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Barren meandering streams in the modern Toiyabe Basin of Nevada, U.S.A., and their relevance to the study of the pre-vegetation rock record

Alessandro Ielpi and Mathieu G. A. Lapotre
Barren meandering streams in the modern Toiyabe Basin of Nevada, U.S.A., and their relevance to the study of the pre-vegetation rock record
Journal of Sedimentary Research (May 2019) 89 (5): 399-415

Abstract

Modern meandering streams devoid of plant life have long been ignored despite their relevance to the study of sedimentary landscapes in the long span of Earth's history that preceded the greening of continents. We present a sedimentologic and remote-sensing analysis of the McLeod Springs Wash, a small-scale, endorheic, and barren fluvial fan in the Toiyabe Basin of Nevada, USA. Fluvial channels therein undergo avulsion at the sub-decadal scale, and follow a morphodynamic cycle from low-sinuosity, higher-gradient, and sediment-starved streams into meandering, lower-gradient channels prone to overspilling. Sedimentation is purely clastic and, unlike in other arid-climate endorheic basins, water recharge maintains positive hydrologic budgets year-round such that any contribution to bank strength due to precipitation of evaporites is ruled out. Likewise, the unvegetated nature of the meandering channels excludes any direct biotic forcing on sedimentation, leaving an equilibrium between discharge, gradient, and bank strength aided by cohesive mud fractions as the main mechanism responsible for channel meandering. Point bars compose a volumetrically significant fraction of the McLeod Springs Wash's stratigraphic record, and consist of sub-meter-thick, fining-upward inclined ripple strata floored by intra-formational conglomerate. Their sedimentary record remains non-diagnostic unless morphodynamic analyses based on accretion and paleoflow vectors are integrated. Interpreting river planform from these deposits is complicated by swift channel avulsion and migration relative to alluvial aggradation, which make the preservation of entire channel-bar complexes exceptional. We conclude that a significant bias may exist against the interpretation and volumetric estimation of the pre-vegetation meandering-fluvial rock record, and that the application of classic point-bar models based on inclined heterolithic stratification to Ordovician and older rocks is intrinsically flawed.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 89
Serial Issue: 5
Title: Barren meandering streams in the modern Toiyabe Basin of Nevada, U.S.A., and their relevance to the study of the pre-vegetation rock record
Affiliation: Laurentian University, Harquail School of Earth Sciences, Sudbury, ON, Canada
Pages: 399-415
Published: 201905
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
Accession Number: 2019-081141
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
N35°00'00" - N42°00'00", W120°00'00" - W114°04'60"
Secondary Affiliation: Harvard University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 201943
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