New Mexico Geological Society Annual Spring Meeting — Abstracts

Carbonate Hill sequences in the Peloncillo Mountains reveal the presence of a relatively nearshore, high clastic, carbonate section. It is dominated by bivalves with relatively less abundant gastropods and thick-walled serpulids. It contains sporadic toucasid and caprinid biostromes that may stack into a biohermal-like mound structure. The presence of a rich fauna of large colonial corals attests to the presence of normal marine salinity conditions at least in part.

The formation is distinctly lithologically different from the nearby, more offshore Mural Limestone (west) and U-Bar Formation (east). It probably is at least in part time-transgressive. The Campagrande Formation of the Rimrock of El Paso and Hudspeth counties may provide an analogous setting where the unit comes off the Diablo platform into the southern Chihuahua trough.

A precise determination of Late Aptian and/or Early Albian age of the Carbonate Hill is not currently possible from available data. The sequence is interpreted to be a progradational, shoaling upward sequence on the northern Bisbee shelf of the Chihuahua trough. The top of the Carbonate Hill most likely represents Kaufmann's (1977) fourth Cretaceous regressive phase at the Aptian-Albian boundary (108Ma).