Date of Graduation

8-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Geosciences (PhD)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Suarez, Celina A.

Committee Member

Hays, Phillip D.

Second Committee Member

Guccione, Margaret J.

Third Committee Member

Zachry, Doy L.

Fourth Committee Member

Tian, Z. Ryan

Keywords

Cretaceous; Diagenesis; Kaiparowits Formation; North America; Paleoclimate; Stable Isotope

Abstract

The Western Interior Basin of the North America preserves one of the best sedimentary and paleontological records of the Cretaceous in the world. The Upper Cretaceous Kaiparowits Formation is a rapidly deposited fluvial sequence and preserves one of the most complete terrestrial fossil record of the North America. Such a unique deposit provides an opportunity to investigate the interaction between the physical environment and ecology. In an effort to decipher such interaction, stable isotope composition of cements in sedimentary rocks, concretions and vertebrate fossils were analyzed.

Despite the difference in facies and sedimentary architecture, the isotope composition does not change significantly at ~110 m from the base of the formation. Among the well-preserved cement samples, stable isotope composition indicates a significant hydrologic change within the informal Middle unit; a 6.37‰ depletion in d13C and 3.30‰ enrichment in d18O occurs at ~300 m above the base of the formation. The isotope values indicate that the sandstone cements below 300 m were precipitated in a mixing zone between marine and terrestrial groundwater, whereas the cements in upper units were precipitated in a terrestrial groundwater.

Despite the difference in physical appearance (i.e. color and shape), the isotopic compositions of cements in concretions are similar to well-cemented sandstone bodies in similar stratigraphic positions. Isotope compositions of the host rock are similar to that of mudrock and weathered sandstone, suggesting the origin of cementing fluids for the sandstone and concretions were the same indicating that: 1) the concretions were formed in shallow groundwater and not related to the groundwater migration, or 2) all cements in upper Kaiparowits Formation are precipitated or altered during later stage groundwater migration.

Average d18Oc from each taxon show the same trend as the d18Op stratigraphic change, suggesting d18Oc is still useful as a paleoclimatic proxy. Compared to other Campanian formations, fossil d18Op are depleted for their paleolatitude, suggesting the Kaiparowits Plateau had higher input from high-elevation runoff, consistent with other paleoclimatic studies. Estimated d18Ow ranged between vadose influenced dry season values of -8.88‰ to high elevation runoff values of -13.76‰ suggesting dynamic hydrologic interactions.

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