncated by a high-angle normal fault.

Fusulinids recovered from the underlying and overlying carbonates range in age from Desmoinesian(?) to Lower Virgilian, indicating that channel formation occurred during the Tombstone supercycle (Late Pennsylvanian).

The overall geometry, lithologic association and age of this channel are consistent with similar channels identified from the Pennsylvanian section in the Big Hatchet Mountains by previous workers. The alignment of this channel is similar to the previously identified channels reflecting a paleotransport direction in a southwest-northeast direction. Most probably transport was toward the southwest with detrital material being fed into the channels from the nearby Florida-Moyotes uplifts to the northeast.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada