Numerical modelling of fan-shaped fluvial deposits in low-latitude regions of Mars and their relationship to basin boundary conditions
Abstract
Fan-shaped sedimentary deposits are common in the low latitudes of Mars. These features commonly form at breaks in slope associated with either crater rims or the topographic dichotomy between the southern highlands and the northern lowlands. A prominent example of these deposits occurs at the terminus of Hypanis Valles (11.2º N, 45.5º W), where multiple depositional lobes span an area of >1000 km2 at the transition from Xanthe Terra to the Chryse basin. These deposits have been interpreted as originating from a delta or an alluvial fan. In the delta scenario, the deposits formed due to a downstream decrease in sediment transport capacity as a channel entered a standing body of water in the northern lowlands. Alternatively, the deposits may instead represent the remnants of an alluvial fan, where deposition was triggered solely by the slope break at outlet of Hypanis Valles. These end-member scenarios differ markedly in their implications for the presence of an ancient, northern ocean. Yet the potential for distinguishing between these depositional scenarios from orbital data is incompletely understood, particularly for partially preserved deposits that lack features diagnostic of deltaic sediments (e.g., preservation of a topset-foreset angular unconformity). We hypothesize that (1) typical topographic transitions at the hemispheric dichotomy are sufficient to generate fan-shaped deposits without standing bodies of water, and (2) the presence or absence of a standing body of water drives distinct spatial patterns in deposit thickness that, if preserved, are potentially distinguishable from orbit. To test these hypotheses, we used a numerical model of landscape evolution, MARSSIM, that models erosion, sediment transport, and deposition but does not include hydrodynamic backwater effects. Model runs were informed by the regional geomorphic context of the Hypanis fan, with a catchment and feeder channel that span a regional slope break from S = 0.004 upstream to S = 0.001 downstream. We will present results from model case studies for scenarios without an ocean (alluvial fan deposition) and versus those with an ocean at either a fixed or a varying base-level (fan-delta deposition). By comparing predictions for deposit thickness between these scenarios, we will reassess the potential for orbital analyses to reconstruct basin boundary conditions from deposits created by ancient environmental flows on Mars.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP24A..02L
- Keywords:
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- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1826 Geomorphology: hillslope;
- HYDROLOGY;
- 5415 Erosion and weathering;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS