Early taphonomic processes in a microbial-based sedimentary system from a temperate salt-pan site (Cervia salterns, Italy)

In the only salt evaporation pond retaining its natural setting of the historic Salina di Cervia (Italy), the northernmost salterns of the Mediterranean area, a number of potentially preservable textures derive from the interactions between photosynthetic mat producers and the sedimentary substrate. These morphologies occur at the beginning of the taphonomic processes when repeated emerged-submerged conditions take place. In these conditions the cohesive nature of the diatom- and cyanobacterial-derived mucilage favours the stabilization of otherwise ephemera structures. Surface micromorphologies for which diatoms and cyanobacteria have played some active role when still living in the soft microlayer and down to the sediment-water interface, such as during the gliding motility, can overcome the surface layer of most intense mixing (i.e., the taphonomically active zone) and keep traces of them in the fossil record either as body fossils or as texture contributors. Tiny microbial-derived remnants, such as filaments and biofilm strands of halotolerant microorganisms, while fragile upon their formation, can therefore stabilize as biosignatures when combined with salt precipitation. Halophilic and halotolerant ecosystems are models for life in extreme environments (analogue sites) with similarity to those strongly suspected to occur and/or have occurred on Mars and on other planetary bodies. The study of hypersaline systems such as Salina di Cervia which harbour diverse and abundant microbial life, can be relevant for astrobiology since it allows the investigation of potential biosignatures and their preservation, and of further understand the range of conditions and the planetary processes sustaining potentially habitable systems

Unusual manganese enrichment in the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa

An unusual sediment-hosted manganese deposit is described from the Mesoarchean Mozaan Group, Pongola Supergroup, South Africa. MnO contents up to 15 wt.% were observed in marine clastic and chemical sedimentary rocks. Mn enrichment is interpreted to have resulted from the hydrothermal alteration of manganiferous shale and BIF parent rocks, the primary MnO contents of which are as high as 8.5 wt.%. A detailed mineralogical and petrographic study shows that these parent rocks are characterized by manganoan siderite, ferroan rhodochrosite and other Mn-Fe-rich mineral phases, such as kutnohorite and Fe-Mn-chlorite. Their hypogene alteration gave rise to a diversification of mineral assemblages where ferroan tephroite, calcian rhodochrosite, rhodochrosite, pyrochroite, pyrophanite, cronstedtite, manganoan Fe-rich chlorite and manganoan phlogopite partially or totally replaced the previous mineral assemblage. Thermodynamic modeling performed on chlorite phases associated with the described mineral assemblages illustrates a decrease of average crystallization temperatures from ca. 310 °C during early metamorphic stages to ca. 250 °C during a hydrothermal stage. Mineral transformation processes were thus related to retrograde metamorphism and/or hydrothermal alteration post-dating metamorphism and gave rise to progressive Mn enrichment from unaltered parent to altered rocks. The timing of hypogene alteration was constrained by 40Ar/39Ar dating to between about 1500 and 1100 Ma ago, reflecting tectonic processes associated with the Namaqua-Natal orogeny along the southern Kaapvaal Craton margin. Manganiferous shale and BIF of the Mozaan Group may represent the oldest known examples of primary sedimentary Mn deposition, related to oxidation of dissolved Mn(II) by free oxygen in a shallow marine environment. Oxygenic photosynthesis would have acted as a first-order control during Mn precipitation. This hypothesis opens a new perspective for better constraining secular evolution of sediment-hosted mineral deposits linked to oxygen levels in the atmosphere-hydrosphere system during the Archean Eon

Editorial: Terrestrial field analogues for planetary exploration

Field analogues for planetary exploration are terrestrial environments and/or associated geomaterials that share physical, chemical and/or geological similarities with modern or ancient extraterrestrial environments or with conditions or features that approximate those found on other planetary bodies

Ultra-small microorganisms in the polyextreme conditions of the Dallol volcano, Northern Afar, Ethiopia

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars

Bioturbation beyond Earth: potential, methods and models of astroichnology

Traces – burrows, borings, footprints – are important evidences of biological behaviour on Earth, yet they received relatively little attention in the field of astrobiology. This study aims to discuss the application of ichnology (i.e. the study of life activity traces) to the search for past and modern life beyond Earth (i.e. herein called Astroichnology)

