Evidence for Extensive Diagenesis in Gale Crater, Mars from X-ray Amorphous Component Compositions
Abstract
The CheMin instrument on the Mars Science Laboratory rover Curiosity detected ubiquitous high abundances (~15-70 wt%) of X-ray amorphous components (AmCs) in ancient sedimentary rocks of Gale crater. Mechanisms and timing of their formation are poorly constrained although compositions and volatile contents indicate at least some portion formed through aqueous processes. As of sol 2300, CheMin data are available for 19 sedimentary rock samples along the rover traverse, representing each of the major stratigraphic units. AmC compositions are estimated indirectly based on bulk chemistry from the APXS instrument and on the nature and abundance of the crystalline phases in each sample. AmC abundances positively correlate with AmC SiO2 contents, and a mixing relationship appears to exist between SiO2 and FeOT-rich AmC endmembers. The FeOT-rich endmember makes up a few to ~30 wt% of all sedimentary rocks sampled, and likely represents non-unique mixtures of several materials including Fe-oxides (± Fe-sulfates and Fe-silicates), silica, and non-Fe-bearing materials. The SiO2-rich endmember is not pure SiO2, but 72.3% (± 8.5%) SiO2 (at 2-standard error). The most FeOT-rich AmCs are found in older Bradbury group rocks, but also occur in the much younger Siccar Point group. The presence of the FeOT-rich endmember in all sedimentary rocks suggests that these AmCs precipitated during or shortly after sediment deposition (possibly as cement). SiO2-rich AmCs are found in the progressively younger Mount Sharp and Siccar Point groups. Some SiO2-rich AmCs likely precipitated from groundwater during or shortly after sediment deposition, possibly co-precipitating with the FeOT-rich endmember, while the most SiO2-rich AmCs likely formed through interactions with late-stage local fluids sometime after the lithification of the parent sedimentary rocks. The compositional variations outlined here demonstrate that there were multiple substantial diagenetic fluid events in Gale crater likely occurring over an extended period of Mars' history, with each leading to a distinctive assemblage of amorphous components. Accordingly, formation and preservation of amorphous sedimentary materials appears to be a ubiquitous consequence of aqueous diagenetic processes on Mars.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP028...05S
- Keywords:
-
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 5416 Glaciation;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS