Earth and Planetary Sciences ETDs


Kevin Hobbs

Publication Date



This dissertation follows the hybrid format as defined by the Office of Graduate Studies at the University of New Mexico. The three chapters herein were prepared as manuscripts to be submitted for publication to peer-reviewed journals in the field of Earth sciences. Chapter 1 will be submitted to New Mexico Geology. Chapter 2 will be submitted to Geology. Chapter 3 will be submitted to the Geological Society of America Bulletin. The main theme of these works is an exploration of paleoenvironmental conditions recorded in the Paleocene siliciclastic sediments of the San Juan Basin, northwestern New Mexico. Chapter 1 is an investigation of the lithologic and stratigraphic properties of Cretaceous and Paleogene terrestrial siliciclastic rock units in the San Juan Basin. I used petrography, stratigraphy, and geochemistry to show that marked changes occurred in sedimentation styles, sedimentary sources, and regional landscape evolution in the study area during the Laramide Orogeny and that these changes caused observable trends in San Juan Basin rocks. Chapter 2 explores the enigmatic silcretes of the Nacimiento Formation. My work shows that these silcretes represent a product of silica diagenesis that cannot be explained using currently accepted models of silcrete genesis and that significant accumulation of volcanic ash occurred in the Paleocene San Juan Basin. Chapter 3 is an exploration of the paleosols preserved in the Nacimiento Formation. This work shows that widely used methods of estimating paleoclimate conditions based upon the geochemical composition of paleosols will produce inaccurate estimates in many realistic sedimentary basin environments. The major properties of Nacimiento Formation paleosols appear to be controlled by non-climate factors. I show that the evolution of a fluvial system can explain the observed trends.

Degree Name

Earth and Planetary Sciences

Level of Degree


Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

McFadden, Leslie

Second Committee Member

Weissmann, Gary

Third Committee Member

Williamson, Thomas




Sedimentology, Stratigraphy, Paleopedology, Paleoclimatology, San Juan Basin

Document Type