Diagenetic origin of nodules in the Sheepbed member, Yellowknife Bay formation, Gale crater, Mars

Abstract

The Sheepbed member of the Yellowknife Bay formation in Gale crater contains millimeter-scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits on Mars. Three types of nodules have been identified in the Sheepbed member in order of decreasing abundance: solid nodules, hollow nodules, and filled nodules, a variant of hollow nodules whose voids have been filled with sulfate minerals. This study uses Mast Camera (Mastcam) and Mars Hand Lens Imager (MAHLI) images from the Mars Science Laboratory Curiosity rover to determine the size, shape, and spatial distribution of the Sheepbed nodules. The Alpha Particle X-Ray Spectrometer (APXS) and ChemCam instruments provide geochemical data to help interpret nodule origins. Based on their physical characteristics, spatial distribution, and composition, the nodules are interpreted as concretions formed during early diagenesis. Several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids. The occurrence of concretions interpreted in the Sheepbed mudstone and in several other sedimentary sequences on Mars suggests that active groundwater systems play an important role in the diagenesis of Martian sedimentary rocks. When concretions are formed during early diagenetic cementation, as interpreted for the Sheepbed nodules, they have the potential to create a taphonomic window favorable for the preservation of Martian organics.

Geological Evidence of Planet‐Wide Groundwater System on Mars

“…A. Rodriguez et al, ; Tanaka et al, ), followed by the retreat of surface water into subsurface aquifers underneath a thick ice‐rich permafrost zone (Clifford & Parker, ) where it became part of groundwater stores (Andrews‐Hanna et al, ). Groundwater could have been a major factor in the origin and evolution of water‐related sedimentary systems on Mars (Andrews‐Hanna et al, , ; Goldspiel & Squyres, ; Howard, ; Malin & Carr, ; Siebach et al, ; Stack et al, ).…”

Reconstructing the past climate at Gale crater, Mars, from hydrological modeling of late‐stage lakes

“…Spectral analyses of the Gale crater mound deposit noted the presence of clays at the base of the deposit, mixed with sulfates at higher levels, together making up the lower~250 m of the mound [Milliken et al, 2010;Thomson et al, 2011]. Recent observations by MSL revealed further evidence for a past wet environment in Gale [e.g., Palucis et al, 2014;Grotzinger et al, 2014;Stack et al, 2014;. Mudstone layers forming the basal unit of Aeolis Mons on the crater floor, deltaic deposits extending from the crater rim, and millimeter-scale varves provide evidence for stable lakes in Gale crater and lake sediments forming the basal unit of Aeolis Mons early during the evolution of Gale crater [Grotzinger et al, , 2015Ehlmann and Buz, 2015;Hurowitz et al, 2017].…”

A terrestrial weathering and wind abrasion analog for mound and moat morphology of Gale crater, Mars

“…Turbulent vortices trap and transport sand, abrading the central deposit and causing it to become a reduced mound that retreats to the center until all material is eroded away. The physical proxy evidence for wind erosion and abrasion at Gale crater consists of yardangs, ventifacts, dune sand, wind streaks, and streamlined bedrock nodules with elongate tails in the lee side of the nodules [Bridges et al, 2014;Stack et al, 2014]. A local area of deformed sandstone could have caused anisotropies that facilitated erosion around a pillar form toward the center of the pit.…”