Recent Sediments Research Articles

Опыт определения копромаркеров в отложениях археологических памятников (по материалам стоянки Сельунгур, Южный Кыргызстан)

Introduction. The article discusses the results of a study of ash layers from Holocene deposits at the Selungur (Surungur) Cave. Goals. So, the work attempts a practical evaluation of a method of identifying coprostanols in archaeological sediments. The investigation of Holocene deposits of the site was carried out in 2018 and 2021 field seasons. The study identifies a total of 7 Holocene layers that represent the typical ‘fumier’ facies of cave and rock shelter deposits connected to pastoralism and animal husbandry practices, and built up of stratified layers of burnt herbivore dung. The sequence contains a record of multiple earthquakes that disturbed the sediments and effected in water escape structures, plastic deformations, and faults. Nevertheless, the stratigraphy remains easily readable. Unfortunately, archaeological and paleofaunistic materials were never found but a series of ash-containing interlayers suggests that the cave was repeatedly visited by ancient humans. Materials. In the ash deposits, our micro charcoal analysis has identified areas of concentration of burnt dungs which was used for fire. Series of samples were taken throughout the section of Holocene deposits for gas mass spectrometry analysis. The research efforts have also included the analysis of modern dung from herbivores inhabiting the area, such as cows, sheep, goats, horses and donkeys, for the latter obtained data to serve as a reference collection. Results. Unfortunately, layer 7 of the Selungur Cave proved characterized by poor preservation of fire products, while layers 6–1 yielded somewhat rich data. The obtained results make it possible to identify coprosterols and determine that equine dung was used in layers 6-2 as a fuel, and goat dung — in the first layer. The most widespread distribution of equines in this region occurred during the existence of Dayuan (Parkan) state, in the third century BC and later in the Middle Ages. Most likely, during these periods the mountain corridor comprising the Selungur Cave could have been used as a pass of the Silk Road that connected the Fergana and Alay valleys. The accumulation of the upper layer, in our opinion, is associated with the modern era.

Geologic Map of the Bedford 30- x 60-minute Quadrangle, Indiana

The Geologic Map of the Bedford 30- x 60-minute Quadrangle shows the Mississippian and lower Pennsylvanian bedrock units and the overlying Pleistocene and Holocene deposits distributed over eight counties. The mapped area includes five physiographic divisions of the Southern Hills and Lowlands Region in south-central Indiana. Bedrock units and unconsolidated deposits were characterized by outcrop field observations, and new and archived borehole data. Bedrock data was consolidated into a single mapping database, which was then processed using gridding and contouring tools in ArcGIS Pro, resulting in rock formation contact lines, mappable at 1:100,000 scale. Additional information used to delineate contacts for unconsolidated deposits was based upon Indiana Department of Natural Resources water well database and soils data from the Soil Survey Geographic (SSURGO) database. Light detection and ranging (LiDAR) digital elevation models were also used to identify landforms and refine contacts between surficial units. The mapped bedrock units, from east to west, range in age from the Borden Group (lower Mississippian) to the Raccoon Creek Group (Lower Pennsylvanian) with the strike oriented generally from northwest to southeast. Quaternary deposits are found in river and stream valleys and filling the Wabash and Scottsburg lowlands with glacial deposits. Quaternary sediments were mostly deposited during the last two major advances of the Laurentide Ice Sheet into south-central Indiana. Brief summaries of all mapped bedrock units and unconsolidated deposits are listed on the map sheet, with more detailed descriptions in the accompanying pamphlet. Bedrock survey drill hole data points are also displayed on the map with corresponding links to expanded drill hole information for each of the survey drill holes listed in the pamphlet. In addition to the map and pamphlet, a composite spatial data set that conforms to the standardized database schema known as GeMS (Geologic Map Schema) is also available for download from this site. Both ESRI-licensed geodatabase and open shapefile versions of the spatial data set are available for download. Metadata records associated with each element within the spatial data set contain detailed descriptions of their purpose, constituent entities, and attributes. This geologic map was funded in part through the STATEMAP program supported by the U.S. Geological Survey under Cooperative Agreement No. G21AC10646.

Holocene Depositional History of Low-Lying Reef-Rim Carbonate Islets of Fakarava Atoll, Northwest Tuamotu, Central South Pacific

Assumptions about the fate of low-lying coral reef islands (atolls) facing global warming are poorly constrained, due to insufficient information on their depositional history. Based on the U/Th dating of 48 coral clasts, the chronostratigraphic analysis of excavated sections through rim islets (motu) at the windward and leeward sides of Fakarava Atoll (Tuamotu, French Polynesia) reveal that the deposition of coral detritus started approximately 2000 years ago. Most of these deposits lie on conglomerate pavements or reef flat surfaces, and are about 4500 to 3000 years old. The islet expansion at the windward sites seems to have operated coevally across the reef rim, from the ocean-facing shore lagoonwards. Meanwhile, well-developed, continuous, elongated, vegetated islets mostly occur along the windward, northeast to southeast coast, and isolated islets, vegetated or not, associated with the dense networks of conglomerates, are common on the leeward, partly submerged, western rim. Islet accretion on the windward rim sides is believed to have been mainly triggered by winter storms and occasional cyclonic events, whilst the leeward atoll parts were most likely shaped by distant-source swells from mid to high latitudes. The projections of the accelerated sea level rise in the future suggest that the long-term islet stability at Fakarava could be altered because the islets have accreted under the conditions of the falling sea level.

North Atlantic forcing of Indian Winter Monsoon intensification: Evidence from Holocene sediments from the tropical Indian Ocean Island of Sri Lanka

The teleconnection between the Asian monsoon system and North Atlantic forcing is an enduring prospect of the Earth’s climate. During the Holocene interstadial, the Indian summer monsoon showed asynchronous weakening links to ice rafting events documented in the North Atlantic region. However, the sensitivity of the Indian Winter Monsoon in response to North Atlantic cold spells is unclear due to a lack of compelling evidence. This study aims to extract the deglacial Indian Winter Monsoon signals using lithogenic tracers in coastal sediments and explore its association with the North Atlantic cooling episodes. A 5.1 m sediment core was retrieved from Pottuvil Lagoon in the southeastern coast of Sri Lanka, and the concentrations of K, Rb, Mg, Al, and Ti in 101 sub-sections were analysed using ICP-MS. The core- chronology was established by Bacon 2.2 age-depth modelling based on calibrated AMS 14C dates. The monsoon signal was reconstructed using element proxies and compared with the drift ice indices from the North Atlantic deep-sea sediments. Results revealed distinct phases of intense monsoon activity at 2553–2984 years BP, 3899–5021 years BP, and 5244–5507 years BP intervals with intermittent weak phases during 2253–2553, 2984–3899, and 5021–5244 years BP. The episodes of the intensified Indian Winter Monsoon coincided with Bond Events 2, 3, and 4, showing a strong coherence with the North Atlantic’s deglacial climate. Thus, on a millennial scale, North-Atlantic cooling has triggered intense winter monsoon conditions over the tropical Indian Ocean region from the mid to late Holocene. In comparison with regional monsoon archives, the Pottuvil winter monsoon record exhibits an anti-phase association with the Indian Summer Monsoon during Holocene ice-rafted debris events. The geochemical approach executed in this study could provide new insight into the millennial-scale pacing of the winter counterpart of the Indian monsoon links to climate extremes of high northern latitudes.

