Geology of Crater Millochau, Terra Tyrrhena Region of Mars

Introduction: The martian highlands preserve a long and complex history of degradation by fluvial, eolian, and mass wasting processes [1-8]. The effects of these processes are best observed on impact craters that characterize the ancient highlands. Previous studies of highland terrains Margaritifer Sinus [9,10], Ismenius Lacus [11,12], Arabia Terra [13], and Promethei Terra [14,15] have shown that craters display pristine to highly degraded morphologies. Some craters exhibit distinctive interior deposits, suggesting infilling by sedimentary and (or) volcanic deposits. Several studies [e.g., 16-20] have suggested that large impact craters on Mars may have contained standing bodies of water that could have been ideal environments for life to persist. Studies of Terra Tyrrhena [3,21-27] suggest large amounts of fluvial erosion and deposition occurred during the early part of Mars’ history, followed by remobilization of sediments by eolian activity. Crater Millochau (21.4¡S, 275¡W) is a large (~114 km diam.), highly degraded crater in Terra Tyrrhena that displays a complex geology representative of many of the above-mentioned processes. Detailed analysis of crater Millochau is part of a larger project being undertaken to document the history and characterize the geology of Terra Tyrrhena [26,27]. Due to its size, degree of modification, and apparent age, the geologic record of Millochau could represent a large part of martian history, recording changes in degradational style(s) and (or) climatic changes, as well as serve as a proxy for craters of similar age to understand the degradational history of this part of the highlands. This study intends to (a) characterize the complex geologic and geomorphic terrains within Millochau, (b) determine the origin(s) and ages of floor deposits, and (c) investigate degradation processes that might have affected Millochau and other craters in the region.