We have studied the observed properties of the Nili Fossae olivine-phyllosilicate-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition 2) grain size 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens et al., 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-phyllosilicate-carbonate at Séítah. We include a new CRISM map of the phyllosilicate 2.38 μm band and use in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and VISIR and MastCam-Z observations to show that the phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.

We examine the observed properties of the Nili Fossae olivine-clay-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition (Liu, 2022) 2) grain size (Tice, 2022) 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens, 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-clay-carbonate at Séítah. We include a new CRISM map of the clay 2.38 μm band and use in situ data to show that the clay in the olivine cumulate in the Séítah formation is consistent with talc or serpentine from Mars 2020 SuperCam LIBS and VISIR and MastCam-Z observations. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including clay and carbonate alteration (Clave, this issue; Mandon, this issue).

Oxia Planum, the landing site for the ExoMars rover mission, is a shallow basin on the southern margin of Chryse Planitia that hosts remnants of sediment fans associated with the ancient channel system Coogoon Vallis. This indicates runoff from a catchment in Arabia Terra has transported material into the landing site. To explore this fluvial system we created a model catchment for Oxia Planum and, using 6 m/pixel ConTeXt camera (CTX) orbital remote sensing image data, we digitised the fluvial and lacustrine landforms in Western Arabia Terra in and around this catchment. We find: (1) The catchment has a minimum area of ~2.1×105 km2 and has been episodically deformed by tectonic activity; (2) There were at least two phases of fluvial activity. The first created a mature landscape associated with Coogoon Vallis, which may have deposited alluvial or deltaic deposits in the Oxia Basin. After a substantial hiatus, a second phase of activity incised u-section channels into the pre-existing landscape and channel systems; and (3) Evidence for numerous possible paleolake deposits within the catchment. These are not well connected to the fluvial system and were probably sustained by ground water activity contemporaneous with both phases of fluvial activity. This groundwater might have modified the geochemistry of Oxia Planum. Oxia Planum probably experienced an alluvial or distal deltaic/lacustrine depositional environment during the mid Noachian, which was later overprinted by a younger phase of fluvial activity.