Geology topics

Rachel Kronyak

Publications and source records attributed to Rachel Kronyak.

3 recordsLinked to original sources

USGS2022

Overview of the morphology and chemistry of diagenetic features in the clay-rich Glen Torridon Unit of Gale Crater, Mars

The clay-rich Glen Torridon region of Gale crater, Mars, was explored between sols 2300 and 3007. Here, we analyzed the diagenetic features observed by Curiosity , including veins, cements, nodules, and nodular bedrock, using the ChemCam, Mastcam, and Mars Hand Lens Imager instruments. We discovered many diagenetic features in Glen Torridon, including dark-toned iron- and manganese-rich veins, magnesium- and fluorine-rich linear features, Ca-sulfate cemented bedrock, manganese-rich nodules, and iron-rich strata. We have characterized the chemistry and morphology of these features, which are most widespread in the higher stratigraphic members in Glen Torridon, and exhibit a wide range of chemistries. These discoveries are strong evidence for multiple generations of fluids from multiple chemical endmembers that likely underwent redox reactions to form some of these features. In a few cases, we may be able to use mineralogy and chemistry to constrain formation conditions of the diagenetic features. For example, the dark-toned veins likely formed in warmer, highly alkaline, and highly reducing conditions, while manganese-rich nodules likely formed in oxidizing and circumneutral conditions. We also hypothesize that an initial enrichment of soluble elements, including fluorine, occurred during hydrothermal alteration early in Gale crater history to account for elemental enrichment in nodules and veins. The presence of redox-active elements, including Fe and Mn, and elements required for life, including P and S, in these fluids is strong evidence for habitability of Gale crater groundwater. Hydrothermal alteration also has interesting implications for prebiotic chemistry during the earliest stages of the crater’s evolution and early Mars.

JGR - Planets↗

USGS2021

Diagenesis revealed by fine-scale features at Vera Rubin ridge, Gale crater, Mars

Fine-scale (submillimeter to centimeter) depositional and diagenetic features encountered during the Curiosity rover's traverse in Gale crater provide a means to understand the geologic history of Vera Rubin ridge (VRR). VRR is a topographically high feature on the lower north slope of Aeolis Mons, a 5-km high stratified mound within Gale crater. We use high-spatial resolution images from the Mars Hand Lens Imager (MAHLI) as well as grain sizes estimated with the Gini index mean score technique that uses ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical data to constrain the postdepositional history of the strata exposed on this ridge. MAHLI images were used to examine the color, grain size, and style of lamination of the host rocks, as well as to explore the occurrence of nodules, diagenetic crystals, pits, and a variety of dark-gray iron-rich features. This survey revealed abundant and widespread diagenetic features within the rocks exposed on VRR and demonstrated that rock targets estimated to be coarser generally contain more diagenetic features than those estimated to have finer grains, which indicate that grain size may have influenced the degree and type of diagenesis. A subset of rocks within VRR are gray in color and exhibit the highest proportion of diagenetic features. We suggest that these targets experienced a different diagenetic history than the other rocks on VRR and hypothesize that redistribution and recrystallization of iron within specific intervals may have resulted in both the gray color and the abundance of dark-gray iron-rich diagenetic features.

JGR Planets↗

USGS2017

Chemistry of diagenetic features analyzed by ChemCam at Pahrump Hills, Gale crater, Mars

The Curiosity rover's campaign at Pahrump Hills provides the first analyses of lower Mount Sharp strata. Here we report ChemCam elemental composition of a diverse assemblage of post-depositional features embedded in, or cross-cutting, the host rock. ChemCam results demonstrate their compositional diversity, especially compared to the surrounding host rock: (i) Dendritic aggregates and relief enhanced features, characterized by a magnesium enhancement and sulfur detection, and interpreted as Mg-sulfates; (ii) A localized observation that displays iron enrichment associated with sulfur, interpreted as Fe-sulfate; (iii) Dark raised ridges with varying Mg- and Ca-enriched compositions compared to host rock; (iv) Several dark-toned veins with calcium enhancement associated with fluorine detection, interpreted as fluorite veins. (v) Light-toned veins with enhanced calcium associated with sulfur detection, and interpreted as Ca-sulfates. The diversity of the Pahrump Hills diagenetic assemblage suggests a complex post-depositional history for fine-grained sediments for which the origin has been interpreted as fluvial and lacustrine. Assessment of the spatial and relative temporal distribution of these features shows that the Mg-sulfate features are predominant in the lower part of the section, suggesting local modification of the sediments by early diagenetic fluids. In contrast, light-toned Ca-sulfate veins occur in the whole section and cross-cut all other features. A relatively late stage shift in geochemical conditions could explain this observation. The Pahrump Hills diagenetic features have no equivalent compared to targets analyzed in other locations at Gale crater. Only the light-toned Ca-sulfate veins are present elsewhere, along Curiosity's path, suggesting they formed through a common late-stage process that occurred at over a broad area.

Icarus↗