For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover, Curiosity, has been returning definitive and quantitative mineralogical and mineral–chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars. To date, 40 drilled rock samples and three scooped soil samples have been analyzed during the rover’s 30+ km transit. These samples document the mineralogy of over 800 m of flat-lying fluvial, lacustrine, and aeolian sedimentary rocks that comprise the lower strata of the central mound of Gale crater (Aeolis Mons, informally known as Mt. Sharp) and the surrounding plains (Aeolis Palus, informally known as the Bradbury Rise). The principal mineralogy of the sedimentary rocks is of basaltic composition, with evidence of post-depositional diagenetic overprinting. The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that, in many cases, the diagenetic changes observed are principally isochemical. Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos. A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga sedimentary rocks analyzed to date contain 15–70 wt.% of X-ray amorphous material. Overall, this >800 m section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments, many of which would have been habitable to microbial life.
Volcanism increases when glaciers melt because isostatic rebound during deglaciation decreases the pressure on the mantle, which enhances decompression melting. Anthropogenic climate change is now causing ice sheets and valley glaciers to melt around the world and this deglaciation could stimulate volcanic activity and associated hazards in Iceland, Antarctica, Alaska, and Patagonia. However, current model predictions for volcanic activity associated with anthropogenic deglaciation in Iceland are poorly constrained, in part due to uncertainties in past volcanic output over time compared to ice sheet arrangements. Further work specifically characterizing glaciovolcanic and ice-marginal volcanoes in Iceland is needed to reconstruct volcanic output during time periods with changing ice cover. Here, we describe a previously unrecognized ice-marginal volcanic lava delta on a broad, shallow slope southeast of Langjökull and the Jarlhettur volcanic chain in Iceland’s Western Volcanic Zone.   Although previously mapped as interglacial lavas and sediments, canyons in this area revealed two ~20-30 meter-thick southwest-dipping sequences of pillow-bearing tuff-breccias between pāhoehoe lava flows above modern lake Sandvatn. Clasts within the tuff-breccias include a mixture of pillow lavas and pāhoehoe fragments, requiring that the subaqueous tuff-breccia facies were derived from subaerial flows. The upper subaqueous to subaerial transition in this sequence occurs around 400 m above sea level, much higher than any local topography that could dam water or the highest Icelandic marine transgression, necessitating ice damming. Quenched meter-scale cavities in coherent lava and cube-jointed facies show lava-ice contact, supporting evidence for an ice dam. We propose that an eruption melted through thin ice near Skálpanes during a deglacial period and lavas flowed downslope to the south, melting ice and forming an englacial lake. We constrain that the local ice thickness was tens of meters to a few hundred meters thick. This would represent a similar ice configuration as some interpretations of the ice extent at the time of formation of the Buði moraines around 11.2 ka, with higher ice flow down the valley of the Hvita river than off Langjökull, although it occurred during an earlier deglaciation. Importantly, this finding demonstrates that ice-marginal deposits that can provide paleo-environmental constraints may be hidden in terrains that do not conform to existing classifications of glaciovolcanic edifices.
Abstract The Curiosity rover explored the region between the orbitally defined phyllosilicate‐bearing Glen Torridon trough and the overlying layered sulfate‐bearing unit, called the “clay‐sulfate transition region.” Samples were drilled from the top of the fluviolacustrine Glasgow member of the Carolyn Shoemaker formation (CSf) to the eolian Contigo member of the Mirador formation (MIf) to assess in situ mineralogical changes with stratigraphic position. The Sample Analysis at Mars‐Evolved Gas Analysis (SAM‐EGA) instrument analyzed drilled samples within this region to constrain their volatile chemistry and mineralogy. Evolved H 2 O consistent with nontronite was present in samples drilled in the Glasgow and Mercou members of the CSf but was generally absent in stratigraphically higher samples. SO 2 peaks consistent with Fe sulfate were detected in all samples, and SO 2 evolutions consistent with Mg sulfate were observed in most samples. CO 2 and CO evolutions were variable between samples and suggest contributions from adsorbed CO 2 , carbonates, simple organic salts, and instrument background. The lack of NO and O 2 in the data suggest that oxychlorines and nitrates were absent or sparse, and evolved HCl was consistent with the presence of chlorides in all samples. The combined rover data sets suggest that sediments in the upper CSf and MIf may represent similar source material and were deposited in lacustrine and eolian environments, respectively. Rocks were subsequently altered in briny solutions with variable chemical compositions that resulted in the precipitation of sulfates, carbonates, and chlorides. The results suggest that the clay‐sulfate transition records progressively drier surface depositional environments and saline diagenetic fluid, potentially impacting habitability.
Abstract The impact of asteroids and comets with planetary surfaces is one of the most catastrophic, yet ubiquitous, geological processes in the solar system. The Chicxulub impact event, which has been linked to the Cretaceous-Paleogene (K-Pg) mass extinction marking the beginning of the Cenozoic Era, is arguably the most significant singular geological event in the past 100 million years of Earth’s history. The Chicxulub impact occurred in a marine setting. How quickly the seawater re-entered the newly formed basin after the impact, and its effects of it on the cratering process, remain debated. Here, we show that the explosive interaction of seawater with impact melt led to molten fuel–coolant interaction (MFCI), analogous to what occurs during phreatomagmatic volcanic eruptions. This process fractured and dispersed the melt, which was subsequently deposited subaqueously to form a series of well-sorted deposits. These deposits bear little resemblance to the products of impacts in a continental setting and are not accounted for in current classification schemes for impactites. The similarities between these Chicxulub deposits and the Onaping Formation at the Sudbury impact structure, Canada, are striking, and suggest that MFCI and the production of volcaniclastic-like deposits is to be expected for large impacts in shallow marine settings.
Students from the United States, Taiwan, Canada, Chile, Finland, Italy, and Mexico gathered in June at the National Center for Atmospheric Research (NCAR) headquarters in Boulder, Colorado, to immerse themselves in space weather. For 8 intensive days of lectures, labs, and discussions, students expanded their perspectives on the breadth of physical processes and disruptive events that typify the Sun‐Earth realm.
