A DIVERSE MICROPALONTOLOGICAL MISS ASSEMBLAGE FROM THE LACUSTRINE MILL CANYON DINOSAUR TRACKSITE: EARLY CRETACEOUS CEDAR MOUNTAIN FORMATION, MOAB, UTAH

Modern microbial mats are composed of spectacular diverse microbial suites embedded in extracelluar polymeric substance (EPS). Taphonomic processes typically reduce the recognizable diversity to only a fraction of the biocenosis. The Lower Cretaceous (~115 Ma), Mill Canyon Dinosaur Track Site (MCDT) in the Ruby Ranch Member of the Cedar Mountain Formation near Moab, Utah, developed in a lacustrine shoreline setting and the trackway bed was silificified during diagenesis. Pustularichnus rebeccahuntfosteri, a distinct microbially induced sedimentary structure (MISS), facilitated in the preservation of a remarkably diverse vertebrate ichnofossils. The silicification process has preserved an impressive microbial suite that was responsible for the generation of the MISS and that provides exceptional insight into the true diversity of these seldom preserved communities.

The collected MCDT slabs were decontaminated using an ultra-sound cleaner. Bedding plane and vertical cuts were studied by field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The best preserved MCDT microfossils are located on the bedding plane whereas those below the surface are more altered by diagenesis and mat degradation by heterotrophs. Fifteen morphotypes are recognized, including: single strand cyanobacteria, double strand fungal mycelium or/ bacteria, multiple strand fungal mycelium or/ bacteria, twisted strand bacteria, strands with associated amorphous masses (bacteria with EPS), polygonal (cow-web like) bacteria with EPS or fungal mycelium, capsular bacillus-type bacteria, isolated masses of EPS, isolated spheres and sphere clusters with rough textured fungal spores, isolated smooth spheric fungal spores, folded masses with irregular surfaces plant cuticles, spheres in amorphous matrix (bacteria with EPS), mini-polyhedric bacteria cysts, bacteria rods, and uniserial bacterial strands. This micropaleontological assemblage of the MCDT is one of the most diverse recognized of an ancient MISS community.