Palaeoclimatic implications of high-resolution clay mineral assemblages preceding and across the onset of the Palaeocene–Eocene Thermal Maximum, North Sea Basin

Understanding the composition of clay-rich sediments and their transportation into proximal marine basins allows us to better decipher hydroclimatic changes before and within the Palaeocene–Eocene Thermal Maximum (PETM). Only a limited number of such studies exists from the North Sea Basin, which was proximal to the volcanic activity and early rifting hypothesized to have triggered the PETM. The present study examines core material from well 22/10a-4, UK North Sea, as it exhibits an exceptionally expanded and almost stratigraphically complete fine-grained sedimentary sequence suitable for high-resolution analysis. Quantitative Newmod-for-Windows™-modelled clay mineral assemblages, rather than traditional semi-quantitative estimates, are dominated by smectite-rich, interlayered illite-smectite that probably developed from volcanogenic deposits on continental landmasses. Soil development before the PETM is consistent with the existence of a seasonal tropical climate with a prolonged dry season. A striking rise and fall of kaolinite content within the PETM onset, prior to the principal carbon-isotope excursion, is reported here. This variation is interpreted as a signal of an enhanced hydrologic cycle producing an increase in erosionally derived kaolinite, followed by a dampening of this detrital source as sea-levels rose. Global variations in PETM kaolinite concentrations are consistent with a latitudinal shift in patterns of precipitation in models of global warming

New insights into the reliability of automatic dynamic methods for oral bioaccessibility testing: a case study for BGS102 soil

Dynamic flow-through extraction is attracting a great deal of attention for real-time monitoring of the bioaccessible fraction of metal species in environmental solid substrates compared to its batchwise manual counterparts. There is however a lack of studies on the harmonization and validation of in vitro dynamic methods for physiologically based extraction tests against in vivo bioavailability methods. This work is aimed at evaluating the reliability of dynamic flow-through extraction methods for estimation of oral bioaccessible fractions of Cu, Zn, Pb, Ni, Cr, and As under worst-case extraction conditions in the gastric compartment based on the BGS102 guidance soil using the in vivo validated Unified BARGE (UBM) test, commonly performed under batchwise mode. Good overall agreement between batch and dynamic UBM results was obtained for the tested elements, except for Pb, as a consequence of the slow leaching kinetics identified with the dynamic method and the contribution of readsorption phenomena in the course of the gastric digestion. Metal-soil phase associations and their relationship with gastric bioaccessible fractions were elucidated using the so-called Chemometric Identification of Substrates and Element Distributions method based on sequential extraction with a variety of chemicals of increasing acidity as applied to both static and dynamic bioaccessibility data

The thermal properties of the Mercia Mudstone Group

The Mercia Mudstone Group (MMG) crops-out extensively across England and Wales and its thermal properties are required for the design of infrastructure such as ground source heating and cooling schemes and electrical cable conduits. Data from the literature and new data from a borehole core have been compiled to generate an updated range of thermal conductivities related to rock type and the lithostratigraphy. These indicate a total range in saturated vertical thermal conductivity of 1.67–3.24 W m-1 K-1, comprising 1.67–2.81 W m-1 K-1 for mudstones, 2.12–2.41 W m-1 K-1 for siltstones and 2.3–3.24 W m-1 K-1 for sandstones. These data are all from measurements on samples and there will be uncertainty when considering the thermal properties of the rock mass due to micro and macro structural features. Geometric mean modelling of thermal conductivity based on mineralogy has overestimated the thermal conductivity. Correction factors for the modelled thermal conductivities have been calculated to enable a first estimate of MMG thermal conductivities when only mineralogical data are available. Measured thermal diffusivities from the borehole core were in the range of 0.63–3.07 x10-6 m2s-1 and are the first measured, thermal diffusivities to be reported for the MMG

Gel formation at the front of expanding calcium bentonites

The removal of potentially harmful radioactive waste from the anthroposphere will require disposal in geological repositories, the designs of which often favour the inclusion of a clay backfill or engineered barrier around the waste. Bentonite is often proposed as this engineered barrier and understanding its long-term performance and behaviour is vital in establishing the safety case for its usage. There are many different compositions of bentonite that exist and much research has focussed on the properties and behaviour of both sodium (Na) and calcium (Ca) bentonites. This study focusses on the results of a swelling test on Bulgarian Ca bentonite that showed an unusual gel formation at the expanding front, unobserved in previous tests of this type using the sodium bentonite MX80. The Bulgarian Ca bentonite was able to swell to completely fill an internal void space over the duration of the test, with a thin gel layer present on one end of the sample. The properties of the gel, along with the rest of the bulk sample, have been investigated using ESEM, EXDA and XRD analyses and the formation mechanism has been attributed to the migration of nanoparticulate smectite through a more silica-rich matrix of the bentonite substrate. The migration of smectite clay out of the bulk of the sample has important implications for bentonite erosion where this engineered barrier interacts with flowing groundwater in repository host rocks