Precious Metals in the Holocene Sediments of the Chukchi Sea

Abstract ––We studied the distribution of gold, silver, and platinum group elements (Pd, Pt, Rh, Ir, and Ru) in two bottom sediment cores of the southern Chukchi Sea. It is shown that the Holocene pelite–silty sediments with an age of up to 4.0 ka BP are significantly enriched in these elements, except for Ru and Rh, relative to their clarkes. Native silver minerals were found in all samples by probe microanalysis, whereas gold minerals were revealed only in the surface layer of the sediment core closest to the Chukchi Sea coast. Multicomponent statistical analysis of the chemical composition and grain size of the sediments and the content of organic matter in them has led to the conclusion about the accumulation of clastogenic and chemogenic forms of precious metals. The abnormally high content of gold (0.3 ppm) in the recent sediments near the Chukchi Peninsula coast might be due to its additional removal from the continent as a result of the placer mining there.

Mineralogy of Recent Sediments of Al-Teeb River Basin-East Missan Governorate, Southeastern Iraq

This research aims to define the mineralogical composition of recent sediments that were deposited around the Al-Teeb River basin in the east Missan Governorate and try to determine the provenance or the source of these sediments. The study area represents the southeastern edge of the Mesopotamian Plain and is part of it. 15 samples were collected from eight stations of recent sediment that was deposited around the Al-Teeb River; two field works are covered (December 2019 and August 2021). Mineralogical study of the sediment after separating the light and heavy minerals by heavy liquid Bromoform in order to determine the mineralogical composition of the studied samples by using the petrographic microscope the light mineral fraction composed (95.5%) of the total mineralogy. The light components of these sediments consist mainly of quartz about 25.31%, feldspars (potash and plagioclase feldspar) about 9.53%, sedimentary rock fragments (carbonate rock fragments up to 33.39%, chert rock fragments 7.65%, evaporates fragments, 7.31%), (igneous rock fragments, and metamorphic rock fragments about 6.94%). The major component of the heavy minerals residue is opaque minerals with a range of 36.76% and non-opaque minerals with a range of 63.24%. The non-opaque minerals are mainly of chlorite 7.42%, pyroxenes composed of both orthopyroxene and clinopyroxene 6.37%, amphiboles composed of hornblende, glaucophane, and tremolite 7.02%, (mica: biotite and muscovite) 9.81%, zircon 7.54%, tourmaline 5.1%, epidote group 5.91%, rutile 4.5%, kyanite 2.2%. The sediments have two types of stability: moderately stable and ultra-stable. The mineralogical composition shows that the major sources of these sediments are; the river terraces and flood plain of the river in the Mesopotamian Plain, another source of these sediments is the aeolian deposits that separated from sand dune fields in the studied area, and outcrops of ancient sedimentary formations in the southeastern of Iraq as specified by the incidence of the carbonate rock fragments.

Cryptotephra preserved in Lake Suigetsu (SG14 core) reveals the eruption timing and distribution of ash fall from Japanese volcanoes during the Late-glacial to early Holocene

Long sedimentary successions extracted for palaeoclimate research regularly preserve volcanic ash (tephra) fall from explosive eruptions and are increasingly used to elucidate the timing and scale of past events. This study investigates the non-visible tephra (cryptotephra) layers preserved in the annually laminated and intensively 14C dated sediments of Lake Suigetsu (SG14 core), Japan. The cryptotephra investigations reported here focus on the Late-glacial to early Holocene sediments that were deposited between two visible tephra layers, the Ulleungdo (U)-Oki (10.2 ka) and the Sambe ‘Sakate’ (19.6 ka), and consequently span an interval of abrupt climate change making any newly identified cryptotephra layers invaluable chrono-stratigraphic markers. Using major and trace element volcanic glass compositions the cryptotephra are used to assign provenance to chrono-stratigraphically relevant eruption units. Five new cryptotephra layers are identified within this time interval. Three cryptotephra layers are from Kyushu volcanoes (SG14-1337 and SG14-1554 [Sakurajima]; and SG14-1806 [Kirishima]), all of which offer important chronological constraints on archaeological (Jomon) cultural transitions in southern Japan during the last termination. Another cryptotephra (SG14-1579), is assigned to activity on Niijima Island providing the first known distal occurrence and age of the eruption. Finally, the SG14-1798 cryptotephra precisely dated at 16,619 ± 74 IntCal20 yrs BP (2σ) is linked to Asama (As) volcano and more precisely the later phases of the As-YKU eruption. This discovery greatly expands the distribution of ash fall from this multi-phased eruption at Asama volcano, which affected an area in the region of 120,000 km2. Refining the timing of the eruption and the distribution of As-YKU ash fall is important as it offers an excellent chrono- and climato-stratigraphic marker suitable for assessing spatial variability in environmental response to past climate change during the termination of the last glacial.

