Stratigraphy and paleohydrology of delta channel deposits, Jezero crater, Mars
2018
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.
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