TRANSTENSIONAL FAULTING IN THE SOUTHWESTERN GREAT BASIN GOVERNS EVOLUTION OF ENDANGERED AQUATIC SPECIES

In the middle Miocene, the southwestern Great Basin (between Sierra Nevada, CA, and Spring Mountains, NV) constituted a relatively moist highland with a continuous stream network. Today, the landscape consists of isolated and arid basins. Tectonic dissection of this Miocene landscape was driven by the transition from large-magnitude extension to development of the modern system of transtensional pull-apart basins. This tectonic evolution, along with changing climate, rerouted hydrological drainage networks (including groundwater) by disconnecting formerly continuous drainages and opening new connections. These changes separated and reconnected populations of various obligate aquatic organisms. Many of these endemic organisms exist in very restricted habitats within the present landscape and are therefore classified as threatened or endangered. We seek an understanding of the role that the extensive transtensional fault system evolution has played in the linked hydrological and biological state of affairs.

Here, we couple models of tectonics, landscape evolution, climatic variations, and biological evolution over the last 12 Myr to develop an understanding of the interplay between these systems. A kinematic fault model constitutes the framework for a TISC (Tectonics, Isostacy, Surface transport, Climate) model that simulates the effects of faulting on topography, erosion and sedimentation, and drainage networks. The climate model drives the atmospheric component of the linked terrestrial system. The coupled physical models successfully reproduce the basic configuration of the modern fault network, topography, climate, and hydrological system at the end of 12 Myr of evolution.

Using the TISC reconstruction we have quantified the history of hydrological connections and disconnections, which shows a high degree of variability over time. We have compared this history with the frequency of biological speciation events for aquatic species in the region. The hydrological history and the speciation history show a high degree of congruence, demonstrating that the initiation and linking of the faults in the region has governed the evolution of the aquatic organisms in the region, thus resulting in many unique species that today are threatened or endangered.