Erosion rate and previous extent of interior layered deposits on Mars revealed by obstructed landslides

Abstract

We describe interior layered deposits on Mars that have obstructed landslides before undergoing retreat by as much as 2 km. These landslides differ from typical Martian examples in that their toe height increases by as much as 500 m in a distinctive frontal scarp that mimics the shape of the layered deposits. By using crater statistics to constrain the formation ages of the individual landslides to between ca. 200 and 400 Ma, we conclude that the retreat of the interior layered deposits was rapid, requiring erosion rates of between 1200 and 2300 nm yr-1. We suggest that the interior layered deposits are either extremely friable, if eroded strictly by wind, or composed of a material whose degradation has been enhanced by ice sublimation. These erosion rates also confirm that the interior layered deposits have been in a state of net degradation over the past 400 m.y., suggesting that the process that caused net deposition in the past has ceased or slowed substantially on Mars relative to erosion. Our results imply that interior layered deposits with a similar morphology across Mars, including the mound in Gale Crater, have probably undergone similar rapid erosion and retreat, suggesting that their total modern volume underrepresents the depositional record and thus sedimentary history of Mars. © 2014 Geological Society of America.