Clay Beds Research Articles

Sedimentological Study of Alluvial Deposits on the Congolese Coast: Highlighting the Erosive Character of the Holocene Wet Climatic Phases

A granulometric, mineralogical, morphoscopic and exoscopic study and Rock-Eval analysis carried out on samples taken in the Loango Bay and at Kivesso on the Congolese coast have made it possible to highlight the highly erosive character of the well-documented wet phases ca 9000 - 3000 years B.P. and ca 320 B.P. in the sub-region. Supported by carbon-14 dating, total organic carbon analyses highlight two major phases of peat deposit emplacement. The first, ca. 7000 years B.P., corresponds to the beginning of the deposition of the yellow formation in the entire Loango Bay; the second, ca. 320 years B.P., is contemporary with the deposition of peat in the Kivesso sector. The granulometric analysis of the sediments shows that they are essentially sandy-clay and very poor in silt, alternating with beds of silty clay sometimes rich in organic matter. These sands have a predominant mode of 0.200 mm and an average varying between 0.150 and 0.300 mm. They constitute the flood phase of the carrier current. They are associated with a population of mode 0.125 mm sometimes 0.050 mm with an average varying between 0.100 mm and 0.126 mm which corresponds to the settling phase. Morphoscopic examination showed several varieties of quartz that argue for a source of supply close to the depositional sites.

Noninvasive Monitoring of Subsurface Soil Conditions to Evaluate the Efficacy of Mole Drain in Heavy Clay Soils

Soil degradation and low productivity are among the major agricultural problems facing farmers of the newly reclaimed agricultural area in the Nile Delta region, Egypt. High content of clay and silt characterizes the soil texture of all farms in the area, while farmers still rely on the traditional mole drainage (MD) system to reduce the salinity of the farm soil. We present a comparison of innovative geo-resistivity methods to evaluate mole drains and the salinity affected clay soils. Geoelectrical surveys were conducted on three newly reclaimed farms to image the subsurface soil drainage conditions and to evaluate the efficiency of using the traditional MD systems in these heavy clay environments. The surveys included measuring the natural spontaneous potential (SP), apparent resistivity gradient (RG), and electrical resistivity tomography (ERT). Integrating the results of the three methods reduced the ambiguous interpretation of the inverted ERT models and allowed us to determine the subsurface soil structure. The inverted ERT models were suitable for locating the buried MDs and delineating the upper surface of the undisturbed clay beds. The proximity of these layers to the topsoil reduces the role played by MDs in draining the soil in the first farm and prevents the growth of deep-rooted plants in the second farm. Time-lapse ERT measurements on the third farm revealed a defect in its drainage network where the slope of the clay beds opposes the main direction of the MDs. That has completely obstructed the drainage system of the farm and caused waterlogging. The presented geo-resistivity methods show that integrated models can be used to improve the assessment of in situ sub-surface drainage in clay-rich soils.

Heave and pullout studies of geogrid-encased granular pile-anchors in expansive clay beds

This paper presents heave and pullout studies of plain granular pile-anchors (GPAs) and geogrid-encased GPAs. Experiments were conducted in California bearing ratio (CBR) moulds and fabricated moulds of size 381 × 381 × 457 mm in expansive clays. The GPA method is an innovative technique developed for reducing heave and improving bearing capacity and pullout capacity. In this study, GPAs were encased in geogrids to augment the engineering performance of the system. Tests were conducted in CBR moulds and fabricated larger moulds to study and compare the heave and pullout behaviour of plain GPAs and geogrid-encased GPAs. The results indicated that the clay beds reinforced with geogrid-encased GPAs showed better heave and pullout behaviour. Heave decreased by 90.8% and 92.5%, respectively, in the case of plain and geogrid-encased GPAs installed in the CBR moulds and by 95.12% and 98.3% in the case of plain and geogrid-encased GPAs installed in fabricated large moulds. Pullout load on geogrid-encased GPAs in CBR moulds improved by 42.17% over that on plain GPAs and pullout load on geogrid-encased GPAs in the fabricated large moulds improved by 52.25% over that on plain GPAs.

