MASS MORTALITY AND POST-PALEOWILDFIRE EROSION: EVIDENCE FROM A LATE TRIASSIC DEATH ASSEMBLAGE, CHAMA BASIN, NORTH-CENTRAL NEW MEXICO

The Snyder quarry is an unusual Upper Triassic vertebrate fossil locality located in north-central New Mexico. The site has yielded the remains of a wide-variety of organisms, ranging from terrestrial and aquatic vertebrates to aquatic invertebrates, as well as substantial amounts of charcoalized wood. Taphonomic, facies and petrographic analyses indicate that this bonebed was deposited in the aftermath of a moderate to high temperature ground fire. The primary bone-bearing layer is a matrix-supported conglomerate that is interpreted as the deposit of a hyperconcentrated flood that swept animal remains and downed trees into a topographic low after a paleowildfire had occurred in the area. Scanning electron and reflectance microscopy of the charcoalized wood indicate that the wood was subjected to temperatures between 300 and 450°C. The Snyder quarry is among the first documented Triassic wildfires and the first death assemblage definitively tied to a wildfire event. As such, it demonstrates that wildfire events do leave geologic evidence that can be used to evaluate not only animal mortality, but also rates of erosion and subsequent deposition in a post-fire landscape.