Fluvio-lacustrine Environment Research Articles

Facies, diagenesis, and palaeo-environment significances of the Plio-Quaternary fluvio-lacustrine deposits of Ain Cheggag region, Sais foreland basin, Morocco

Fluvio-lacustrine deposits are promising archives that afford to decipher climate and tectonic signatures, typically when evidence of changes in the depositional settings therein is remarkable. As such, the present work coveys a case study whose fluvio-lacustrine deposits may serve to provide insights into climate and tectonic controls on palaeoenvironmental settings. The study area lies in the northwestern portion of Ain Cheggag, southeastern the Sais foreland basin (northern Morocco). The lithostratigraphical analysis of Plio-Quaternary fluvio-lacustrine deposits in the area has enabled the identification of nine facies. The depositional systems are organized into three deposit units, each of which reflects a typical depositional environment. The first (lower) unit consists of detrital facies implying deposition in alluvial-dominated settings. The alternation of detrital and carbonate facies giving way to the second (middle) unit suggests sedimentation in a fluvio-lacustrine environment. Whilst being carbonate-rich, the third (upper) unit reflects a shift into lacustrine-dominated settings. Accordingly, the vertical succession of the sedimentary pile delivers remarkable insights into a general palaeo-environmental shift from alluvial settings, with enhanced pedogenesis processes, towards carbonate-dominated lacustrine conditions where early- and late-stage diagenesis processes would have prevailed. This broad shift in depositional systems is likely to be the response of palaeohydrological changes that are modulated both by the neotectonic subsidence background and, specifically, the general palaeoclimate evolution towards more humid conditions. Bioturbation, desiccation, and void-filling with internal sediments are key features of early-stage diagenesis processes, whereas cementation, micritization, recrystallization, dissolution, and iron and manganese oxidation are the main features of late-stage diagenesis altering the primary structures of the studied deposits. Finally, we highlight the significance of fluviolacustrine deposits in deciphering palaeoclimatic signatures and tectonic implications.

Paleoenvironmental contribution and visual kerogen assessment of some Upper Cretaceous sediments from southern Egypt

We investigated the palynological organic matter (POM) recovered from shale horizons, intercalating the Nubian-type sandstones in middle Egypt, for paleoenvironmental reconstruction. Our palynofacies are dominated by either amorphous organic matter (AOM) or phytoclasts whereas palynomorphs are relatively rare, but not uncommon. The palynofacies categories revealed two different palynofacies types, reflecting estuarine/tidal and fluvio-lacustrine environments for the Maghrabi and the basal Quseir formations, respectively. The kerogen composition of our investigated material and the colors of the thin-walled spores suggest possible sources of hydrocarbons, which are poorly explored in the middle and southern areas of Egypt. Our findings confirmed the previously described marine origin of the Maghrabi Formation. The complete missing of any marine palynomorphs suggests that the basal sediments of the Quseir Formation are almost exclusively of terrestrial origin. This may reveal that the worldwide Late Cretaceous transgression was not effective during deposition of these basal clastics.

Petrography and geochemistry of siliciclastic sediments in Permo-Triassic transition from the southern Pranhita-Godavari Gondwana basin, India: Implications for paleoclimate

