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13: Geomorphic evolution of the San Luis Basin and Rio Grande in southern Colorado and northern New Mexico

By
C.A. Ruleman
C.A. Ruleman
U.S. Geological Survey, Geosciences and Environmental Change Science Center, Denver Federal Center, Denver, Colorado 80225, USA
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M.N. Machette
M.N. Machette
Paleo Seis Surveys LLC, Port Townsend, Washington 98368, USA
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R.A. Thompson
R.A. Thompson
U.S. Geological Survey, Geosciences and Environmental Change Science Center, Denver Federal Center, Denver, Colorado 80225, USA
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D.P. Miggins
D.P. Miggins
Oregon State University, College of Earth, Ocean, and Atmospheric Sciences, Corvallis, Oregon 97331, USA
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B.M. Goehring
B.M. Goehring
Tulane University, Department of Earth and Environmental Sciences, New Orleans, Louisiana 70118, USA
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J.B. Paces
J.B. Paces
U.S. Geological Survey, Geosciences and Environmental Change Science Center, Denver Federal Center, Denver, Colorado 80225, USA
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Published:
January 01, 2016

Abstract

The San Luis Basin encompasses the largest structural and hydrologic basin of the Rio Grande rift. On this field trip, we will examine the timing of transition of the San Luis Basin from hydrologically closed, aggrading subbasins to a continuous fluvial system that eroded the basin, formed the Rio Grande gorge, and ultimately, integrated the Rio Grande from Colorado to the Gulf of Mexico. Waning Pleistocene neotectonic activity and onset of major glacial episodes, in particular Marine Isotope Stages 11–2 (~420–14 ka), induced basin fill, spillover, and erosion of the southern San Luis Basin. The combined use of new geologic mapping, fluvial geomorphology, reinterpreted surficial geology of the Taos Plateau, pedogenic relative dating studies, 3He surface exposure dating of basalts, and U-series dating of pedogenic carbonate supports a sequence of events wherein pluvial Lake Alamosa in the northern San Luis Basin overflowed, and began to drain to the south across the closed Sunshine Valley–Costilla Plain region ≤400 ka. By ~200 ka, erosion had cut through topographic highs at Ute Mountain and the Red River fault zone, and began deep-canyon incision across the southern San Luis Basin. Previous studies indicate that prior to 200 ka, the present Rio Grande terminated into a large bolson complex in the vicinity of El Paso, Texas, and systematic, headward erosional processes had subtly integrated discontinuously connected basins along the eastern flank of the Rio Grande rift and southern Rocky Mountains. We propose that the integration of the entire San Luis Basin into the Rio Grande drainage system (~400–200 ka) was the critical event in the formation of the modern Rio Grande, integrating hinterland basins of the Rio Grande rift from El Paso, Texas, north to the San Luis Basin with the Gulf of Mexico. This event dramatically affected basins southeast of El Paso, Texas, across the Chisos Mountains and southeastern Basin and Range province, including the Rio Conchos watershed and much of the Chihuahuan Desert, inducing broad regional landscape incision and exhumation.

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GSA Field Guide

Unfolding the Geology of the West

Stephen M. Keller
Stephen M. Keller
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
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Matthew L. Morgan
Matthew L. Morgan
Colorado Geological Survey Colorado School of Mines 1801 19th Street Golden, Colorado 80401, USA
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Geological Society of America
Volume
44
ISBN print:
9780813756448
Publication date:
January 01, 2016

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