LATE-STAGE DIAGENETIC CONCRETIONS IN THE LACUSTRINE MURRAY FORMATION, GALE CRATER, MARS

The Mars Science Laboratory Curiosity rover has investigated more than 310 meters of Murray formation (fm.) deposited in a long-lived lacustrine environment in Gale crater. A diverse suite of diagenetic features, including veins and concretions, are present and provide evidence for post-depositional fluid flow. Concretions are prevalent in the Murray fm. and exhibit diverse morphologies, some of which have not been observed at previous rover landing sites on Mars. These concretions are evidence of post-depositional cementation from diagenetic fluids and indicate environmental changes in temperature, fluid pressure, volatile content, or redox conditions.

Here we present the distribution of diagenetic concretion morphologies, size, density, and chemistry throughout the Murray stratigraphy traversed from Sols 750 to the present, and place constraints on the timing of the depositional and diagenetic processes that formed them. Concretions occur as dendrites, spherules (e.g., Meridiani Planum “blueberries” and Yellowknife Bay “solid nodules”), and in flat and irregular morphologies. Lamination-enhancing cementation is also ubiquitous and may indicate a lower cement to sediment ratio than other concretion morphologies. Lamination-enhancing cementation is dominant in the lower Murray up through the Hartmann’s Valley member, but spherules and flat concretions are more prevalent in stratigraphically higher sections from the Karasburg member and onwards. Trends in concretion morphology may correlate with different host rock properties (grain size, porosity, lamination style) or distinct diagenetic episodes.

No concretions are observed to deflect host rock lamination, suggesting that most of the observed concretions are late-stage diagenetic products that formed after compaction and lithification of sediments. These concretions can be positively correlated with veins or are antithetical with or crosscut by veins, indicating that multiple diagenetic episodes occurred. Variable concretion enrichments in Mg, Ca, Fe, and Mn also suggest multiple diagenetic fluid events of distinct compositions. The diversity of concretion morphologies and compositions, and their complex relations with veins suggest multiple late-stage fluid or diagenetic episodes within the Murray fm.