The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

H 2 O, CO 2 , SO 2 , O 2 , H 2 , H 2 S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H 2 O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO 2 . Concurrent evolution of O 2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from approximately average Martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved indicating arid, possibly cold, paleoclimates and rapid erosion/deposition. Absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low temperature, circum-neutral pH, rock-dominated aqueous conditions. High spatial resolution analyses of diagenetic features, including concretions, raised ridges and fractures, indicate they are composed of iron-and halogen-rich components, magnesium-iron-chlorine-rich components and hydrated calcium-sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. Geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.Introduction: Shortly after leaving its landing site at Bradbury Landing in Gale crater, the Mars Science Laboratory Curiosity rover traversed to Yellowknife Bay (1), where it encountered a flat-lying, ~5.2 meter thick succession of weakly indurated clastic sedimentary rocks ranging from mudstones at the base to mainly sandstones at the top (2). Stratigraphic relationships and

Observations from orbital spacecraft have shown that Jezero crater on Mars contains a prominent fan-shaped body of sedimentary rock deposited at its western margin. The Perseverance rover landed in Jezero crater in February 2021. We analyze images taken by the rover in the 3 months after landing. The fan has outcrop faces, which were invisible from orbit, that record the hydrological evolution of Jezero crater. We interpret the presence of inclined strata in these outcrops as evidence of deltas that advanced into a lake. In contrast, the uppermost fan strata are composed of boulder conglomerates, which imply deposition by episodic high-energy floods. This sedimentary succession indicates a transition from sustained hydrologic activity in a persistent lake environment to highly energetic short-duration fluvial flows.

We measured sand sizes and shapes on diverse eolian bedforms in Gale crater to help constrain models of eolian sediment transport on Mars. All grains are subangular to rounded with circularities of~0.93-0.97, indicating an extensive abrasion history. There are two types of active bedforms based on grain size: (1) ripples composed of 50-to 150-μm grains and (2) ripples that also include 250-to 500-μm grains along their crests, in some cases with small amounts of even coarser grains (up to 1.4 mm). The smallest grain sizes (50-150 μm) are volumetrically the most abundant at all active bedforms. Inactive bedforms have surfaces of 350-to 2,000-μm grains with finer-grained interiors, consistent with observations made by rovers at other landing sites. Grains coarser than~300 μm are less prone to mobilization driven by smaller saltating grains, making bedforms with concentrations of coarser grains more susceptible to surface stabilization and inactivity.Plain Language Summary We used microscopic images taken by a camera on the Curiosity rover at Mars to measure the shapes and sizes of sand grains. There are two types of active ripples that we identified based upon grain size: those that have grain sizes between 50 and 150 microns and those with coarser grains between 250 and 500 microns. Most of the grains on the active Bagnold dunes are very fine sand, except at the crests of larger ripples where the grains tend to be larger. The grains are circular and rounded, indicating that they have experienced an extensive abrasion history. Inactive ripples have coarser grains (350-2,000 μm) armoring finer interior grains, some of which could be locally derived from the Stimson sandstone and Murray Formation outcrops. On Earth, the physical properties of grains partly control bedform morphology and are closely linked with mobility. Because these same principles are expected on Mars, it is important to know sand grain size and shape distributed across diverse ripple morphologies to help constrain models of martian bedform formation.