The Kamthi Formation, in the intracratonic Pranhita-Godavari Gondwana rift basin, bore signatures of climate change from a warm humid climate in Late Permian to hot arid during the Early Triassic. Sedimentation took place mainly under fluvial conditions. The Kamthi sediments were unaffected by burial diagenesis and the source remained the same, therefore this provides an excellent opportunity to study the climatic influence on petrogenesis in an intracratonic rift basin. Subsurface palynofacies data of Kamthi Formation from the southern part of the basin established the presence of Upper Permian rock units equivalent to the Raniganj Formation, which are overlain by Lower Triassic sediments equivalent to Panchet Formation of the Damodar valley Gondwana basins, and are separated by a gradational contact. QFL and trace element compositions reveal transitional continental to craton interior provenance with dominantly felsic source areas, along with some meta-sedimentary and mafic components. Dominance of kaolinite, coal, alteration of K-feldspar, and biotite in the Raniganj equivalent sandstones attests to a humid climate. The presence of mostly fresh K-feldspar, ferruginous matrices, Fe-carbonate nodules, cutans, and microcrystalline silica cement in the Panchet equivalent sandstones mark a shift from humid to arid/semi-arid. This climatic shift is not reflected in the uniform feldspatho-quartzose to quartzose sandstone compositions and mudstone major oxide compositions. The mudstones are depleted in mobile elements, have low K2O/Al2O3 (0.11–0.18), low ICV (0.35–0.72), high SiO2/Al2O3 (2.3–3.4), high K2O/Na2O and moderately high CIA (80.12–87.05) that collectively suggest moderately intense weathering. Despite the humid climate, the Raniganj Formation equivalent rock units did not attain the highest mineralogical maturity due to proximity to relatively high-relief source areas in a fluviolacustrine environment. This relationship resulted in a lack of short-term sediment storage that favoured rapid erosion and sedimentation.

Taxonomy, biostratigraphy and paleoecology of non-marine ostracod fauna of the Maastrichtian intertrappean beds of the lower Narmada Basin, Malwa Plateau, India

Paleontological investigations in the Late Cretaceous sedimentary units associated with Deccan traps of the lower Narmada valley, western Central India were carried out in order to ascertain ostracod diversity and its biostratigraphic and paleoecological implications. Eighteen species of twelve genera of Cytheroidea, Darwinuloidea and Cypridoidea ostracods recovered from four sections of the Deccan intertrappean beds are described. The species include the specimens from two new intertrappean sections, Kakarda and Bara Bheralya and additional ostracod taxa recorded from two previously studied sections, Gujri and Uthawali. The biostratigraphic, taphonomic and paleoecological analysis of the newely recovered ostracod assemblage in conjunction with the recent published data from the study area depict Maastrichtian age and freshwater fluvio-lacustrine environment for the studied sections.

Geochemical bio-signatures in Martian analogue basaltic environments using laboratory experiments and thermochemical modelling

The identification of geochemical bio-signatures is important for assessing whether life existed on early Mars. In this paper, experimental microbiology and thermochemical modelling were combined to identify potential inorganic bio-signatures for life detection on early Mars. An analogue mixed microbial community from an analogue terrestrial fluvio-lacustrine environment similar to an ancient lacustrine system at Gale Crater was used to study microbial dissolution of a basalt regolith simulant and the formation of bio-signatures over a short time frame (1°month) at 14°C, 2 bar. Microbial growth influenced element dissolution (Mg, Fe, Mn, Ca and K) and the formation of morphologies and Fe-Si amorphous layers on mineral surfaces. Thermochemical models were performed at 14°C, 2 bar; the results were compared with experimental data to predict bio-signatures that would occur over geological timescales. The pH was varied to simulate abiotic and biotic experimental conditions. Model results suggest that, at water to rock ratios of 100 to 38, a less complex secondary mineral assemblage forms during biotic dissolution compared to abiotic weathering. Carbonates, quartz, pyrite and hydroxyapatite form under biotic conditions, whereas in the abiotic system magnetite and phyllosilicates would also precipitate. These results could be used to distinguish between abiotic and biotic basalt weathering processes, aiding the interpretation of data from Mars exploration missions.

Metallogenic implications of volcanic quiescence during continental flood basalt eruption – The case of sediment hosted Mn-Fe mineralization in the Ethiopian volcanic plateau

