Clay minerals in delta deposits and organic preservation potential on Mars

Clay-rich sedimentary deposits are often sites of organic matter preservation(1,2), and have therefore been sought in Mars exploration(3). However, regional deposits of hydrous minerals, including phyllosilicates and sulphates(4,5), are not typically associated with valley networks and layered sediments that provide geomorphic evidence of surface water transport on early Mars(6-8). The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)(9) has recently identified phyllosilicates(10) within three lake basins with fans or deltas that indicate sustained sediment deposition: Eberswalde crater(7,11,12), Holden crater(12,13) and Jezero crater(14). Here we use high-resolution data from the Mars Reconnaissance Orbiter (MRO) to identify clay-rich fluvial-lacustrine sediments within Jezero crater, which has a diameter of 45 km. The crater is an open lake basin on Mars with sedimentary deposits of hydrous minerals sourced from a smectite-rich catchment in the Nili Fossae region. We find that the two deltas and the lowest observed stratigraphic layer within the crater host iron-magnesium smectite clay. Jezero crater holds sediments that record multiple episodes of aqueous activity on early Mars. We suggest that this depositional setting and the smectite mineralogy make these deltaic deposits well suited for the sequestration and preservation of organic material.