Mars Sedimentary Geology: Key Concepts and Outstanding Questions

Processes that operate at planetary surfaces have the potential to record a history of planetary evolution in the form of sedimentary rocks. This is important because our experience on Earth shows that sediments and sedimentary rocks are the dominant archive of high-resolution proxies of present and past tectonic, climatic, and biological processes. Our understanding of the evolution of Earth’s very ancient climate and paleobiological records derives from detailed examination of the mineralogical, textural, and geochemical signatures preserved in the sedimentary rock record. Sedimentary rocks were first recognized on Mars less than a decade ago (Malin and Edgett, 2000). Recent interpretations of data collected by the Mars Express and Mars Reconnaissance Orbiter spacecraft have confirmed the surprising abundance of these sedimentary rocks, the past role of water on the martian surface, and the similarity—in some cases—to sedimentary rocks formed on Earth. Thick sulfaterich deposits invite comparison to terrestrial evaporites (Grotzinger et al., 2005). In other cases, clay-rich strata are interpreted as the terminal deposits of source-to-sink systems with well-developed fluvial networks in the upper reaches of watersheds that date back to a much wetter period in Mars’ earliest history (Ehlmann et al., 2008; Metz et al., 2009). However, these Earth-like depositional systems contrast with other deposits that may be unique in the Solar System: for example, vast terrains as large as Earth’s continents covered by thick veneers of strata that may derive entirely from settling out of wind-transported dust (Bridges et al., 2010). Whatever their origin, it is now clear that the sedimentary rocks of Mars represent a new frontier for research. Mars science is in its golden era of exploration—the past decade of orbiter and landed missions has produced an extraordinary amount of new data relevant to the analysis of sediments and sedimentary rocks, and robust international programs exist for future missions. To help stimulate discussion of these data, the First International Conference on Mars Sedimentology and Stratigraphy was convened in El Paso, Texas, in April 2010. The contents of this white paper represent the most significant findings of the conference, with additional information provided by the coauthors, and focus on seven key questions for future investigation by the sedimentary geology community

SARS-CoV-2 susceptibility and COVID-19 disease severity are associated with genetic variants affecting gene expression in a variety of tissues

Variability in SARS-CoV-2 susceptibility and COVID-19 disease severity between individuals is partly due to genetic factors. Here, we identify 4 genomic loci with suggestive associations for SARS-CoV-2 susceptibility and 19 for COVID-19 disease severity. Four of these 23 loci likely have an ethnicity-specific component. Genome-wide association study (GWAS) signals in 11 loci colocalize with expression quantitative trait loci (eQTLs) associated with the expression of 20 genes in 62 tissues/cell types (range: 1:43 tissues/gene), including lung, brain, heart, muscle, and skin as well as the digestive system and immune system. We perform genetic fine mapping to compute 99% credible SNP sets, which identify 10 GWAS loci that have eight or fewer SNPs in the credible set, including three loci with one single likely causal SNP. Our study suggests that the diverse symptoms and disease severity of COVID-19 observed between individuals is associated with variants across the genome, affecting gene expression levels in a wide variety of tissue types

A first update on mapping the human genetic architecture of COVID-19

peer reviewe

Laboratory simulation of debris flows over sand dunes: Insights into gully-formation (Mars)

Gully morphology (often summarized as comprising an alcove, channel and debris apron) is one of the key elements used to support the argument for liquid water in the recent past on Mars. Nevertheless, the processes that create different gully morphologies, on both Mars and Earth, are not fully understood. One of the puzzling morphologic attributes of Martian dune gullies is their apparent lack of an apron, or terminal deposit, which has caused debate about their formation process. Several physical processes such as runoff, debris flows, granular flows, and sliding blocks falling downslope could explain the formation of these gullies. In this work, we focus on the role of liquid in the substrate as well as in the flow and choose to experimentally test the plausibility of this hypothesis. We performed a series of analogue experiments to investigate the formation of gullies on sand dune-like substrates. We used controlled flows of water over an inclined sand-box to produce gully-like forms. Ice-rich sedimentary substrates were used, including substrates that included a thin liquid water-saturated thawed layer (an ‘active layer’) above the ice-saturated zone to give an analogue for a ‘periglacial’ environment. We quantitatively demonstrate that debris flow processes in ‘periglacial’ experiments are conducive to the formation of narrow and long channels with small terminal deposits with perched channels. By re-analysis of Martian elevation data for dune-gullies on Mars, we have found good evidence that such terminal deposits could exist. Our experiments revealed that increased water content in the thawed layer above the frozen bed increases flow-length due to the subsequent reduction in infiltration capacity. Water is incorporated into the flow by erosion of the wet thawed layer (sand plus water) and by drainage of the thawed layer. Using a Mars environment simulation chamber, we found that atmospheric pressure conditions seem to have a limited influence on the morphology of the flows. Our experimental investigation allowed the reproduction of terrestrial debris flow and Martian gully morphologies, suggesting that a substrate that is resistant to infiltration could be present beneath the dune gullies on Mars. We suggest that, like in our laboratory experiments, the presence of ice at shallow depth is a possible explanation for the formation of these morphologies and that a wet thawed layer is a possible explanation for the long flow-length