The north-western volcanic province of Ethiopia is constituted by Continental Flood Basalt and Shield Volcanoes. A paucity in volcanism allowed the deposition of immature continental sediments in fluviolacustrine environment. A recent geologic expedition in the north-western volcanic plateau discovered an Mn-Fe mineralization hosted in nearly 100 m thick mudrock and volcaniclastic sandstone at two localities called Kulfamba and Wogeltena. This research was conducted to investigate the Mn-Fe mineralization hosted in the inter-trappean sediments. Geologic mapping, mineralogic and geochemical methods were employed to investigate the orebodies and host sediments. Mineralogical investigation was carried out using X-ray Diffraction, thin and polished section analysis under petrographic and ore microscopy. Major and trace element analyses was also conducted using ICP-MS. The Mn-Fe orebodies are dominantly layered occupying the transition zone between the mudrock and the sandstone. The orebody is about 1.6 m thick occupying the upper part of the mudrock (the Fe orebody) and the lower part of the sandstone (the Mn orebody). Mn ore is dominated by pyrolusite followed by manganite. Fe is in the form of hematite and goethite. Average ore grade is 34% MnO and 38% Fe2O3. Gangue minerals are quartz, alkali feldspar and clays. The dominantly layered nature of the orebody, absence of typical hydrothermal Mn ore minerals like todorokite and birnessite, high concentration of ∑REE, and other geochemical data support dominantly hydrogenous origin. The presence of distinct orebodies of Mn and Fe suggests the presence of redox-stratified water in the depositional environment. Sporadic occurrences of vein type, concretionary, and botryoidal textures of ores signify later hydrothermal and weathering remobilization and overprinting on the previously formed hydrogenous deposit. The geographic distribution of exposed sediments, their thickness and facies variations throughout the plateau suggests existence of a large shallow lake fed by streams flowing towards northern/north-eastern part of the plateau.

Characteristics, Origins, and Biosignature Preservation Potential of Carbonate-Bearing Rocks Within and Outside of Jezero Crater.

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine‐bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake‐inhabiting lifeforms. Here, we show that carbonate‐bearing rocks within and outside of Jezero crater have the same range of visible‐to‐near‐infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate‐bearing rock cross‐sections in Jezero crater are ∼75–90 m thicker than typical ROB unit cross‐sections in the Nili Fossae region, but have similar thicknesses to ROB unit exposures in Libya Montes. These similarities in carbonate properties within and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg‐ and more Fe‐rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non‐deltaic carbonates within and outside of Jezero crater.

First 2D and 3D interpretative models of sedimentation in the Cretaceous Hama-koussou sedimentary basin: Litho-bio-stratigraphy and palaeoenvironment records

The Hama-Koussou Basin is one of the offset structures of the eastern end of the Benue Trough in Northern Cameroon. This sedimentary basin is an asymmetrical syncline whose axis is strongly shifted towards the East, filled predominantly with Cretaceous deposits, The basin has experienced at least three (3) phases of sedimentation during its geological history: two (2) fluvial phases with one at the top and the second at the bottom consisting of conglomerate, micro-conglomerate, and sandstone, sandwiching one fluvio-lacustrine phase consisting of fossiliferous claystones and marlstones with intercalations of siltstones and carbonate cemented fine sandstone. Numerous sedimentary structures including planar, oblique, and cross stratifications, convolute bedding, desiccation cracks, ripple marks and loadcast have been recorded. The mineral assemblage is dominated by quartz, plagioclase, mica and microcline, accompagnied by diagenetic phases (iron oxide, silica and carbonate). Clay minerals consist of kaolinite, illite and chlorite/smectite. Palynofloral analysis reveals various taxa indicative of a fluvio-lacustrine environment: These include Classopollis sp., Eucommiidites sp., Concavisporites sp., Cicatricosisporites sp, Araucariacites australis, Callialasporites dampieri, Callialasporites microvelatus. The occurrence of Callialasporites microvelatus confirms the Cretaceous age whereas age determination for all other samples was uncertain due to scarcity in palynomorphs. Low numbers of bisaccate, grass, and other angiosperm pollen grains may be indicative of a Cenozoic or younger age, although contamination by modern pollens cannot be excluded.The region experienced volcanism represented by explosive and effusive phases, recorded as sills and dykes. Plutonism is characterized by the establishment of intrusive granite. The East-West elongation observed in the HSB is the same in the Mayo-Oulo-Lere and Babouri Figuil basins and can be interpreted as the result of the same tectonic event linked to the opening of the Atlantic Ocean resulting in the formation of the Benue Trough and adjoins basins.

Calcretes from the Quaternary alluvial deposit of Purna basin, central India: Lithological and climatic controls

The Purna alluvial basin of central India, infilled largely with areno-argillaceous sediments of Quaternary age, is also marked by occurrences of both pedogenic and non pedogenic calcretes of diverse shape and size. The previous includes nodular, laminar, hardpan and root calcretes along with rhizolith balls and rhizospheres, whereas non pedogenic type is represented by groundwater calcretes. These calcretes have been investigated for their morphological details, lithological associations in both vertical and lateral profiles of the alluvial deposit and paleoclimatic reconstructions. This study shows that the area under investigation has undergone through subtropical, arid and semiarid climatic conditions having low to medium humidity, high rainfall and evaporation that favored formation of various types of calcretes. Nodular calcretes, the most dominant morphotype, are preserved in a wide spectrum of lithology and fluvio-lacustrine environment. To some extent, their formation is controlled by parent material, irregular rainfall and mild temperature. Rapid accumulation of carbonate material, in and around the plant roots giving rise root calcretes of various shapes and size is a common phenomenon in warm and dry climatic conditions. Both hardpan and groundwater calcretes are formed due to CaCO3 precipitations in humid condition having heavy rainfall. Besides, the later also indicates arid to semiarid conditions facilitating the movement of Ca rich solution in the unconsolidated sediments through capillary action that later deposited calcium carbonate in the voids during wet and dry conditions. Well preserved rhizolith balls and rhizospheres in the palaeosols, constituting together the lower part of succession in almost entire alluvial basin, acts as potential paleoclimatic indicator.

Thermodynamic Constraints on Smectite and Iron Oxide Formation at Gale Crater, Mars: Insights into Potential Free Energy from Aerobic Fe Oxidation in Lake Water–Groundwater Mixing Zone

The presence of saponite and iron oxides in Sheepbed mudstone of Yellowknife Bay at Gale crater on Mars is considered as evidence of a habitable fluvio-lacustrine environment for chemolithoautotrophy. However, the energetic availability for metabolic reactions is poorly constrained. Herein, we propose the possible mixing of surface water and groundwater that (i) explains the formation of magnetite and hematite detected in Sheepbed mudstone and (ii) may work as a potential habitable zone for aerobic Fe2+-oxidizing microbes. Our thermodynamic modeling of water–rock reactions revealed that the formation of abundant saponite in Sheepbed mudstone may occur under various conditions of water-to-rock mass ratios, temperatures (5–200 °C), and initial fluid compositions. In contrast, the formation of iron oxides in the mudstone can be explained only by the mixing of Fe2+-rich groundwater and more oxidized surface waters, where the Fe2+-rich groundwater can be generated by the low-temperature water–rock reactions with a CO2-bearing initial fluid. The calculated bioavailable energy of aerobic Fe2+ oxidation in the fluid-mixing zone on Mars is similar to that estimated for a fluid-mixing zone on Earth actually inhabited by aerobic Fe2+-oxidizing microbes. The findings will contribute to a better understanding of potential habitability on Mars.

Mechanisms of sedimentation in lacustrine environment of Babouri-Figuil and Mayo Oulo-Lere basins deposits (North Cameroon) during the Southern Atlantic opening: sedimentary structures and geochemistry constraints

