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Publication Type:

Journal Article

Source:

Geological Society of America BulletinGeological Society of America Bulletin (2018)

Abstract:

<p>Vegetation-free fluvial meanders are exceptional on modern Earth, and their abundance in pre-Silurian rock records is debated. Whether or not landscapes devoid of plant life could sustain sinuous planforms is nonetheless a fundamental concept that could disclose parallels with extraterrestrial sedimentary realms. The sedimentology and morphometry of an extensive (∼200 km2) unvegetated meander plain in the lower Amargosa River (Death Valley, California, USA) is investigated through remote sensing and ground checking. Results reveal sinuous bends generated by channels &lt;2 m deep and &lt;35 m wide that migrated laterally for as much as 200 m at rates of &lt;1.5 m/year. The Amargosa River’s ephemeral regime excludes the proposal that discharge modulation directly aids meandering. Likewise, 97.7% of ground-checked meanders are devoid of plant life, ruling out direct control by vegetation on bank stability. Cohesion offered by mud-rich banks is predominant and aided by salt cementation, which also hinders wind erosion of fines. Overall, the meanders’ morphometry is in overlap with that of other sinuous (vegetated) channels, pointing to shared scalar properties. Meanders span over a continuum of a few large channels with lower aspect (width:depth) ratios and abundant smaller channels with higher aspect ratios. The migration of larger meandering channels generates distinctive scrolls and inclined accretionary packages; the migration of smaller widespread meanders only generate sub-tabular sets, producing an undistinctive depositional record. These results make the Amargosa River topical for the analogue modeling of pre-vegetation rivers, and suggest that unvegetated meanders might have been overlooked in the rock record.</p>

Notes:

HES