Detrital Sediments Research Articles

A Detailed Insight into the Detrital and Diagenetic Mineralogy of Metal(oid)s: Their Origin, Distribution and Associations within Hypersaline Sediments

Hypersaline environments are among the most vulnerable coastal ecosystems and are extremely noteworthy for a variety of ecological reasons. Comprehensive assessment of metal(oid) contamination in hypersaline sediments from Sečovlje (Northern Adriatic, Slovenia) was addressed by introducing the detrital and diagenetic mineralogy and geochemical properties within the solid sediment material. Close associations between Fe/Mn oxides and oxyhydroxides with As, Cr, Ni, Pb and Zn, and between organic matter with Cu, Pb and Zn were confirmed using X-ray powder diffraction, SEM-EDS and ICP emission spectrometry analysis. Possible incorporation or adsorption on the crystal lattices of clay minerals (As, Cr, Pb, Sn and Zn), halite (As) and aragonite/calcite (Cd, Cu, Pb, Sr and Zn) were also detected. All presented correlations were highlighted by various statistical analyses. The enrichment factor (EF) values showed a low degree of anthropogenic burden for As, Bi, Hg and Zn, while Cd, Cr, Cu, Ni, Pb, Sn and Sr originated from the geological background. These results emphasise that a detailed mineralogical and geochemical characterisation of solid (especially detrital and diagenetic) sediment particles is crucial in further understanding the metal(oid) translocation within the hypersaline ecosystems.

Geological, Mineralogical and Geochemical Studies of Kolosh Formation, Dokan Area, Kurdistan Region, Iraq

The geology, mineralogy and geochemical of The Kolosh Formation in Dokan area, northern Iraq has been studied. The formation sequence includes gray and dark gray marl that alternate from clastic submarine sediments represented by turbid deposits resulted from the last stages of the collision movement between the continental plates. The geochemical study showed that the Kolosh Formation is mainly dominated by detrital sediments (Clay) with a dominance of kaolinite illite, and albite wıth low amounts of quartz. The analysis revealed that the Kolosh Formation is dominated by relatively marginal marine sedimentation where shelf bay facies was deposited with carbonate facies deposited as shallow marine. In contrast, SiO2 is strongly negatively correlated with CaO and MgO, this supports their derivation from terrigenous sources during the deposition of Kolosh sediments.

Stable isotope geochemistry of silicon in granitoid zircon

Zircon is often used to study granites (sensu lato) and continental crust because it is very resistant and can be analyzed for various isotope systems that provide time and source information about their parental melts. Granites with different petrological histories have distinct bulk-rock silicon isotope compositions but it is unclear if these differences are also detectable in zircon because of superimposed fractionation effects (e.g., related to temperature, silica content, magmatic processes). The present study explores the Si isotope signatures of zircon from various granite types to constrain their isotope fractionation behavior and uses them as igneous petrogenetic tools, and possibly as granite source discriminators when zircon is found in detrital sediments. Our results show that although Si isotope compositions in zircon can be modified by secondary (post-crystallization) processes such as alteration/weathering and metamorphism, they are primarily controlled by zircon-melt isotope fractionation, which depends on both zircon crystallization temperature and magma silica content. Once these fractionation effects are understood and filtered out, a pattern emerges between Si isotope signatures of zircons from different granite types that is consistent with theoretical and experimental results as well as with known Si isotope differences at the bulk-rock scale. Silicon isotope ratios in zircon can track magma evolution (e.g., temperature and SiO2 changes) and, hence, reveal complex processes that involved magma mingling, fractional crystallization, and/or multiple sources. This study, therefore, illustrates that Si isotopes in zircon can be used to investigate magma evolution and represents a useful complement to existing techniques in granite studies involving zircon (e.g., U-Th-Pb, Lu-Hf and O isotopes) provided that it is not used as a stand-alone technique.

Mesozoic-Cenozoic tectonic events of eastern Junggar Basin, NW China and their significance for uranium mineralization: Insights from seismic profiling and AFT dating analysis

For sandstone-type uranium deposits, an unobstructed recharge-runoff-discharge (RRD) groundwater system strongly constrained by tectonic events is one of the most important cornerstones for uranium mineralization. Junggar Basin, located in NW China, is proposed to be an intracontinental Mesozoic basin with great sandstone-type uranium metallogenic potential but no large uranium deposits so far. Compared with other uranium-bearing basins in Northern China, the Junggar Basin experienced episodic strong tectonic events in the Meso-Cenozoic era, resulting in more intense stratigraphic deformation and dislocation, so the detailed analysis of tectonic evolution and ore-controlling structures is indispensable to deciphering the uranium mineralization process in the region. This study interprets the seismic profiles and analyzes the apatite fission track (AFT) thermochronological signatures of the Jurassic Toutunhe Formation detrital sediments in the eastern Junggar Basin, which reveals that the Junggar Basin experienced four tectonic events: the Middle Triassic-Early Jurassic episodic uplift of basin margin (ca. 240–180 Ma), the Late Jurassic or Early Cretaceous modest deformation and uplift within the basin (ca. 140 Ma), the Late Cretaceous-Paleocene rapid uplift (ca. 100–60 Ma), the Eocene-Present episodic rapid uplift (ca. 38–0 Ma). On this basis, the tectonic couples comprising tectonic window and structural pattern is dissected. The ore-controlling structures that can build the good RRD system are identified, such as Jurassic slope in the eastern Luliang Uplift, Jurassic hanging wall of fault propagation fold, Neogene foredeep of the foreland basin, and so on. Meanwhile, the rapid uplifts in ca.100–60 Ma and ca.38–0 Ma are ascertained as the key tectonic events constrained uranium mineralization. Afterward, a uranium metallogenic model based on the thread of basin tectonic evolution is established, which is of great significance for further deployment of uranium exploration in the basin.

Sinuous stromatolites of the Chandi Formation, Chattisgarh Basin, India: their origin and implications for Mesoproterozoic seawater

AbstractRemnants of some of the planet’s most ancient life forms, stromatolites in the late Mesoproterozoic sea of the Chattisgarh Basin, India, preserve a conspicuous sinuous pattern. They occur as successive biostromes, 10–30 cm thick, separated by 2–5-cm-thick marly layers and discrete bioherms up to several metres thick and 20 m across. Stromatolite columns in the Chandi Formation are 5–10 cm high, sinuous, inclined and straight, with both branched and non-branched types. These stromatolites are composed of calcite micrite and show well defined light and dark laminae with evidence of erosion between lamina sets. The column sinuosity probably originated as a response to changes in direction and strength of currents. Successive flat beds of stromatolite (biostromes), separated by marl/clay horizons, impart a rhythmic pattern to the succession. The Chandi sinuous stromatolite columns resemble those occurring in China, North America and Siberia, of a comparable age, suggesting that similar marine conditions of stromatolite formation might have been operating in the late Mesoproterozoic seas worldwide. However, the petrographic and sedimentological analyses of these stromatolites indicate their development throughin situproduction of carbonate with some trapping and binding of detrital sediment. As a result of the presence of terrigenous material within the stromatolites, whole-rock geochemical analyses for trace elements and rare earth elements cannot be used for interpretation of seawater chemistry and the redox conditions at the time.

Systematics of detrital zircon U–Pb ages from Cambrian–Lower Devonian rocks of northern Morocco with implications for the northern Gondwanan passive margin

The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession.

Transcontinental retroarc sediment routing controlled by subduction geometry and climate change (Central and Southern Andes, Argentina)

AbstractCentral Argentina from the Pampean flat‐slab segment to northern Patagonia (27°–41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. Combined with previous research focused on coastal sediments, this actualistic provenance study uses framework petrography and heavy‐mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ca. 1,500 km and next northwards for another 760 km along the Atlantic coast. Although detritus generated in the Andes is largely derived from mesosilicic volcanic rocks of the cordillera, its compositional signatures reflect different tectono‐stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as different character and crystallization condition of arc magmas through time and space. River sand, thus, changes from feldspatho‐litho‐quartzose or litho‐feldspatho‐quartzose in the north, where sedimentary detritus is more common, to mostly quartzo‐feldspatho‐lithic in the centre and to feldspatho‐lithic in the south, where volcanic detritus is dominant. The transparent‐heavy‐mineral suite changes markedly from amphibole ≫ clinopyroxene > orthopyroxene in the north, to amphibole ≈ clinopyroxene ≈ orthopyroxene in the centre and to orthopyroxene ≥ clinopyroxene ≫ amphibole in the south. In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds and temporarily accumulated in dune fields. During the Quaternary, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment‐laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today towards the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary.

Stratigraphic variability of Mississippian Meramec chemofacies and petrophysical properties using machine learning and geostatistical modeling, STACK trend, Anadarko Basin, Oklahoma

Mississippian Meramec deposits and reservoirs in the Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher counties (STACK) play of Oklahoma are comprised of silty limestones, calcareous sandstones, argillaceous-calcareous siltstones, argillaceous siltstones, and mudstones. We used core-derived X-ray fluorescence (XRF) data and established environmental proxies to evaluate the occurrence of specific elements (Al, K, Ti, Zr, Sr, Ca, and Si) and to illustrate their stratigraphic variability. For the Mississippian Meramec, six indicator elements or element ratios serve as proxies for clay (Al and K), detrital sediment (Ti and Zr), carbonate deposits (Sr and Ca), calcite cement (Sr/Ca), and quartz (Si/Ti and Si/Al). We used an unsupervised K-means classification to cluster elemental data from which we interpret three chemofacies: (1) calcareous sandstone, (2) argillaceous-calcareous siltstone, and (3) detrital mudstone. We used random forest to relate core-derived chemofacies to well logs and classify chemofacies in noncored wells with an accuracy of up to 83% based on blind tests. We integrated core-derived XRF, conventional well logs, and chemofacies logs to produce a cross-sectional chemofacies model that trends from the northwest to the southeast across the STACK trend. Chemofacies distribution indicates an upward increase of detrital mudstone from parasequences 1 to 3. Parasequence 3 is capped by a maximum flooding surface. From parasequences 4 to 5, an increase in argillaceous-calcareous siltstone and calcareous sandstone reflects the progradational stacking. Porosity is low in calcareous sandstones primarily due to calcite cement. Water saturation is high in argillaceous-calcareous siltstone, moderate in calcareous sandstone, and low in detrital mudstone. Interpreted biogenic quartz from element profiles corresponds to the calcareous sandstone chemofacies, which can be estimated from well logs and mapped. Effective porosity and water saturation models reflect the stratigraphic variability of chemofacies and rock types and can be predicted within the defined chemostratigraphic framework.

PILLOWED METABASALTS AND METABRECCIAS FROM THE VALAISAN OCEAN-CONTINENT TRANSITION PRESERVED IN THE BREUIL VALLEY, AOSTA (ITALIAN WESTERN ALPS)

Subduction plate margins have an intrinsically poor preservation potential for pre-subduction settings because most rocks sink and disappear into Earth’s mantle. However, a preserved pre-subduction setting has been reported in the Lower Penninic Units (Valaisan Basin) of the Italian Western Alps (Beltrando et al., 2012). Here, we review two main aspects of the Valaisan Basin cropping out in Italy: the nature of the syn-rift detrital sediments and the characteristics of the metabasalts in proximity to the continental crust metagranitoid. New fossil findings are reported, which confirm a Mesozoic age for the Valaisan rifting. Field and petrographic data from metabreccias and pillowed metabasalts near the fossil-rich high-pressure metasediments support the interpretation of the Valaisan Domain in the Breuil valley (Aosta) as a fossil ocean-continent transition zone.

Disentangle the sediment mixing from geochemical proxies and detrital zircon geochronology

Detrital zircon UPb geochronology and geochemical proxies derived from immobile elements and isotopes are commonly applied to trace sediment sources because of their durability and stability in most earth surface processes and environments. However, little is known on whether these different tracers can contain identical or similar provenance signals for sediments of interest. This study presents the UPb ages of detrital zircons from a grain-size fraction of 63–125 μm and elemental and Nd isotopic compositions for bulk sediments from the Mulanxi, a small mountainous river in southeast China. We aim to retrieve provenance signals preserved by different tracers and to test whether they are robust in discriminating the effect of sediment mixing in this tidal-dominated river. Our results show that detrital zircons in the Mulanxi catchments and estuarine have two major age groups at 90–110 Ma and 120–150 Ma. Moreover, the results of probability density plots (PDPs) suggest there is no significant difference in detrital zircon UPb ages between the sediments from non-tidal and tidal reaches. The detrital zircon age distributions in the Mulanxi catchments are significantly different from those in the Changjiang (Yangtze River) catchments and in the inner shelf mud belt of the East China Sea which have distinct multiple age populations. A statistical multidimensional scaling (MDS) analysis suggests there is no a source-to-sink connection between the Changjiang and Mulanxi zircons. On the contrary, the geochemical proxies of Sc/Th, Cr/Th, and Nd isotopes reveal different sediment sources between the non-tidal and tidal reaches of Mulanxi, with the fine tidal-reach sediments having mixed sources from the offshore mud and the Mulanxi River, while the coarse-grained sediments from the non-tidal upstream being completely contributed by the Mulanxi. The contradictory results from these different provenance proxies suggest their implications and limitations for sediment source tracing. Detrital zircon ages can track the ‘inherited’ source signals of zircons and relating coarse fractions in sediments, but they are less sensitive to source changes in fine fractions than the geochemical proxies of Nd isotopes, Sc/Th and Cr/Th ratios. It is therefore essential and a prerequisite to carefully evaluate all possible factors controlling detrital sediment compositions, and to weigh the pros and cons of different tracers for sediment provenance discrimination especially in dynamic Small Mountainous Rivers (SMRs) and continental margins.

U- and Th- series disequilibria in separated soil mineral fractions: Insight into the mechanism and timescale of U, Th and Ra redistribution

In recent decades, U- and Th- series nuclides have been successfully used to determine weathering rates in soils and regoliths. However, the redistribution of the nuclides within secondary minerals and/or organic matter may interfere with the recorded U- and Th-series weathering signals and can result in inaccurate and/or poorly constrained weathering rate determinations. In addition, the migration of radionuclides in the environment represents a major current issue. The objective of this study, therefore, was to evaluate the meaning of bulk soil data for weathering investigations and to assess the processes and timescales of U, Th and Ra redistribution in a forested-soil profile, both at the bulk soil scale level and for separated mineral fractions. This study was carried out at the INRAE-Andra experimental beech-forested site of Montiers (Meuse, France), which was developed on acidic detrital sediments inherited from tropical paleosoils erosion. U- and Th-series activity nuclides were measured in bulk soil samples and in separated Fe nodules and clay-size (<2 μm) fractions. Furthermore, the analyses of atmospheric particles allow discussing the potential influence of atmospheric inputs.While bulk soil disequilibria suggested negligible to moderate mobility of the nuclides, an important transfer between mineral fractions was highlighted; this resulted in contrasting redistributions of U, Th and Ra within soil fractions. Fe-oxide nodules controlled the overall mobility of U on the bulk soil scale, while the fine <2 μm fraction controlled the mobility of Ra. A capture of 234U by Fe-oxide nodules (mainly comprised of goethite) was observed within the entire soil profile, most likely occurring for several hundred ky. In the shallow soil layers, a leaching of U from the <2 μm fraction that was not re-adsorbed onto Fe-oxides occurred. In contrast, Fe-oxides appeared to retain all U mobilized from the <2 μm fraction in the deep soil layers, resulting in negligible U mobility and an apparent “closed-system” at the bulk soil scale. This transfer, however, seemed to occur over shorter timescale than the one in the shallowest soil layers. No mobility of 226Ra was observed at the bulk soil scale, despite the large release of this nuclide from Fe-oxides. The measured (210Pb/226Ra) activity ratios suggested that up to 50% of 226Ra in Fe-oxides is available for desorption. However, the <2 μm fraction strongly readsorbed the released Ra and prevented the loss of this nuclide at the bulk soil scale. Considering the short half-life of 226Ra, such transfer from Fe-oxides to the <2 μm fraction occurred over a significantly shorter timescale than U mobilization. In addition, the analysis of the short-lived 228Ra isotope emphasized the flux involved in the biological cycle and the potential impact of vegetation on the soil radionuclide redistribution over a short timescale.Our results suggest that the fine <2 μm fractions might be suitable for probing the residence time of clay minerals in soils by the U-series dating method, if the soil profile can be assumed to consist of homogenous inherited clays.

Impact of sedimentary environment on pore parameters of thermally mature Permian shale: A study from Kommugudem Formation of Krishna Godavari Basin, India

The pores are significant factors to assess the fracture system of a shale reservoir. The present study evaluates organic matter-associated parameters, redox condition, paleoclimate and paleosalinity and their role on the pore structure of thermally mature Kommugudem shale of Krishna Godavari Basin. The XRD analysis supported by FE-SEM mainly indicates silica-dominated lithotype and clay-rich siliceous mudstone in the Kommugudem Formation. Intercrystalline and intracrystalline pores were observed in association with mineral and organic matter that provide storage sites for hydrocarbon. Excellent TOC content and genesis of gas prone, type III kerogen dominantly observed in admixture with type II or type IV kerogen. The clay, TOC and Tmax have a positive correlation with micropore volume indicating a good contribution of clay micropore and associated organic matter. Fractal dimensions were estimated using the fractal FHH method with an average value of 2.65 suggesting that the pore surfaces are rough and exhibit complex and heterogeneous pore structure. The Kommugudem Formation constitutes detrital sediments sourced from felsic volcanic rocks in humid and warm climate along the passive tectonic continental margin. The redox and paleosaline investigations reveal the fluvio-marine transitional environment preserved under suboxic to oxic conditions. The REEs and trace elements are positively correlated with pore volume indicating their possible role in the pore genesis of silicate minerals and corroborating the positive influence of the environment. The redox proxies are strongly correlated with TOC and pore volume supports the probable development of organopores. The investigation reveals the significant role of multiproxy paleoenvironmental indices to understand the complex mechanism of pore characteristics.

Sequence stratigraphy of the Niobrara Formation: Implications for age-constraining tectonic events and stratigraphic complexities in the Denver-Julesburg Basin, United States

The Upper Cretaceous Niobrara Formation in the Denver-Julesburg (D-J) Basin, United States, records late Turonian–early Campanian transgressive–regressive cycles that governed the rhythmic character of pelagic and detrital sedimentation along the former carbonate ramp of the Western Interior seaway (WIS). The general stratigraphic and architectural complexity of the full Niobrara section has long been recognized; however, fine-scale subdivision of the formation from a sequence stratigraphic aspect has been lacking and is critical for basin-scale analysis. The timing and controls of significant changes in architectural and sediment-accumulation patterns have important implications for the Niobrara petroleum system. As part of this study, we present a sequence stratigraphic framework appropriate for the distal carbonate ramp of the WIS. We project published biozone mapping and radiometric ages into basin-wide well control to establish the timing of chronostratigraphic surfaces. Age-constrained isochore maps reveal a chronology of dynamic paleoseafloor morphology that is critical to understanding the stratigraphic and architectural evolution of the Niobrara. At a regional scale, thickness patterns suggest that the north-south–oriented flexural forebulge in the Sevier foreland basin had migrated eastward to the position of the future Rocky Mountains, a location coincident with the western edge of dominantly pelagic carbonate deposition in the backbulge of the WIS basin. At the D-J Basin scale, chronostratigraphic isochore maps of four third-order sequences, and their finer-scale subintervals, record two broadly distinct periods of depositional influence in the Niobrara. Between ca. 90.0 and ca. 85.7 Ma (upper Turonian–lower Santonian), relatively even deposition was dominated by a pattern of differential sediment accumulation. Systematic reversals of thicks and thins through time are indicative of compensational infilling patterns with no influence of tectonic uplifts along the seafloor. In contrast, from ca. 85.7 to ca. 81.7 Ma (lower Santonian–lower Campanian), a reorganization of earlier architecture was driven by the influence of sublinear uplifts along the trend of the emergent Transcontinental arch. As a result, sediment accumulation was dominated by patterns of draping over the long-lived paleohighs. Absolute timing of the architectural changes of the Niobrara suggests a link among Sevier thrusting events, a migrating flexural forebulge, and uplifts at reactivated basement shear zones in the distal foreland. Thus, both active tectonics and the inherited Proterozoic basement fabric of the WIS influenced the evolution of the Niobrara Formation. This example from the Cretaceous WIS shows that age-constraining sequence stratigraphy for regional isochore mapping can reveal relationships among the structural response to far-field tectonic events, oceanographic variations, and stratigraphic architecture.

Characteristics of Deposited mine tailing on the Senunu Canyon, Indonesia

The characteristics, distribution, and accumulation of detrital sediment on the surface sediment in the Senunu Sea are used as a preliminary study to identify the detrital and sedimentation processes’ origin. This study aims to present the characters and composition of detrital sediment on Senunu seabed. It illustrates the influence of land sediment sources on sediment compositions settled on the bottom of the surrounding seas. Specific review on the sediment character in this region was done to identify surface sediment layers carrying tailings materials from ore mining on land and differentiate them from natural sediment. 53 sediment core from the Senunu bottom were collected and analyzed for their detrital characteristics using a binocular microscope. In general, sediment composition in Senunu seabed was terrigenous sediment with dominant material quartz, andesite, and tuffaceous breccia. Based on the detrital analysis, sediment lithology of natural seabed sediment and sediment containing tailing material is distinguished by color, layer contact, grain packing, grain shape, biota association, and specific mineral content quartz, mica, and magnetite. Surface sediment containing tailing material had more quartz mineral, had more similar grain size and crystal shape, fresher mineral condition, clearer color, and looser grain relation than seabed sediment that did not contain tailings material.. Based on the different characters and distribution patterns, sediment carrying tailings in the Senunu seabed. Based on the other characters and distribution patterns, sediments carrying tailings in the Senunu seabed on average were 2-167 centimeter thick at the surface with accumulated tailing 1-50% of total sediment at the sea bottom. Furthermore, the distribution of these tailing deposits is influenced mainly by morphodynamic, hydrodynamic conditions and the process of redeposition.

Macroalgae degradation promotes microbial iron reduction via electron shuttling in coastal Antarctic sediments.

Colonization of newly ice-free areas by marine benthic organisms intensifies burial of macroalgae detritus in Potter Cove coastal surface sediments (Western Antarctic Peninsula). Thus, fresh and labile macroalgal detritus serves as primary organic matter (OM) source for microbial degradation. Here, we investigated the effects on post-depositional microbial iron reduction in Potter Cove using sediment incubations amended with pulverized macroalgal detritus as OM source, acetate as primary product of OM degradation and lepidocrocite as reactive iron oxide to mimic in situ conditions. Humic substances analogue anthraquinone-2,6-disulfonic acid (AQDS) was also added to some treatments to simulate potential for electron shuttling. Microbial iron reduction was promoted by macroalgae and further enhanced by up to 30-folds with AQDS. Notably, while acetate amendment alone did not stimulate iron reduction, adding macroalgae alone did. Acetate, formate, lactate, butyrate and propionate were detected as fermentation products from macroalgae degradation. By combining 16S rRNA gene sequencing and RNA stable isotope probing, we reconstructed the potential microbial food chain from macroalgae degraders to iron reducers. Psychromonas, Marinifilum, Moritella, and Colwellia were detected as potential fermenters of macroalgae and fermentation products such as lactate. Members of class deltaproteobacteria including Sva1033, Desulfuromonas, and Desulfuromusa together with Arcobacter (former phylum Epsilonbacteraeota, now Campylobacterota) acted as dissimilatory iron reducers. Our findings demonstrate that increasing burial of macroalgal detritus in an Antarctic fjord affected by glacier retreat intensifies early diagenetic processes such as iron reduction. Under scenarios of global warming, the active microbial populations identified above will expand their environmental function, facilitate OM remineralisation, and contribute to an increased release of iron and CO2 from sediments. Such indirect consequences of glacial retreat are often overlooked but might, on a regional scale, be relevant for the assessment of future nutrient and carbon fluxes.

Reliability of detrital marine sediments as proxy for continental crust composition: The effects of hydrodynamic sorting on Ti and Zr isotope systematics

The isotopic composition of the detrital sediment record harbours a valuable proxy for estimating the composition of the erodible upper crust since the Archaean. Refractory elements such as titanium (Ti) and zirconium (Zr) can display systematic variations in their isotopic composition as a result of magmatic differentiation. Hence, the isotopic composition of such elements in detrital sediments could potentially be used to infer the average composition (e.g., SiO2 content) of their source region, even when elemental systematics are obfuscated by weathering and diagenetic processes. A key premise of this approach is that the isotopic composition of sediments remains unbiased relative to their protolith. To what extent isotopic fractionation can occur during sedimentary processes, notably the hydrodynamic sorting of heavy mineral assemblages with contrasting isotopic compositions, remains poorly understood. We investigate the effects of such processes on the Ti and Zr isotope composition of a suite of detrital sediments from the Eastern Mediterranean Sea (EMS). These sediments are binary mixtures of two main provenance components, Saharan dust and Nile sediment, with strongly contrasting mineralogical and geochemical signatures.The EMS sediments display clear evidence for hydrodynamic sorting of zircon, expressed as a large variation in Zr/Al2O3 and deviation of εHf relative to the terrestrial εNd-εHf array. Our new data, however, do not show pronounced Zr isotope variation resulting from either hydrodynamic sorting of zircon or sediment provenance. Although this agrees with theoretical models that predict negligible equilibrium zircon-melt Zr isotope fractionation, it contrasts with recent observations suggesting that kinetic Zr isotope fractionation might be a common feature in igneous rocks. For the EMS sediments, the negligible shift in Zr isotope composition through hydrodynamic sorting means that fine-grained samples accurately reflect the composition of their source. The nearly overlapping Zr isotope compositions of Sahara- and Nile-derived sediment, however, mean that Zr isotopes, in this case, have insufficient resolution to be a useful provenance proxy.Titanium behaves differently. A small but resolvable, systematic difference in Ti isotope composition is observed between the Sahara and Nile provenance components. Samples with a strong Saharan dust signature show some Ti isotope evidence for hydrodynamic sorting of oxides in tandem with zircon, but a much stronger effect is inferred for Nile sediment. Regression of the EMS sediment samples shows that the Ti isotope composition of the Nile-derived component is strongly fractionated compared to its protolith, the Ethiopian flood basalts. Whereas Ti in Nile sediment is carried in essentially unmodified concentration, and by inference isotope composition, from its sources to the delta, large-scale hydrodynamic sorting of Fe-Ti oxides occurs in the littoral cell. This process causes a decrease in TiO2/Al2O3 of the residual fine-grained sediment fraction and shifts its Ti isotope composition to heavier compositions. The potential of such an “oxide effect” in detrital sediments has implications for crustal evolution models that use Ti isotopes as a proxy for the proportion of felsic crust and can account for the observed scatter in the shale record.

Application of mineral liberation analysis (MLA) for investigations of grain size distribution in submarine density flow deposits

Textural and structural features of submarine mass density flow sediments are a record of depositional flow evolution and hydrodynamics. Record of changes in such flow movement are difficult or impossible to detect, especially in fine sediments, without quantitative grain size analysis. This study shows an automated measurement system of mineral liberation analysis MLA applied for the first time to grain size distribution. The analysis concerns heavy minerals extracted from very fine- and fine-grained sandstones of the Cergowa Beds (Lower Oligocene) in the Polish and Slovak Outer Carpathians, which macroscopically show unclear textural trends and represent deposits of steady and uniform turbidity currents, possibly initiated by hyperpycnal effluents. The MLA analysis showed that the tested material represents sediments deposited by flows with developing turbulence. Simultaneously, the study verified that a turbulence damping contributes to size-density sorting during transport and demonstrated that maximum rather than average grain size is controlled by flow concentration, therefore reflects flow hydrodynamics. Besides, MLA measurements recognised variations in flow motion recorded by three types of grain-size breaks: (i) in high-density flow when capacity-controlled conditions are changing so that high energy flow erodes the previously deposited material; (ii) at a sharp interface between high-concentration basal layer and the overriding flow with lower concentration, and (iii) at a transition between low- and high-density flows during deposition of the Bouma interval Tb or between Tb and Tc. The MLA test study appears to be promising because this method increases objectivity of large amount of data collection, therefore provides significant statistical representation. Besides, this automated system reduces human errors, bias and tedious manual analyses, thus opening new perspectives in analysis of detrital sediments and interpretation of depositional processes.

Speleogenesis and depositional history of paleokarst phreatic caves/cavities; Podgrad, SW Slovenia

The studied paleokarst corresponds to an uplifted peripheral foreland bulge when Upper Cretaceous diagenetically immature eogenetic carbonates were subaerially exposed, karstified and subsequently overlain by upper Paleocene/lower Eocene palustrine limestone.Among the subsurface paleokarstic features, both vadose and phreatic forms occur. The phreatic caves/cavities include features characteristic of the mixing zone speleogenesis at the interface between freshwater (brackish water) lenses and the underlying seawater. They were found in various positions with respect to the paleokarstic surface, the deepest being about 75 m below the surface. Three indistinct horizons of cavities/caves and intermediate vugs were recognized. Subsequently, all cavities were completely filled with detrital sediments and speleothems in the phreatic and vadose zones. In general, the phreatic cavities of the lower two horizons are geopetally filled with mudstone derived from incomplete dissolution of the host rock and overlain by coarse-grained, blocky calcite. Shallower below the paleokarst surface, a large phreatic cave of the third horizon is filled with flowstone overlain by reddish micritic carbonate sediment with intercalated calcite rafts. In the upper part of the cave, sediments derived from the paleokarst surface are gradually becoming more abundant. Vadose channels, which may also intersect the cave sediments, are mainly filled with "pedogenic" material derived from the paleokarst surface. Immediately prior to marine transgression over the paleokarst surface, some cavities were filled with marine-derived microturbidites. In general, the diversity of cave fills and the amount of surface material decrease with distance from the paleokarst surface. Below the paleokarst surface, the δ13C and δ18O values of a host rock and cavity deposits show good correlation with trends significant for meteoric diagenesis. It is shown that deposits associated with phreatic caves can be of great importance for the study of the speleogenetic, geomorphological and hydrogeological evolution of certain paleokarst regions.

Hybrid event beds generated by erosional bulking of modern hyperpycnal flows on the Choshui River delta front, Taiwan Strait

AbstractHyperpycnal flows are important agents for transporting detrital sediments from rivers to oceans. Previous studies often assumed that the deposits of flood‐controlled delta fronts would be dominated by graded sand with common hummocky cross‐stratification. This study documents, for the first time, hybrid event beds and plumite deposits inside the succession of a modern delta front. This delta in the Taiwan Strait is fed by the Choshui River, which is considered a highly efficient sediment transport system with individual floods with extremely high suspended sediment concentrations. The deltaic event beds recorded in the core were interpreted as hyperpycnal flow‐generated hybrid event beds and turbidites triggered by hypopycnal flows. Accelerator Mass Spectrometry 14C dating, grain‐size analysis and measurements of stable isotopic composition of organic matter were conducted to delineate the depositional process of the recognized beds. The internal subdivisions of the hybrid event beds were differentiated mainly based on sedimentary textures, including cohesive mud content, sand content and sorting. The disorganized portion (division H3) appears internally chaotic and contains large rafted substrate clasts but also displays an upward increase in dispersed cohesive mud from 35% (division H3a) to 50% (division H3b). In contrast, massive H1 divisions are characterized by much lower cohesive mud of ca 8%. The vertical arrangement between depositional facies allows the discrimination of three hybrid event bed types. The stable carbon isotopic composition of the organic matter reveals that the cohesive mud in each division of the hybrid event beds was sourced from marine substrate, rather than supplied by the original hyperpycnal flows. Therefore, the hybrid event beds are generated by energetic hyperpycnal flows, which can delaminate the muddy sea‐floor and incorporate large quantities of substrate fragments. The bulking of erosional hyperpycnal turbulent flow forces flow transformation and generates a more cohesive flow with a turbulent, dense head and trailing bipartite debris flow. The occurrence of hybrid event beds in modern shallow delta front settings is also an important novelty, implying a high density of hyperpycnal flows at the mouth of sediment‐laden rivers as well as the crucial impact of substrate entrainment on the development of hybrid event beds.

Residual liquid from deep magma ocean crystallization in the source of komatiites from the ICDP drill core in the Barberton Greenstone Belt

Komatiites and sedimentary rocks sampled during the International Continental Drilling Program (BARB1-2–3-4–5) in the Barberton greenstone belt, South Africa, were analyzed for 146Sm-142Nd systematics. Resolved negative μ142Nd values (down to −7.7 ± 2.8) were identified in komatiites from the 3.48 Ga Komati Formation and this signature correlates with low Hf/Sm ratios measured in these samples. The negative μ142Nd point to a source with subchondritic Sm/Nd ratio which formed during the Hadean. No analytically resolvable 142Nd anomalies were measured in crustal detritus-rich, Si-rich, Ca-Fe-rich sediments and cherts from the Buck Reef (3.42 Ga) and the Fig Tree Group (3.23–3.28 Ga). Our new measurements are incorporated into a larger set of 147Sm-143Nd and 176Lu-176Hf data to better understand the 142,143Nd-176Hf isotope signatures in the mantle source at the time of komatiite crystallization. Our calculations show that the 142,143Nd-176Hf isotope signatures and Hf/Sm ratios cannot be produced by recycling into the komatiite source of detrital sediments like those sampled in the Barberton area. Only cherts have the required trace element characteristics – low Hf/Sm, radiogenic ε176Hf –but the trace element concentrations in the cherts are so low that unrealistic amounts of chert would need to be added.We propose a four-stage model for the formation of these rocks. Negative μ142Nd and low Hf/Sm ratios developed during the crystallization of a deep magma ocean soon after Earth accretion. The material that ultimately became the source of komatiites was a residual liquid produced by 50% crystallization leaving a bridgmanite/ferropericlase/Ca-perovskite cumulate. The Lu-Hf and Sm-Nd isotope systems were decoupled at this stage. After extinction of 146Sm around 4 Ga, parent/daughter ratios fractionated during a melt extraction event. With this model we explain the positive ε176Hf and slightly negative ε143Nd in these samples. The 3.55 Ga Schapenburg komatiites in another part of the Barberton belt share similar chemical signatures, supporting our model of fractionation in a deep magma ocean early in Earth's history.