Sedimentary structures are very useful to characterize sedimentation environments. In this study, sedimentary structures are documented in the Lower Cretaceous Babouri-Figuil and Mayo Oulo-Lere intracontinental Basins whose genesis is linked to the opening of the Southern Atlantic Ocean. Geochemical data is also presented with the aim to discriminate the paleoenvironment. Field investigations and facies analyses revealed synsedimentary and postsedimentary structures related or not to tectonic. Synsedimentary structures not affected by tectonic are lamination or bedding (rhythmic), graded bedding, cross-stratification, loads casts, channels, and ripple marks. Those affected by tectonic are convolute bedding, slump (Slump sensus stricto and olistolith). Desiccation cracks and print marks are postsedimentary structures not related to tectonic; others are stratigraphic unconformity, oblique bedding, clastic injection, and volcanic veins. The bottom of the sequence in the two basins is fluvio-lacustrine deposits with oblique stratification and global positive graded bedding; sometimes there is alternation of positive and negative graded beddings related to progressive variation of energy of sedimentation from high to low and low to high. The intermediate level is lacustrine dominated by lamination or bedding that characterizes a calm sedimentation environment marked by regular seasonal fluctuation. The ripple marks, desiccation cracks, and dinosaur footprints indicate the emersion period, and their fossilization indicates slow phases of sedimentation. Channels and load casts correspond to a rapid sedimentation phase. Seismic shocks at time break the fragile stability of deposited materials causing gravitational flows of the sublacustrine avalanche type and give olistolith and convolute bedding to slumps. The clastic or chemical injections and volcanic veins are related to brittle tectonic that affects consolidated deposits. From the geochemical data, the high accumulation of LREE (average: 142.93 ppm) over HREE (average: 13.10 ppm); La/La* generally 2) and the slight to very slight negative Ce/Ce* (0.87–0.99) suggest the nonmarine deposition, and the Y/Ho ratios (< 45) and ratios indicate river condition or transportation. The Sr/Ba ratios, ranging from 0.55 to 6.41, suggest a freshwater environment with fluctuant salinity and sometimes hypersaline (Hypersaline Lake). Thus the synsedimentary structures were essentially formed in lacustrine milieu, and some structures such as graded bedding and cross-stratification affecting the basal deposit indicate a fluviatile to fluvio-lacustrine environment.

A wet climatic terrestrial carbonate record in the middle-upper Pleistocene, north Tunisia

The middle-upper Pleistocene Borj Edouane unit records a singular spectrum of terrestrial carbonates in a shallow depression on Cretaceous rocks in north Tunisia. This study aims to decipher the depositional system and reveal the climatic and paleohydrological conditions of the carbonate facies deposition. They are grouped into two facies associations: (1) a calcrete–palustrine and (2) a composite microbialite-travertine, surrounded by a marginal alluvial association along the western and northern borders of the basin. The calcrete–palustrine association extends along the westernmost south–north strip of the basin, reflecting calcrete development on distal alluvial fan deposits and pedogenic modification (palustrine facies) of shallow fresh-water carbonates. The composite microbialite-travertine, extending along north–south strips in the middle and eastern areas of the basin, consists of microbialite, clastic microbialite–travertine, and travertine associations. Microbialites were developed in fluvio-lacustrine environments within the central strip and pass eastward into the travertines through the clastic microbialite–travertine association. The latter was deposited from currents and in shallow ponds along a bench next to the travertine-depositing springs, linked to a fault system in the eastern margin of the basin. The carbonate depositional system shows an asymmetrical distribution of facies that parallels the paleohydrological asymmetry along the basin. Water supply was restricted in the western part of the basin and abundant in its eastern areas linked to spring waters that kept stable lake levels in the basin center, favoring the genesis of microbialites. The presence of lacustrine carbonates in the studied area indicates higher water availability during the Middle-Late Pleistocene and that climate in North Africa was wetter than today.

Stable climate in India during Deccan volcanism suggests limited influence on K–Pg extinction

Large igneous provinces (LIPs) have been temporally correlated to mass extinctions throughout the Phanerozoic, including the emplacement of the Deccan Volcanic Province (DVP; 66.3–65.6 Ma) in western and central India, which has been invoked as either a cause or exacerbating factor in the Cretaceous-Paleogene (K-Pg) extinction. However, relatively little is known about local paleoclimatic and paleoenvironmental responses to volcanism. To investigate the DVP's role as a driver of local environmental change and to provide climatic background for known ecological shifts, new inter-basaltic paleosol profiles at the eastern edge of the DVP are used in conjunction with profiles from the literature to reconstruct paleoclimate and terrestrial environments before and after the K–Pg. These profiles provide a novel opportunity to study the sediments within basalt flows before, during, and after a mass extinction event and in the midst of a LIP emplacement event. Paleoclimate proxies and the Floral Humidity Province proxy reflect little long-term change in either climate or environment across the K–Pg, with stable precipitation values and temperatures accompanied by a constant forest signal. These interpretations are corroborated by macrofloral records and sedimentology from India, which suggest some environmental turnover but generally support a forested, fluvio-lacustrine environment throughout the duration of volcanism. Our results support the possibility of rapid recovery times for terrestrial ecosystems during volcanism and suggest that while DVP eruptions may have exacerbated long-term environmental perturbation, the emplacement of the DVP is not likely to have caused the terrestrial mass extinction at the K–Pg boundary.

Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Sedimentary deposits characterized by the Mars Science Laboratory Curiosity rover provide evidence that Gale crater, Mars intermittently hosted a fluvio-lacustrine environment during the Hesperian. However, estimates of the CO2 content of the atmosphere at the time the sediments in Gale crater were deposited are far less than needed by any climate model to maintain temperatures warm enough for sustained open water lake conditions due to the low solar energy input available at that time. To reconcile some of the in-situ sedimentological evidence for liquid water with climate modeling studies, we perform the water budget of evaporation against precipitation to estimate the minimum lifetimes and the rainfall requirements for open water and ice-covered lakes in Gale crater, for a wide range of pressures and temperatures. We found that both open water and ice-covered lakes are possible, and that ice-covered lakes provide better consistency in regards of the low erosion rates estimates for the Hesperian. We incrementally test the existence of open water conditions using energy balance calculations for the global, regional, and seasonal temperatures, and we assess if the preservation of liquid water was possible under perennial ice covers. We found scenarios where lacustrine conditions are preserved in a cold climate, where the resupply of water by the inflow of rivers and high precipitation rates are substituted by an abutting glacier. For equatorial temperatures as low as 240 K–255 K, the ice thickness ranges from 3 to 10 m, a value comparable to the range of those for the perennially ice-covered lakes in Antarctica (3–6 m). The ice-covered lake hypothesis is a compelling way to decouple the mineralogy and the climate by limiting the gas exchanges between the sediment and the CO2 atmosphere, and it eliminates the requirement for global mean temperatures above the freezing point. Not only do ice-covered lakes provide a baseline for exploring the range of possible lake scenarios for Gale crater during the Hesperian that is fully consistent with climate studies, but also they might have been ideal environments to sustain life on Mars.

Polyonyx-like tracks from Middle-?Upper Jurassic red beds of Morocco: Implications for sauropod communities on southern margins of tethys

A new dinosaur tracksite is reported from continental red beds of the Jurassic (Late Bathonian-?Callovian) Isli Formation along the northern flank of the Aït Ali ou Ikkou Syncline of the Imilchil area, Central High Atlas, Morocco. The succession was deposited in a fluvio-lacustrine environment, and contains at least fourteen track-bearing levels. The diverse dinosaur-dominated ichnofauna includes the footprints of crocodylomorphs, pterosaurs, theropods, sauropods and ornithischians, together with numerous invertebrate traces. Here, we focus on a long sauropod trackway, which comprises nine consecutive manus-pes sets preserved as concave epireliefs. The low heteropody and asymmetry of manus prints with a large digit I (pollex) impression oriented medially, and a large triangular claw trace, which is posteriorly oriented, are characteristic of the ichnogenus Polyonyx. Different from typical Polyonyx is the narrow gauge pattern compared to the wide gauge observed in the type trackway from Portugal. Additional material from Morocco, similar to Polyonyx, comprises the trackway of a very small (?juvenile) individual found close to the main trackway, as well as a short trackway from a different locality in the Isli Formation. Our data from the Moroccan High Atlas indicates the presence of basal eusauropods in the Middle Jurassic-Early Cretaceous interval in the northwestern part of Gondwana for the first time, and suggests they inhabited a lacustrine paleoenvironment.

