POSSIBLE CLIMATIC INFLUENCE ON DENSITY OF COMPLEX, LARGE-DIAMETER BURROW NETWORKS IN UPPERMOST LATE TRIASSIC CHINLE FORMATION STRATA FROM WARD’S TERRACE, ARIZONA

High-resolution stratigraphic and paleoclimatic trends from time-equivalent strata at Ward’s Terrace (WT) and Petrified Forest National Park (PEFO), Arizona demonstrate semi-arid to arid climatic conditions within the latest Triassic. Complex networks of large-diameter burrows from a confined interval of Owl Rock Member “equivalent” strata at WT present a unique window to supplement these paleoclimatic and sedimentologic reconstructions. From preliminary investigations, this cumulic (~6 m thick), regionally traceable (~100 km) paleosol houses over 200 carbonate-replaced, large-diameter burrows in an approximately 45 meter long exposure. Burrows display complex architectural morphologies: diameters (~6-40 cm) are circular to sub-circular, shafts are sub-vertical and commonly helical, tunnels connect shafts and/or chambers at 45-90 degree angles, and chambers (up to 5 times shaft/tunnel diameter) are found terminating shafts and connecting tunnels. Burrow density decreases with depth. In the uppermost horizon (Bk1), burrows constitute over 75% of the area and are comprised of tortuous tunnels, helical shafts and chambers. In the underlying horizons (Bk2-Bk3) density is approximately 45% and 25% respectively, and burrows are dominantly comprised of helical shafts and large chambers. Mean annual precipitation (MAP) estimates from the underlying paleosol (~600 mm), the burrowed paleosol (~150 mm), and the overlying paleosol (~427 mm) suggest that this interval has experienced a dramatic decrease in precipitation. The noticeable lack of burrow density in bracketing paleosols, may suggest that the observed density and architectural complexity is related to climate driven behaviors.