Paper No. 4
Presentation Time: 8:50 AM
AN OVERVIEW OF PAST DEPOSITIONAL ENVIRONMENTS EXPLORED BY THE CURIOSITY ROVER AT BRADBURY LANDING AND YELLOWKNIFE BAY, GALE CRATER, MARS
The Mars Science Laboratory Curiosity rover examined a series of rock outcrops during its 500-meter traverse east from Bradbury landing to Yellowknife Bay. Upon landing, the rover drove across Bradbury rise, a topographic high located several kilometers north of Mt. Sharp and down slope from the Peace Vallis fan. On the hummocky plains of Bradbury rise, the rover encountered isolated outcrops of pebble conglomerates representing the first in-situ evidence for sustained fluvial transport over the martian surface. Curiosity then crossed a major unit boundary as it descended into Yellowknife Bay, an embayment characterized from orbit by bedded, fractured, and light-toned rocks mapped as part of a distal fan facies. Here the rover characterized a 5 meter-thick interval of continuously exposed rocks informally named the Yellowknife Bay formation. The Yellowknife Bay formation is primarily a sedimentary siliciclastic assemblage of bulk basaltic composition representing deposition in a fluvio-lacustrine environment. The Yellowknife Bay formation has been split into four members (from base to top): the Sheepbed, Gillespie Lake, Point Lake, and Shaler members. The clay-bearing mudstones of the basal Sheepbed member suggest suspension settling in a distal alluvial or proximal lacustrine setting. A sharp contact traceable in orbital images for hundreds of meters separates the Sheepbed member from the Gillespie Lake member. The Gillespie Lake member consists of sheet-like beds of poorly sorted medium- to coarse-grained sandstone. The lateral continuity of these beds and the lack of channel bodies in the Gillespie Lake member indicate deposition in distal fan lobes. Overlying the Gillespie Lake member is the Point Lake member, characterized primarily by the presence of centimeter-scale vugs. Both volcanic and sedimentary interpretations are being considered for this enigmatic member. The overlying Shaler member consists of coarse-grained trough cross-bedded sandstone and pebble beds and recessive finer-grained intervals consistent with a fluvial environment dominated by bedload and suspended load transport. A set of diagenetic features observed throughout the Yellowknife Bay section suggests a complex aqueous history involving multiple phases of alteration.