ANALYSIS OF FRESHWATER LIMESTONES AT THE CLEVELAND-LLOYD DINOSAUR QUARRY, EMERY COUNTY , UTAH

A dense micritic limestone (10 to 120 cm thick) overlies the dinosaur-bone-bearing calcareous mudstone at the Cleveland-Lloyd Dinosaur Quarry. This is one of many localized freshwater limestone units in this part of the Morrison Formation. Bones at the quarry mostly occur in the mudstone, but some are incorporated into the overlying limestone. Additional bones are located within a limestone unit located ~ 0.5 km northeast of the quarry. Utilization of rare earth element (REE) signatures in bones determined whether bones incorporated in the quarry limestone were re-worked from the mudstone, or deposited during an event unique from that represented by bones in the mudstone. REE data were also used to evaluate the relationship between the outlying limestone to the northeast and the quarry limestone. The REE data suggest that bones incorporated in the quarry limestone represent re-worked material from the underlying mudstone. REE data from bones in the outlying limestone indicates that the bones represent an event unique from that represented by the bones in the quarry site. In addition to the geochemical analyses, this study used paleontology, detailed rock descriptions, and thin section analyses to reassess the stratigraphy of the quarry site. The above data was used to determine a possible depositional environment scenario. It was determined that there is a second limestone unit above that which is present in the quarry. This second unit has been correlated with the quarry limestone in the past. The proposed depositional environment concurs with studies of the Morrison Formation, which suggests an alternating wet/dry environment.