GEOLOGIC MAPPING OF MORAVA VALLES AND MARGARITIFER BASIN ON MARS

One of the most impressive landscapes carved by water on Mars is a segmented, mesoscale outflow system in northwestern Noachis Terra and Margaritifer Terra consisting of Uzboi Vallis, Ladon Valles, and Morava Valles. These major valley segments are thought to have formed by overflow from the Argyre impact basin near the Noachian-Hesperian boundary. The Uzboi-Ladon-Morava (ULM) mesoscale outflow system dominates the regional northward drainage through the Chryse Trough, alternately incising the southern highlands and infilling the intervening Early to Middle Noachian Holden and Ladon impact basins, and the informally named Margaritifer basin, eventually reaching the northern plains via Ares or Mawrth Valles.

Here we present results from a geological mapping investigation at 1:500,000 scale of two Mars Transverse Mercator (MTM) quadrangles (-10022 and -15022) that encompass Morava Valles, the lowermost segment of the ULM system, as well its catchment, the SW-NE elongated Margaritifer basin (~11°S, 338°E). The geologic history of this region on Mars records a long history of fluvial incisement, flooding, and resurfacing by multiple processes. During the Late Noachian, sedimentary processes were dominated by the formation of Morava Valles, where early flow and associated flooding formed probable lacustrine plains that are preserved on some elevated surfaces and (or) streamlined outcrops of the older terra unit. In the Hesperian, plains of likely volcanic origin embayed the lacustrine sediments within Margaritifer basin, which were subsequently incised by the latest episode(s) of fluvial activity from Morava Valles. The water in Margaritifer basin, sourced from Morava Valles, Loire Vallis, and the Samara-Himera valley systems, likely ponded in Margaritifer basin and may have later infiltrated into the subsurface. The late Hesperian to Amazonian volcanoes south of Margaritifer basin in MTM -15002 are consistent with an increase in subsurface heating, which may have triggered the collapse and formation of the Margaritifer Chaos north of Margaritifer basin. The water that was released during the formation of the Margaritifer Chaos may have contributed to the incision of Ares and (or) Mawrth Vallis.