Paper No. 5-5
Presentation Time: 9:20 AM
THINGS ARE NOT ALWAYS AS THEY SEEM: DETANGLING INTERSECTING PLANAR AND CURVI-PLANAR VEINS AND FRACTURES FROM PRIMARY BEDDING IN THE VERA RUBIN RIDGE MEMBER, MURRAY FORMATION, MARS
Sedimentary deposits in Gale crater were deposited, buried, lithified, exhumed, and eroded before 3.3-3.1 Ga. A critical component of the Mars Science Laboratory mission is to determine whether the strata infilling Gale Crater preserve environments capable of supporting life, principally though the recognition of rock types and stratigraphy indicative of having interacted with water or brine. Curiosity has gained approximately 400 m of elevation, ~300 m of which has been assigned to the Murray formation, a unit thought to have been deposited in a lacustrine and lacustrine-margin setting. Throughout the Murray formation, sulfate veins are relatively common, but more concentrated in some localities. In Mastcam images, the lower part of the Vera Rubin Ridge (VRR) member has a distinct pattern of resistant layers that are variably inclined relative to the inferred primary bedding; this results in outcrops with the appearance of abundant cross stratification. In higher resolution images, the inclined surfaces occur as curvi-planar millimeter-thick sheets that are both discordant and concordant to primary layering, and here are interpreted as veins. As elsewhere in the Murray formation, the sulfate veins are commonly more resistant to weathering, and so stand in positive relief making their presence even more prominent. Veins are commonly spaced by only centimeters. It is common for a single vein to cross-cut primary layering then curve into parallel with it; examples where Ca sulfate is only parallel to layering raise the notion at least some sulfate could be primary depositional, an hypothesis that needs continued study. Exposed vein margins take on a color similar to, but distinct from the host, although freshly broken edges reveal their bright white internal color, again similar to many sulfate veins elsewhere in the Murray formation. Intepreting a significant part of these features in the as later fracture fills has important implications for considering depositional conditions for this part of the VRR member as it reduces the number of examples of potential cross bedding and indicates that the overwhelming volume of sulfate, even layer parallel, is diagenetic. The sulfate vein network extends the timing for potentially habitable conditions within the sedimentary infill well past the time of deposition.