Micro-column testing of the dynamic adsorption of Pb by Fe-Mg clay–quartz beds

AbstractClays have been used widely as sorbents of potentially toxic elements, especially Pb. However, their adsorption efficiency has been studied mostly under static experimental conditions, which are labour-intensive. In this study, dynamic adsorption experiments were established using micro-columns to assess the adsorption behaviour of natural Fe-Mg-rich clays for Pb ions by varying the inlet solution pH, Pb concentration and flow rate. The clays, consisting of varying amounts of palygorskite and Fe-smectite, were diluted with quartz (Qz) sand to enhance their permeability. Greater adsorption capacity was observed for the mixed palygorskite/Fe-smectite-rich clay beds (45.2 ± 0.01 mg g–1) followed by the Fe-smectite-rich (35.7 ± 0.07 mg g–1) and palygorskite-rich (20.0 ± 0.03 mg g–1) clay beds. The results indicated that the greater adsorption efficiency of palygorskite/Fe-smectite-rich clays could be attributed to synergistic effects due to the coexistence of palygorskite and Fe-smectite clay phases, which have distinct physicochemical characteristics. Moreover, the results obtained showed good agreement with the static experiments, implying that the use of micro-columns could describe adsorption adequately over shorter experimental times.

A Novel Proof of Concept Experimental Setup for Seabed-Pipe Interface Friction Measurements

Abstract Offshore hydrocarbon pipelines operate at relatively high pressures and temperatures. These conditions lead to their expansion and contraction and ultimately result in pipeline buckling or “walking” after multiple cycles of operation. Such movements are typically opposed by the axial resistance of the pipe-soil interface, which has to be accurately evaluated to optimize the engineering performance of the pipelines while minimizing testing and construction costs. To date, different testing techniques have been adopted to evaluate this resistance throughout the pipeline operational life. These include laboratory soil element testing, laboratory model testing, and in situ testing using specialized, complex, and costly devices. Despite being the most reliable testing technique, in situ tests are limited by the very small number of available specialized field equipment, e.g., the Fugro SMARTPIPE and the recently developed “pipe-like” penetrometers, both of which suffer from some drawbacks related to high costs, practicality, and testing conditions. This paper presents an attempt at addressing most of the limitations that were identified in the currently available methods, leading to the development of a new in situ, cost-effective apparatus for measuring axial pipeline resistance. A laboratory proof of concept experimental setup that could be adapted in future work to become an autonomous field apparatus was designed, produced, deployed on a clay bed and tested under normal stresses in the low-pressure range. The prototype reliably captured the effects of normal stress on the drained interface resistance. It produced accurate interface friction factors that are comparable to those obtained from the direct shear tests on the same soil and interface. The results obtained are very promising and confirmed the practicality and functionality of the proposed prototype. Some areas of improvement that would enhance the efficiency and reliability of the test were identified and will be applied to future versions of the device.

Petrography and Lithogeochemistry of the Uppermost Middle Jurassic–Lowermost Lower Cretaceous Strata in the Lower Reaches of the Anabar River (East Siberia, Arctic)

Abstract —Based on the analysis of the petrographic and lithogeochemical features of the Middle Jurassic–Lower Cretaceous strata in the lower reaches of the Anabar River, we have studied the regularities of changes in the composition of the upper parts of the Yuryung-Tumus and Sodiemykha formations and the lower part of the Buolkalakh Formation. It has been established that the silt–sandy rocks of the first and basal beds of the second formation are graywacke arkoses and essentially feldspathic varieties, and most of the Sodiemykha Formation is composed of quartz–feldspathic and scarcer feldspar–quartz graywackes. A chemical classification of the rocks was made; most of them were assigned to normosiallites. The rocks of the marker beds, namely, the Fe-containing deposits of the Sodiemykha Formation, the basal glauconite bed of the Buolkalakh Formation, and the overlying clay bed, were classified as hypohydrolysates. All the studied deposits are of low sedimentary maturity, with essentially petrogenic clastic material. These are predominantly igneous rocks of intermediate and, less, felsic composition. The provenances were characterized by moderate chemical weathering. In the periods of the formation of the marker beds, chemical weathering intensified, and the amount of mafic and, partly, ultramafic rocks increased. The established changes in the composition of the parental strata are observed in the Middle Jurassic–Lower Cretaceous deposits of the entire considered petromineralogical province, which permits them to be used for correlation.

