GEOLOGY OF THE KIMBERLEY WAYPOINT, GALE CRATER: OBSERVATIONS FROM ORBIT AND MSL CURIOSITY

In May 2014, the Mars Science Laboratory (MSL) Curiosity rover completed a detailed investigation at its Kimberley waypoint using its full science instrument payload. From orbiter images examined before landing, the Kimberley area was identified as a key location to characterize stratigraphic relationships because of the erosional exposure of a complex stratigraphy and the prevalence of a geomorphic unit characterized by NE-trending lineations. The lineations of this “striated unit,” seen to occur in Mars Reconnaissance Orbiter HiRISE images over a region of several kilometers, are remarkably consistent in their trend directions of 65-75 degrees north. Because an equivalent to the striated unit had not previously been identified on Mars, and because these outcrops could help illuminate the relationship between Aeolis Palus and lower Aeolis Mons (informally, Mt. Sharp), this unit was selected as a high-priority science target for Curiosity along its traverse. The Kimberley waypoint, in particular, was selected to characterize the apparent good exposures and to test the stratigraphic relationships observed. On the ground, with its Mastcam and Navcam instruments, Curiosity observed the striated unit to consist of southward-dipping sandstone clinoforms with decimeter-thick beds. Mars Hand Lens Imager observations revealed grain sizes and laminae that are consistent with fluvial deposition. The southward-dipping sandstones are underlain by a conglomerate of mm- to cm-sized sub-angular clasts, and overlain by thinly-bedded, medium- to fine-grained sandstone with sub-meter-scale cross-stratification. These facies are overlain by massive, butte-forming rock with remnants of a fine-grained, dark-toned capping material. Variants of this same fining-upwards sedimentary sequence was observed in multiple locations along Curiosity’s immediate approach to Kimberley, increasing in elevation along the traverse to the south. We interpret these outcrops as fluvial sequences with a predominant flow direction to the south-southwest, consistent with a sediment source from the northern rim of Gale crater. Sediment might have been deposited in an aggrading system, which could explain the increasing elevations of these fluvial sequences in the direction of transport, and we evaluate alternative hypotheses.