New Mexico Geological Society Annual Spring Meeting — Abstracts

Lithofacies distribution, paleocurrent, and provenance data are used to define the evolution of the Gila Conglomerate in the Basin and Range tectonic province ofthe Duncan and Canador Peak Quadrangles, southwestern New Mexico. Crustal extension in this part ofthe Basin and Range resulted in fault-block mountains and complementary basins filled with up to 250 m ofconglomerate, sandstone, siltstone, and mudstone ofthe Gila Conglomerate. The Gila Conglomerate is divided into upper and lower stratigraphic units that are separated by an angular unconformity. The lower unit consists ofstrongly consolidated conglomerate, sandstone, and mudstone and the upper unit has unconsolidated to poorly consolidated siltstone, mudstone, and sandstone with uncommon conglomerate. Three mappable members were identified in these two units including the Wilson Mine and Nichols Canyon Members ofthe lower Gila Conglomerate and the Pearson Mesa Member ofthe upper Gila Conglomerate.

The Gila Conglomerate ofthe Duncan and Canador Peak Quadrangles shows a two-stage evolution. The initial stage was the deposition ofthe late Oligocene(?) to early Miocene Wilson Mine and Nichols Canyon Members, which consist of 175 m of sediment deposited on the distal edge of an alluvial fan and alluvial flat and in a lacustrine playa. Clast composition and paleocurrent directions indicate a provenance for both members to the southeast in the southern Big Burro Mountains. This initial stage was followed by uplift and tilting ofthe strata ofthese two members. The second stage was the deposition ofthe Pliocene to Pleistocene(?) Pearson Mesa Member, which consists of 75 m of alluvial-flat and distal to mid alluvial-fan lithofacies, in a northwest-trending, northeast-tilted, internally drained half graben. Clast composition and paleocurrent directions indicate a provenance for this member to the north in the Rileys Peak area. There is no depositional record of a major through-flowing, axial-fluvial system during the time ofdeposition ofthe Gila Conglomerate in the study area that would be analogous to the modem Gila River.