IMPLICATIONS OF CYANOBACTERIAL COMMUNITIES PRESERVED IN THE EARLY CRETACEOUS STIKES DINOSAUR QUARRY: UPPER YELLOW CAT MEMBER, CEDAR MOUNTAIN FORMATION, EASTERN UTAH, USA

A remarkable concentration of mainly Utahraptor bones (Utahraptor block) was found in the Stikes Quarry within the Early Cretaceous upper Yellow Cat Member, Cedar Mountain Formation, eastern Utah. The Utahraptor block (3.2 by 2.5 by 0.5-0.85 m) is a complex association of nearly pristine bones and accompanying sedimentary features, such as unusual soft-sediment deformation structures, that led to the hypothesis of quicksand-induced sinking as the probable trapping mechanism. The largest fossil-bearing sediment-sill intrusion in the Utahraptor block displays evidence of development in a prolonged subaqueous setting, probably a spring that provides both a mechanism for quicksand formation and an ideal environment for cyanobacteria-dominated mat systems. This study documents the preservation and distribution of microfossils attributable to cyanobacteria in the Utahraptor block.

The soft-sediment deformed mudstone, siltstone, sandstone and carbonate strata within the Utahraptor block preserve microbes. Calcium carbonate encrustations on bones contain a variety of ministromatolic (mm-scale) cyanobacterial forms, from turbunate- to hemispherical-shapes. The overall form of the calcium carbonate encrustations is sheet-like near the bone and distally becoming more chip-like in nature. SEM and EDS analyses document carbonate preservation of filament sheaths, some with coiled, secondary filaments. Potassium-rich filaments with no calcium carbonate present are associated with clays. As clay size reduces vertically, potassium-rich filament diameter decreases.

Microbial communities have the ability to enhance preservation of organic material by organomineralization. Two settings preserved microbes in the Utahraptor block. Decomposition of and by microbes near the bones consumed oxygen, creating waters with anoxic conditions ideal for preservation. The adipocere, a wax-like organic substance formed from decomposition, provided carbonate and metal ions, aiding mineral precipitation. In addition, the probable endemic bacteria are preserved by the potassium-rich clays. The confirmed presence of microbial communities provides further insight into the taphonomic history of the Utahraptor block.