MAPPING CHANNELS AND VALLEYS IN MARGARITIFER SINUS, MARS

Detailed geologic and drainage mapping in the Margaritifer Sinus region of Mars defines a complex history of water transport, storage, and release along the Chryse Trough near the eastern end of Valles Marineris. Mapping is being completed at 1:500,000 and is accompanied by assessment of drainage basin morphometry and hypsometry.

The segmented Uzboi-Ladon-Margaritifer mesoscale outflow system drains about 9% of Mars and incises and fills as it crosses a series of ancient multi-ringed impact basins on the western flank of the Chryse Trough. By contrast, the well-integrated Samara and Parana-Loire Valles drain an area covering about 0.5% of the planet along the eastern flank of the Trough.

The degraded Ladon and Holden multi-ringed impact basins are the oldest features in Margaritifer Sinus and their formation was followed by three widespread resurfacing events that deposited competent materials interpreted to be of sedimentary and/or volcanic origin on the basis of preserved wrinkle ridges and occasionally lobate morphology. The first two resurfacing events occurred during early Noachian heavy bombardment, whereas the third event took place during the middle to late Noachian and was coincident with waning highland volcanism. Incisement of all channels and valleys in the region occurred from late Noachian into the early Hesperian during a period of increased geomorphic activity elsewhere on Mars. Valley morphometry and hypsometry suggest evolution was dominated by precipitation-recharged ground water sapping with only limited contributions from runoff. A final, more localized resurfacing event during the early to middle Hesperian emplaced materials that always embay the channels and valleys.

Channels and valleys converge on Margaritifer Basin, a depositional plain along the Trough axis that extends to the head of Ares Vallis and perhaps well beyond. Discharge into Margaritifer Basin led to ponding, subsurface infiltration, and storage of water that was released during subsequent collapse of Margaritifer and Iani Chaos in the early-to-mid Hesperian, thereby contributing to incisement of Ares Vallis. Hence, formation of Ares Vallis was the final stage in a long history of repeated water transport, storage, and discharge in the Margaritifer Sinus region.