DEPOSITION OF A RICH MICROVERTEBRATE LOCALITY IN THE CRETACEOUS KAIPAROWITS FORMATION, GRAND STAIRCAISE-ESCALANTE NATIONAL MONUMENT (GSENM), UTAH, USA

The Campanian Kaiparowits Formation records the rapid deposition of sediments in a low-lying fluvial system in southeastern Larimidia. Abundant, well-preserved freshwater and terrestrial fossil faunas and floras are likely the result of high depositional rates and have been the subject of numerous taphonomic studies. While vertebrate microsites are among the most diverse and significant fossil localities in the Kaiparowits Fm., their deposition and taphonomy have not been extensively investigated. A recently discovered microvertebrate locality in the middle unit of the Kaiparowits Fm. has thus far yielded hundreds of microfossil elements comprising several dozen genera of freshwater and terrestrial vertebrates and invertebrates. The locality consists of two densely fossiliferous and laterally extensive <1 to 2m thick mudstone horizons overlain by a poorly preserved carbonaceous shale. The two primary fossil bearing horizons are distinct, separated by a <1m thick zone with markedly less abundant fossil material. A fine-scale stratigraphic analysis of the site, paired with surface and screenwash fossil collection suggests the accumulations of vertebrate and invertebrate fossils were most likely formed through overbank processes. Highly bioturbated sediments together with weakly developed paleosols suggest floodplain pond and channel fills progressing upward to a shallow, vegitated environment above the fossil bearing horizons. Microanalysis of the locality's sediments paired with local analysis of the sequence of channel and floodplain sedimentation may help predict where other rich microvertebrate localities will be found in the Kaiparowis Fm. and should aid in reconstructing the overall paleoenvironment of the Kaiparowits Fm.