THE PALEOECOLOGY OF THE COCONINO SANDSTONE DEPOSITIONAL ENVIRONMENT: THE CASE FOR AVAILABLE SURFACE WATER
The classical sedimentological interpretation of the Coconino depositional environment has been that of a hyper-arid desert with no available surface water, with the primary input of water being supplied by periodic fogs. To a large degree, this interpretation was based on the lack of recognized inter-dune deposits within the Coconino.
The Namib Desert in western Africa has been suggested as a viable modern analog for the Coconino Erg. The Namib, however, is not a suitable analog for several reasons. The limited area of the Namib, its proximity to an open sea, the lack of a cold offshore current as a fog producing mechanism proximal to the Coconino Erg along with the size and metabolic requirements of the Namib fauna all combine to limit its suitability as a viable analog for the Coconino Erg.
New trace fossil evidence from a previously un-described locality in Grand Canyon suggests a relatively high concentration of organisms, both vertebrate and invertebrate, in a restricted area within the Coconino for an extended period of time. This locality, as well as others, provides sedimentological evidence for the presence of surface or near surface water within the Coconino Erg. This evidence includes well developed desiccation cracking and horizontal clay rich sediments associated with bounding surfaces. This new evidence, coupled with a re-examination of the Namib as a suitable analog, suggests that a re-evaluation of previous ideas regarding the environment in which the Coconino Sandstone was deposited is needed.