Paleoenvironment reconstruction of the Proterozoic carbonate platform, Ombella-M'poko formation (Central African Republic)

Petrographic studies, geochemistry, δ13C and δ18O isotopes have been used to characterize the well-preserved carbonate depositional environments of the Bobassa and Ndimba unit in the 640-565 Ma Ombella-M'poko Formation, Central African Republic. The carbonate facies are mainly composed of calcite, dolomite and quartz with some accessory minerals (opaque minerals, muscovite and pyrite). The Ca/Mg ratios show that the Bobassa carbonates are slightly metamorphosed dolomitic limestones, while those of Ndimba correspond to slightly metamorphosed highly dolomitic limestones and cipolins. The Bobassa unit recorded a depositional evolution from fluvial to peritidal environments in a possible tectonically active platform as evidenced by changes of lithology and slump structures. The Ndimba was deposited in a tidal-influenced fluvio-lacustrine environment under dry conditions. Geochemistry revealed that the Bobassa and Ndimba units recorded variable redox conditions from anoxic to oxic. The PAAS-normalized REE + Y distributions indicate that the both units were slightly altered by freshwaters and detrital materials in reduced and acidic environments. The lowest δ18O and highest δ13C values suggest warm surface waters and deeper water column respectively. The carbon isotope profiles of Bobassa and Ndimba units show values varying between −0.89 and −0.34‰ that are not stratigraphic coeval with the cap carbonates δ13C profiles deposited in the aftermath Marinoan Glaciation, but rather are correlated to the middle to upper part of the Schisto-Calcaire Group in Gabon and Republic of Congo and the time-equivalent Lukala Subgroup in DRC.

An improved method for paleoflood reconstruction and flooding phase identification, applied to the Meuse River in the Netherlands

This study investigates Holocene floodplain evolution and flooding phases as experienced in the Lower Meuse catchment, primarily based on grain-size distributions of channel-fill and floodplain deposits in sediment cores. The presence of post-depositional Fe[sbnd]Mn concretions and resistant organic particulate materials impedes the direct use of grain-size data. By combining end-member modelling results with laboratory observations, we have constructed a Flood Energy Index (FEI), which allows identification of phases of past increased flooding from the grain-size signal. Since concretions and organic-rich sediments regularly occur in floodplain sediments, we emphasize that the quality of a grain-size dataset should be assessed prior to its use for reconstruction of flood events. We suggest that the new approach has potential to become standardized within paleoflood research. The temporal variation of FEI in Meuse sediment cores highlights multi-centennial flooding phases occurring at c. 8500, c. 8000, c. 7600, c. 7000 and c. 5900 cal BP within the fluvio-lacustrine environment (early–middle Holocene). The record of low flood activity in the Subboreal is attributed to a cooler and dryer climate anomaly after the Holocene Climatic Optimum. In the late Holocene, the first flooding phase occurring at c. 2800 cal BP can be linked to the 2.8 ka climate anomaly. During the last two thousand years, the variation of FEI index reveals oscillating flood regimes in the Lower Meuse floodplain. The last three recorded flooding phases most likely coincide with the Roman Period (c. 12 BCE–250 CE), the Medieval Warm Period (c. 950–1400 CE) and the Little Ice Age (c. 1400–850 CE). Despite uncertainty in the age-model, the rapid accumulation rate and amplified flood magnitudes imply increased fluvial instability during the late Holocene, indicating that humans exerted a profound influence on fluvial dynamics in the Meuse. © 2019 Elsevier B.V.

Mineral‐Filled Fractures as Indicators of Multigenerational Fluid Flow in the Pahrump Hills Member of the Murray Formation, Gale Crater, Mars

AbstractMineral‐filled fractures (veins) are valuable indicators of deformation and fluid flow within a sedimentary package. Information obtained from vein morphology, texture, and chemistry may elucidate the sequence and nature of postdepositional fluid events. Additional information from vein patterns and interactions between veins and host rock provides insight into fracture formation mechanism(s). The widespread occurrence of veins and other diagenetic features in the sedimentary rock record preserved in Gale crater, Mars, indicates that postdepositional fluids were regionally active considerably later in time than the primary fluviolacustrine environments responsible for the deposition of Mount Sharp strata. Here we report a suite of veins within the Murray formation at the Pahrump Hills locality that were investigated using the scientific payload of the Mars Science Laboratory Curiosity rover. Based on an analysis of vein color, morphology, and texture, and corroborated by vein chemistry, we interpret three distinct vein types at Pahrump Hills: gray veins, white veins, and dark‐toned veins. These veins represent distinct, separate episodes of postdepositional fluid flow, suggesting a protracted history of fluid stability in Gale crater. Additionally, we utilize vein patterns across multiple lithologies at the Pahrump Hills field site to suggest hydrofracture as the primary mechanism of fracture formation.

