Abstract
The purpose of this field trip is to provide an overview of Miocene basin development in the Lake Mead region, demonstrate how basin-fill deposits reflect tectonic activity on a variety of structures, and highlight the work of Ernie Anderson in this region. The Basin and Range province is superb for the study of major normal and strike-slip fault systems that accommodate large-magnitude extension. Within this province, the Lake Mead region provides exceptional exposures of synextensional Miocene basins and faults and is a transition zone between predominantly half-graben-style basins and ranges to the north and the highly extended Colorado River Extensional Corridor to the south. The region also embraces a change from thick Phanerozoic sedimentary rocks in the north to Precambrian crystalline basement rocks overlain by late Tertiary volcanic rocks in the south. The early Paleozoic "Cordilleran hingeline" and the southeast margin of east-directed Mesozoic thrusting are also within this transition zone, but the area contains a strong overprint of late Tertiary tectonism. This overprint is strongest near the intersection between two major strike-slip fault systems: the right-lateral Las Vegas Valley shear zone and the left-lateral Lake Mead fault system. Miocene sedimentary rocks record the onset of major extension and the development of numerous, complex structures. Details of the extension and the resulting complexity are not fully understood and many issues remain unresolved. The relative importance of normal versus strike-slip faults is debated as are the details of how and why faults develop through time.