Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California

Abstract

Research Article| November 01, 2011 Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California Jeffrey S. Pigati; Jeffrey S. Pigati † 1U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, Colorado 80225, USA †E-mail: jpigati@usgs.gov Search for other works by this author on: GSW Google Scholar David M. Miller; David M. Miller 2U.S. Geological Survey, 345 Middlefield Road, MS-973, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Jordon E. Bright; Jordon E. Bright § 3School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA §Current address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA. Search for other works by this author on: GSW Google Scholar Shannon A. Mahan; Shannon A. Mahan 4U.S. Geological Survey, Denver Federal Center, Box 25046, MS-974, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Jeffrey C. Nekola; Jeffrey C. Nekola 5Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar James B. Paces James B. Paces 6U.S. Geological Survey, Denver Federal Center, Box 25046, MS-963, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (11-12): 2224–2239. https://doi.org/10.1130/B30357.1 Article history received: 21 Jun 2010 rev-recd: 16 Dec 2010 accepted: 29 Jan 2011 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey S. Pigati, David M. Miller, Jordon E. Bright, Shannon A. Mahan, Jeffrey C. Nekola, James B. Paces; Chronology, sedimentology, and microfauna of groundwater discharge deposits in the central Mojave Desert, Valley Wells, California. GSA Bulletin 2011;; 123 (11-12): 2224–2239. doi: https://doi.org/10.1130/B30357.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract During the late Pleistocene, emergent groundwater supported persistent and long-lived desert wetlands in many broad valleys and basins in the American Southwest. When active, these systems provided important food and water sources for local fauna, supported hydrophilic and phreatophytic vegetation, and acted as catchments for eolian and alluvial sediments. Desert wetlands are represented in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits. Groundwater discharge deposits contain information on the timing and magnitude of past changes in water-table levels and, thus, are a source of paleohydrologic and paleoclimatic information. Here, we present the results of an investigation of extensive groundwater discharge deposits in the central Mojave Desert at Valley Wells, California. We used geologic mapping and stratigraphic relations to identify two distinct wetland sequences at Valley Wells, which we dated using radiocarbon, luminescence, and uranium-series techniques. We also analyzed the sediments and microfauna (ostracodes and gastropods) to reconstruct the specific environments in which they formed. Our results suggest that the earliest episode of high water-table conditions at Valley Wells began ca. 60 ka (thousands of calendar yr B.P.), and culminated in peak discharge between ca. 40 and 35 ka. During this time, cold (4–12 °C) emergent groundwater supported extensive wetlands that likely were composed of a wet, sedge-rush-tussock meadow mixed with mesic riparian forest. After ca. 35 ka, the water table dropped below the ground surface but was still shallow enough to support dense stands of phreatophytes through the Last Glacial Maximum (LGM). The water table dropped further after the LGM, and xeric conditions prevailed until modest wetlands returned briefly during the Younger Dryas cold event (13.0–11.6 ka). We did not observe any evidence of wet conditions during the Holocene at Valley Wells. The timing of these fluctuations is consistent with changes in other paleowetland systems in the Mojave Desert, the nearby Great Basin Desert, and in southeastern Arizona, near the border of the Sonoran and Chihuahuan Deserts. The similarities in hydrologic conditions between these disparate locations suggest that changes in groundwater levels during the late Pleistocene in desert wetlands scattered throughout the American Southwest were likely driven by synoptic-scale climate processes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.