T19 Active and Anticipated Science from Planetary Science Research, Programs and Future Flight Projects

Sunday, 22 September 2024
8:00 AM - 12:00 PM
213A

THE GEDIZ VALLIS RIDGE: CURIOSITY’S IN-SITU INVESTIGATIONS OF A REMNANT LATE-STAGE DEBRIS-FLOW DOMINATED FAN ON MARS

Paper number: T19-14
Program: Technical Sessions
Time: 11:20 AM – 11:35 AM

Authors

Abstract

Recent studies using orbital imagery (HiRISE and CTX) have identified widespread fan-shaped deposits, interpreted as resulting from a combination of fluvial and debris-flow processes, across the surface of Mars that likely formed during the Hesperian and Amazonian periods. Curiosity’s in-situ observations of the Gediz Vallis Ridge (GVR) now provide our first cross-sectional observation of a fan on Mars. The deeply eroded landform lies near the base of Mt. Sharp at the outlet of a 127 km2 catchment. The fan was deposited unconformably on top of the Stimson formation – a laterally extensive aeolian sandstone that unconformably mantles the Greenheugh pediment. The stratigraphy of the remnant fan consists of a discontinuous fine-grained (≤ gravel size) basal unit above the Stimson that is unconformably onlapped by layered boulder-rich deposits. Onlapping boulder-rich strata are laterally discontinuous and exhibit bed thicknesses ranging from ~0.25 to 3 m, with a mean dip of four degrees (much gentler than the slope of the basal contact) oriented parallel to the ridge axis. Boulder-rich strata consist of two facies with variable occurrence and lateral extent up-section: 1) a light-toned, typically matrix-supported, boulder conglomerate with scattered erosionally resistant dark-toned cobble-to-boulder sized clasts and 2) a dark-toned, typically clast-supported, cobble-boulder conglomerate facies with occasional isolated light-toned clasts. Grain-size analysis from RMI data indicates similar median grain sizes (170-190 mm) in both facies with isolated 1-3 m boulders scattered throughout. The light-toned strata are interpreted to be debris flow deposits. The dark-toned strata are more likely fluvial in origin, probably derived from surface runoff that concentrated dark-toned boulders from the light-toned unit into channels and sheetflood deposits while destroying the relatively weaker light-toned boulders during transport. Such water-driven deposits call for a water source derived from Mt. Sharp, the eroded 5 km mountain at the center of Gale Crater. The fan is composed five distinct on-lapping depositional units, marked by changes in the frequency of the two facies. These changes likely record significant changes in the magnitude and frequency of surface runoff and sediment supply that may be a response to variable climate conditions.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403739

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.