Mineralogical, Elemental, and Spatial Variability of Volcaniclastics in Fluvio-Coastal-Aeolian Sedimentary Systems and Their Insights for Mineral Sorting on Mars

This study investigates the mineralogical, elemental, and spatial variability from source (proximal) to sink (distal) of Merapi basalt-andesitic stratovolcano (Java, Indonesia) to better constrain volcaniclastic mineral sorting in fluvial, aeolian, and coastal environments. Merapi volcaniclastics are products of an active volcano with an ongoing quadrennial eruption, which can provide insights to constrain Mars' older and more recent volcaniclastics by focusing on anorthite, albite, and pyroxenes found on Mars' surface. We collected stream sediment samples across the Opak River that connects Merapi with the Indian Ocean. In addition to grain size analysis, all collected samples were subjected to X-ray diffractometer and X-ray fluorescence to quantify their mineralogical and elemental composition, respectively, like the CHEMIN instrument used by the Curiosity rover on Mars to investigate the geochemistry and mineralogy of geological units in Gale crater. Implementation of multivariate statistical analysis based on principal component analysis and Hierarchical Clustering of Principal Component are able to discriminate between fluvial, fluvio-coastal-aeolian, and marine influenced deposits. The quantitative assessment shows that the dominant mineralogy is influenced by pyroclastic materials dominated by plagioclase feldspars (albite and anorthite), followed by pyroxenes (augite and enstatite). Alteration modeling of Merapi samples favors a fluvial depositional environment rather than mass-wasting from the crater rim for Gale crater rocks (i.e., Pahrump Hills, Hartmann's Valley, Karasburg, Sutton Island member) on Mars. Plain Language Summary This research provides a detailed characterization of stream samples and surface deposits from the Opak River, the Parangkusumo Shoreface, and parabolic coastal sand dunes from an active Merapi stratovolcano (Java, Indonesia) transported from the source toward the sink. The paper aims to constrain pyroclastic mineral sorting from a basaltic to basalt-andesitic volcanic origin throughout fluvial, coastal, and wind-driven (aeolian) environments. We use similar methods as the MSL (Mars Science Laboratory) Team to investigate mineral sorting of volcaniclastic sediments in Gale Crater, specifically using X-Ray spectroscopy collected by CheMin. The results of our research suggest that mineralogical sorting occurs throughout the depositional subenvironments, and they are related to the geomorphology of the river. Furthermore, the aeolian environment provides an additional sorting mechanism for the sand grains deposited in the shoreface. We also discovered a similar weathering trend of Merapi volcanic sediments with the findings from Stimson and Murray formation in Gale Crater, which supports their origin as sediment transported by the river during the wet phase of Mars.