STRATIGRAPHIC CONTEXT OF BRADBURY RISE CONGLOMERATES IN THE MSL LANDING ELLIPSE

After Curiosity’s landing on Bradbury Rise, the first rocks encountered along the initial traverse to Yellowknife Bay were conglomerates. These conglomerates have clasts up to 1 cm in diameter, many of which have eroded from the outcrop and produce a pebbly lag. Orbital mapping using 0.25 cm/pixel orthophotos classified the surface as the ‘hummocky plains’ unit (HP) due to the smooth image texture and subdued crater forms that provide the major topographic relief. The HP unit was initially mapped as laterally extensive across the landing ellipse, but appears dissected by several other geologic units. The traverse to Murray Buttes, so far, reveals a patchy, though seemingly continuous outcrop of conglomerates beneath the rover. Outcrops like Twin Cairns Island, Elsie Mountain, and many others, appear topographically above conglomeritic material capped with smoother, finer-grained textures. Some fine-grained units are topographically lower than surrounding conglomeritic units, as is the case in and around the Kimberley geologic waypoint. However, isolated sandstone units almost always exist in topographic lows, draping and thinning towards conglomeritic ridges. One interpretation is these sandstone units are a later deposition over an older conglomeritic surface shaped by heavy degraded crater forms. The HP surface near the Kimberley resembles the surrounding bajada-like surface expression east of the Peace Vallis fan minus the sandstones. HP unit elevation differences over several kilometers are on order of 15 m from Bradbury Landing (~-4500 m) to the Kimberley (~-4485 m). A cross-section from the Kimberley heading north for ~1 km reveal a similar topographic offset (~20 m). If the HP unit does represent a continuous conglomeritic deposit, its surface dips slightly towards the north away from Aeolis Mons (i.e. Mt. Sharp). Whether this points to its origin from the rim or mound remains unclear. Further investigation of the relationships of the conglomerates with other geologic units is necessary to elucidate their proper stratigraphic position.