MIOCENE STRATIGRAPHY, VERTICAL AXIS ROTATIONS, AND TRANSTENSIONAL TECTONICS OF THE LAKE MEAD AREA, NEVADA: AN EXAMPLE OF PAUL UMHOEFER’S DEDICATION TO MENTORSHIP, TEACHING, AND RESEARCH

Dr. Paul Umhoefer of Northern Arizona University, was passionate about transtensional tectonics and basins. His contributions to unraveling the complicated stratigraphy and tectonics of the Lake Mead area spanned over a decade of research and student mentorship. Paul used the exceptional rock exposures of the area as a natural classroom and research area for over a dozen graduate students. Paul was a passionate mentor with infectious energy and an excitement for geology that naturally inspired his students. Paul taught his students to make astute and detailed field-based observations and apply them to the regional tectonics. He was a tireless advisor, never hesitating to spend days in the field or hours poring over maps and literature with his students, while always keeping things entertaining and fun.

Paul and his students, and colleagues covered over 500 km² of the Lake Mead area with detailed (1:5,000 and 1:10,000 scale) geologic and lithofacies mapping, collected thousands of structural measurements, measured and sampled thousands of meters of Miocene section for tephrochronology, geochronology, and paleomagnetic analysis. These data refine 1) the stratigraphic framework, chronology, and nomenclature of the Miocene Rainbow Gardens Formation and the Horse Spring Formation, 2) the structural model for the accommodation of up to 100° of clockwise vertical axis rotations related to dextral shear on the northwest-striking Las Vegas Valley shear zone, 3) the structural model for strain accommodation at the intersection of the dextral Las Vegas Valley shear zone and the sinistral Lake Mead fault system, and 4) the timing and style of tectonics that accommodated 60 km of west-southwest transport of the Frenchman Mountain block.