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Arid Continental Rift Systems: Exploration of the Rio Grande Rift Basin Complex

Abstract

The Rio Grande rift system (RGR) of New Mexico and Colorado, U.S. is a Tertiary age system that provides an excellent analog for arid, continental rifts worldwide (e.g., Red Sea Rift). Its extensive development, friendly location and data density make the RGR ideal for study. Such analogs provide important insights into rifts worldwide which host up to 30% of the world's giant hydrocarbon fields (Mann et al., 2001), several giant copper and other mineral deposits (Neoproterozoic rifts of southern Africa), and are important regional aquifer systems throughout the world. The strong link between extensional tectonics and sedimentary fill produces complex cross-basin changes in strata thickness and facies distributions that are poorly understood and likely unmappable in deeper subsurface studies alone. This research focuses on the RGR's three northernmost basins (Albuquerque, Española and San Luis basins) their differences in structure, fill and sub-basins, with emphasis on the rift's initiation and climax periods. Cross-sections denote asymmetrical changes across the basins, indicative of potentially overlooked sub-basins. Newly acquired geophysical data and cores are integrated with lithology information from 1000's of water wells to form a highly detailed stratigraphic framework of each temporal segment of the RGR. This data combined with outcrop studies will examine both the active and inactive margins of each phase of basin development and enable improved understanding of sediment sources, channel architectures and orientations and axial versus transverse architecture and identification of current previously unidentified facies, and corroborate additional documentation for pre-, post- and syn-rift sediments within each sub-basin. Currently the thickest documented syn-rift sediments (a combination of piedmont facies and alluvial/fan, axial river fluvial sediments) are located in the Albuquerque basin. Preliminary results suggest extensional events, and the timing of surrounding and overlapping faults influenced the stratigraphic differences within the basins more than initially addressed. It can be hypothesized that recent geophysical data and a new scope of fieldwork to be conducted will result in more conclusive interpretations related to fill, fill percentages and feeder sources, especially related to the Espanola Basin and the seismically slow parts of the RGR which are located to the east and west of the currently designated boundaries of the rift.