BASIN-FILLING ENVIRONMENTS IN THE MARTIAN CRATERED HIGHLANDS: THE HADRIACUS CAVI EXAMPLE

Evolutionary models for structurally-controlled terrestrial basins have been predicted, documented, and refined. Equivalent models do not exist for extraterrestrial basins perhaps because these depend on observations that are beyond the observational range of orbiting instruments (e.g., lithology, grain-size). Terrestrial models can be leveraged with interpreted geologic processes on non-terrestrial surfaces to assess depositional style, predict outcrop characteristics, and target observations. We use strata exposed in a series of depressions in the Martian cratered highlands as a type example of intercrater basin deposits. These depressions, named Hadriacus Cavi, were deposited between interpreted horst blocks uplifted by the Hellas giant impact (4.1 to 3.8 Ga). Horst-bounded strata are up to 600 meters thick and collectively record an estimated 200 million years of post-Hellas deposition. We postulated that exposed strata would include basal (fault) breccia overlain by north-dipping strata composed of impact breccias, volcanic units, and undifferentiable aeolian, colluvial, alluvial, and (or) lacustrine sediment sequences. We completed 1:24,000 scale mapping and section analyses using a digital terrain model (1.5 m/px) and orthoimage (0.5 m/px) derived from a satellite-acquired stereo-pair. Though lithology and grain size could not be reliably distinguished, we observed particular geologic characteristics that helped resolve the basin architecture and post-depositional deformation. In particular, we observed: (1) four distinct rock groups based on tone, meter-scale texture, and lateral continuity (implying (~) changes in depositional settings through time), (2) cliff- and slope-forming sub-units, (~varying mechanical competence), (3) a lack of truncated beds (~continuous deposition), (4) two sets of channels in section (~episodic through-going fluvial systems), (5) near uniform 3-5˚ dip to NNW (~material transportation from south to north), (6) surface polygons and vertical columns (~volcanic units), and (7) several sets of near-vertical faults with m-scale offset (~post-depositional tectonism). Our work demonstrates that resolving the architecture of non-terrestrial basins using limited orbital data is feasible and reveals complex depositional histories.