Paper No. 196-8
Presentation Time: 9:00 AM-6:30 PM
FIRST TWO SEASONS SURVEYS OF FOSSILS FROM FOUR HEMPHILLIAN LOCALITIES AT PETRIFIED FOREST NATIONAL PARK
Since 1917, published reports of fossiliferous sediments at the Bidahochi Formation from White Cone peak in the Hopi and Navajo Nations have garnered interest. The fossils from White Cone peak include both vertebrate (Actinopterygii, Amphibia, Reptilia, Aves and Mammalia) and invertebrate (Mollusca) materials. Biochronologic and radiometric dating place this material at the Hemphillian (Late Miocene – Early Pliocene) North American land mammal age. In the spring of 2018 and 2019 we conducted multiple day surveys of presumptive Bidahochi Formation materials at Petrified Forest National Park (PFNP). The nearest site surveyed lies approximately forty miles to the southeast of the White Cone peak sediments. Except for a small amount of unidentified Artiodactyla innominate fragments collected at the B1 locality, these represent the first surveys for fossil materials at four presumptive Bidahochi sites in PFNP. These Hemphillian sediments overlay the Upper Triassic Chinle Formation, with a nearly 200-million-year unconformity. Of the four sites we have surveyed, each turned up fossil materials. And each had supported distinct fossil taxa at each. The variety of taxa supports distinct paleo environments of dry lands and perennial or ephemeral aquatic habitats for each. Here we make a preliminary report of these two surveys of fossil materials from the only Neogene localities at PFNP. At the southern B1 locality we located additional indeterminate large mammal fragments. The central B2 locality had an abundance of freshwater bivalves, supporting permanent water. Both Triassic and Neogene bivalves were mixed in this material. The northern B3 locality contains the most diverse assemblage of microvertebrates (rodentia, Serpentes, Lacertia) and two taxa of gastropods. Also located here was the first Equid fossil from PFNP. A fourth site, B3B, revealed the first non-Triassic Actinopterygii specimens and the first avian fossil specimens from PFNP. We intend to further constrain the dating of these sites using biochronologic analyses and a collaborative radiometric dating. We suspect that the B3 locality may be more recent than the B1 site.