Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge

Abstract

Ground-based bedding orientation measurements are critical to determine the geologic history and processes of sedimentation in Gale crater, Mars. We constrain the dip of lacustrine strata of the Blunts Point, Pettegrove Point, and Jura members of the Murray formation using a combination of regional stratigraphic correlations and bed attitude measurements from stereo Mastcam images taken by the Mars Science Laboratory Curiosity rover. In situ bed attitude measurements using a principal component analysis-based regression method reveal a wide range of dips and dip azimuths owing to a combination of high stereo errors, postdepositional deformation of strata (e.g., fracturing, rotation, and impact cratering), and different primary depositional dips. These constrain regional dips to be within several degrees of horizontal on average. Stratigraphic correlations between targets observed in the Glen Torridon trough and at the Pettegrove Point-Jura member contact of Vera Rubin ridge (VRR) constrain dips to be between 3°SE and 2°NW, consistent with nearly flat strata deposited horizontally on an equipotential surface. The Jura member is determined to be stratigraphically equivalent to the northern portion of the Glen Torridon trough. Rover-based dip magnitudes are generally significantly shallower than the orientation of VRR member contacts measured from High Resolution Imaging Science Experiment-based traces, suggesting the sedimentary strata and VRR member contacts may be discordant.Plain Language Summary The orientation of sedimentary strata is one of the most fundamental measurements of structural geology because it records information about the processes of deposition and subsequent deformation of those strata. For the last 7 years, the Curiosity rover has traversed predominantly fluviolacustrine (river-and lake-deposited) strata. Recently, the rover traversed the Vera Rubin ridge (VRR), a topographic rise within a larger collection of strata with rock exposures whose orientation can be measured using overlapping (stereo) images taken by cameras aboard the rover. By measuring the orientation of beds in stereo rover images and comparing the elevation of similar rock lithologies found along the traverse, we constrain the strata that comprise the VRR to be horizontal or only shallowly dipping. This result is consistent with the sediment that formed the VRR being deposited on a nearly horizontal surface, suggesting that at least the strata that make up the lower portion of Mount Sharp, the large sedimentary mound in Gale crater that dips more steeply outward, may not have directly contributed to its primary formation. The near-flat orientation also indicates that some portion of the VRR occurs at the same elevation as the region south of the ridge called Glen Torridon.

APXS‐Derived Compositional Characteristics of Vera Rubin Ridge and Murray Formation, Gale Crater, Mars: Geochemical Implications for the Origin of the Ridge

“…Compositional trends in both major and trace elements associated with the Blunts Point/Pettegrove Point and Pettegrove Point/Jura contact, cutting across elevation, imply that the chemical characteristics and morphology of the ridge are not the result of primary sedimentary or depositional processes, assuming that the strata are relatively flat lying (Stein et al, 2020). In particular, the contacts between the high Si, Al and low Fe, Ti, Mn gray/blue patches and more typical bedrock are observed to occur at relatively high angles to the observed bedding (e.g., Figure 13 in Fraeman, Edgar, et al, 2020).…”

“…The erosional expression of the Greenheugh pediment, and the associated cap rock to the south of VRR, mimics the geomorphology of the ridge (Bryk et al, 2019; Fraeman et al, 2016). The dips of the Greenheugh pediment capping unit, and extrapolation toward VRR, indicate that the caprock may have extended unconformably over the ridge (Bryk et al, 2019; Stein et al, 2020). This could explain the relatively more varied chemistry within the Jura member.…”

The Chemostratigraphy of the Murray Formation and Role of Diagenesis at Vera Rubin Ridge in Gale Crater, Mars, as Observed by the ChemCam Instrument

“…These observations imply that the Murray formation, extending vertically from the Pahrump Hills location and through VRR (Figures 1b and 2), is more than 350 m thick. Observations acquired upon entering the Glen Torridon area south of VRR show that the rocks just south of VRR likewise belong to the Jura member of the Murray formation (Fedo et al, 2020; Stein et al, 2020). Observation points from the Glen Torridon area will, however, be designated as belonging to a “Glen Torridon” class here to avoid confusion with the Jura member observations on VRR.…”

Extraformational sediment recycling on Mars

“…Figure 2D shows a summary of the rock units investigated as a function of elevation through September 2019 (rock units encountered thereafter were still in discovery, discussion, and refinement at the time of this writing). Bedding is nearly flat, with dips usually of the order of 0° to 3° (Grotzinger et al, 2015;Lewis and Turner, 2019;Stein et al, 2020). The thickest stratal package investigated during the MSL mission, thus far, is the Murray formation ( Fig.…”