The evolution of sedimentary systems on Mars, and implications for climate in the Hesperian-Amazonian epochs

Abstract

Alluvial deposits within Martian impact craters are sensitive morphologic records of modification by liquid water, and can help constrain past climate conditions. This study explores the evolution of Late Hesperian-Amazonian-age sedimentary deposits within two craters, Mojave and Eberswalde. For Mojave crater, the evolution of intracrater alluvial fan systems and the climatic context are poorly understood. Analysis of stratigraphic relationships between the fans and crater infill suggests that precipitation which formed the systems was temporally closely associated with the impact process. Regional mapping of youthful fluvial features within a ~300 km radius of Mojave supports a genetic link between the impact event and precipitation, due to dense clustering around the crater. Analysis of five additional Late Hesperian-Amazonian craters, which also contain evidence for catchment-fan formation by precipitation, shows similar clustering of fluvial activity. Two mechanisms of water production are suggested to have formed the features observed: (a) localised impact-induced precipitation due to impact plume-related atmospheric effects, and (b) a regional snowpack which melted locally due to impact-induced heating. Eberswalde crater contains multiple sedimentary systems sourced from channels which breach the crater rim, and the depositional system as a whole is poorly understood. Mapping of rocks with differing characteristics within the second largest depositional system, and reconstruction of stratigraphic architecture, shows that the deposit records backstepping of putative deltaic lobe sedimentary bodies. The observed sedimentary architecture is best explained by a net transgression, likely caused by lake level rise through time. This behaviour is not recorded within the best-studied and largest Eberswalde deposit likely due to subsequent burial by progradational lobes. In addition, planform evolution of sinuous channels within the largest Eberswalde deposit is investigated, and mapped chute cutoffs are suggested as implying that overbank flooding occurred.