Stratigraphy and paleohydrology of delta channel deposits, Jezero crater, Mars

Abstract The Jezero crater open-basin lake contains two well-exposed fluvialsedimentary deposits formed early in martianhistory. Here, we examine the geometry and architecture of the Jezero western delta fluvial stratigraphyusing high-resolution orbital images and digital elevation models (DEMs). The goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position. The delta outcrop contains three distinct classes of fluvial stratigraphythat we interpret, from oldest to youngest, as: (1) point barstrata deposited by repeated flood events in meanderingchannels; (2) inverted channel-filling deposits formed by avulsivedistributary channels; and (3) a valley that incises the deposit. We use DEMs to quantify the geometry of the channel deposits and estimate flow depths of ∼7 m for the meanderingchannels and ∼2 m for the avulsivedistributary channels. Using these estimates, we employ a novel approach for assessing paleohydrology of the formative channels in relative terms. This analysis indicates that the shift from meanderingto avulsivedistributary channels was associated with an approximately four-fold decrease in the water to sediment discharge ratio. We use observations of the fluvial stratigraphyand channel paleohydrology to propose a model for the evolution of the Jezero western delta. The delta stratigraphyrecords lake level rise and shoreline transgression associated with approximately continuous filling of the basin, followed by outlet breaching, and eventual erosion of the delta. Our results imply a martian surfaceenvironment during the period of delta formation that supplied sufficient surface runoffto fill the Jezero basin without major drops in lake level, but also with discrete flooding events at non-orbital (e.g., annual to decadal) timescales.