Short-Lived Aeolian Excavation and Catastrophic Flooding in Gale Crater: Implications for Reshaping Mars by Wind- and Water-Driven Perturbations During the Late Noachian Period

An aeolian event and a fluvial episode affected Gale crater, Mars, prior to 3.6 billion years ago. Both were short-lived and catastrophic. The same two events also modified the Southern Highlands of the red planet during the same time interval. We show that events in Gale crater were a part of those that modified vast areas of the southern hemisphere of Mars. As such, the patterns documented in Gale crater are consistent with reshaping of large portions of Mars by short-lived catastrophic events by wind and water, although data from other regions are needed to establish this on a planetary scale. The study is based on data collected by the Curiosity rover during the past 14 years. The aeolian event excavated Gale crater and formed two distinct morphological provinces with two contrasting rock types. One was the cone-shaped ancestral Aeolis Mons, informally known as Mt. Sharp, that consists of sandstone, siltstone, and mudstone. The other was the nearly flat hollowed margin, the ancestral crater floor, that was initially covered by loose pebbles, cobbles, and boulders which were reworked and lithified to a conglomeratic rock unit later. Commonly reported Martian aeolian erosion rates cannot account for the abrasion and transport of 39,000 km3 of sediments out of Gale crater. This conclusion is supported by little modification of Gale crater during the past 3.6 billion years by ordinary winds. Our evaluation indicates that the excavation of Gale crater took place by a powerful aeolian perturbation that resembled a sand-blasting operation. It was short-lived, had extremely high erosion rates, and occurred during a cold and dry climate. The fluvial episode followed the aeolian event. The study of its sedimentary record indicates that it began with intense precipitation-driven great floods that eroded the ancestral Mt. Sharp, carved large canyons on its slope, and reworked gravels of the ancestral crater floor into giant bedforms. Flood waters also formed a deep lake that experienced one rise and one fall of lake-level and had a dynamic storm-driven sedimentation. The fluvial episode was also short-lived and indicates catastrophic actions of water during a warm and wet climate. As such, this study suggests that the extensive reshaping of the red planet during the Late Noachian period, including formation of valley networks, occurrence of hundreds of crater lakes, and excavation of numerous craters, were also due to short-lived, intense, climate-related perturbations by powerful wind and water rather than by ordinary, slow rate, long-duration processes. Another implication of the study is for the mineralogical evolution of Martian sedimentary rocks. It indicates that the Late Noachian period may have been mostly cold and dry, similar to the modern Mars. Its low water/rock ratio and cold temperatures halted chemical weathering that resulted in preservation of highly unstable minerals such as olivine and pyroxene. The fluvial perturbation with its high water/rock ratio was not long and/or warm enough to alter or significantly affect the mineralogy by weathering at the source region, or during the transport, or at the depositional site.