A new locality of fossiliferous Harding Sandstone: evidence for freshwater Ordovician vertebrates

Abstract

ABSTRACT The Ordovician Harding Sandstone has played an important role in studies of the environment of the earliest types of “ostracoderms” (armored jawless fish-like vertebrates). Such studies have concentrated on fossil collections from the type locality, a quarry near Canon City, Colorado, which contains a mixed fossil fauna of “ostracoderms” and marine invertebrates. This co-occurrence has been used in the past as evidence that the vertebrates from the Harding Sandstone were marine animals. Fossil associations alone, however, do not provide sufficient data for paleoenvironmental interpretations. It is also necessary to analyze depositional facies. A previously unpublished locality of the Harding Sandstone allows interpretations of depositional environments by sedimentary facies analysis. Vertebrate fossils of the Harding Sandstone are restricted mainly to supratidal and, to a lesser extent, intertidal deposits. They are most abundant in channelized, granular conglomerates, units devoid of marine inve...