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GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 215-3
Presentation Time: 2:15 PM

GLOBAL DISTRIBUTION OF ALLUVIAL FANS AND DELTAS ON MARS


MORGAN, Alexander M., Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 600 Independence Ave SW, Washington, DC 20560, WILSON, Sharon A., Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Independence Ave at 6th St, SW, Washington, DC 20560 and HOWARD, Alan D., Department of Environmental Sciences, University of Virginia, PO Box 400123, Charlottesville, VA 22904-4123

The distribution and morphology of alluvial fans on Mars can provide insights into the prevailing geologic, hydrologic, and climate conditions during their formation. We conducted a systematic global survey for these features using the near-global coverage of 7 m/pixel resolution CTX images, documented fan locations, obtained morphometric properties, and estimated surface ages using emplaced crater densities. We use these measurements to make inferences about their formation.

We identified ~1300 identified fan-shaped depositional landforms and categorized them into three distinct types:

(1) Alluvial fans (~800 features) are semi-conal landforms ranging in length from hundreds of meters to tens of kilometers with average slopes of 4°. These are generally sourced from deeply eroded alcoves and generally do not appear to have had a sediment or flow source beyond the crater rim.

(2) Stepped deltas (84 features) are characterized by their terraced topographic profile, generally steep slope (>7°, but varies widely), and deeply incised, low order source valleys.

(3) Deltas (65 features) have a low surface gradient of ~1-2° and are either branched features at the mouth of larger valley systems (e.g. the feature in Jezero crater) or unbranched features with little evidence for channelization, segmentation, or scarp dissection (e.g. the “Pancake Delta” in Gale crater).

We show that these features are much more widespread than previously reported but are not globally distributed. Alluvial fans and stepped deltas are primarily found within impact craters, and stepped deltas and deltas are more concentrated along the dichotomy boundary than alluvial fans.

Relative to their source catchment, martian alluvial fans are larger than their terrestrial counterparts, which is likely a consequence of no tectonic subsidence. Alluvial fans and stepped deltas predominately source from northern or southern crater rims. This is a strong indicator of control by solar insolation. Combined with the lack of evidence for groundwater we infer snowpack accumulation and melt to be the most likely source for alluvial fan-forming runoff. Crater counts of fan surfaces indicate the they were active during the late Hesperian to early Amazonian.

Session No. 215

T151. The G.K. Gilbert Award Session: Planetary Surface Processes from Mars to the Outer Solar System
Tuesday, 6 November 2018: 1:30 PM-5:30 PM
Room 236-237 (Indiana Convention Center)
Geological Society of America Abstracts with Programs. Vol. 50, No. 6
doi: 10.1130/abs/2018AM-317138
© Copyright 2018 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.
Back to: T151. The G.K. Gilbert Award Session: Planetary Surface Processes from Mars to the Outer Solar System
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