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A MAGNIFICENT OUTCROP IN THE KIMBERLEY REGION OF GALE CRATER, MARS
At the base is a gray conglomerate that consists of varicolored clasts ranging in size from silt to cobble. It is highly unsorted and its poorly-defined beds strike about N60ºE and dip 3-5ºSE. The bottom contact of the gray conglomerate is not exposed, so its thickness is not known. It extends beyond the outcrop and becomes the Hummocky Plains Unit of the geological map of the landing ellipse.
The middle interval forms a single, one meter thick cross bed layer that consists of dark gray coarse sandstone and sandy conglomerate. It extends across the entire length of the outcrop. The basal parts of cross beds are tangential to the underlying gray conglomerate, but the tops are truncated. The dip of the cross beds ranges from 20ºNE to 40ºNE.
The top interval consists of three rhythmically-deposited packages of rocks that were previously mapped as the Striated Unit of the landing ellipse's geological map. Each package begins with thinly-bedded sandstone or conglomerate, followed by cross-bedded sandstone, and terminated by resistant laminated sandstone. Layers strike about N65ºE and dip about 10ºSE.
The three lithologic intervals represent three separate depositional environments. Sedimentological characteristics of the basal gray conglomerate suggest deposition in an alluvial fan, most likely extending from the northern wall of the crater. We interpret the middle cross bed layer to be a fluvial origin, likely a bar in a river. Cross bed orientations suggest that the bar was migrating northeast. The fining upward of grain size and the succession of sedimentary structures suggest that three layers of the top interval are most likely turbidites deposited in a subaqueous environment in a lake. The sequence of lithogies in this outcrop suggest that sedimentation began with alluvial fan, followed by an episode of fluvial process, and ended with lacustrine environment.