Selective sorting of basaltic fluvial sand revealed through coordinated mineralogy and geochemistry near Sandvatn, Iceland as a Mars analog

Session: Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part I

Presenting Author:

Audrey Putnam

Authors:

Putnam, Audrey R¹, Siebach, Kirsten L², Thorpe, Michael T³, Tu, Valerie M⁴, Bedford, Candice C⁵, Rampe, Elizabeth B⁶, Costin, Gelu⁷, Tamborski, Joseph J⁸

(1) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (2) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (3) University of Maryland College Park, NASA Goddard Space Flight Center, CRESST, Greenbelt, MD, USA, (4) Texas State University (TXST) Amentum-JETSII at, NASA Johnson Space Center, Houston, TX, USA, (5) Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafeyette, IN, USA, (6) NASA Johnson Space Center, Houston, TX, USA, (7) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (8) Ocean and Earth Sciences, Old Dominion University, Norfolk, VA, USA,

Abstract:

The archive of detrital watershed material preserved in sedimentary rocks on Mars and Earth can allow the characterization of rocks present in watersheds that are either temporally inaccessible due to erosion or spatially inaccessible due to sampling/rover constraints. For example, in-situ Curiosity rover CheMin XRD detections of sanidine and tridymite in sedimentary rocks provided a valuable window into the evolution of protolith igneous rocks in the watershed of Gale crater, expanding the known range of igneous compositions on Mars. However, sedimentary records of protolith rocks are subject to bias because source rock textures control the grain size range of initial sediment, and sedimentary processes cause grain sorting that changes phase proportions. This bias generates uncertainty, for example, in the multiple hypotheses for explaining chemical trends in the Bradbury formation in Gale crater, Mars: are there multiple igneous protoliths with different degrees of igneous evolution? Or is efficient sorting of a plagioclase-phyric basalt generating a wide range of compositions?

 

 

In this study, we seek to improve understanding of the efficacy of sorting processes on first-order basaltic sediments by studying the effect of sorting on the preservation of provenance information in Mars analog basaltic fluvial sediments near Sandvatn, Iceland. This area provides a texturally diverse watershed composed of basaltic lavas and volcaniclastics which record igneous diversity, lava-water/ice interaction, and hydrothermal alteration analogous to Mars. We analyze the bulk chemistry and mineralogy of downstream fluvial sediments to test how well provenance signals are preserved.

We observed two main axes of variation within fluvial sediments: 1) sorting of olivine and plagioclase phenocrysts (but not groundmass), and 2) variation in clast crystallinity inherited from the volcaniclastic breccias. These crystallinity differences reveal the presence or proximity of surficial water, ice, or groundwater during lava crystallization. Additionally, on the lakeshore, wave action concentrated exotic evolved tephra into distinct layers. Observing these sorting trends requires both geochemistry and mineralogy and indicates ways that sediments may not mirror their sources.

 

These results suggest that sorting of plagioclase phenocrysts from mafic minerals may be a viable hypothesis for explaining the grain-size dependent chemical differences in the Bradbury group. Further, it hints that the potassic sediment intervals in the Kimberly area do not require a volumetrically major potassic source in the Gale crater rim.