49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083) 2839.pdf HYPANIS VALLES DELTA: THE LAST HIGH-STAND OF A SEA ON EARLY MARS. P. Fawdon1, S. Gup- ta2, J. Davis3. N, Warner4, E. Sefton-Nash5, J. Adler6, J. Bell6, M. Balme1, P. Grindrod3, 1Dept. of Physical Scienc-es, Open University, Milton Keynes, UK, (
[email protected]), 2Dept. of Earth Science and Engineering, Imperial College, London, UK, 3Dept. of Earth Sciences, Natural History Museum, London, UK, 4Department of Geological Sciences, SUNY Geneseo, Geneseo, NY, 5ESTEC, European Space Agency, The Netherlands, 6Arizona State Universi- ty School of Earth and Space Exploration, Tempe, AZ Introduction: The sediment fan complex at the tification of sedimentary fans around the martian dichot- termination of Hypanis Valles is the largest proposed omy boundary along an equipotential surface (-2,540 m; delta system on Mars (Fig. 1), and is likely late- [3]). Here we describe the palaeogeomorphology of the Noachian/early-Hesperian in age [1, 2]. The location of Hypanis fan and consider the evidence for its origin. such a large delta here, at the dichotomy boundary be- Observations: The Hypanis sediment fan is located tween the northern lowlands and southern highlands, in a tectonically stable region at the boundary between suggests the past presence of a large water-body in the the Noachian-aged Xanthe Terra region and the Amazo- northern plains. However, the concept of a stable stand- nian-aged surface of Chryse Planitia [1]. The fan com- ing body of water filling the northern lowlands is conten- plex comprises a series of distinct semi-circular to lobe- tious: while many Noachian-aged surfaces display evi- shaped sediment bodies, connected by multiple bifurcat- dence for ancient water flow such as the valley networks ing flat-topped ridges.