THE CLIMATE HISTORY OF MARS, ENCAPSULATED IN THE AEOLIS DORSA REGION (Invited Presentation)

North of the Highland-Lowland Boundary (HLB) and ~800 km east of Gale Crater, the Aeolis Dorsa region reflects landscape evolution – from a clement climate of rivers, possibly groundwater flow and lakes, to an arid aeolian regime – that encapsulates the global climate history of Mars. At the same time, the regional geomorphology gives evidence for local climatic variations. Regional topography is provided by the highstanding Aeolis and Zephyria plana, the two westernmost lobes of the Medusae Fossae Formation (MFF). Named for the extensive sinuous ridges (dorsa) interpreted as inverted fluvial deposits on the margins of the interplana depression, the region also exhibits a fluvial system revealed in thermal nighttime data, suggesting earlier fluvial activity. Early aqueous activity is also suggested by fluvial and possibly lacustrine units within craters in the interplana depression. Around the depression margins, the more numerous fluvial deposits are superposed by scattered alluvial fans, reflecting a transition in time and space from a more consistent to a more intermittent hydrology and associated climate. A geographic dichotomy in the fluvial and alluvial morphologies – meandering and debris flow deposits in the south, channel fills and sheet flood deposits in the north – is consistent with more clay in the south, implying greater weathering that is attributable to orographic precipitation along the HLB. Subsequent deposition is attributed to aeolian and/or volcaniclastic processes continuing to build the plana. The pervasive yardangs on the plana, along with the eroded crater morphologies in the interplana depression, reflect persistent abrasion by wind-blown sand, the same process that exhumed and inverted the alluvial and fluvial deposits. Some of this sand is covered and therefore immobilized by dust, although revealed by scour marks around knobs. Other sand deposits are darker, although dust devil tracks along dark sand sheet margins point to minimal to moderate dust cover. Thus, as in near-by Gale Crater, the AD deposits offer an at-a-station record of the climatic evolution of the red planet. Comparison and contrast with on-going discoveries of the Mars Science Laboratory will enable extension and extrapolation of the Gale Crater record to the AD region and western Medusae Fossae Formation.