The Geology and Astrobiology of McLaughlin Crater, Mars: An Ancient Lacustrine Basin Containing Turbidites, Mudstones, and Serpentinites.

McLaughlin crater is a 92‐km diameter complex crater that formed on Mars ~4 billion years ago. The resulting basin was the site of a large (~3,000 km2), deep (~500 m), voluminous (~1,500 km3) Martian lake circa 3.8 Ga. While there is strong evidence that hundreds of lakes have existed on Mars at some point during the same time period, the geology of McLaughlin crater is extraordinary for a number of reasons. Detailed spectral analyses show that the deep‐water sediments include detrital inputs of olivine and pyroxene, but the lake‐floor sediments include lithologies with abundant Fe‐rich, Mg‐bearing smectite, serpentine‐rich deposits, and ferrihydrite. For astrobiologists, this site provides a treasure trove of high‐priority targets. Serpentinization reactions are thought to have played a key role in abiogenesis on Earth, and within McLaughlin crater, deposits of subterranean and probably sublacustrine serpentinites are well preserved. In addition, delta sequences are well exposed throughout the east side of the basin; such deposits are endorsed by some as the highest priority targets for preservation of organics on Mars. Yet deep‐water turbidites, which might have flowed through hydrothermal environments, may be the most intriguing aspect of this geology. Such rapid sedimentation could have sequestered and preserved any potential organic materials for future exploration by a rover. Plain Language Summary: Though Mars is cold, dry, and inhospitable today, it contains evidence for many dry lake beds—relics of an ancient climate that was at least episodically warmer and wetter. Considering that lakes can be an excellent environments for life on Earth, a common thread of Mars research has been to characterize the environmental conditions under which Martian lakes formed in order to better understand their implications for past habitability of the red planet. The goal of this work is to characterize the geology of McLaughlin crater, where a lake existed on Mars over 3.8 billion years ago. McLaughlin lake was vast, deep (~ 500 m), and probably long lived. Many characteristics of McLaughlin lake are unlike those seen in any other ancient lake basins on Mars. This lake contained a range of sedimentary environments including delta deposits, shallow‐water fan deposits, and deep‐water, fine‐grained materials. It is the only known place on Mars where fine‐grained, subaqueous "landslides" called turbidites are identified, and these are important because we know that such deposits can be sites of excellent preservation of organic matter on Earth (due to rapid burial). Key Points: McLaughlin crater contained a deep, voluminous lake >3.8 Ga with features unlike any other known Martian paleolakesSedimentary units include delta deposits, turbidites, and deep‐water sediments; and hydrothermal deposits include serpentinitesGeochemical gradients occurred in a long‐lived lake that was in sustained communication with groundwater and subsurface environments [ABSTRACT FROM AUTHOR]