Gone with the wind: dune provenance and sediment recycling in the northern Rub’ al-Khali, United Arab Emirates

The Rub’al-Khali dune field in southern Arabia is the largest sand sea in the world. Deciphering thepalaeoenvironmental history of the Rub’al-Khali is critical to understanding its role as a barrier to human migration, dispersaland settlement. To determine sediment provenance and transport pathways, we combined data from a geological mappingproject with traditional heavy mineral optical point-counting methods, heavy mineral geochemical fingerprinting and detritalzircon U–Pb geochronology of Miocene and Quaternary sediments in the United Arab Emirates (UAE). Detrital zircon U–Pbage spectra demonstrate that most Neogene and Quaternary sediments in the UAE are ultimately sourced from the PrecambrianArabian Shield. Heavy mineral and geochemical signatures indicate that the dune sands are locally recycled from the deflationof Miocene sandstones and Quaternary siliciclastic palaeodunes exposed along the Arabian Gulf coast, whereas carbonatepalaeodunes along the Gulf coast are derived from the deflation of sediments deposited by the Tigris–Euphrates River system inthe Gulf during Pleistocene lowstands. In the eastern Emirates, Miocene and Quaternary alluvial fan deposits emanating fromthe Hajar Mountains have an ophiolitic heavy mineral signature. The data reveal new insights into the origin and developmentof the Rub’al-Khali dune field

Dissolved inorganic carbon export from rivers of Great Britain: Spatial distribution and potential catchment-scale controls

Dissolved inorganic carbon (DIC) fluxes from the land to ocean have been quantified for many rivers globally. However, CO2 fluxes to the atmosphere from inland waters are quantitatively significant components of the global carbon cycle that are currently poorly constrained. Understanding, the relative contributions of natural and human-impacted processes on the DIC cycle within catchments may provide a basis for developing improved management strategies to mitigate free CO2 concentrations in rivers and subsequent evasion to the atmosphere. Here, a large, internally consistent dataset collected from 41 catchments across Great Britain (GB), accounting for ∼36% of land area (∼83,997 km2) and representative of national land cover, was used to investigate catchment controls on riverine dissolved inorganic carbon (DIC), bicarbonate (HCO3−) and free CO2 concentrations, fluxes to the coastal sea and annual yields per unit area of catchment. Estimated DIC flux to sea for the survey catchments was 647 kt DIC yr−1 which represented 69% of the total dissolved carbon flux from these catchments. Generally, those catchments with large proportions of carbonate and sedimentary sandstone were found to deliver greater DIC and HCO3− to the ocean. The calculated mean free CO2 yield for survey catchments (i.e. potential CO2 emission to the atmosphere) was 0.56 t C km−2 yr−1. Regression models demonstrated that whilst river DIC (R2 = 0.77) and HCO3− (R2 = 0.77) concentrations are largely explained by the geology of the landmass, along with a negative correlation to annual precipitation, free CO2 concentrations were strongly linked to catchment macronutrient status. Overall, DIC dominates dissolved C inputs to coastal waters, meaning that estuarine carbon dynamics are sensitive to underlying geology and therefore are likely to be reasonably constant. In contrast, potential losses of carbon to the atmosphere via dissolved CO2, which likely constitute a significant fraction of net terrestrial ecosystem production and hence the national carbon budget, may be amenable to greater direct management via altering patterns of land use

Sources, composition, and export of particulate organic matter across British estuaries

Estuaries receive and process a large amount of particulate organic carbon (POC) prior to its export into coastal waters. Studying the origin of this POC is key to understanding the fate of POC and the role of estuaries in the global carbon cycle. Here, we evaluated the concentrations of POC, as well as particulate organic nitrogen (PON), and used stable carbon and nitrogen isotopes to assess their sources across 13 contrasting British estuaries during five different sampling campaigns over 1 year. We found a high variability in POC and PON concentrations across the salinity gradient, reflecting inputs, and losses of organic material within the estuaries. Catchment land cover appeared to influence the contribution of POC to the total organic carbon flux from the estuary to coastal waters, with POC contributions >36% in estuaries draining catchments with a high percentage of urban/suburban land, and <11% in estuaries draining catchments with a high peatland cover. There was no seasonal pattern in the isotopic composition of POC and PON, suggesting similar sources for each estuary over time. Carbon isotopic ratios were depleted (−26.7 ± 0.42‰, average ± sd) at the lowest salinity waters, indicating mainly terrigenous POC (TPOC). Applying a two-source mixing model, we observed high variability in the contribution of TPOC at the highest salinity waters between estuaries, with a median value of 57%. Our results indicate a large transport of terrigenous organic carbon into coastal waters, where it may be buried, remineralized, or transported offshore

Cretaceous climate change evidenced in the Senegalese rock record, NW Africa

Climate change directly impacts the source, mode and volume of sediment generation which can be observed in the rock record. To accurately model source to sink systems, in addition to hinterland geology, tectonics and transport distance, a thorough comprehension of the climate is essential. In this study we evaluate the role of climate on Cretaceous sediment delivery into the Senegal Basin, NW Africa, using data recorded from extensive sampling of basinal sediments. This is achieved through the mineralogical characterisation by X-ray diffraction and 146Nd/144Nd and 86Sr/88Sr isotopic analyses, which are correlated against existing, climate, tectonic and oceanographic models. Examples of climatic indicators include the change from predominantly smectitic deep marine basinal-clays recorded from the Cretaceous in DSDP wells 367 and 368 to clays with increased illite and kaolinite content, observed during the Albian and Cenomanian-Turonian, interpreted to be representative of higher humidity following the kaolinisation of hinterland source-rocks. Another climate indicator is the observation of palygorskite in deep-marine sediments, noted to be indicative of ocean anoxia related to the authigenesis of marine-smectite, a product of warm saline bottom waters and increased abundancy of silicon. The increase in salinity is interpreted to be a biproduct of elevated temperatures throughout the Cenomanian and increased denudation of the North Atlantic circumjacent continental evaporite-belts. Increase in silicon (biogenic) is related to a result of ocean-wide mass extinction of foraminifera during OAE2 triggered by the eruption of the Caribbean large igneous province. The results suggest that Cretaceous climate evolution of Senegal can be divided into four stages: 1. Berriasian-Barremian; an arid-period with monsoonal weather producing modest fluvial systems restricted to coastal regions. 2. Aptian-Albian; the establishment of a paleo-Intertropical Convergence Zone began to increase global temperature and humidity as recognised by the increase in kaolinite content. 3. Cenomanian-Turonian; the Cretaceous Thermal Maximum hothouse period incurring exceptional temperatures and humidity. This is represented as an antithetical shift in clay mineralogy from chlorite-illite to smectite-kaolinite throughout most of the onshore and nearshore basinal sediments. 4. Coniacian-Maastrichtian; transitional from tropical-to-tropical swamp-like conditions evidenced by increased onshore basin sediment capture and a shift in vegetation to aquatic-fern species. The impact of climate change throughout the Cretaceous produced dynamic shifts in both river size and source-catchment, witnessing exception rates of denudation during the hotter and more humid periods, which climaxed during the Cenomanian and Turonian as a result of the Cretaceous Thermal Maximum. This eroded sediment was deposited in both the onshore and offshore basins during the mid-late Cretaceous but became increasingly restricted to the onshore segment of the basin during the Late Cretaceous

Cenozoic to modern-day source to sink systems of Senegal: a record of provenance, transport, recycling and climate controls

This study presents an integrated mineralogical assessment for the provenance of sediments derived from modern-day rivers and Cenozoic deposits in Senegal and Gambia. Two distinct populations are identified from discrimination of the heavy mineral assemblages; the Senegal River sediment, sourced from the West African Craton and Mauritanides and Meso-Cenozoic sediment sourced from the onshore Senegal Basin, demonstrating prevalent recycling of Senegal Basin sediments by the Ferlo, Saloum, Gambia and Casamance Rivers throughout the Quaternary. The Senegal River records the occurrence of amphibole, epidote, garnet and pyroxene, which indicates denudation of Neo to Paleo-Proterozoic granites, low-medium grade meta-sediments and a skarn-type lithology. Meso-Cenozoic recycled sediments within the onshore Senegal Basin exhibit a heavy mineral component which has been modified through the chemical-weathering and diagenesis of less-stable amphibole, pyroxene and garnet. U/Pb dating of zircons from the Casamance and Gambia provinces indicates that, at least in part, the Mesozoic sediments of the onshore Senegal basin may have been ultimately derived from the Leo-Man Shield. Kaolin occurrence is associated with tropical weathering of laterites. The occurrence of terrigenous-smectite sourced from high altitude regions of the Mauritanides and West African Craton is interpreted to have formed under hyper-arid conditions prior to erosion and transportation, during the African humid periods of the Holocene. This integrated mineralogical study of modern-day and Cenozoic sediments has established prevalent recycling of Senegal Basin-sediments by the Ferlo, Saloum, Gambia and Casamance Rivers and continued erosion and recycling of hinterland-sediments via the modern-day Senegal River. This identification of two distinct provenance groups and the strong climatic signal provides the important framework for future studies assessing the source to sink systems during the Meso-Cenozoic

Assessment of high-purity limestone resources of the UAE

As part of the drive to develop non-oil based economy the UAE is continuing a programme of economic diversification, and is keen to develop its non-oil assets, such as its industrial mineral resources. A review of the industrial minerals sector in the UAE was carried out in 2002 to 2006 by the BGS as part of the work commissioned by the UAE federal Ministry of Energy. One of the highest priority recommendations from the review was that an evaluation of the potential for the production of industrial limestone and dolomite from resources within the UAE be carried out. It was considered that this would yield the benefit as there is potential to develop a sustainable industry that could remove the need for high-value mineral filler imports and create a lucrative export market. Currently the limestone and dolomite resources of the UAE are mainly exploited for construction aggregate. They have an intrinsically low value. There is little production of higher value limestone and dolomite products in the UAE and such commodities are imported. In 2008 the British Geological Survey (BGS) was commissioned by the UAE Ministry of Energy to carry out a resource assessment to identify high-purity limestone and dolomite resources that could be used for higher value applications. An initial market survey was carried out in Dubai to determine the requirements of industry in the UAE for limestone and dolomite. In addition a review was made of the commercial applications of limestone (which industry refers to as ‘calcium carbonate’) and dolomite and the physical properties required for individual applications, and the market for the commodities. High purity limestone is used as a raw material for the production of paint, paper, plastic, rubber, adhesives, caulks and sealants, agricultural, sports and environmental applications, ceramics, food and pharmaceuticals, animal feed and glass. High-purity dolomite is used for agricultural lime and the production of magnesia (MgO) for the manufacture of refractories, glass, magnesium chemicals, pharmaceuticals, fertilizers and magnesium metal. The assessment project started with a desk study and evaluation of limestone and dolomite samples collected by previous work in the UAE, to identify the resources with the best potential. A reconnaissance survey collected 221 samples from the limestone resources identified by the desk study. These were analysed in BGS laboratories to determine their chemical, mineralogical and physical properties. The limestones identified as having potentially the best quality were revisited in a second phase of field work when ten bulk samples were collected. These were analysed for their suitability as mineral filler, lime and construction aggregate. The analyses are summarised on a limestone and dolomite resource map of the northern emirates which illustrated the distribution of all limestones, colour-coded in terms of their purity. The main commercial quality criterion used to assess the purity of limestone is the calcium carbonate content and for dolomite it is the dolomite content. The magnesia, silica and iron oxide contents, and the brightness were also considered. The mineral filler properties, construction aggregate properties and lime burning properties were assessed for ten limestone occurrences. Approximately a third of the limestone in the northern emirates of the UAE has been found to be ‘high-purity’. This means it can be used to produce high-value limestone products that could be used by industry in the UAE as a substitute for the limestone they are currently importing. The resources identified to be high-purity include the Ruus al Jibal Group (undivided) and the Rus, Musandam 3, Musandam 2 and Dammam Limestone formations. In addition, ‘high-purity’ dolomite was also identified with the potential for industrial use. This study has shown that the UAE has resources of high purity limestone and dolomite, the development of which has the potential to make a substantial contribution to the economic diversification of the UAE economy. As a consequence of the assessment, the following recommendations are made: • Undertake investment promotion activities to alert interested parties to the limestone and dolomite resources available in the UAE. This could include the production of a freely available investment brochure and attendance at trade exhibitions. • Make more detailed assessment of the five top priority limestone resources to include more sampling and a drilling programme to increase the confidence of the resource assessment. • Undertake further assessment of the high-purity dolomite resources including additional sampling and a drilling programme. • Consider investigating further with companies in the UAE the end-use suitability of the limestone and dolomite resources of the UAE for the manufacture of paper, paint, rubber, plastic, ceramics and glass. • Make an assessment of the potential industrial suitability of the fine waste produced by limestone quarries in the UAE. • Establish an ‘Industrial Minerals Industry Forum’ to promote a better understanding of the needs of industry, provide information to the government and support the development of an indigenous minerals industry in the UAE