The Hypanis Valles delta: The last highstand of a sea on early Mars?

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Title: The Hypanis Valles delta: The last highstand of a sea on early Mars?
Author(s): Peter, F
Gupta, S
Davis, J
Warner, N
Adler, J
Balme, M
Bell III, J
Grindrod, P
Sefton-Nash, E
Item Type: Journal Article
Abstract: One of the most contentious hypotheses in the geological history of Mars is whether the northern lowlands ever contained an oceanic water body. Arguably, the best evidence for an ocean comes from the presence of sedimentary fans around Mars' dichotomy boundary, which separates the northern lowlands from the southern highlands. Here we describe the palaeogeomorphology of the Hypanis Valles sediment fan, the largest sediment fan complex reported on Mars (area >970 km2). This has an extensive catchment () incorporating Hypanis and Nanedi Valles, that we show was active during the late-Noachian/early-Hesperian period (∼3.7 Ga). The fan comprises a series of lobe-shaped sediment bodies, connected by multiple bifurcating flat-topped ridges. We interpret the latter as former fluvial channel belts now preserved in inverted relief. Meter-scale-thick, sub-horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins. The inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of Hypanis Valles and descend ∼500 m in elevation. The progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water, assuming the elevation of the northern plains basin floor is stable. We interpret the Hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system. At its location at the dichotomy boundary, the Hypanis Valles fan system is topographically open to Chryse Planitia – an extensive plain that opens in turn into the larger northern lowlands basin. We conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least Chryse Planitia. Given the open topography, it is plausible that the Hypanis fan system records the existence, last highstand, and retreat of a large sea in Chryse Planitia and perhaps even an ocean that filled the northern plains of Mars.
Publication Date: 15-Oct-2018
Date of Acceptance: 27-Jul-2018
ISSN: 0012-821X
Publisher: Elsevier
Start Page: 225
End Page: 241
Journal / Book Title: Earth and Planetary Science Letters
Volume: 500
Sponsor/Funder: UK Space Agency
Funder's Grant Number: ST/L006413/1
Copyright Statement: © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (
Keywords: Science & Technology
Physical Sciences
Geochemistry & Geophysics
Mars geology
Mars ocean
02 Physical Sciences
04 Earth Sciences
Geochemistry & Geophysics
Publication Status: Published
Open Access location:
Online Publication Date: 2018-08-24
Appears in Collections:Earth Science and Engineering

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