Foraminifera in the Holocene sediments at the shallow sea from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) (0÷60 m of water depth)

The shallow sea (0÷60 m of water depth) from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) belongs to the internal shelf in Central Vietnam. This is quite a good geological structure for the land-sea interaction study, especially during the Holocene. Therefore, it is necessary to study the geological history of the area during the Holocene period. Foraminifera is the subject of geological studies to solve the environmental problems of sedimentary, stratigraphic, and paleogeography. However, at present, the research documents on Foraminifera in the sediments in Vietnam in general as well as in the research area in particular are still very modest. This paper presents research results of Foraminifera fauna in Holocene sediments from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) (0÷60 m of water depth). 93 species, belonging to 48 genera, 28 families and 5 suborders Foraminifera have been identified based on the analysis of 59 available samples. Miliolina Delage et Hérouard, 1896 has 06 families, 18 genera and 40 species; Rotaliina Delage et Hérouard, 1896 has 12 families, 15 genera and 29 species; Textulariina Delage et Hérouard, 1896 has 03 families, 05 genera and 07 species; Lagenina Delage et Hérouard, 1896 has 03 families, 04 genera and 07 species; Globigerinina Delage et Hérouard, 1896 has 04 families, 06 genera and 10 species. The quality of the benthonic Foraminifers is dominant, clearly showing the geological environment of the shallow sea near shore, where the hydrodynamic regime is high and the salt concentration is not stable.

Impact of Natural and Anthropogenic Factors on Late Holocene Sedimentation in the Chukchi Sea

Impact of Natural and Anthropogenic Factors on Late Holocene Sedimentation in the Chukchi Sea

Application of mid-infrared spectroscopy for the quantitative and qualitative analysis of organic matter in Holocene sediment records

The organic matter composition of lake sediments influences important in-lake biogeochemical processes and stores information on environmental changes. Extracting this information is notoriously difficult because of the complexity of the organic matter matrix, which routinely imposes trade-offs between high temporal and analytical detail in the selection of methods of analysis. Here, we demonstrate the potential of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) for achieving both of these objectives using untreated bulk samples from two Holocene lake-sediment cores from central Sweden. We develop quantitative models for sediment total organic carbon (TOC) with the same predictive abilities as models based on samples diluted with KBr and qualitatively characterize the organic matter using a spectra processing-pipeline combined with principal component analysis. In the qualitative analysis we identified four organic matter sub-fractions and the interpretation of these is supported and further advanced with molecular data from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Within these organic fractions, compound groups such as aromatics, lignin, aliphatics, proteins and polysaccharides were identified by means of DRIFTS and the analyses and processes outlined here enables rapid and detailed quantitative and qualitative analysis of sediment organic matter. The DRIFTS approach can be used as stand-alone method for OM characterization with high temporal resolution in Holocene sediment records. It may also function as a screening process for more specific analyses of sample subsets, such as when coupled with pyrolysis-GC/MS to further tease apart the OM composition, identify sources and determine degradation status.

