Integrating the sedimentary stratigraphy of Arabia Terra, Mars: depositional history of Sera and Jiji craters.

Abstract:

Layered deposits in the Arabia Terra region of Mars preserve a record of the climate history of Mars during the Late Noachian to Hesperian geologic epoch. Previously, we have shown the presence of two statistically distinct subunits of the layered deposits by measuring bed thickness across nine crater locations in Arabia Terra using HiRISE stereo topography. To determine if the intracrater layered deposits were formed in lacustrine environments, by aeolian processes, or by a basin-independent process like airfall of dust, we used a geologic modeling technique to reconstruct three-dimensional bedding geometry from the HiRISE topography within two adjacent crater basins, Sera and Jiji Craters. Using the geologic models, we were able to assess the total thickness of the stratigraphy that is partially represented by a number of isolated outcrops in both craters. We found that in both locations, the bedding geometry is non-horizontal, but it is planar, parallel, and conformal to underlying topography. Bedding thickness is consistent over long length scales (100's of m to km(s)) across the crater basins. Bed thicknesses in both sites are highly rhythmic, forming layers of similar, and laterally consistent thickness. Our observations favor models of duststone formation resulting from airfall sedimentation. Layers do not conform to equipotential surfaces, as expected in lacustrine or playa environments. Airfall deposits would instead form layers of consistent thickness over large areas, conformal to underlying topography. These deposits are consistent with an ancient Martian climate similar to the modern day, dominated by dry, dusty conditions. However, moisture from some undetermined process could still drive the subsequent alteration and lithification of the layers. Future work to understand and compare the mineralogy and thermophysical properties of the layers in these sites will help further constrain the deposition and lithification mechanisms for these deposits.