DIVERSE ARRAY OF SOFT-SEDIMENT FOSSIL VERTEBRATE TRACKS FROM THE LAKES OF WORLD’S LARGEST GYPSUM DUNE FIELD

Sediment in the White Sands Dune Field is sourced from accumulations of gypsiferous sediment associated with lakes and saline mudflats that have existed on the floor of the Tularosa Basin, from Pleistocene time to the present. Thousands of Late Pleistocene “megafauna” vertebrate tracks and trackways known as the “White Sands Megatracksite”, have been found in sediments in and around the lacustrine deposits. Fossil prints were first described from the Tularosa Basin in the 1930’s, but have only recently been discovered within White Sands National Monument. The trace fossil assemblage is dominated by proboscidean (mammoth) footprints along with associated camelid (camel-like), undetermined artiodactyl, and large and small carnivore tracks. These fossil tracks have unusual preservation in soft gypsiferous lacustrine and playa lake-margin sediments. Here we describe this preservation in order to better understand paleo environments and aid in preservation and management.

Prints are preserved in soft gypsum and carbonate sediment, making them extremely fragile and susceptible to rapid weathering once exposed. Some prints and trackways have an ephemeral expression, only visible when sediment moisture is high enough to create a contrast with surrounding sediment. The prints can be raised above or depressed below the surface. We interpret the raised tracks to represent the compressed sediment below the track exposed by wind erosion, and in some cases affected by diagenetic alteration to, or precipitation of dolomite.Sediment surrounding these tracks are distorted as seen in natural vertical exposures or excavations into track-bearing strata. Sediment that infills the tracks includes fine or coarse grained gypsum sand, siliciclastic mud, and dolomite. Many tracks are very fragile, but those comprised of dolomite are comparatively resistant. In addition to the prints, layers of vegetation have been found preserved beneath and above many of the tracks, and hair and possible coprolites have also been found in association with the trackways. This ongoing survey continues to discover new trackways as they are exposed from eroding sediment. This study is part of an ongoing effort to catalog and correlate sediments and trackways at White Sands National Monument to better plan for their preservation and interpretation.