Biogeochemical Cycling in Globally Distributed Hypersaline Environments

Studying extremophiles allows the characterisation of the boundaries of life on Earth and the identification of metabolic processes that fuel biogeochemical cycling under extreme conditions. Here we present an analysis of the microbiomes of globally distributed hypersaline environments. We screened published metagenomes produced from a range of hypersaline environments (Marine salterns in Spain, hypersaline lakes in Chile and Antarctica, and soda lakes in Egypt and Mongolia [1–5]) for the presence, diversity, and abundance of shared functional genes that encode for the enzymes relevant to biogeochemical cycling. The study was expanded by generating metagenomes from DNA extracted from the salt and water of an Ethiopian hypersaline lake in the Dallol Depression. Analysis was performed to compare the functional gene profiles between the hypersaline environments. The microbial community within the Ethiopian Lake was comprised of Cyanobacteria, Candidate Phyla, and halophilic bacteria and archaea. Screening of the metagenomes identified that phototrophs in hypersaline environments typically possessed the majority of the genes relating to carbon dioxide and nitrogen fixation, indicating that they play a major role in driving both the carbon and nitrogen cycles [6-7]. High abundances of genes involved in denitrification, methylamine utilisation, and carbon monoxide oxidation classified as Halobacterial were also identified in all the metagenomes, indicating that these taxa are also key players in biogeochemical cycling in hypersaline environments [8-9]. Cultivation efforts are required to further define the interactions between the distinct functional clades identified in the hypersaline environments. References: 1. Zhao D, Zhang S, Xue Q, Chen J, Zhou J, Cheng F, et al. Front Microbiol. 2020;11(July):1–17. 2. Hagagy N, Hamedo H, Elshafi N, Selim S. Shotgun Metagenomic Sequencing of Extremophilic Community from Soda Lake, Ga’ar Lake, in Wadi Al-Natrun, Egyt. Egypt. J. Exp. Biol. (Bot.). 2021;1. 3. Fernandez AB, Ghai R, Martin-Cuadrado AB, Sanchez-Porro C, Rodriguez-Valera F, Ventosa A. Genome Announc. 2013;1(6). 4. Yau S, Lauro FM, Williams TJ, Demaere MZ, Brown M v., Rich J, et al. ISME Journal. 2013;7(10):1944–61. 5. Kurth D, Elias D, Rasuk MC, Contreras M, Farias ME. PLoS One. 2021;16:1–21. 6. Lay CY, Mykytczuk NCS, Yergeau É, Lamarche-Gagnon G, Greer CW, et al. Appl Environ Microbiol 2013;79:3637–3648. 7. Mehda S, Ángeles Muñoz-Martín M, Oustani M, Hamdi-Aïssa B, Perona E, et al. Microorganisms 2021;9:1–27. 8. Sorokin DY, Merkel AY, Messina E, Tugui C, Pabst M, et al. ISME J 2022;1–13. 9. King GM. Proc Natl Acad Sci 2003;51:278–291. Acknowledgements to the Europlanet Society, Science and Technology Facilities Council and the Research England Expanding Excellence in England (E3) fund for funding the research

Draft genome sequence of <i>Bacillus</i> sp. strain X and <i>Salarachaeum</i> sp. strain III isolated from Lake Karum, Danakil Depression, Ethiopia

Here, we report the draft genome sequences of strains of Bacillus and Salarachaeum that were isolated from hypersaline water samples collected from Lake Karum, Danakil Depression, Ethiopia. The sequences pave the way for more targeted studies into the potential biological activities and secondary metabolite synthesis of these organisms

Late Pleistocene–Holocene Palaeoenvironmental Evolution of the Makgadikgadi Basin, Central Kalahari, Botswana: New Evidence From Shallow Sediments and Ostracod Fauna

The Makgadikgadi Basin in Botswana hosts a system of salt lakes, which developed from the Upper Pleistocene onward due to the gradual shrinking of the giant Lake Palaeo-Makgadikgadi. Stratigraphic and palaeoclimatic studies of this area are difficult due to the influence of several factors, such as a complex history of regional tectonic activities, as well as climatic changes coupled with dryland diagenetic processes. This lake, in the central Kalahari, is the key to understanding the climatic variability in the southern part of Africa in the Quaternary and has played an important role in the evolution of numerous taxa, including our own. In this study, detailed sedimentological analyses (grain size and major elements distribution) of shallow sediments from the Makgadikgadi Pans were combined with the first comprehensive study of the encountered ostracod fauna to establish trends in the environmental changes in the area from the late Quaternary. Ostracod fossil assemblages from the cores of the Makgadikgadi Pans are dominated by the Limnocythere ssp., an opportunistic taxa commonly colonizing the littoral areas of shallow evaporative, ephemeral lakes, together with the subordinate occurrences of Sarcypridopsis ochracea, Sclerocypris cf. bicornis, Candonopsis spp., and Ilyocypris spp. The sediments from the pans show fluctuations in the Cl/K and Ca/Cl ratios, often in phase with the relative abundance of Limnocythere suggesting a cyclicity induced by changes of salinity and alkalinity in the water. This multi-proxy study of the cores collected from the pans suggests a Late Pleistocene shallow, playa lake environment with strongly alkaline water, interrupted by a prolonged drought with sustained aeolian conditions between ∼16 and 2 ka BP. Increasing diversity of ostracod fauna in the top 20–30 cm of the cores indicates that a temporary shift toward higher humidity occurred around 2–1.5 ka BP and lasted through the Medieval Warm Period. This humid period was followed by an overall desiccation trend that started with the Little Ice Age and continues until the present day

Can facies act as a chronostratigraphical tool?

Results demonstrate that the Appalachian ironstones seem to reflect the same microbially-mediated iron mineralization already documented in the Carnic Alps

Diversity of Microbial Mats in the Makgadikgadi Salt Pans, Botswana

The Makgadikgadi Salt Pans are the remnants of a mega paleo-lake system in the central Kalahari, Botswana. Today, the Makgadikgadi Basin is an arid to semi-arid area receiving water of meteoric origin during the short, wet season. Large microbial mats, which support primary production, are formed due to desiccation during the dry season. This study aimed to characterise the microbial diversity of the microbial mats and the underlying sediment. The focus was the Ntwetwe Pan, located west of the Makgadikgadi Basin. Metagenomic analyses demonstrated that the mats consisted of a high relative abundance of Cyanobacteriota (synonym Cyanobacteria) (20.50–41.47%), Pseudomonadota (synonym Proteobacteria) (15.71 to 32.18%), and Actinomycetota (synonym Actinobacteria) (8.53–32.56%). In the underlying sediments, Pseudomonadota, Actinomycetota, and Euryarchaeota represented over 70% of the community. Localised fluctuations in water content and pH did not significantly affect the microbial diversity of the sediment or the mats