Modern Sediments Research Articles

The birth of backbarrier marshes in Culatra Island (Ria Formosa, South Portugal)

The rapid elongation of Culatra Island, a sandy barrier in the Ria Formosa chain (S. Portugal), since the mid-1940s led to the formation of three new embayments in its backbarrier that were gradually colonised by halophytic vegetation. This provided a rare opportunity to collect information and data on the very early stages of backbarrier marsh plant establishment and evolution. Sediment (surface and subsurface) sampling in two of the recently formed bays, combined with information extracted from vertical aerial photographs, allowed us to assess modern sedimentation characteristics and vertical accretion rates since the shift from a bare sandflat to a vegetated marsh platform. Present-day topography appears largely inherited by overwash or/and inlet-related tidal deposits that provided the necessary sediment pulse for the formation of an intertidal sandy substrate, suitable for colonisation. The variability in accretion rates, noted even within the same embayment, as well as the differences in accretion balance with similarly young backbarrier marshes, highlight the importance of local conditions (sediment import, distance to creeks and marsh edge, storm frequency and intensity) to marsh build-up, even during the very early stages. Variable accretion rates were also identified over intertidal seagrass patches, indicating similar influences. Organic deposition rates were very low in all vegetated intertidal habitats, indicating the dominance of mineral deposition to the vertical growth. A lag, ranging from roughly 10–30 years, was observed between the formation of the intertidal sandy platform and plant establishment in all embayments. The different timescales in the observed lag are likely linked to differences in hydrodynamic conditions, promoted by the embayment morphology (opening width). The lowest lag was observed in protected embayments, which could reflect a ‘typical’ delay for plant establishment in the system, while the highest lag was associated with higher energy backbarrier environments.

Lead isotope compositions and modern sediments sources in the radial sand ridges from the Jiangsu coast, East China

The formation of the Jiangsu radial sand ridges (RSRs) in East China has received extensive attention. However, the provenance of the Jiangsu RSRs sediments is still controversial. In this study, the Pb isotopic compositions of residual fractions were used to elucidate the provenance of the Jiangsu RSRs sediments. The results showed that Pb isotopic compositions of sediments in onshore RSRs were not significantly different with those of the landward offshore RSRs, indicating the shoreward transport of sediments from the landward offshore RSRs. The combination of Pb–Nd isotopic compositions revealed that the seaward offshore sediments mainly originated from the Yangtze River Mouth, while the onshore and landward offshore sediments were dominantly supplied by the Old Yellow River Delta through the southward flow. This study provides a deep insight into the evolution of Jiangsu RSRs, and is of great value to the Jiangsu coastal protection.

Modern morphodynamic processes and deposits in Western Srednogorie and Kraishte

The present paper addresses investigation of modern morphodynamic processes, which lead to relief modelling on one hand and the formation of new landforms and deposits on the other. Erosional, denudational and gravitational landforms and deposits were observed in three key areas in the Zavalska Mountain (Western Srednogorie), Strazha and Lyubash (Kraishte). The aim of this study is to trace the intensity of exogenous landforming processes, to characterize the deposits and elucidate the connection between the geological base, the topography and the local hydroclimatic conditions for their genesis and dynamics. To achieve this goal, field and laboratory methods were employed, as well as data from an automatic weather station in the territory of the Breznik Municipality. Despite the short observation period of three months, the data reveal significant dynamics, rendering the selected study areas interesting for future research.

Investigating limnological processes and modern sedimentation at Lake Żabińskie, northeast Poland: a decade-long multi-variable dataset, 2012–2021

Abstract. Here, we present a dataset of a decade-long monitoring project of Lake Żabińskie, a hardwater eutrophic lake in northeast Poland. The lake contains annually laminated (varved) sediments that form a unique archive of past environmental variability. Regular measurements of the lake water physical and chemical characteristics were done using a multiparameter sonde and a set of temperature sensors deployed in the water column. Seasonal variability in sediment fluxes was documented by a sediment trap. Field sampling provided information about the hydrochemistry of incoming streams and of the lake outflow. The overall monitoring program was designed to assess relationships among meteorological conditions, limnological processes, and modern sedimentation and to answer the question of whether meteorological and limnological phenomena can be precisely tracked with varves. However, this dataset can also be used for modeling physical and biogeochemical processes in lakes. The dataset is archived at https://doi.org/10.34808/w8w7-9x34 (Tylmann et al., 2023).

