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Fluvial stratigraphy of valley fills at Aeolis Dorsa, Mars; evidence for base-level fluctuations controlled by a downstream water body

Benjamin T. Cardenas, David Mohrig and Timothy A. Goudge
Fluvial stratigraphy of valley fills at Aeolis Dorsa, Mars; evidence for base-level fluctuations controlled by a downstream water body
Geological Society of America Bulletin (September 2017) 130 (3-4): 484-498

Abstract

Aeolis Dorsa, a large sedimentary basin on Mars, contains an array of fluvially dominated sedimentary deposits. These deposits preserve a record of fluvial erosion and deposition during early Martian history. We present evidence that some of these fluvial deposits represent incised valleys carved and filled during falls and rises in base level, which were likely controlled by changes in water-surface elevation of a large lake or sea. The valley stratigraphy consists of three low-albedo, channelized corridors, each several tens of kilometers long in the streamwise direction. Deposits composing the basal valley fills are characterized by laterally amalgamated point-bar strata confined between valley walls that preserve scoop-shaped segments cut by the erosive outer banks of meandering river bends. Both the point-bar deposits and valley walls were produced by a net-erosional river system. Subsequent valley-filling deposits are defined by both channels and associated overbank strata. The stacked channel-filling deposits are sinuous in form, but unlike the basal strata, they preserve no evidence of river migration. Within each valley, there are multiple sinuous ridges ranging from a few meters to several tens of meters thick, which we interpret as channel-belt deposits that have been topographically inverted via differential erosion. Evidence for channel avulsions and reoccupations, the overall cutting and filling patterns, and consistent up-section decreases in recorded channel migration support the interpretation of the low-albedo corridors as valley stratigraphy cut and filled in the presence of a migrating backwater zone. Crosscutting valleys require at least two episodes of base-level fall and rise at >50 m per episode. These base-level cycles are consistent with the presence of an ancient large lake, sea, or ocean and its fluctuating water-surface elevation. Additionally, channel bend asymmetry preserved in channel-belt deposits indicates a southeastern flow direction.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 130
Serial Issue: 3-4
Title: Fluvial stratigraphy of valley fills at Aeolis Dorsa, Mars; evidence for base-level fluctuations controlled by a downstream water body
Affiliation: University of Texas at Austin, Jackson School of Geosciences, Austin, TX, United States
Pages: 484-498
Published: 20170914
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 102
Accession Number: 2018-022484
Categories: Extraterrestrial geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 201812
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