Morphological and mechanical characterization of gullies in a periglacial environment: The case of the Russell crater dune (Mars)

Gullies on terrestrial sand dunes are rare, and their presence on Mars, as well as their mechanical properties, and the quantity of fluid required for their formations currently remain poorly understood. This study focuses on gully morphologies on the Russell megadune (54.5°S; 12.7°E) using High Resolution Imaging Science Experiment (HiRISE) images and Digital Terrain Models (DTM). Based on the scenario of ground ice melting in a periglacial environment, we propose to test the hypothesis that Martian gullies on dunes are debris flows. This implies a flow with a significant proportion of liquid water (>10% in volume). We used an original method to study Martian gullies based on empirical equations from terrestrial debris flows in order to calculate the physical properties of Martians flows. We observe a decrease in viscosity induced by the relative increase of fluid concentration (from 28% to 39%) during the flow advance. The total estimated volume of eroded and deposited material range from ∼14850 m^3 to ∼18890 m^3. The volume of liquid water required to generate one gully ranges from 4450 m^3 to 6900 m^3. The calculated results for Martian gullies are consistent with terrestrial studies on debris flows. Based on a morphological description and on the estimated physical parameters, we propose a model for gully formation on Martian dunes. The melt water from near-surface ground ice is incorporated in the debris flow and water concentration increases during its propagation. The increase of water concentration in the debris flow can be explained by a progressive increase of water/ice content in the permafrost downstream. Consequently, the lack of a final deposit at the front of the gullies tends to demonstrate that the flow became relatively highly concentrated in liquid downstream and all the water could have been lost in the final stage of the flow. This process could explain the lack of terminal lobes at the front of the gullies. We conclude that a process of formation similar to terrestrial debris flows is plausible. The large amount of liquid water involved requires formation of Martian gullies on dunes during a warmer climatic episode

Morphological characterization of springtime seasonal activity on the Russell dune (Mars)

International audienceFrom a theoretical point of view, pure liquid water is not likely to be found at the present time on the Martian surface because atmospheric pressure/temperature conditions are below the water triple-point. However, gullies discovered by Malin and Edgett (2000) suggest that significant amounts of liquid water have flowed on Mars in a recent past. Recent works showed that Martian dunes have exhibited modifications over the past years, including topographic changes on aprons and new channel incisions into dune surfaces (Diniega et al., 2010; Dundas et al., 2010; Reiss et al., 2010; Hansen et al., 2011). These seasonal activities can be explained by CO 2 frost processes (Diniega et al., 2010; Dundas et al., 2010; Hansen et al., 2011) or melting of water frost and/or near surface ice triggering sand-water flows (Reiss et al., 2010). The new possibility given by HiRISE images to perform precise monitoring of present modifications of the surface of Mars allows to improve our understanding of the seasonal activity and of the topographic evolution of dunes. Numerous changes could be observed during the last three Martian years. Here, we show that there is a perennial activity on the Martian dune Russell: surface flows appear seasonally (Reiss et al., 2010), after the total disappearance of CO 2 at spring (Gardin et al., 2010; Reiss et al., 2010), and are able to erode their substrate. This perennial activity is constituted by a complex interconnected rill system that is recorded all year long and which grows from one year to the next at a rate of 10000 m2.yr-1. These flows are viscous and able to erode as well to transport a non negligible quantity of sand with a grain size of 500±100 [U+F06D]m at a minimum velocity of ∼1.4.10-4m.s-1. These flows could be composed in part of liquid water. The origin of the liquid water is probably from the melting of the water ice (accumulated on the dune surface by vapour condensation during winter) at spring or/and from the defrosting of a small active layer of permafrost. There are at least four processes that could explain the physical properties of this perennial activity: (1) brine flow (Chevrier et al., 2008), (2) liquid water flow mixed with sand (Reiss et al., 2010), (3) liquid water flow mixed with snow or ice, (4) a combination of the previous three processes

Morphological characterization of springtime seasonal activity on the Russell dune (Mars)

