SEDIMENTOLOGICAL FRAMEWORK, SEQUENCE STRATIGRAPHY, AND RELATIVE DATING OF GEOLOGICAL EVENTS IN THE LANDING ELLIPSE OF THE CURIOSITY ROVER, GALE CRATER, MARS

Four rock units and two surfaces were identified and mapped by the MSL Science Team members in the landing ellipse of the Curiosity Rover in Gale crater, Mars (Calef et al., 2013; Rice et al., 2013; Stack et al., 2013; Sumner et al., 2013). This investigation summaries the results of previous studies and provides the following new interpretations: (1) the relationships among the four rock units and the two surfaces, (2) the origins of the two surfaces, (3) the presence of three sequences, (4) the relative age of geological events, and (5) the date when nearly all geological processes ended in Gale crater.

The Striated Unit and the Murray formation are the oldest rocks exposed. The first crops out in several patches in the central part of the study area and consists of over 1000 m of rhythmicaly layered conglomerates and sandstone that strike N65ºE and dip 20º SE. The Striated Unit transitions into 300 m of mudstone and sandstone layers of the Murray formation in the southern part of the landing ellipse.

The Rugged Terrain Unit overlies both the Murray formation and the Striated Unit throughout the landing ellipse. It is few meters thick and consists of thick- to thin-bedded layers of sandstone and conglomerate.

The Hummocky Plains Unit is also few meters thick and primarily fills impact craters on top of the Rugged Terrain Unit. It is dark in color, displays smooth surface and consists of conglomerate in few localities investigated.

The Fractured Surface separates the Striated Unit and the Murray formation from all overlying strata. It is an erosional unconformity that represents the removal of 3 - 4 km of strata during the excavation of margins of Gale crater.

The Cratered Surface is actually the top surface of the Rugged Terrain Unit and is characterized by high concentrations of impact craters. We attribute its formation to the Late Heavy Bombardment event at the Noachian - Hesperian boundary. This indicates that virtually all geological events of the landing ellipse formed during Noachian time because the Cratered Surface is nearly the youngest event there. The Hummocky Plains Unit is the only rock unit that was deposited afterward.

The two unconformable surfaces divide the four rock units into three stratal packages, or sequences. The three sequences could have formed millions of years apart.