The erosional history of the Dao Vallis outflow channel on Mars

Kurzfassung

The Dao outflow channel is located at the eastern rim of the Hellas impact basin at 92°E and 37°S. Its source region is located at the boundary of the Hesperia Planum plains and it debouches into the Hesperian-aged Hellas Planitia impact basin in the west. Mechanisms for formation have been proposed by several authors. Theories include groundwater sapping and catastrophic flooding, combined with underflow currents for parts of the Dao Valles system. Although no layering could be observed in earlier observations, a composition of volcanic and sedimentary material of Hesperian to Amazonian age is rather probable. The Dao Valles systems also show small-scale morphological features which are possibly connected to recent ice- and water-related activity. Gully erosion with depositional aprons have been observed on the valley walls as well as flow features which might be attributed to ice-saturated flow of sediments from the valley walls and on the valley floor (e. g., lineated valley fill, debris aprons). We have performed a detailed mapping of geological as well as geomorphological surface features with the available image material from Viking, Mars Global Surveyor and Mars Odyssey. The complex stratigraphic sequence of the erosional and depositional history of the outflow channel and adjacent areas and the episodic cycles and morphometric characteristics of the channel system has been obtained on the basis of crater counting methods for absolute age determinations. The influence and age relation of impact, volcanic lava flow, depositional processes and recent erosional water and ice related processes which shaped the Dao Valles channel system have been analyzed in detail.