International audienceFrom a theoretical point of view, pure liquid water is not likely to be found at the present time on the Martian surface because atmospheric pressure/temperature conditions are below the water triple-point. However, gullies discovered by Malin and Edgett (2000) suggest that significant amounts of liquid water have flowed on Mars in a recent past. Recent works showed that Martian dunes have exhibited modifications over the past years, including topographic changes on aprons and new channel incisions into dune surfaces (Diniega et al., 2010; Dundas et al., 2010; Reiss et al., 2010; Hansen et al., 2011). These seasonal activities can be explained by CO 2 frost processes (Diniega et al., 2010; Dundas et al., 2010; Hansen et al., 2011) or melting of water frost and/or near surface ice triggering sand-water flows (Reiss et al., 2010). The new possibility given by HiRISE images to perform precise monitoring of present modifications of the surface of Mars allows to improve our understanding of the seasonal activity and of the topographic evolution of dunes. Numerous changes could be observed during the last three Martian years. Here, we show that there is a perennial activity on the Martian dune Russell: surface flows appear seasonally (Reiss et al., 2010), after the total disappearance of CO 2 at spring (Gardin et al., 2010; Reiss et al., 2010), and are able to erode their substrate. This perennial activity is constituted by a complex interconnected rill system that is recorded all year long and which grows from one year to the next at a rate of 10000 m2.yr-1. These flows are viscous and able to erode as well to transport a non negligible quantity of sand with a grain size of 500±100 [U+F06D]m at a minimum velocity of ∼1.4.10-4m.s-1. These flows could be composed in part of liquid water. The origin of the liquid water is probably from the melting of the water ice (accumulated on the dune surface by vapour condensation during winter) at spring or/and from the defrosting of a small active layer of permafrost. There are at least four processes that could explain the physical properties of this perennial activity: (1) brine flow (Chevrier et al., 2008), (2) liquid water flow mixed with sand (Reiss et al., 2010), (3) liquid water flow mixed with snow or ice, (4) a combination of the previous three processes

1 2 3 Dunes on planet Tatooine: Observation of Barchan Migration at the Star Wars film set in Tunisia 4 5 6 7

Sand dune migration is documented with a readily-available tool (Google Earth) near Chott El Gharsa, just north-west of Tozeur, Tunisia. As fiducial markers we employ a set of buildings used to portray the fictional city Mos Espa. This set of ~20 buildings over roughly a hectare was constructed in 1997 for the movie Star Wars Episode 1 – The Phantom Menace. The site now lies between the arms of a large “pudgy ” barchan dune, which has been documented via satellite imaging in 2002, 2004, 2008 and 2009 to have moved from ~140 m away to only ~10 m away. Visits by the authors to the site in 2009 and 2011 confirm the barchan to be in a threatening position: a smaller set nearby was substantially damaged by being overrun by dunes circa 2004. The migration rate of ~15 m/yr decreases over the observation period, possibly as a result of increased local rainfall, and is consistent with barchan migration rates observed at other locations worldwide. The migration rate of this and two other barchans suggest sand transport of ~50 m 3 /m/yr, somewhat higher than would be suggested by traditional wind rose calculations: we explore possible reasons for this discrepancy. Because of the link to popular science fiction, the site may be of pedagogical interest in teaching remote sensing and geomorphic change. We also note that nearby playa surfaces and agricultural areas have a time-variable appearance. The site’s popularity as a destination for Star Wars enthusiasts results in many photograph

Immagini aeree a Tusculum: un approccio multidisciplinare

Trabajo presentado en el 2nd International Conference of Aerial Archaeology (Secondo Convegno Internazionale di Archeologia Aerea), celebrado en Roma del 3 al 5 de febrero de 2016.Since 1994, the Escuela Española de Historia y Arqueología en Roma-CSIC coordinates a research project focusing on the ancient site of Tusculum (Monte Porzio Catone) located less than 30 km. south-east of Rome. This is the institutional project of the CSIC (Spanish National Research Council) in Italy to which many universities and research bodies both Spanish and Italian have contributed. In 2012, a new multidisciplinary archaeological project, titled "Tusculum medievale: territorio, paesaggio economia e società" (Medieval Tusculum: territory, landscape, economy and society), focusing on the post-classical phases of the site, was initiated with a clear willingness to explore novel research trends and different methodological approaches. These have included aerial archaeology, geophysical surveys and archeobiological studies which have been developed with the aim of improving our knowledge on the less-known phases of the city During the last 4 years, the use of aerial images has allowed a better understanding of the urban structure of the medieval city. In fact, in 2012 and 2013 a series of UAV low-level flights over the entire archaeological area were carried out in collaboration with the International Research School of Planetary Science (Università ¿G. D¿Annunzio¿ from Chieti-Pescara) which have allowed the development of a new digital cartographic base of the site. Furthermore, during the 2013-2014 season of excavation, a series of kite aerial photographies (KAP) were taken over the acropolis (Rocca), heart of the Medieval city, producing a new set of medium/low-level (at 50-100 m. of altitude) georeferenced photographs. Finally, during the 2015 archaeological campaign, in cooperation with the Instituto de Agricultura Sostenible (IAS-CSIC) new flights have been carried out using thermal, hyperspectral, infrared and RGB cameras to obtain a diverse range of images. The integration of the data provided by aerial archaeology together with the analysis of the underground features through the use of geophysical techniches (georadar and magnetometry) and the archaeological data coming from excavations are making possible a detailed study of the city urban development as well as the exploration of the real extension of the Medieval city. What is more, the development of non-invasive techniques have permitted the identification of areas of higher archaeological interest and, therefore, the possibility of planning theis excavation saving time and costs.N