APXS Compositional Investigation of the Greenheugh Pediment Capping Unit and Underlying Murray Formation: Déjà Vu
Abstract
Curiosity recently examined the contact between the predominantly fine grained, lacustrine upper Murray formation and overlying, resistant sandstones that cap the erosional Greenheugh pediment. Chemical data acquired by APXS reveal compositional similarities between these rocks and those encountered earlier in the mission.
Murray formation targets analyzed within 3 m of the contact exhibit elevated Na, excess Ca (not as CaSO4) and similar elemental patterns to Murray bedrock from the base of the section, within 5 m of overlying, capping sandstones. Post-depositional concretions and veins within the Murray targets closest to the pediment contact fall into two categories; those with elevated Mn and Fe, and those with elevated Mg (+/- K). The distinct composition of Murray strata close to the contact with overlying, capping sandstones at both the base and top of the section may indicate enhanced post-depositional fluid flow and alteration associated with this contact. Sandstone targets exposed immediately above the pediment have basaltic compositions consistent with those of Stimson formation sandstones, some with elevated S. More massive and resistant sandstone outcrops, ~4 m above the contact have higher K, Mn and Na and lower Ni concentrations than underlying and typical Stimson sandstone. This may reflect a change in provenance from the typical basaltic composition Stimson, or changes in transport/sorting or diagenesis. The higher K sandstones are compositionally similar to several potential cap-rock, float blocks analyzed by APXS as Curiosity climbed through the Murray formation as well as Bradbury group sandstone outcrops encountered at the very beginning of the mission. This indicates a possible relationship between the Bradbury group and Stimson formation. The more massive, higher K, pediment sandstones may have a similar provenance and/or depositional setting as at least some of the Bradbury group sandstones.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP069.0001T
- Keywords:
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- 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5415 Erosion and weathering;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5470 Surface materials and properties;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS