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Aeolian strata – the preserved products of wind-transported sediment – provide important information about atmospheric processes, climate, and surface conditions at the time the strata were deposited. Careful interpretation of the sedimentary texture, facies, and their architecture yields information about changes in sediment transport processes, dune morphology, and transport direction over time. Interpreting such strata correctly yields vital information that can be used to calibrate palaeo-atmospheric circulation models. Stimson formation sandstones exposed at the Greenheugh pediment record evidence of frequent facies changes and architectural arrangements within a vertical succession, interpreted to be caused by changes in wind direction at multiple time scales.
Stimson formation rocks exposed in the pediment are subdivided into 3 intervals, recording 3 distinct depositional phases. The lower Hutton interval is characterised by compound cross-sets composed of northeast-dipping cross-sets and bounded by northwest-dipping bounding surfaces. This records migration of oblique compound dunes (draas) toward the north-northeast. The central Ladder interval is characterised by a south-dipping planar cross-set, which records southward migration of a straight-crested dune. Within this interval, interstratified avalanche and wind ripple strata record sediment transport across, and oblique to, the dune crest. The upper Edinburgh interval is records westward-dipping trough cross-bedding, recording migration of sinuous-crested simple dunes.
These strata record sediment transport by the wind at multiple temporal scales. The Hutton section records the northward migration of large, slow-migrating draas, driven by competing winds blowing from obtuse angles. This is was followed by a sustained episode of wind reversal driving dunes up-slope (possibly 0.5-2 k Mars years), preserved as the Ladder interval. Planar cross-sets are also indicative of short-term wind reversals. Interstratified avalanche and wind ripple strata are interpreted to have arisen from seasonal changes in wind direction. Finally, the Edinburgh interval indicates a final episode of unidirectional wind transport to the west.