‘HIGH’ BUT NOT SO DRY ON AEOLIS MONS: TRANSIENT LAKE SYSTEMS IN HESPERIAN DESERTS IN GALE CRATER.
Résumé
The stratigraphy preserved within Aeolis Mons in Gale crater (Mars) shows a major transition from a phyllosilicate-bearing unit, which in situ data show is composed of mudstone-rich strata (with subordinate sandstones) recording deposition in lacustrine to fluvial settings into a major sulfatebearing
unit that is hundreds of meters thick (the Layered Sulfate-bearing unit (LSu)) [1,2,3,4]. The origin of the LSu unit is not yet constrained.
Comparison to other terrains on Mars has led to the hypothesis that the transition from clay minerals to sulfates records a planet-wide change in climate from relatively warm and wet to cold and arid [1]. A leading question is whether this transition is so unidirectional. The lower section of the LSu (claysulphate transition stratigraphy) contains strongy diagenetically altered strata or stacked, cross-bedded facies (Dunnideer and Port Logan mbs of the Mirador fm) that likely records a purely dry aeolian dune environment [5]. However, higher up in the studied section within the Contigo member, we observe sandstone lenses interstratified within aeolian strata that show distinctive sedimentary structures indicative of deposition by lacustrine and fluvial processes in shallow interdune depressions [6]. In late 2022, Curiosity investigated a distinctive dark-toned, resistant unit even higher within the sulfate-bearing stratigraphy of Aeolis Mons – the “Marker Band” [1,4,7,8]. Stratigraphically it has been informally designated the Amapari member of the Mirador formation (Mt. Sharp gp). This unit can be traced for tens of kilometers around Aeolis Mons [7], and from early in the mission was considered an important geologic target for investigation [1]. The key question concerning the “Marker Band” is what geological process led to its formation and how does it relate to the Layered Sulfate-bearing unit. Orbital-scale observations led to favored interpretations of the “Marker Band” as a volcanic ash deposit or a more indurated sulfate unit [7]. The first edge-on view in the distance favored an eolian deflation surface [3]. Here we describe the sedimentology of unit and go on to discuss initial implications for paleoenvironmental and paleoclimatic interpretations.
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