Hydrochemical assessment with respect to arsenic and other trace elements in the Lower Katari Basin, Bolivian Altiplano

Hydrochemical investigations of groundwater and surface water were carried out to better understand the spatial distribution of As, major ions and trace elements. The study was carried out to evaluate the sources of dissolved species and elucidate the processes that govern the evolution of natural water in the Lower Katari Basin. The study area is close to the Titicaca Lake (Cohana Bay) formed by sediments of the Quaternary system, deposited in the fluvio-glacial to fluvio-lacustrine environment and geologic formations of the Devonian and Neogene system of volcanic origin. The study area has several environmental problems mainly caused by contaminants such as heavy metals, nutrients, and bacteria. These problems are linked to the urban and industrial wastes, natural geologic conditions, and mining activities carried out upstream of the Katari Basin, where rivers discharge into the Cohana Bay.A total of 37 water samples were collected during wet season, 31 groundwater samples including drinking water wells and six surface water samples. The hierarchical cluster analysis and principal component analysis were applied to hydrochemical data. Results show high salinity in groundwater related to the evaporation causing serious problems for the groundwater quality and rendering it unsuitable for drinking. Dissolved As concentration ranges from 0.7 to 89.7 μg/L; the principal source of As could be the alteration of volcanic rocks, more than 48% of the shallow groundwater samples exceeded the WHO guideline value for As and more than 22% for NO3-. Groundwater has neutral to slightly alkaline pH, and moderately oxidizing character. The groundwater chemistry reveals considerable variability, ranging from Na-SO4,Cl type through mixed Na-HCO3 type and Ca,Na-HCO3,Cl type. The distribution of trace elements shows a large range of concentrations. Speciation of As indicates that the predominant oxidation state is As (V). The geochemical modelling indicates that As could be associated with iron oxides and hydroxides which are probably the most important mineral phases for the As adsorption. The spatial distribution and the variation of dissolved As concentration in groundwater is governed by the variability in geological characteristics of the region that raises a significant concern about drinking water quality.

A Complex Fluviolacustrine Environment on Early Mars and Its Astrobiological Potentials.

Chloride-bearing deposits and phyllosilicates-bearing units are widely distributed in the southern highlands of Mars, but these phases are rarely found together in fluviolacustrine environments. The study of the coexistence of these minerals can provide important insights into geochemistry, water activity, and ultimately the climate and habitability of early Mars. Here we use high-resolution compositional and morphological orbiter data to identify and characterize the context of diverse minerals in a Noachian fluviolacustrine environment west of Knobel crater (6.7°S, 226.8°W). The chlorides in this region are likely formed through the evaporation of brines in a closed topographic basin. The formation age of chlorides is older than 3.7 Ga, based on stratigraphic relationships identified and previously obtained crater retention ages. The timing of the alteration of basaltic materials to iron-magnesium smectites in relation to the chloride formation in this location is enigmatic and is unable to be resolved with currently available remote sensing data. Importantly, we find that this close relationship between these key minerals revealed by the currently available data details a complex and intimate history of aqueous activity in the region. Of critical importance are the evaporitic deposits as analogous terrestrial deposits have been shown to preserve ancient biosignatures and possibly even sustain microbial communities for hundreds of millions of years. These salts could have protected organic matter from ultraviolet radiation, or even allow modern habitable microenvironments in the shallow subsurface through periodic deliquescence. The high astrobiology potential of this site makes it a good candidate for future landed and sample return missions (e.g., the Chinese 2020 Mars mission).