New geophysical and zircon data support an impact hypothesis for the Velingara structure (Senegal)

On Earth, impact structures are rare in intertropical zones. Here we evaluate the 35–40 km diameter Velingara depression in Senegal as a candidate impact structure. The depression has a topographic relief of only 50 m and is essentially buried under modern sediments. For the first time, potential-field ground observations and a microstructural survey of detrital zircons for shock features were conducted at Velingara. A 15 mGal gravity low in a 10 km diameter central anomaly was found, while significant (100 nT) amplitude magnetic field anomalies were observed in the depression. Forward modeling was used to explain the crustal sources of the anomalies, arguing in favor of the presence of a buried impact structure. An electron backscatter diffraction survey of circa 5,000 detrital zircons from a sample of modern alluvium identified a single granular zircon; orientation data for the grain does not record the former presence of reidite, but does closely resemble grains with highly dispersed neoblast orientations that have only been reported from impact settings. Age determination by LA-ICP-MS indicates the unusual granular zircon recorded an age of ca. 550 Ma. Results of the geophysical data and zircon microstructural survey reported here are consistent with, but do not yet prove, an impact origin hypothesis for the Velingara structure. The difference in amplitude between the diameter of the depression, and that of the gravity anomaly remains puzzling. Several impact scenarios are considered, which include the subsequent evolution via surface processes of a 10-km crater into a larger depression, or a large-scale (d = 40 km) complex impact crater with a peculiar geophysical anomaly limited to its central region.

Vanadium in modern sediments of urban lakes in the North of Russia: natural and anthropogenic sources

Studies have found that vanadium tends to accumulate in the sediments of lakes located in urban areas where fuel oil thermal power plants or boiler houses are present. The highest concentration of vanadium, amounting to 4785 mg/kg, was found in a lake situated less than a kilometer away from a thermal power plant. In contrast, pristine lakes typically have vanadium levels that are consistent with or below the background levels. In certain regions of Karelia, the elevated concentration of vanadium in lake sediments can be attributed to the presence of uranium‑vanadium ores. In urban sediments, vanadium is closely associated with nickel, which can also be released into the environment through the emissions of thermal power plants and boiler houses. It has been observed that vanadium in lakes primarily exists in the solid insoluble fraction, possibly bonded with natural minerals.

Luminescence for sedimentary provenance quantification in river basins: A methodological advancement

Multiple luminescence signals such as optically stimulated luminescence, infrared stimulated luminescence and thermoluminescence etc. are characteristic of the crystal/material. Recent studies have shown the potential of luminescence signals for sedimentary provenance studies, sediment fingerprinting and tracking. It is based on the premise that different provenances have different compositions of trace impurities in minerals which are responsible for the luminescence properties of the minerals. However, use of luminescence for provenance studies is still in its developmental stage and needs validation in modern sediments. The current work utilizes the differences in the luminescence signals from different geological provenances to quantitatively estimate the sediment influx to the mainstream from its tributaries based on a 2-component mixing model. Samples from natural river confluences and control samples prepared by mixing two samples in a known proportion by weight were used to estimate the sediment flux based on the luminescence characteristics. This study successfully demonstrates the use of luminescence parameters for sediment fingerprinting and budgeting using natural and controlled samples.

Organic matter enrichment in shale deposited proximal to paleo-uplifts and its impact on shale gas exploration

Much of the global exploration and development of shale gas is focused on organic-rich shale deposited in basin or slope/basin margin settings. There is a clear need to assess the degree to which organic-rich shale deposited in other settings, notably proximal to paleo-uplifts, are promising shale gas prospects. Organic-rich sediments that accumulated proximal to paleo-uplifts are recognized globally and include the Cambrian Niutitang Formation, Ordovician-Silurian transition “hot shales”, and modern sediments of the Black Sea. Though the subject of recent research efforts, much remains to be learned of the mechanisms of organic matter enrichment of fine-grained sediment deposited adjacent to paleo-uplifts. Our study focuses on the Ordovician Wufeng Formation that accumulated proximal to uplifted areas of the Upper Yangtze platform. Though the TOC content of the analyzed Wufeng Formation samples recovered from near the paleo-uplifts is less than that of Wufeng samples collected from basin or slope/basin margin settings, average TOC value of the former can still reach more than 2%. Wufeng Formation shale deposited proximal to paleo-uplifts accumulated under conditions of medium to high paleoproductivity, elevated terrigenous clastic input and sedimentation rate, and oxic-suboxic water column conditions. Principal component analysis suggests that the factor most critical to organic matter enrichment of Wufeng deposits proximal paleo-uplifts was paleo-redox conditions. The TOC abundance in Wufeng Formation shale deposited during late Katian stage is higher than that of shale deposited during Hirnantian stage. It was at the Hirnantian stage that the paleo-uplifts became most active in association with the Kwangsian Orogeny resulting in diminished paleoproductivity and preservation conditions as reflected in the reduced organic matter abundance of associated shale. Uplift of the paleo-uplift of the Yangtze Platform, a manifestation of the Kwangsian Orogeny during the Ordovician-Silurian transition, appears to have been largely responsible for spatial and temporal distribution differentiation of organic matter abundance of the Wufeng Formation of the Upper Yangtze Platform. Results of the present study contribute supplementary information regarding the mechanism of organic matter enrichment in shale and can provide guidance for shale gas exploration and development in geologically similar regions.

Clay minerals and provenancial implications of surface sediments in the Dongping Lake, North China

Clay minerals have great potentials in pinpointing sediment provenance for large depositional systems. However, source identification using clay minerals for small floodplain lakes is not well known. Situated in the North China Plain, the Dongping Lake receives sediments from both the Yellow River and the Dawen River, thereby representing an ideal site for testing the utility of this method. Here we use clay minerals in conjunction with the Bayesian end-member modeling analysis (BEMMA) to quantify the riverine contribution to modern sediments in the Dongping Lake. Results showed that modern sediments of the Dongping Lake are characterized by four primary clay minerals: illite, smectite, kaolinite, and chlorite, with average contents of 60.53%, 11.37%, 12.70%, and 15.40%, respectively. Clay minerals in modern sediments of the Dongping Lake are mainly delivered by the Yellow River, accounting for approximately 58.99–72.33%; whereas those originating from the Dawen River only account for 27.67–41.01%. It is also found that clay mineral from these rivers have a marked spatial variability. For example, source materials from the Yellow River are widely distributed across the lake, while those from the Dawen River only occur at the estuary of the river and slightly spread out in all directions under the action of water flow.

Palynological response deduced through spatially distinct surface samples to reconstruct palaeoecology and palaeoclimate of the Barak Valley, Assam (Indo-Burma region), northeast India

Establishing modern pollen analogues under various vegetation types in a location is necessary without which it is difficult to accurately interpret fossil pollen assemblages in any region in terms of the past environment and palaeoclimate. We have analysed the modern pollen dataset of 30 surface soil and sediment samples from the forested, cropland, wetland and river sites of the Karimganj District in south Assam, to comprehend the connection between the recent pollen assemblage and the vegetation patterns in the Barak Valley. The overall pollen data reflect the tropical moist deciduous and semi-evergreen forest comprising Syzygium, Schleichera, Terminalia, Lagerstroemia, Duabanga, Sapotaceae, Ilex, Mesua and Schima under a warm and humid climate in response to rainfall variations in the region. The presence of Euphorbiaceae and Convolvulaceae inferred high monsoonal activity in and around the region. A robust relationship between local herbaceous vegetation and pollen was observed. The steady occurrence of cereal pollen (average 18.67%) along with other cultural pollen taxa like Brassicaceae, Coriandrum and Solanaceae illustrate intense agricultural activity around the valley areas. Multivariate principal component analysis (PCA) and box plot were applied to the quantified data obtained from pollen frequency analyses of the surface samples which clearly revealed a significant variation and similarity in vegetation types. Thus, an attempt has been commenced to precisely observe the behavioural pattern of modern pollen deposition in a varied depositional setting, which could, in turn, help in assessing the expanse of agricultural practices and the depth of deterioration of pristine forests and surrounding areas. This modern training dataset could also help in the precise reconstruction of past climate and vegetation shifts in the Barak Valley region. A correlation of regional palynodata with other regions of the Indian subcontinent and Indo-Burma will also be assessed for better interpretation.

Changes in midge assemblages reflect climate and trophic gradients across north temperate and boreal lakes since the pre‐industrial period

Abstract North temperate and boreal lakes are affected by a complex suite of anthropogenic stressors, yet little is known about how these ecosystems are faring across the most lake‐rich nation, Canada. The NSERC Canadian Lake Pulse Network is the first large‐scale national survey of its kind, with the aim of assessing the health of Canadian lakes, determined by the deviation of key variables from baseline pre‐industrial conditions (pre‐1880 CE). We examined midge remains (chironomids and Chaoborus) from modern and pre‐industrial sediment intervals in 67 lakes, spanning a range of sizes, ecozones, and degrees of catchment land‐use change. A marked northwest/southeast divide was evident in the modern chironomid assemblages, which was partially associated with water quality, physiographical and climatic variables, with a small portion of the variance explained by geography alone. Between the pre‐industrial and modern sediment intervals, taxa typically found in warmer waters increased across the country (p < 0.001); this pattern also was evident in the littoral assemblages (p = 0.01), providing additional support for the influence of warming. Turnover in chironomid assemblages varied across trophic classes. Mesotrophic lakes showed increases in macrophyte‐associated taxa, whereas eutrophic lakes showed declines in littoral taxa, perhaps reflecting increased turbidity, and the increase of low‐oxygen‐tolerant profundal taxa in eutrophic lakes with high human impacts. Overall, the distribution and dynamics of chironomid assemblages across Canadian lakes appear to be strongly linked to changes in climate and deep‐water oxygen conditions.

Magmatic records from the Karakoram terrane: U–Pb zircon ages from granites and modern sediments in the Nubra Valley, NW Himalaya

The Karakoram terrane is a sliver of peri-Gondwana continental crust preserved within the Karakoram and Saltoro ranges in Ladakh, India. It became a part of Eurasia during the Jurassic, and until Late Cretaceous its southern margin was an active continental margin represented by the Karakoram (Arc) Batholith. Its magmatism is thought to be extinguished during Late Cretaceous by collision with the Shyok ophiolite, however, geochronological data are limited. The Karakoram terrane is a key element in the geodynamics of Himalaya and more studies are needed to improve geological understanding and tectonic evolution of the southern margin of Eurasia pre- and post- final continental collision with the Indian continent. We present petrographic, geochemical, and geochronological observations for anatectic magmatism which formed granitic intrusions within the terrane at c. 14 Ma and 12 Ma. Results from detrital zircon dating of modern sediments from the Karakoram terrane reveal three distinct age populations at c. 108, 82, and 13 Ma which correspond to known geological events. Current geochronological data for the Karakoram terrane indicate presence of two major magmatic episodes, the first occurred during Jurassic–Cretaceous and was related to subduction processes, and second, occurred during the Miocene and was related to the anatexis of the Karakoram lithosphere upon the terminal continental collision. The intervening magmatic events are still uncharacterised.

Modern Sedimentation Patterns in Lake Issyk Kul (Kyrgyzstan), Derived From Surface Sediment and Inlet Stream Samples

AbstractThis study provides a descriptive characterization of the modern sedimentary processes in Lake Issyk Kul, Kyrgyzstan, important for the selection of a suitable coring or deep‐drilling site, interpretation of future core data and applicability of proxies. The quasi‐equidistant sampling grid of 66 sediment surface samples covers the entirety of the lake basin and is complemented by 10 samples from the major inflows. The methodological approach includes geochemical, granulometric, lipid biomarker, diatom, and statistical analyses. The quantitative and qualitative changes in sediment composition yield information on its generic origin and prevailing transport and depositional environments. The composition of the surface sediments in Issyk Kul is highly heterogenous. Nearshore deposition is mainly controlled by wave action and by fluvial sediment supply with highest quantities of detrital input coming from the high‐energetic, eastern tributaries. Sediments in the deep central basin are mainly produced in situ and dominated by authigenic calcite. Biogenic accumulation is overall low, except for the western extremity of the lake, where the nearshore, shallow‐water, and low‐energetic environment favors aquatic productivity and subsequent preservation of organic material and diatoms. Redeposition of sediments is a dominant process along the slopes across the southern and western basin floor, where run‐out distances of mass movement deposits are up to 5 km. Directional sediment transport by lake currents appears to be less important, except for the transport of very fine‐grained organic matter. Biomarker‐inferred temperature reconstructions suggest lake surface temperatures of ∼15°C in the western littoral zone and in Tyup Bay and a decrease to ∼13°C basinward.

Typomorphic features of garnet xenocrysts from the crater and diatreme parts of the high diamondiferous V. Grib kimberlite pipe (Arkhangelsk diamondiferous province): application in prospecting and exploration for diamonds in the north of the East European platform

Research subject. Morphology of garnet xenocryst grains from the crater and diatreme parts of the highly diamondiferous V. Grib kimberlite pipe of the Arkhangelsk diamondiferous province. Aim. To reconstruct the main stages of endogenous and exogenous morphogenesis of garnet xenocrysts from the crater and diatreme parts of the kimberlite pipe based on a detailed study of their morphological features. To demonstrate the applicability of the data obtained in the interpretation of the morphology of grains of kimberlite indicator minerals from modern alluvial sediments during prospecting and exploration for diamonds in the north of the East European Platform. Materials and methods. A detailed study of the morphology of 655 garnet grains was carried using the methods of optical and electron-scanning microscopy. Garnet grains were selected from the heavy mineral concentrate of crushed rocks, representing the crater (sandstones) and diatreme (kimberlite) parts of the V. Grib pipe. All visually diagnosed garnet grains were handpicked selected from the rocks of the crater part, extracted from the core of one borehole and representing an interval from 70 to 174 m from the surface. For comparison, out of 1100 grains of garnet xenocrysts, selected by random sampling from the concentrate of minerals of the heavy fraction of kimberlite of the diatreme part, 180 garnet grains were selected, representing four-color groups: purple, red, red-orange and orange. Results. The majority of garnets from the crater (96%) and diatreme (89%) parts of the V. Grib kimberlite pipe were shown to exhibit the “primary” magmatic morphology. Nevertheless, the garnet grains with well-developed pyramidal shingle-like (3% in the crater and 11% in the diatreme) and drop-shaped (1% in the crater) reliefs have been identified. These types of garnets were formed under the influence of postmagmatic processes. For the first time, in the deep diatreme part of the pipe (more than 200 m from the surface), composed of dense kimberlite, garnets with a well-developed pyramidal shingle-like relief were found, which had been previously interpreted for the East European Platform only as components of the secondary deposits or the upper horizons of the crater parts of the pipes. Conclusions. Garnets with a well-developed pyramidal shingle-like relief, found in modern alluvial sediments, can be interpreted as from a secondary deposit only if they show signs of mechanical abrasion; the absence of traces of mechanical abrasion on such grains does not allow us to exclude the proximity of the primary source. The presence of drop-shaped relief garnets in the crater of the V. Grib pipe (150-168 m from the surface) also calls into question the unambiguous interpretation of such grains as a sign of secondary deposits: only the maximum degree of chemical abrasion of garnets with the formation of cuboids grains can indicate their redeposited nature. The results confirm the need to improve the method of prospecting for diamond deposits according to the typomorphic features of kimberlite indicator minerals recovered from the modern sediments, sampled in the north of the East European Platform.

Identification and differentiation of vertical movement through morphological changes and stratigraphic imprint: Two distinct uplifting mechanisms in the upper Calabrian accretionary wedge, western Ionian Sea

AbstractThe seafloor morphology reflects both past and on‐going sedimentary, oceanographic and tectonic processes. Vertical movement is one of the drivers responsible for reshaping the seafloor through forming steep flanks that decrease slope stability, favour landslides, change current paths, form minibasins and control the sediment deposition, distribution and geometry. Here, we make use of these interactions to derive vertical movements and constrain the active tectonic processes at the western termination of the upper Calabrian accretionary wedge from the integrated analysis of bathymetric, backscatter, surface attributes and high‐resolution reflection seismic data. Within this area, we identify two types of deformational features and mechanisms that affect the depositional, erosional and tectonic processes at different scales. These include the deviation of channels, landslide scars, mass transport deposits (MTDs), separated drifts, sediment waves, lineaments and offset seafloor structures. The first type (long‐wavelength uplift) is an uplifted 22‐km‐wide region, in which seismic onlap relationships and the dip of deep reflectors suggest long‐lasting but slow tectonic uplift affecting sedimentation, and the second type (short‐wavelength uplift) includes three narrow elongated structures and one circular dome encircling the first region of uplift. We interpret that the first type of uplift feature was caused by tectonic deformation, while the second type is interpreted as formed by the fast uplift, tilting and faulting of modern sediments caused by diapirism due to rapid sedimentation in response to the first tectonically driven uplift. The study provides insight into the complex interaction of tectonic and sedimentary processes in the upper Calabrian accretionary wedge.

Detrital Garnet Geochronology by In Situ U‐Pb and Lu‐Hf Analysis: A Case Study From the European Alps

AbstractDetrital geochronology employing the widely‐used zircon U‐Pb proxy is biased toward igneous events and metamorphic anatexis; additionally, zircon is highly refractory and frequently polycyclic. Garnet, a rock‐forming and thus commonly occurring mineral, is predominantly metamorphic and much less refractory. Here, we report in situ U‐Pb and Lu‐Hf ages from detrital garnet hosted in ancient and modern sediments of the European Alps. Both geochronometers are biased toward the most recent garnet‐crystallizing metamorphic event in the source area, with fewer inherited ages. This likely reflects efficient removal of inherited garnet during diagenesis and metamorphism, and is in contrast to detrital zircon, apatite, and rutile U‐Pb data, which largely record pre‐Alpine ages. Neither the U‐Pb nor Lu‐Hf system in garnet exhibits a relationship between age recovery and composition. However, the Lu‐Hf system in garnet yields significantly better age recovery than the U‐Pb system. Estimated initial 238U/206Pbc values at the time of crystallization are near unity, suggesting that garnet does not significantly partition U from Pb during crystallization, at least for the generally almandine‐rich garnets analyzed in this study. Hence, Lu‐Hf geochronology of detrital garnet offers an effective method to detect and date the most recent phase of mid‐grade metamorphism in sub‐anatectic source areas, in which detrital zircon U‐Pb analysis may be of less utility.

Modern sedimentation on the eastern continental shelf of India: Assessing the provenance and sediment dispersal pattern

Sediments deposited on the eastern continental shelf of India are studied for texture, mineralogy and their major, trace, and rare earth elemental composition in lithogenic fraction. The objective of this study was to identify the sources, and evaluate the factors affecting the erosion and weathering in the catchment area and dispersal and deposition of sediments over the shelf region. Here, we present an extensive dataset covering the entire eastern continental shelf of India from the Ganges-Brahmaputra (G-B) basin in the north including the shelf off major peninsular Indian river basins of Mahanadi, Godavari, and Krishna up to the Kaveri basin in the southern tip.Textural and geochemical studies have shown that the lithology of the source rocks plays an important role in governing the chemistry and mineralogy of the sediments. The results show that the G-B shelf sediments are primarily derived from the Higher Himalaya Crystalline sequence (HHCS) and the Tethyan sedimentary series (TSS) exposed along the peaks and drainage divide of the Himalayas. Mahanadi shelf sediments are mainly derived from the felsic rocks belonging to Precambrian metamorphic formations of the Eastern Ghats, limestones, sandstones, and shales of the Gondwanas and recent deltaic alluvium deposits, whereas the Krishna-Godavari (K-G) sediments find a part of their source in the Deccan Basalts. The shelf sediments off River Kaveri are derived from a mixture of peninsular granitic gneisses, tonalite-trondjhemite gneisses, and charnockites. The sediment geochemistry has also allowed us in assessing the weathering patterns in the source areas. The sediments have undergone a moderate degree of weathering. Weathering intensities were found to have varied with the source area lithology.The least square regression of the geochemical data allowed us to estimate the relative contribution of each of these sources and their geographic extent. Unlike the massive offshore deposition and formation of a major Fan system (the Bengal fan), the fluvial sediment dispersal of the mighty Himalayan Rivers on the continental shelf is significant only at the G-B mouth and their contribution reduces to <50% at about 18oN. The sediment dispersal from the Godavari River is seen to extend on either side of the mouth of the river which is attributed to the reversing East India Coastal Current (EICC), which plays an important role, in the sediment transport along the central and south-central part of the east coast of India. The influence of the Mahanadi, Krishna, and Kaveri River sediments is however confined to a small area near their mouths and has a limited geographic extent of influence in the shelf region.

Investigating paleoclimate and current climatic controls at Lago Argentino using sediment pixel intensity time series

The quantity and characteristics of sediment deposited in lakes are affected by climate to varying extents. As sediment is deposited, it provides a record of past climatic or environmental conditions. However, determining a direct relationship between specific climatic variables and measurable sediment properties, for instance between temperature and sediment optical reflectance, is complex. In this study, we investigate the suitability of sediment reflectance, recorded as sediment pixel intensity (PxI), as a paleoclimate proxy at a large ice-contact lake in southern Patagonia, Lago Argentino. We also evaluate whether sediment PxI can be used to investigate the present-day climatic drivers of sedimentation across Lago Argentino. First, we show that sediment PxIs relate to underlying sediment composition, and are significantly correlated with XRF-derived major element composition. Secondly, we find that PxIs correlate with both austral summer temperatures and wind speeds, but not with precipitation. PxI timeseries reach the p<0.1 correlation significance threshold for use as a paleo-wind proxy in as many as 6 cores and a paleo-temperature proxy in up to 4 cores. However, high spatial variability and the non-unique relationship between PxI and both temperature and wind speed challenges the necessary assumption of stationarity at Lago Argentino. While not suitable as a paleoclimatic proxy, correlations between PxI and instrumental climate data do chronicle current climatic controls on sediment deposition at Lago Argentino: high summer temperatures enhance settling of coarse, optically dark grains across the lake basin by promoting ice melt and lake stratification, while high wind speeds reduce the settling of fine, optically bright grains in the ice-proximal regions by transporting sediment-rich waters away from the glacier fronts. The assumptions required for quantitative paleoclimatic reconstruction must be carefully evaluated in complex lacustrine environments, but records unsuitable for use as proxies might nevertheless yield valuable information about the drivers of modern sedimentary transport and deposition.

Temporal variations in Rare Earth Element distributions in the Cenozoic succession and modern sediments of the Cayman Islands

The Rare Earth Elements (REEs) in limestones and dolostones that develop on isolated oceanic islands, like the Cayman Islands, were acquired from the seawater in which they formed and various diagenetic processes that led to their lithification and, in some cases, pervasive dolomitization. Modern sediments from North Sound, Grand Cayman, contain up to 30.93 ppm ∑REEs and 45.23 ppm ∑REEs + Y, whereas modern corals contain up to 2.30 ppm ∑REEs and 3.65 ppm ∑REEs + Y. The limestones and dolostones in the Brac Formation (late Oligocene), the Cayman Formation (Miocene), and Ironshore Formation (Pleistocene) generally contain <7 ppm and <10 ppm, ∑REEs and ∑REEs + Y, respectively. In contrast, the Pedro Castle Formation (Pliocene) contains up to 14.18 ppm ∑REEs and 20.81 ppm ∑REEs + Y. The Distribution Coefficients for the REEs from the modern Cayman corals are similar to those determined for corals elsewhere in the world. In the modern sediments from North Sound there is a high correlation between the ∑REEs + Y and Fe and Al but a low correlation with Na and Mn. In contrast, the correlation between the ∑REEs + Y and other elements in the limestones of the Ironshore Formation and dolostones/limestones of the Brac Formation and Cayman Formation is low. The light REEs were >Limit of Quantification (LoQ) in most samples, whereas the medium REEs and heavy REEs were commonly <LoQ. There is no recognizable pattern to the presence/absence of the light, medium, and heavy REEs. Collectively, these data show that (1) the REEs in the limestone/dolostone succession on Grand Cayman are similar to those from Cayman Brac, (2) dolomitization does not seem to have modified the REEs of the original limestones, and (3) the content of the REEs of the limestones and dolostones of the Pedro Castle Formation is higher than those in the Brac Formation and Cayman Formation. This may indicate that the concentration of the REEs in the seawater during the Pliocene highstand was higher than those when the original sediments of the Brac Formation and Cayman Formation were deposited.

Genetic Biosignatures of Deep-Subsurface Organisms Preserved in Carbonates Over a 100,000 Year Timescale at a Surface-Accessible Mars Analog Site in Southeastern Utah.

In recent years, strong evidence has emerged indicating the potential habitability of the subsurface of Mars. Occasional discharge events that bring subsurface fluids to the surface may carry with them the biological traces of subsurface organisms. Similar events are known to take place on Earth and are frequently associated with long-term mineralogical preservation of organic material, including DNA. Taking advantage of this process may allow for the development of life-detection strategies targeting biosignatures from the more habitable subsurface environment without the need for direct subsurface exploration. To test the potential for this approach to life-detection, we adapted a protocol to extract microbial DNA preserved in carbonate rocks and tested its efficacy in detecting subsurface organisms at a Mars analog site in southeastern Utah, USA, using samples from ancient and modern carbonate deposits associated with natural and artificial springs. Our results indicated that DNA from deep-subsurface organisms preserved in carbonate deposits can remain recoverable for up to 100,000 years, supporting life-detection strategies based on the detection of deep-subsurface biosignatures in surface-exposed rocks on Mars.