ABSTRACTS
W. R. Barnhart*
A group of 32 impressions is documented in the top of the Tapeats Sandstone at Plateau Point, Grand Canyon. These may be biological in origin, and a brief history of relevant local research is reviewed. This analysis assumes the rapid deposition shown in earlier work, and the implications of that model are explored. One is that thixotropic mobility in the sand when the impressions were formed adversely affected their clarity. Evidence of an original, thin, clay-sheet substrate is explored, as are its implications for preservation. This clay diminished the details of the impressions but served as a mold to faithfully preserve forms in the more mobile sand. Organic and inorganic explanations are considered, and the recognition of regular, linear groups suggests a possible biogenic origin