Recent increase in sediment dry matter, carbon, and phosphorus accumulation in small boreal lakes with clayey catchments

This study estimated the mass accumulation rates of sediment (MAR), carbon (CMAR), and phosphorus (PMAR) in small Finnish lakes with agricultural clayey catchments over a 25-year period (1986–2011) and compared these with the conditions before major agricultural land use. Twenty-two lakes were cored for recent and reference (pre-disturbance) sediments. The recent sediment section was selected based on the 1986 137Cs fallout peak (TOP), whereas the pre-disturbance section (REF) was selected immediately below the first signs of human-induced erosion. The 50-cm reference section was dated with 14C at both ends. The mass accumulation rates were estimated based on dating, weighing, and chemical analysis for both sediment sections. Furthermore, sediment-penetrating echo soundings were used to estimate the amount of sediment in the whole lake basins. These data were used to examine area-specific loading from clay-rich catchments. The average whole-basin pre-disturbance MAR, PMAR, and CMAR were 62 g m−2 a−1, 0.06 g m−2 a−1, and 4.7 g m−2 a−1, respectively. The corresponding recent rates were 11, 13, and 8-fold (693 g m−2 a−1, 0.79 g m−2 a−1, and 37 g m−2 a−1). In the recent conditions, sediments were generally more minerogenic and MAR, PMAR, and CMAR were higher in lakes with more arable fields in their catchments. Average area-specific suspended sediment load from the catchment for the region (∼39% clayey soils) was approximately 69–137 kg ha−1 a−1 in the undisturbed state and 767–1534 kg ha−1 a−1 in recent conditions based on 100–50% retention. The results demonstrate that the increases in sediment, nutrient, and organic matter accumulation due to agriculture can be several fold over undisturbed state.

Impact of aerobic reworking of biomass on steroid and hopanoid biomarker parameters recording ecological conditions and thermal maturity

Steranes and hopanes are the biomarkers of eukaryotic sterols and bacterial hopanols. Extracted from sedimentary rock, they are widely used to assess burial temperatures and palaeoecological conditions. The relative proportion of steranes and hopanes is commonly applied as a measure of the flux of eukaryotic versus bacterial biomass into sediments, and the relative abundances of C27, C28 and C29 steranes are proxies for shifts in eukaryote ecology. In Recent sediments, intact sterols provide additional information about particular eukaryotic origins. However, biological lipid distributions are not always recorded faithfully in sediments. Based on observations on modern algae and plants, and on 558 million year old fossil macroalgae from the Ediacaran of the White Sea, we suggest that these biomarker proxies can be severely altered by aerobic microbial reworking, to the extent that a complete loss of primary ecological information may occur. Network analysis on the biomarker data suggests that oxic degradation also affects isomer and homolog distributions of saturated and aromatic steroids, hopanes, cheilanthanes and n-alkanes, generating anomalies in apparent thermal maturity indicators and other proxies. In our dataset, between Ediacaran macroalgae that experienced the least and the most oxic degradation, the absolute concentration of biomarkers decreases 80-fold, and at the same time the proportion of steranes over hopanes decreases by a factor of 82, while the proportion of C29 steranes among total steranes decreases from 91% to 47%. Such redox dependent offsets may explain the recurrently erratic behaviour of numerous biomarker parameters. While these results impart constraints on the interpretation of biomarker distributions, they do provide a tool for evaluating the effects of oxygen exposure and microbial degradation on organic matter preservation in recent and ancient environments and may point towards a solution for the correction of such effects.

Geological Aspects of the Formation and Distribution of Gas Anomalies in Bottom Sediments of the New Siberian Sedimentary Basin and Adjacent Geostructures of the East Siberian Sea

Abstract —In bottom sediments of the New Siberian sedimentary basin and adjacent geostructures of the East Siberian Sea, we identified СН4, as well as its limit and unsaturated homologues (up to and including C5H12), CO2, CO, H2, He, H2S, O2, N2, and Ar. Isotope-gas-geochemical parameters δ13С СО2, СН4 and С2Н6, of the molecular mass of hydrocarbon fraction and genetic coefficients indicate the presence of both syngenetic and epigenetic gases of various gas sources in sediments, including recent sediments, peatlands, coal-bearing and gas-bearing formations, solid bitumen, igneous formations, accumulations of gas hydrates and prognostic condensate-gas, condensate, oil-and-gas and gas-and-oil reservoirs. Concentrations of CO2 and CO reach 29.25 and 0.06 cm3/kg, CH4 and the sum of its homologues – 5.93 and 0.031, Н2 and He – 0.78 and 0.318, H2S – 0.092 cm3/kg; this indicates that gas-geochemical anomalies, exceeding the anomaly criteria by 6–124 times, form in bottom sediments. The formation and distribution of abnormal concentrations of natural gases depend on the complex influence of gas-controlling factors – geological structure, fold and fault tectonics, magmatism, coal-oil-gas content, bituminous content, organic saturation, lithological composition, water-physical and reservoir properties of sediments, hydrogeological, geocryological and other conditions for accumulation of natural gases or their degassing.

Subfluvial tunnel layout design: Mapping recent sediment fill in Bilbao Estuary using H/V spectral ratio

Mapping the soil-bedrock interface is crucial for tunnelling projects in engineering geology. This investigation demonstrates the effectiveness of a novel technique to calculate the horizontal-to-vertical (H/V) spectral ratio using ambient vibration measurements to characterize the unconsolidated sediment thickness and geometry of the top of the engineering bedrock in the city of Bilbao (northern Iberian Peninsula). Engineering bedrock is defined here as the consolidated rock layer underlying the Holocene sediments infill in the region. The non-invasive technique was integrated into the geophysical surveys conducted in 2019 for a subfluvial tunnel construction project beneath the Bilbao Estuary. We calculated the H/V transfer function at 37 sites using an AutoRegressive Moving Average (ARMA) model, which has been shown to be robust in extracting the ground fundamental resonant frequency with high spectral resolution. Lithological information from coincident stations and boreholes supports the empirical interpretation of the H/V spectral peaks in terms of peak impedance contrast depth. The estimated engineering bedrock exhibits morphological complexity with depths ranging from ∼10 m to ∼47 m below the surface. The obtained unconsolidated sediment thickness map is consistent with the geology known from the scattered historical borehole data and is supported by the results of the soil geotechnical characterization conducted in 2021 to advance the planning phase of the subfluvial tunnelling project. We show that the novel H/V approach used in this work is robust and yields somewhat higher resolution results than other commonly used H/V methods. The resolution of the method enables the use of H/V estimates to efficiently plan well campaigns and minimise costs, even for relatively shallow targets. We conclude that H/V mapping using this novel technique can help select layout alternatives in the early stages of tunnel construction planning, especially in heavily urbanized areas.

BrGDGT-based quantitative reconstructions of paleotemperature in lakes: Regional vs. site-specific calibrations

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that have been widely used as tools for the quantitative reconstruction of past terrestrial temperatures in lakes. Two approaches, i.e., regional/global and site-specific calibrations, have been previously employed in the reconstruction. However, their strengths and weaknesses have not been properly evaluated yet, making it challenging to choose a suitable approach to paleoreconstruction. Here, we investigated the distribution of brGDGTs in surface sediments of 65 lakes along a mean annual lake water temperature (MLWT) transect in West China and developed a regional MBT'5ME (methylation degree of 5-methylated brGDGTs) calibration for MLWT reconstruction. Meanwhile, a site-specific brGDGT calibration for Lake Yangzonghai (YZH), located within the West China transect, was generated based on the relationship between the instrumental temperature record over the past 100 years and individual brGDGT abundances in a short sediment core taken from the lake. These two calibrations were applied to global lake surface sediments, as well as a long sediment core spanning the Holocene from Lake YZH. The linear correlations between MBT'5ME and temperature are highly consistent among lakes from different regions, indicating the near-universal response of brGDGTs in global lakes to temperature. However, MLWT inferred from the site-specific calibration shows a weak relationship with actual MLWT in global lakes, indicating that the site-specific calibration might be only a result of overfitting rather than reflecting the response of brGDGT distribution to ambient temperature. Applications to a Holocene sediment core in Lake YZH suggest that the regional MBT'5ME calibration is more suitable for reconstructing paleotemperature than the site-specific calibration. The regional MBT'5ME calibration derived temperature record shows a cold Younger Dryas (YD), followed by a rapid warming of ∼3 °C during the last deglaciation, and a long-term cooling of ∼1 °C from 9.9 to ∼0.2 cal ka BP. The principal component analysis shows that temperature is the dominant factor affecting brGDGT distributions in the long sediment core whereas the site-specific calibration is strongly affected by human activities rather than reflecting the ambient temperature. We highlight the importance of using appropriate approaches to developing calibrations for paleotemperature reconstruction and assessing the reliability of the temperature records.

Structure and Depositional Environment of the Upper Cenozoic Ulan-Zhalga Reference Section, Western Transbaikalia

The results of a comprehensive study of the Upper Cenozoic Ulan-Zhalga reference section in western Transbaikalia are presented. The paleontological, paleomagnetic and rock magnetic, lithological-mineralogical, and geochemical data obtained allowed us to identify and characterize the Lower, Middle, and Upper Pleistocene and Holocene deposits in the section and to reveal the features and conditions of sedimentation. Five members recognized in the section are combined into two sequences: the lower (layers 1–27, units 1–3) and the upper (layers 28–35, units 4–5). The boundary between Matuyama and Brunhes chrons (0.773 Ma) is determined at a depth of 15 m and the upper boundary of the Jaramillo subchron (0.990 Ma) at a depth of 23 m. The Matuyama/Brunhes boundary coincides with the boundary of Lower and Middle Pleistocene faunal complexes. The formation of the section corresponds to two major stages of sedimentation, which boundary is between the units 3 and 4 (depth 11.8 m). Changes in rock magnetic and granulometric parameters over the section has a climatic nature and reflect environmental changes. The formation of the lower part of the section (unit 1), which was accompanied by active pedogenesis, is characterized by the most heat- and moisture-enriched conditions. The upper strata of the section accumulated in colder and drier conditions with increased dynamics of aeolian processes.

Multi-method characterization of the recent sediment from the Dibi subsidence lake in the tropical Adamawa region (central Cameroon): Implications for the palaeoenvironmental reconstruction

The evolution and functioning of various tropical ecosystems is poorly understood due to a lack of quantitative techniques to characterize the physicochemical composition of soils and sediment. Here, a detailed multi-method study of lithological changes is provided from a core taken from the silted-up Dibi subsidence lake (central Cameroon). To unravel the provenance of sediment, mineral constituents, and organic matter sources, an array of tools are applied including a spectrophotometer, a laser particle sizer, Rock-Eval pyrolysis, X-ray diffractometer (XRD), a portable X-ray fluorescence (XRF) spectrometry, and an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) instruments. The studied core consists of light-colored deposits at the base (Unit 1) overlain by dark humic deposits (Unit 2). The sediment is very well graded (grading index Sd < 0.35Ф), indicative of bottom suspended to rolling transport. Unit 1 is characterized by relatively low values of total organic carbon (TOC: 2%–5%) whereas the dark Unit 2 has high contents of TOC (10%–33%). The core shows a high oxygen index (OI) value (average = 207 mg carbon dioxide (CO2)/g TOC) and a low hydrogen index (HI) value (average = 107 mg hydrocarbon (HC)/g TOC). This indicates highly altered organic matter (OM), likely from decomposed terrestrial plants. The chlorophyll-α fingerprint (peak around 675 nm) also reveals an autochtonous primary production of organic matter. The mineralogical assemblage of Unit 2 comprises kaolinite, quartz, feldspars, montmorillonite, ilmenite, siderite, gibbsite, rutile, and anatase whereas that of Unit 1 is similar but differs with the presence of illite and the absence of gibbsite. The high titanium dioxide (TiO2) and zirconium (Zr) contents confirm that the source rocks also are comprised of granites, and gneiss without volcanic rocks, such as basalts and trachytes. The source rocks have been intensively weathered using some parameters such as ln(Al2O3/Na2O), K2O/Rb, K/Al, and weathering indices, where Al2O3 denotes aluminum oxide, Na2O denotes sodium oxide, K2O denotes potassium oxide, Rb denotes rubidium, K denotes potassium, and Al denotes aluminum. The enrichment factors (EF) of redox-sensitive trace elements and their relation with TOC, the negative values of manganese/iron ratio (Mn∗) associated to three elemental ratios (cupper/zinc (Cu/Zn), thorium/uranium (Th/U), and vanadium/chromium (V/Cr)) attest to the predominance of sub-oxic to anoxic bottom waters in Dibi lake during sediment deposition. The data also show low primary productivity at the base of the core, followed by an increase towards the top, linked to the intensification of weathering and facilitated by humid climatic conditions, usually increase terrestrial input and palaeoproductivity. The petrological data show a generally warm and humid palaeoclimate. This climatic variation has contributed to the large spread of the savannah and disappearance of the forest. This study sheds light on the late Pleistocene to Holocene palaeoenvironment evolution of the Adamawa region which could be integrated into the context of the Pleistocene to Present regional evolution of the tropical palaeoenvironment.

Bryozoan statoblasts from lake sediments in Madagascar, including two new species

Madagascar is a freshwater biodiversity hotspot, yet the current understanding of freshwater bryozoan diversity is limited. Using a dissecting microscope, bryozoan statoblasts were collected during macrofossil analysis of a sediment core, which was taken from Lake Sofia, Madagascar, in 2019. There was a peak in the abundance of statoblasts prior to 1900, with 67 statoblast valves found at 45.5 cm and a decline in more recent sediments. A subsample of 14 specimens was examined under a scanning electron microscope to determine species identification. One of the species found was Plumatella kinesis. Two new species, Plumatella tsimiheta sp. nov. and Plumatella sofiae sp. nov. were also found and described. These results show the potential of lake sedimentary bryozoan remains for categorising species presence and distribution. Although poor preservation was a limitation for identification, there is still value in having a historical record of past biodiversity, especially when species may no longer be extant. This study highlights the need for further research to better understand the status of these species and other potential new species of bryozoan in Madagascar.

Global climate forcing on late Miocene establishment of the Pampean aeolian system in South America

Wind-blown dust from southern South America links the terrestrial, marine, atmospheric, and biological components of Earth’s climate system. The Pampas of central Argentina (~33°–39° S) contain a Miocene to Holocene aeolian record that spans an important interval of global cooling. Upper Miocene sediment provenance based on n = 3299 detrital-zircon U-Pb ages is consistent with the provenance of Pleistocene–Holocene deposits, indicating the Pampas are the site of a long-lived fluvial-aeolian system that has been operating since the late Miocene. Here, we show the establishment of aeolian sedimentation in the Pampas coincided with late Miocene cooling. These findings, combined with those from the Chinese Loess Plateau (~33°–39° N) underscore: (1) the role of fluvial transport in the development and maintenance of temporally persistent mid-latitude loess provinces; and (2) a global-climate forcing mechanism behind the establishment of large mid-latitude loess provinces during the late Miocene.

Considerations on premises of recent (&lt; 120 years) sedimentation rate models with unsupported 210Pb: a study case of sediment cores from mud shelf depocenters

Considerations on premises of recent (&lt; 120 years) sedimentation rate models with unsupported 210Pb: a study case of sediment cores from mud shelf depocenters