THE GEOLOGIC HISTORY OF MAJA VALLES, MARS THROUGH THE LENS OF CTX

Maja Valles is a 1200-km outflow system ­­originating at Juventae Chasma and debouching into Chryse Planitia on Mars. Early authors placed its origin in the late Hesperian on the basis of impact crater densities derived using Viking imagery. However, evidence of crater density variations on the channel floor derived by recent authors using images from the Mars Orbiter Camera (MOC) suggests that the formation history of Maja Valles may involve multiple resurfacing events that have greatly influenced the large–scale topography of the region. The objective of this study is to determine the geologic history of Maja Valles using key observations of stratigraphic relationships and crater counts derived from the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO). Our results suggest that the Maja Valles region has undergone a minimum of three episodes of fluvial resurfacing from the middle to late Amazonian and near-continuous volcanic resurfacing by thin flows sourced from vents located in Lunae Planum to the west during that period. Topographic analysis using elevation data from the Mars Orbiter Laser Altimeter (MOLA) instrument and spatial trends of resurfacing ages calculated suggests that fluvial resurfacing was focused more on the eastern edge of the system with younger flooding events, possibly in result of the topographic influence of volcanic infill from the northwest, which may have effectively served as a dam that gradually shifted the topographic gradient eastward. Additionally, observations of older fluvial resurfacing ages associated with the northernmost outlets may suggest lower flood volumes for younger floods and/or refocusing of fluid flow through the larger southern outlet. These new spatial and timing constraints will improve flood volume estimates for Maja Valles as well as understanding of its role in sedimentation of Chryse Planitia during the Amazonian period.