Mars is a mirror – Understanding the Pahrump Hills mudstones from a perspective of Earth analogues

Abstract

Mudstone‐dominated lacustrine strata in the Pahrump Hills area of Gale Crater, Mars, have the most extensive data set of physical and geochemical observations yet collected. Although sparse by Earth standards, a source‐to‐sink portrayal of the sedimentary system that differs substantially from previous work has been extracted by integrating sedimentology, stratigraphy, mineral and elemental analyses, geochemical modelling, laboratory experiments and Earth analogues in a sequence‐stratigraphic and palaeogeographical framework. Approximately 3.5 Ga, these 15 m thick strata contain five facies that range from fine to coarse detrital mudstone with abundant sediment‐incorporative evaporite pseudomorphs. The section is dominated by first‐cycle grains of minimally weathered primary igneous minerals but with four distinct compositions. Bedding in the mudstones comprises planar‐parallel beds, current ripples and wave‐induced structures, with common and widespread truncation. The absence of primary desiccation and synaeresis cracks is probably due to minimal clay‐mineral content, as supported by laboratory experiments. Evaporite minerals formed on and within detrital muds shortly after accumulation by evapoconcentration and cooling. The succession contains 16 parasequences in five depositional sequences with all the sequence‐stratigraphic elements known from terrestrial strata. Two of the sequence boundaries are unconformities that record significant shifts in the behaviour and palaeogeographical configuration of the fluvio‐lacustrine system. This contrasts with the previous view that all facies are genetically related. Most of the variability in rock composition can be attributed to stratigraphic changes in provenance that integrate changing drainage basin configurations, type of exposed bedrock and changes in weathering regime. These strata are interpreted as evaporative lake deposits that accumulated in an underfilled lake basin with closed surface hydrography but through‐flowing groundwater. Lake waters were saline to hypersaline, and lake levels, shorelines and salinities fluctuated greatly at various temporal scales.

Detection of Copper by the ChemCam Instrument Along Curiosity's Traverse in Gale Crater, Mars: Elevated Abundances in Glen Torridon

“…This alternative view will be referred to as the “provenance model”. Indeed, based on the relative proportions of igneous minerals detected by CheMin (e.g., Rampe et al., 2017; Schieber et al., 2022) or on compositional trends based on ChemCam data (e.g., Bedford, Bridges, et al., 2019), there is considerable evidence that multiple source regions existed for Murray and Carolyn Shoemaker sediments. After all, the rubbly bedrock in Jm/GT is the continuation of the lacustrine Murray sediments below the VRR, where very few Cu detections have been made according to Figure 2.…”

Depositional and Diagenetic Processes of Martian Lacustrine Sediments as Revealed at Pahrump Hills by the Mars Hand Lens Imager, Gale Crater, Mars

“…Additionally, continuous laminae, laminae containing syndepositional evaporitic phases, potential Aeolian pinstripe lamination, the presence of cross-bedded sandstone in incised lenses, and the rapid variation between these facies within a relatively thin stratigraphic sequence together indicate a dynamically changing depositional environment. Observations at the MAHLI scale reported here (e.g., Schieber et al, 2015Schieber et al, , 2022aYawar et al, 2018) therefore reveal a potentially complex environment of lacustrine deposition including quiet-water deposition, evaporation and ephemeral water presence, possible aeolian deposition, and fluvial incursion-all within the lowermost 15 m of the Mt. Sharp group.…”

“…A major break in deposition occurred beneath the Chinle bed (e.g., Schieber et al., 2022a; Yawar et al., 2018), followed by the deposition of the upper interval. Chinle sedimentation shows distinct pinstripe laminae, an absence of strong post‐depositional cementation along lamina boundaries, and low angle truncation surfaces that are consistent with a transition to predominantly aeolian sedimentation.…”

“…Discontinuous ledges of more resistant material are interbedded within the recessive rocks. The ledges appear concordant with lamination planes and are laterally continuous (Minitti et al., 2019; Schieber et al., 2022a; Yawar et al., 2018), suggesting a stratigraphic control on their occurrence.…”

Determination of Spatial Scale in Martian Landscape Images Acquired by the Curiosity Rover, and Viewing Image Scale and Target Chemistry Using the ASIC Website

“…Instruments Onboard the Curiosity Rover That Are Relevant to This Work (Modified From Table 1 inSchieber et al, 2022) …”