Conclusions: The sedimentary rocks of Sinus Meridiani preserve a rich and complex geologic history, of which very little is presently known. The bedrock of both Meridiani Planum and the adjacent heavily cratered terrains can be described as a layered, cratered, and “valley-ed” volume. Orbiter images show a diversity of rocks in the form of erosional expression, relative albedo, and bedding styles. Material deposited in impact craters is usually different from the material deposited outside the crater, suggesting different depositional environments in close proximity (e.g., the crater may have been a lake or pond at the same time that the surrounding areas were not). No unambiguous, primary volcanic landforms or rock units are discerned. When deposited, the rocks were generally horizontally bedded except where dipping locally in response to previous, buried topography. Interbedded craters and valleys indicate the presence of buried surfaces, including erosional surfaces, representing unconformities in the rock record. Four basic rock units are identified in western Sinus Meridiani; they represent a stratigraphic section of > 800 m thickness. Near (but not quite at) the top of this stratigraphic section lies the ~7 m of section explored by the MER-B team in Eagle, Fram, and Endurance craters. The occurrence of similar rocks in the plains cut by the Valles Marineris (considered to be Hesperian in age) and Mawrth Vallis (considered to be Noachian) suggests that conditions for deposition, lithification and diagenesis of sedimentary materials in the presence of water or groundwater might have persisted on Mars beyond the end of the period of heavy impact cratering (i.e., beyond the Noachian).

This paper was referenced here earlier, but I didn't look too closely.  I wish I had.