DETERMINING THE CHEMOSTRATIGRAPHIC RECORD OF THE CEDAR MOUNTAIN FORMATION USING δ13CORG ISOTOPES

Stikes Quarry UT, holds several well-preserved Utahraptor skeletons within a predator-trap style deposit. It is found within the upper Yellow Cat Member of the Cedar Mountain Formation, an Early Cretaceous aged terrigenous deposit. Previous work by our research team suggests the prominent C3 negative C-isotope excursion (~120 Ma) found at the base of the Aptian occurs within the upper part of the Yellow Cat Member. This negative C-isotope excursion (CIE) reaches a minimum of -29.5‰ VPDB. In an attempt to correlate these sections and to determine the age of the Utahraptor remains at Stikes Quarry, we sampled a stratigraphic section every 25 cm, spanning a total thickness of 42.5 m for bulk organic C-isotope values.

A total of 116 samples have been decarbonated in 3M HCl, rinsed, dried, and will be wrapped in 5 x 9 mm tin capsules. Samples will be analyzed on an elemental analyzer attached to a ThermoFinngan Delta Plus Isotope Ratio Mass Spectrometer at the University of Arkansas Stable Isotope Laboratory. We hypothesize that a prominent negative C-isotope value as low as approximately -29‰ VPDB will be preserved in the upper part of the Yellow Cat Member above the first occurrence of carbonate but below the overlying Poison Strip Sandstone.

Our data has important implications for determining the age of dinosaurs within the Cedar Mountain Formation and understanding the evolutionary changes that occur during the deposition of the Formation.