Genesis of the Wangpo bed in the Sichuan Basin: Formation by eruptions of the Emeishan large igneous province

During the Guadalupian–Lopingian transition, the widely distributed Wangpo bed in the Sichuan Basin recorded the voluminous eruptions of the Emeishan large igneous province (ELIP). However, it remains unclear whether the Wangpo bed was formed by submarine volcanic activity of the ELIP or is the weathering product of the Emeishan basalt. Furthermore, its causal relationship with the end-Guadalupian mass extinction and contemporaneous environmental changes is also uncertain. To investigate these issues, we conducted a study of the Wangpo bed of the Shangsi section in the northwestern Sichuan Basin, including analysis of its mineralogy, whole-rock major/trace elements, and zircon UPb chronology, Hf isotopes, and trace-element geochemistry. Petrological observations of the appearance of pumice in the upper Wangpo bed suggest that the pumice could have been formed by submarine volcanic activity of the ELIP. Mineralogical investigation also shows large amounts of vermicular kaolinite and anatase in the Wangpo bed, suggesting that it is the alteration product of volcanic ash that was deposited in a deep water column. Geochemical comparisons further confirm that the Wangpo bed shows affinity with the felsic extrusive rocks of the ELIP but differs from the clay beds at the bottom of the Xuanwei Formation in the eastern ELIP. More importantly, the results of zircon UPb chronological, Hf isotope, and trace-element geochemical analyses indicate that the bed formed as a result of intraplate volcanic activity at ca. 257 Ma. Thus, our robust array of evidence suggests that the Wangpo bed was formed as a direct sedimentary response to the eruptions of the ELIP. On the basis of a comprehensive analysis of the possible influence of the eruptions on environmental change, we propose that the violent submarine volcanic activity that was accompanied by strong magma degassing during the Guadalupian–Lopingian transition, which released large amounts of volatiles to the seafloor, could have exacerbated the contemporaneous environmental degradation and eventually led to the end-Guadalupian biotic crisis.

Imaging mass‐wasting sliding surfaces within complex glacial deposits along coastal cliffs using geophysics

AbstractThis study presents a multidisciplinary survey combining geological fieldwork and geophysical data to better constrain the parameters influencing the morphology and behaviour of a retreating coastal cliff. Erosion rates are spatially highly variable and hard to predict because of the manifold parameters acting on them. Among these parameters, rock resistance exerts a paramount influence on cliff retreat. Characterizing the rock resistance distribution along a coastal region requires the mapping of several key subsurface properties including the bulk lithology, faulting, fracturing, or weathering. This is a difficult and expensive task because of the high spatial variability of these factors linked to the spatial complexity of the geology. Geophysical methods can be used to tackle this challenge by quickly providing the 3D visualization and distribution of these parameters within the subsurface. A fast‐eroding portion of the Norfolk coast (UK) at West Runton is investigated using a multidisciplinary approach, combining ground‐penetrating radar, electrical resistivity tomography (ERT), cone penetration tests, and outcrop studies. The results allowed us to build a 3D geological and geophysical model of a highly complex area of glacial geology. It forms part of a relict glaciotectonic thrust‐tip moraine and sand basin sequence. The surfaces interpreted on radar data are associated with strong resistivity contrasts on the ERT data. These contrasts have been attributed to petrophysical variations between the lithological units. The base of the sand basin is marked by a low‐permeability clay bed. Its low shear strength is likely to be more susceptible to failure, hereby accelerating the erosion rate of an already fast‐eroding sand basin. The resulting model can be used as input for locally constraining the ground parameters in coastal recession and erosion models.

Geosynthetic Encased Concrete Debris Stone Columns

Rapid urbanization has compelled the building industry to improve the soft soil grounds which otherwise are unsuitable for construction activities. Ground improvement helps achieve better performance by avoiding several problems like excessive settlements, large lateral flow of soft soil beneath the structures, and loss of global or local stability under operational loading conditions by modification of foundation soils. The growing quantities and types of waste materials, shortage of landfill spaces, and lack of natural earth materials highlight the urgency of finding innovative ways of recycling and reusing waste material additionally can reduce the demand for natural resources creating sustainable ecosystem. The aim of this experiment is to use crushed concrete debris (CCD) in soil stabilization. A series of experiments are to be carried out to develop an understanding on the performance of soft clay foundation beds reinforced using geosynthetic encased stone-concrete debris column. Model tests was conducted on clay reinforced with encased vertical columns filled with both CCD and aggregates. A comparative study is to be done and an assessment of ultimate bearing capacity of the composite ground is to be done. The column failure mechanism in the both the cases are to be carefully studied. Modal tests and later numerical analysis is done in PLAXIS 2D for analyzing the behavior of geosynthetic encased stone column stabilized clay bed numerically. Analyses were carried out using Mohr-Coulomb’s criterion. Lab conditions were simulated in PLAXIS for accurate comparison for same model tests.

Технологические решения по локализации очагов эндогенных пожаров при отработке прибортовых запасов системами с обрушением руды и вмещающих пород

Technological solutions are developed to localize and isolate spontaneous fires in mining of the near-edge reserves using the ore and host rock caving systems. The developed technology envisages two implementation stages: a) formation of a clay and sand bed on the pit wall with the thickness of the insulating layer not less than 10 m; b) silting of the pit walls and floor with clay and sand mixture (slurry) up to the assumed level of the fire sources at the final stage of oxidation processes liquidation. Three technological options have been developed to supply the silting slurry, the choice of which is made according to the mining, geological and technical conditions of the deposit. The work is performed based on the accumulated experience of silting operations, research results, improvements of the processing scheme, methods of their transportation and laying in the mined-out space of the open pit. The proposed solutions make it possible to limit the access of oxygen to the sources of spontaneous fires within a minimum period of time and ensure timely prevention of local fire seats in case the oxidation processes intensify.

Mineralogical and geochemical characteristics of tonsteins from the Middle Jurassic Yan'an Formation, Ordos Basin, North China

Although the Jurassic features a considerable accumulation of coal worldwide, only a few tonsteins within coal seams in this coal-forming period have been investigated. This paper presents the detailed mineralogical and geochemical compositions of six tonstein layers from the Middle Jurassic Yan'an Formation, Ordos Basin, North China. Based on the typical evidence of the distinct field characteristics occurring as paler thin beds with lateral continuity; conchoidal and flint-like fracture planes; sharp contacts with adjacent coals; and the mineralogical compositions, such as vermicular kaolinite, angular quartz, and euhedral zircon crystals with a single UPb age peak, the intra-seam clay beds of the Yan'an Formation were determined to have been mainly derived from a significant pyroclastic source. However, rounded quartz, muscovite, and detrital zircon grains in the tonsteins reflect minor contribution of terrigenous debris from sediment source regions. Moreover, a line of geochemical features including low TiO2/Al2O3 values, Al2O3/TiO2-Nb/Yb, and Al2O3/TiO2-Zr/TiO2 diagrams; low REY concentrations with high fractionation between light REE and heavy REY (REY, rare earth elements and Y; REE, rare earth elements); and pronounced negative Eu anomalies, suggest that the tonsteins have a felsic (rhyolitic) magma origin. A systematic geochemical analysis of enclosing coals of the tonsteins was also conducted to determine the leaching behavior of the trace elements from the tonsteins into the enclosing coals. The results show that Th, U, Nb, Ta, Zr, and Hf tend to be enriched in the overlying and underlying coals and have an enrichment width of up to 30 cm. Similarly, the elevated concentrations of Zn, Rb, Cs, Pb, La, Ce, Pr, and Nd only occur in a relatively narrow zone above and below the tonsteins. The width of the enrichment in the enclosing coals may be mainly related to the properties of the tonsteins, e.g., thickness and original volcanogenic material, the characters of elements including mobility and concentration, and the nature of coals, such as coal rank.

Recently Discovered Thick Bentonite Bed Hosted by the Lithothamnium Limestones (Badenian) in the Polish Part of the Carpathian Foredeep: The Evidence for Volcanic Origin

In this paper, we discuss the hypothesis on the volcanic origin of the precursor sediments for a thick (0.6 m) clay bed, hosted by the sequence of lithothamnium limestones of the Pińczów Formation. Combined X-ray powder diffraction, imaging methods (optical and electron microscopy), and chemical analysis were used to document the volcanic markers, which were preserved in the rock studied. The results obtained show that the clay bed discussed is bentonite in origin. This bentonite, which can be called Drugnia Rządowa bentonite, is composed almost entirely of montmorillonite with little admixtures of quartz and biotite. A small amount of calcite is present, but only in the top of the bed. Despite that, the bentonite contains nothing but clay material—it is a model example of entirely altered pyroclastic rock, which retains texture originally developed in volcanic glass fragments and reveals the preserved original features of the precursor fallout pyroclastic deposits (rhyolitic in character). The thick bentonite beds, discovered for the first time within the Badenian lithothamnium limestones of the Pińczów Formation, can be considered as a record of a violent, explosive volcanic event related to the closure of the Outer Carpathian basin and the development of the Carpathian Foredeep.

Experimental Evaluation of the Bending Behavior of a Drilled Shaft with Partial Casing under Lateral Loads

Few studies, especially those related to field tests, have examined the bending behaviors of drilled shafts with partial casings (DSPCs). This work reports the results of experimental studies on the behavior of DSPCs under lateral loads, including an in situ test and a set of laboratory tests. First, a DSPC with a diameter of 2 m and length of 87.9 m was studied in clay beds, and a steel casing with a diameter of 2.0 m and length of 33 m was used. In this test, strain gauges were distributed along the steel rebars in the concrete pile and the wall of the steel tube at different depths, and thus the longitudinal strains of the concrete pile and the steel tube could be studied. Second, laboratory experiments were implemented with reinforced concrete-filled steel tubular columns under pure bending conditions. In these tests, strain gauges were distributed along the steel rebars in the concrete pile and the walls of the steel tubes at the pure bending section of the specimens. Different wall thicknesses and drilling fluid conditions were considered. The field test results show that the strain of the concrete piles and the steel tubes were linearly distributed at the same cross-section. This means that a DSPC remains a flat plane after it deforms. Whereas a correction coefficient related to the loading level need to be considered in the calculation of the bending stiffness. Laboratory studies show that the strain of DSPCs was linearly distributed at a small bending moment under the best bond-quality condition, whereas obvious nonlinear behaviors were shown under a large bending moment with poor bond-quality conditions.

Heave and load-settlement behaviour of a chemically stabilised expansive clay bed

ABSTRACT Structures found in expansive soils are subjected to heave and downward movement when they absorb water and lose water to the atmosphere, respectively. The upward and downward movements of structures built on the expansive clay strata are controlled through various treatment methods such as chemical stabilisation. As these clay strata are subjected to stresses due to superstructures, an understanding of their load-carrying capacity in the light of changing moisture content is required to assess this behaviour. This paper presents the heave and load-settlement behaviour of a remoulded expansive clay bed stabilised with varied amounts of lime, cement, fly ash and ground granulated blast furnace slag (GGBS). A series of laboratory-scale plate load tests were conducted on the beds of chemically stabilised clay compacted at the respective OMC and MDD. The plate load tests were conducted in two series: one on the as-compacted beds of the blends, and the other on the saturated beds of the blends to compare their stress-settlement behaviour. The amount of heave and the rate of heave were also monitored during the process of saturation. Chemically stabilised expansive clay beds reflected improved load-settlement behaviour in both the as-compacted and the saturated states.

Evaluation of Recycled Materials as Aggregate of End Bearing Stone Columns: a Comparative Study

The object of this research is to compare the behavior of floating and end bearing stone columns made of recycled aggregates of building debris with natural aggregate. To do so, both types of stone columns were constructed by crushed concrete and crushed brick as recycled aggregates and compared with the same models made of gravel as natural aggregates. All the columns were constructed with the same size, density, and grading in a clay bed. To evaluate the initial quality of materials of the stone columns, the index tests were performed. The results of such tests illustrated the less resistance of recycled materials in comparison to the natural materials; On the contrary, according to the results of the index tests, crushed bricks are not recommended to construct stone columns. Despite the index tests, results of loading on a floating column filed with natural and recycled aggregate were approximately the same, but the bearing capacity of the end bearing column made of natural aggregates was higher than the same model made of recycled aggregates.

Influence of positions of the geotextile on the load-settlement behaviour of circular footing resting on single stone column by 2D Plaxis software

Purpose: This study aims to study the load – settlement behaviour of circular footing rested on encased single stone column. Design/methodology/approach: The effect of vertical, horizontal and combined verticalhorizontal encasement of stone column on the load carrying capacity were examined numerically. The effect of stone column dimension (80 mm and 100 mm), length (400 mm and 500 mm), and spacing of reinforcement on the load carrying capacity and reinforcement ratio were assessed. Findings: The obtained results revealed that the load carrying capacity of geotextile encased stone columns are more than ordinary stone columns. For vertically encased stone columns as the diameter increases, the advantage of encasement decreases. Whereas, for horizontally encased stone column and combined vertical- horizontal encased stone column, the performance of encasement intensifies as the diameter of stone column increases. The improvement in the load carrying capacity of clay bed reinforced with combined verticalhorizontal encased stone columns are higher than vertical encased stone columns or horizontal encased stone column. The maximum performance of encasement was observed for VHESC1 of D = 80 mm. Research limitations/implications: For this study, the diameter of footing and stone column was kept same. The interface strength factor between stone column and clay bed was not considered. Practical implications: The encased stone column could be use improve the laod bearing capacity of weak soils. Originality/value: Many studies are available in literature regarding use of geosynthetic as vertical encasement and horizontal encasement of stone column. The study on combined effect of vertical and horizontal encasement of stone column on load carrying capacity of weak soil is very minimal. Keeping this in view, the present work was carried out.

Shear Strength Behaviour of Pervious Concrete Column Improved Soft Clay Bed: A Numerical Study

Shear Strength Behaviour of Pervious Concrete Column Improved Soft Clay Bed: A Numerical Study

Local scale interventions dominate over catchment scale controls to accelerate the recovery of a degraded stream.

A premise of stream restoration theory and practice is that it is often futile to attempt to restore a stream at the reach scale (101–103 metres) until catchment scale problems have been addressed. This study considers reach scale restoration actions undertaken in Bryan Creek, a sand bed river in south east Australia impacted by a sediment pulse, after catchment sediment sources have been addressed. Local scale interventions, which were in-stream sand extraction, fencing to exclude stock and riparian revegetation, were evaluated by quantifying cross-section and thalweg variability, mapping in-stream and riparian vegetation and by classifying the morphology that emerged following each intervention. Following intervention channel reaches moved to one of three distinct states: simple clay bed, eroding reaches dominated by Juncus acutus, and reaches with deep pools and Phragmites australis. Boundaries between the intervention reaches were sharp, suggesting local scale interventions dominate over catchment scale processes. The magnitude and spread of variability metrics were similar between all reaches and differences in variability bore no relation to intervention type, despite the stark difference in post-intervention morphology. These findings suggest that cross-section and thalweg variability metrics are an inadequate proxy for the effectiveness of local scale interventions in accelerating the recovery of sand bed reaches from a bedload pulse. The most important implications for river managers is that local scale interventions can lead to substantial and rapid improvements in condition, and the change in condition of these reaches is almost independent of other reaches. In this case, the key to the pattern of reach scale geomorphic recovery is excluding stock from waterways so that a specific macrophyte can establish, trap sediment and develop pools.

Saraswati River in northern India (Haryana) and its role in populating the Harappan civilization sites—A study based on remote sensing, sedimentology, and strata chronology

AbstractThe Saraswati River used to flow from the glaciated peaks of the Himalaya to the Arabian sea, covering a distance of about 1800 km. It possibly sustained the Harappan civilization in the Indian subcontinent. This river has been studied as a part of the Ghaggar–Satluj–Hakra–Nara channel system in India and Pakistan. This study investigated its independent existence and evolution in the Himalayan foothill terrain and the proximal alluvial plains. Use of satellite imagery, shuttle radar topography mission data, accelerator mass spectrometry14C dating and optically stimulated luminescence chronology is being made to identify the possible palaeo‐path of this ancient river and to characterize the trench sediment log architecture of the Saraswati River palaeochannels in northern India (Haryana). Our investigations reveal that this river formed a dense web of interconnecting channels which are continuously networked for more than 2,984 km in Haryana and their individual floodplain width varies from 1.5 to 13 km. The Harappan settlements in Haryana and Rajasthan nucleated and prospered in the fertile channel bars and interfluves of this river system. Majority of these habitation sites were located within a radius of less than 500 m from these palaeo‐water channel networks. Enormous amount of water was flowing through this channel network until BC 11,147. Sediment characteristics and their chronology reveal that flow of water in the river channel decreased with time as the glacial cover diminished. The varying thickness of clay beds in sediment logs is indicative of the fluctuations in water flow possibly as a consequence of terrain slope modifications and consequent gradual channel avulsion, climate change, and global drought events. The flow of water continued through the Himalayan foothill input channels of the palaeo‐Saraswati River in Haryana until AD 1402.

Multiproxy analysis of paleoenvironmental, paleoclimatic and paleoceanographic changes during the early Danian in the Caravaca section (Spain)

After the Chicxulub impact and mass extinction at the Cretaceous-Paleogene boundary (K-PgB), ecosystems haltingly recovered under unstable conditions. An early Danian (65.9 Ma) perturbation of the carbon cycle known as Dan-C2, which includes two carbon isotopic excursions (CIEs), has been ascribed to inputs of greenhouse gases through large-scale volcanism of the Deccan Traps. However, the relationship between Dan-C2, volcanism and environmental and climatic changes during the early Danian remains ambiguous. Based on stable isotopes, calcium carbonate content, magnetic susceptibility and planktic foraminifera, we present a paleoenvironmental, paleoclimatic and paleoceanographic reconstruction of the early Danian from the Caravaca section, Spain, one of the most complete and continuous K-PgB sections worldwide. The paleobiological response of planktic foraminifera suggests very volatile environmental conditions during the first 230 kyr of the Danian, as reflected in the rapid succession of opportunistic/generalist blooms and episodic high occurrences of aberrant specimens. According to our age model, the Dan-C2 has been identified at the Caravaca section from 65.92 to 65.74 Ma. No evidence of strong carbonate dissolution through ocean acidification was observed in the Dan-C2 interval or the rest of the studied section, excluding the K-PgB clay bed. We find that blooms of highly eutrophic Chiloguembelitria and increases in aberrant planktic foraminifera coincided with a major early Danian eruptive episode of Deccan Traps (Ambelani Formation), occurring before the Dan-C2. Conversely, during both Dan-C2 CIEs, less opportunistic taxa thrived, indicating changes in the upper part of the water column. This study demonstrates that the relationship between marine biota and climate change was very complex and rapidly changing during the early Danian. In addition, we propose that the Deccan volcanism had adverse effects on marine plankton, mostly through strong eutrophication, while an increased water column stratification during the Dan-C2 event resulted in a transient boost in the recovery of ecosystems.