Abstract: Origin of Rhizocorallium in Cretaceous Dakota Sandstone, Colorado

R. W. Scott, P. B. Basan

The trace fossil, Thalassinoides, leads into the Rhizocorallium irregulare Mayer trace on bedding planes of the Dakota Sandstone near Canyon City, Colorado. This relation indicates that the same animal formed both trace fossils, but by different behavioral activities. The Thalassinoides trail shows locomotion, whereas the Rhizocorallium trace probably was made while the animal fed on organic detritus. The animal produced the web of concentric, imbricated spreite, which is distinctive of Rhizocorallium, by curving its body to one side and scooping the sediment to the inside of the "U." The spreites curve into one of the U-shaped arms that was formed during locomotion. Eventually the animal terminated the feeding behavior and returned along the opposite edge of the spreites thereby truncating them and forming the second arm of the U-shaped trail. The oval cross-section of the trail indicates that the animal had a cylindrical shape and was possibly a crustacean or annelid. One or several Rhizocorallium structures may originate from the same point on the Thalassinoides trail, showing that the supposed feeding behavior was repeated several times by the same animal. These epirelief traces probably were formed at a sand-mud contact. They are common in some Cretaceous nearshore sandstones in the Western Interior Province of the United States.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC