Clay mineralogy and shear strength of subglacial and glaciomarine sediments in the southern Bellingshausen Sea

The Belgica Trough and the adjacent Belgica Trough Mouth Fan in the southern Bellingshausen Sea (Pacific sector of the Southern Ocean) mark the location of a major outlet for the West Antarctic Ice Sheet during the Late Quaternary. The drainage basin of an ice stream that advanced through Belgica Trough across the shelf during the last glacial period comprised an area exceeding 200,000 km**2 in the West Antarctic hinterland. Previous studies, mainly based on marine-geophysical data from the continental shelf and slope, focused on the bathymetry and seafloor bedforms, and the reconstruction of associated depositional processes and ice- drainage patterns. In contrast, there was only sparse information from seabed sediments recovered by coring. In this paper, we present lithological and clay mineralogical data of 21 sediment cores collected from the shelf and slope of the southern Bellingshausen Sea. Most cores recovered three lithological units, which can be attributed to facies types deposited under glacial, transitional and seasonally open-marine conditions. The clay mineral assemblages document coinciding changes in provenance. The relationship between the clay mineral assemblages in the subglacial and proglacial sediments on the shelf and the glacial diamictons on the slope confirms that a grounded ice stream advanced through Belgica Trough to the shelf break during the past, thereby depositing detritus eroded in the West Antarctic hinterland as soft till on the shelf and as glaciogenic debris flows on the slope. The thinness of the transitional and seasonally open-marine sediments in the cores suggests that this ice advance occurred during the last glacial period. Clay mineralogical, acoustic sub-bottom and seismic data furthermore demonstrate that the palaeo-ice stream probably reworked old sedimentary strata, including older tills, on the shelf and incorporated this debris into its till bed. The geographical heterogeneity of the clay mineral assemblages in the sub- and proglacial diamictons and gravelly deposits indicates that they were eroded from underlying sedimentary strata of different ages. These strata may have been deposited during either different phases of the last glacial period or different glacial and interglacial periods. Additionally, the clay mineralogical heterogeneity of the soft tills recovered on the shelf suggests that the drainage area of the palaeo-ice stream flowing through Belgica Trough changed through time.

Clay mineralogy of sediment cores from the Arctic Ocean

This study focuses on sedimentological investigations of sediment cores recovered during the international Arctic'91, expeditions with the German research ice breaker RV "Polarstern" to the European sector of the Arctic Ocean. Here, we deduce the last glacial/interglacial changes in transport mechanism and sedimentation from the clay mineral group smectite. We choose the smectites as an example of how sediment mineralogy can be linked with particular source regions (the Kara and Laptev seas), distinct transport mechanism (sea ice and surface currents) and sedimentation processes. Smectite contents in Arctic sediments discussed for two time slices, including the Last Glacial Maximum (LGM), and the last deglaciation (Termination I), reveal the highest variability subsequent to the retreat of the Eurasian ice sheets. Our results show that smectite anomalies in the Eurasian Basin are associated with distinct meltwater pulses and occurred around 13.5-13.0 14C ka B.P. Compelling evidence is provided that these anomalies are deduced from sea-ice entrained sediments from the eastern Kara Sea that entered the Arctic Ocean after ice-sheet break-up and eventually flooding of the Kara Sea. We propose that smectite anomalies in sediments of the eastern Arctic Ocean can be utilized to identify deglacial events and to help decipher configurations of the Eurasian ice sheets. The identification of smectite maxima along the modern sea-ice edge in the Eurasian Basin further indicates biologically enhanced sedimentation from melting sea ice allowing the reconstruction of seasonally open water in the region. Hence, considering the poor preservation conditions of primary paleoceanographic proxies in the Arctic Ocean, the clay mineral contents, particularly the smectite group, may be one alternative tool for paleoclimatic reconstruction in the Eurasian Basin.

Clay minerals in the Norwegian Sea and Fram Strait, investigation from sediment traps and cores

The grain size distribution and clay mineral composition of lithogenic particles of ice-rafted material, sinking matter, surface sediments, as well as from deep-sea cores are analysed. The samples were collected in the Fram Strait, the Arctic Ocean, and the Norwegian Sea during several expeditions with the research vessels "Polarstern", "Meteor" and "Poseidon", and Norwegian rearch vessels. Sinking matter was caught with sediment traps, fitted with timer-controlled sample changers, which had been deployde in the sea for usually one year.

Nd, Sr and Pb isotopes and clay minerals in sediment cores from the Gulf of Cadiz and the Portuguese margin

The assemblages of marine sediments on the SW Iberian shelf have been controlled by contributions from distinct sources, which have varied in response to environmental changes since the Last Glacial Maximum (LGM). The rapid, decadal scale Mediterranean overturning circulation permits mixing of suspended particles from the entire Mediterranean Sea. They are entrained into the suspended particulate matter (SPM) carried by Mediterranean Outflow Water (MOW), which enters the eastern North Atlantic through the Strait of Gibraltar and spreads at intermediate depths in the Gulf of Cadiz and along the Portuguese continental margin. Other major sediment sources that have contributed to the characteristics and budget of SPM along the flow path of MOW on the SW Iberian shelf are North African dust and river-transported particles from the Iberian Peninsula. To reconstruct climate- and circulation-driven changes in the supply of sediments over the past ~23000 cal yr B.P., radiogenic Nd, Sr and Pb isotope records of the clay-size sediment fraction were obtained from one gravity core in the Gulf of Cadiz (577 m water depth) and from two gravity cores on the Portuguese shelf (1745 m, 1974 m water depth). These records are supplemented by time series analyses of clay mineral abundances from the same set of samples. Contrary to expectations, the transition from the LGM to the Holocene was not accompanied by strong changes in sediment provenance or transport, whereas Heinrich Event 1 (H1) and the African Humid Period (AHP) were marked by significantly different isotopic signatures reflecting changes in source contributions caused by supply of ice rafted material originating from the North American craton during H1 and diminished supply of Saharan dust during the AHP. The data also reveal that the timing of variations in the clay mineral abundances was decoupled from that of the radiogenic isotope signatures.

Neodymium isotopic ratios and clay mineral composition from ODP Hole 1147A and Site 184-1148

Ocean Drilling Program sampling of the distal passive margin of South China at Sites 1147 and 1148 has yielded clay-rich hemipelagic sediments dating to 32 Ma (Oligocene), just prior to the onset of seafloor spreading in the South China Sea. The location of the drill sites offshore the Pearl River suggests that this river, or its predecessor, may have been the source of the sediment in the basin, which accounts for only not, vert, similar ~1.8% of the total Neogene sediment in the Asian marginal seas. A mean erosion depth of not, vert, similar ~1 km over the current Pearl River drainage basin is sufficient to account for the sediment volume on the margin. Two-dimensional backstripping of across-margin seismic profiles shows that sedimentation rates peaked during the middle Miocene (11-16 Ma) and the Pleistocene (since 1.8 Ma). Nd isotopic analysis of clays yielded epsilonNd values of -7.7 to -11.0, consistent with the South China Block being the major source of sediment. More positive epsilonNd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin. As the drainage basin developed and erosion shifted from within the rift to the continental interior epsilonNd values became more negative. A rapid change in the clay mineralogy from smectite-dominated to illite dominated at not, vert, similar 15.5 Ma, synchronous with middle Miocene rapid sedimentation, mostly reflects a change to a wetter, more erosive climate. Evidence that the elevation of the Tibetan Plateau and erosion in the western Himalaya both peaked close to this time supports the suggestion that the Asian monsoon became much more intense at that time, much earlier than the 8.5 Ma age commonly accepted.

Clay mineral distribution in sediment core AND-2A

Clay mineral assemblages in sediments from ANDRILL drill core AND-2A were used to reconstruct the Neogene palaeoenvironment. For the first time a clay mineral data set can be presented for southern McMurdo Sound, Ross Sea, Antarctica, that covers an expanded and fairly continuous Lower and Middle Miocene section. Although the occurrence of some authigenic smectites, zeolites and opal-CT documents diagenetic processes, the clay mineral assemblages allow a subdivision of the core into three intervals that reflect changes in provenance and volcanic activity. Interval I (1000-440 mbsf, 20.0-16.5 Ma) is characterised by a dominant sediment source in the Transantarctic Mountains. Frequent and short-term changes in the illite and smectite concentrations were caused by the influx of volcanic sediment components from southern McMurdo Sound and by diagenesis. Interval II (440-225 mbsf, 16.5-15.0 Ma) has much more uniform illite and smectite contents. The assemblage is derived from the Transantarctic Mountains. Interval III (225-0 mbsf, 15.0-0 Ma, containing major hiatuses) shows a distinctly enhanced volcanic influence and sediment components that come from the south of McMurdo Sound. The AND-2A clay mineral assemblages indicate persistent physical weathering conditions and do not mirror the Mid-Miocene Climatic Optimum. They indicate that the climatic changes were probably not strong enough to cause a modification in the weathering regime on the Antarctic continent.

(Table 2) Relative contents of clay minerals in aeolian pelagic clays from the Pacific Ocean

For determining importance, composition, and history of aerosol material accumulation in formation of pelagic clays a study with use of light microscopy and scanning electron microscopy, X-ray diffractometry, and chemical methods has been carried out.

Clay mineral analysis of sediments from the Amundsen Sea

The Amundsen Sea embayment is a probable site for the initiation of a future collapse of the West Antarctic Ice Sheet. This paper contributes to a better understanding of the transport pathways of subglacial sediments into this embayment at present and during the last glacial period. It discusses the clay mineral composition of sediment samples taken from the seafloor surface and marine cores in order to decipher spatial and temporal changes in the sediment provenance. The most striking feature in the presentday clay mineral distribution is the high concentration of kaolinite, which is mainly supplied by the Thwaites Glacier system and indicates the presence of hitherto unknown kaolinite-bearing sedimentary strata in the hinterland, probably in the Byrd Subglacial Basin. The main illite input is via the Pine Island Glacier. Smectite originates from the erosion of volcanic rocks in Ellsworth Land and western Marie Byrd Land. The clay mineral assemblages in diamictons deposited during the last glacial period are distinctly different from those in corresponding surface sediments. This relationship indicates that glacial sediment sources were different from modern ones, which could reflect changes in the catchment areas of the glaciers and ice streams.

Multivariate statistical analysis on the kaolinite/chlorite ratios from 20 South Atlantic sediment cores

Multivariate statistical analysis on the kaolinite/chlorite ratios from 20 South Atlantic sediment cores allowed for the extraction of two processes controlling the fluctuations of the kaolinite/chlorite ratio during the last 130,000 yrs, (1) the relative strength of North Atlantic Deep Water (NADW) inflow into the South Atlantic Ocean and (2) the influx of aeolian sediments from the south African continent. The NADW fluctuation can be traced in the entire deep South Atlantic while the dust signal is restricted to the vicinity of South Africa. Our data indicate that NADW formation underwent significant changes in response to glacial/interglacial climate changes with enhanced export to the Southern Hemisphere during interglacials. The most pronounced phases with Enhanced South African Dust Export (ESADE) occurred during cold Marine Isotope Stage (MIS) 5d and across the Late Glacial/Holocene transition from 16 ka to 4 ka (MIS 2 to 1). This particular pattern is attributed to the interaction of Antarctic Sea Ice extent, the position of the westerlies and the South African monsoon system.

Clay mineralogy of sediment cores from the South-East Atlantic off Namibia

Independent proxies were assessed in two Late Quaternary sediment cores from the eastern South Atlantic to compare deep-water changes during the last 400 kyr. Two cores were recovered from beneath North Atlantic Deep Water (NADW) at approximately 3 000 m depth. Late Quaternary presence of NADW is indicated by the Cibicidoides wuellerstorfi assemblage on the Walvis Ridge (Core GeoB 1214) and the Bulimina alazanensis assemblage on the Namibian continental slope (Core GeoB 1710). The propagation of NADW is exclusively observed during interglacials, with maximum factor loadings in Stages 1, 5, 7, 9 and 11. These maxima are consistent with peaks in kaolinite/chlorite ratios and maxima of poorly crystalline smectite in the clay-mineral record. Kaolinite and poorly crystalline smectite are products of intense chemical weathering. They are injected into the NADW at low latitudes, north of the study area, and advected south. Chlorite, which is stable under cold weathering regimes, is a characteristic mineral of water masses of southern origin. During glacial stages, it is advected north with Southern Component Water (SCW). Above the NADW/SCW depths, kaolinite/chlorite ratios vary only slightly without a significant glacial-interglacial pattern, as measured in a core (GeoB 1712) from 1 000 m deep on the same profile of the Namibian continental slope off Walvis Bay.

(Table 1) Clay and non-clay mineral composition of dirty ice samples from across the Arctic

Extensive dirty ice patches with up to 7 kg/m**2 sediment concentrations in layers of up to 10 cm thickness were encountered in 2005 and 2007 in numerous areas across the central Arctic. The Fe grain fingerprint determination of sources for these sampled dirty ice floes indicated both Russian and Canadian sources, with the latter dominating. The presence of benthic shells and sea weeds along with thick layers (2-10 cm) of sediment covering 5-10 m2 indicates an anchor ice entrainment origin as opposed to suspension freezing for some of these floes. The anchor ice origin might explain the dominance of Canadian sources where only narrow flaw leads occur that would not favor suspension freezing as an entrainment process. Expandable clays, commonly used as an indicator of a Kara Sea origin for dirty sea ice, are present in moderately high percentages (>20%) in many circum-Arctic source areas, including the Arctic coasts of North America. Some differences between the Russian and the North American coastal areas are found in clay mineral abundance, primarily the much higher abundance of chlorite in North America and the northern Barents Sea as opposed to the rest of the Russian Arctic. However, sea ice clay mineralogy matched many source areas, making it difficult to use as a provenance tool by itself. The bulk mineralogy (clay and non-clay) does not match specific sources possibly due to reworking of the sediment in dirty floes through summer melting or the failure to characterize all possible source areas.

Mineralogical (bulk rock and clay fraction) and stable isotope composition (d13C, d18O) of Aptian deposits of the Bir Oum Ali succession, central Tunisia

Alternations between siliciclastic, carbonate and evaporitic sedimentary systems, as recorded in the Aptian mixed succession of southern Tunisia, reflect profound palaeoceanographic and palaeoclimatic changes in this area of the southern Tethyan margin. The evolution from Urgonian-type carbonates (Berrani Formation, lower Aptian) at the base of the series, to intervals dominated by gypsum or detrital deposits in the remainder of the Aptian is thought to result from the interplay between climate change and tectonic activity that affected North Africa. Based on the evolution of clay mineral assemblages, the early Aptian is interpreted as having been dominated by slightly humid conditions, since smectitic minerals are observed. Near the early to late Aptian boundary, the onset of a gypsiferous sedimentation is associated with the appearance of palygorskite and sepiolite, which supports the installation of arid conditions in this area of the southern Tethyan margin. The evaporitic sedimentation may have also been promoted by the peculiar tectonic setting of the Bir Oum Ali area during the Aptian, where local subsidence may have been tectonically enhanced linked to the opening of northern and central Atlantic. Stress associated with the west and central African rift systems may have triggered the development of NW-SE, hemi-graben structures. Uplifted areas may have constituted potential new sources for clastic material that has been subsequently deposited during the late Aptian. Chemostratigraphic (d13C) correlation of the Bir Oum Ali succession with other peri-Tethyan regions complements biostratigraphic findings, and indicates that a potential expression of the Oceanic Anoxic Event (OAE) 1a may be preserved in this area of Tunisia. Although the characteristic negative spike at the base of this event is not recognized in the present study, a subsequent, large positive excursion with d13C values is of similar amplitude and absolute values to that reported from other peri-Tethyan regions, thus supporting the identification of isotopic segments C4-C7 of the OAE1a. The absence of the negative spike may be linked to either non preservation or non deposition: the OAE1a occurred in a global transgressive context, and since the Bir Oum Ali region was located in the innermost part of the southern Tethyan margin during most of the Aptian, stratigraphic hiatuses may have been longer than in other regions of the Tethys. This emphasizes the importance of integrating several stratigraphic disciplines (bio-, chemo- and sequence stratigraphy) when performing long-distance correlation.