Clay mineralogy of late Eocene to early Miocene sediments of McMurdo Sound, Antarctica

The clay mineral assemblages of upper Eocene to lower Miocene sediments recovered at the CIROS-1 and MSSTS-1 drill sites on the McMurdo Sound shelf, Antarctica, were analyzed in order to reconstruct the Cenozoic Antarctic paleoclimate and ice dynamics. The assemblages are dominated by smectite and illite, with minor amounts of chlorite and kaolinite. The highest smectite amounts and best smectite crystallinities occur in the upper Eocene part of CIROS-1, below 425-445 mbsf. They indicate that during their deposition, chemical weathering conditions prevailed on the nearby continent. Large parts of East Antarctica were probably ice-free at that time, but some glaciers reached the sea and contributed to the glaciomarine sedimentation. In contrast, only minor total amounts of smectite are present in Oligocene and younger sediments due to the shift to mainly physical weathering on an ice-covered Antarctic continent. However, relative smectite percentages rise to more than 60% during two late Oligocene intervals (ca. 27.5-26.2 and 25.0-24.5 Ma) and during one early Miocene interval starting at ca. 23.3 Ma. These intervals are characterized by ice masses coming probably from the south, where volcanic rocks acted as a source, as also indicated by the composition of the sand and gravel fractions. During the other intervals, the ice came from the west, where the physical erosion of basement rocks and sedimentary rocks of the Beacon Supergroup in the Transantarctic Mountains provided high illite concentrations. Because the two drill sites are only 4 km apart, their clay mineral records can be correlated. This led to a new interpretation of the Oligocene paleomagnetic data of the MSSTS-1 site and to a more detailed lithostratigraphic correlation of the Miocene parts of the cores.

Bulk composition and clay mineralogy at DSDP Legs 56 and 57

Altogether 513 samples from sediments of Cretaceous to Pleistocene age from DSDP Legs 56 and 57 were examined by x-ray methods. The main constituents are clay minerals, quartz, feldspar, opaline silica, and volcanic glass. The sediment composition reflects the position of the sites in relation to the main source area, the Japanese Island Arc. For example, relatively coarse-grained material rich in quartz and feldspar was deposited closest to the islands, whereas finer-grained material rich in clay minerals (mainly smectite and illite, with lesser amounts of kaolinite and chlorite) was deposited farther seaward. Vertical fluctuations in the composition of the sediments show the same trend in all sites and are caused mainly by a fluctuating contribution of biogenic silica with time. A trend reversal in the chlorite/kaolinite ratio at Site 438 supports the conclusion that the subsidence of the Oyashio ancient landmass took place during the middle Miocene. That ratio also indicates a northwest drift in the position of Site 436 by sea floor spreading. Oscillations of the illite/smectite ratio during the Pleistocene at Site 436 show the variations of climate during this period. During early diagenesis potassium is fixed in smectite. With increasing depth of burial a smectite-illite mixed layer is formed, with increasing illite layering. At Sites 434, 440, and 441, stepwise changes confirm intensive tectonic process at the midslope terrace and the lower inner slope of the Japan Trench.

Clay mineral and stratigraphic record of two sediment cores from the Aegean Sea

Different source areas, oceanography and climate regimes influenced the clay mineral assemblages and grain size distribution of two sediment cores from the North and South Aegean Sea during the last glacial and the Holocene. In the North Aegean Sea, clay mineral composition is mainly controlled by sea level evolution, melting of southeastern European glaciers, and establishment of the connection between the Black Sea and Aegean Sea. The long-term development of clay mineral assemblages in the South Aegean Sea reflects changes in the Nile discharge and African dust input. At this site, the establishment of pluvial conditions in the Nile catchment during the early to middle Holocene resulted in a substantial rise in smectite/illite ratios. In the late Holocene, stepwise aridification of the southern borderlands caused an increase in windblown sediment material and a decrease in Nile suspended material. The clay mineral records exhibit periodic millennial-scale fluctuations. In the North Aegean Sea, the changes are centred at a period of 1.3-1.8 ka and can be attributed to short-term climate and weathering changes in the northern borderlands. The changes in the South Aegean Sea are centred at periods of 3.2-4.3, 1.9-2.4 and 1.3-1.7 ka reflecting short-term changes in wind strength and Northeast African hydrology.

Mineralogy and isotope chemistry of GISP2 and potential source areas

Samples of dust from the Greenland Ice Sheet Project 2 (GISP2) ice core, Summit, Greenland, dated within marine isotope stage 2 (between 23,340 and 26,180 calendar years B.P.) around the time of the coldest, local, last glacial temperatures, have been analyzed to determine their provenance. To accomplish this, we have compared them with approximately Coeval aeolian sediments (mostly loesses) sampled in possible source areas (PSAs) from around the northern hemisphere. The <5-µm grain-size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale, which was sufficiently fine grained to be transported over long distances. On the basis of comparison of the clay mineralogy and Sr, Nd and Pb isotope composition with ice dust and PSAs and assuming that we have sampled the most important PSAs, we have determined that the probable source area of these GISP2 dusts was in eastern Asia. The dust was not derived from either the midcontinental United States or the Sahara, two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling. Except for a brief period during an interstadial, when dust transport was exceptionally low (for glacial times) and had a mineralogical composition indicative of a slightly more southern provenance, the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size. This includes the high-dust period that correlates with the Heinrich 2 period of major iceberg discharge into the North Atlantic. Variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size.

Age determination and clay content of sediment core GeoB5804-4

Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per mil reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.

Distribution of clay minerals in surface sediments of the Eurasian Arctic Ocean

Clay-mineral distributions in the Arctic Ocean and the adjacent Eurasian shelf areas are discussed to identify source areas and transport pathways of terrigenous material in the Arctic Ocean. The main clay minerals in Eurasian Arctic Ocean sediments are illite and chlorite. Smectite and kaolinite occur in minor amounts in these sediments, but show strong variations in the shelf areas. These two minerals are therefore reliable in reconstructions of source areas of sediments from the Eurasian Arctic. The Kara Sea and the western part of the Laptev Sea are enriched in smectite, with highest values of up to 70% in the deltas of the Ob and Yenisey rivers. Illite is the dominant clay mineral in all the investigated sediments except for parts of the Kara Sea. The highest concentrations with more than 70% illite occur in the East Siberian Sea and around Svalbard. Chlorite represents the clay mineral with lowest concentration changes in the Eastern Arctic, ranging between 10 and 25%. The main source areas for kaolinite in the Eurasian Arctic are Mesozoic sedimentary rocks on Franz-Josef Land islands. Based on clay-mineral data, transport of the clay fraction via sea ice is of minor importance for the modern sedimentary budget in the Arctic basins.

Grain sizes, carbon content and clay minerals of sediments obtained from north Germany and the Baltic Sea

Clay mineralogy and geotechnical properties of Tarras clay, basin clays and tills from some parts of Schleswig-Holstein: Tarras clay of lower Eocene age, Quaternary till containing various admixtures of Tarras clay as well as basin clay and varve-clay from Schleswig-Holstein were investigated. Grain size distribution and soil mechanic characteristics were determined, which indicated different geotechnical properties for each sediment type.

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 mineralogy of ODP Site 131-808 sediments

Drill core recovered at Ocean Drilling Program Site 808 (Leg 131) proves that the wedge of trench sediment within the central region of the Nankai Trough comprises approximately 600 m of hemipelagic mud, sandy turbidites, and silty turbidites. The stratigraphic succession thickens and coarsens upward, with hemipelagic muds and volcanic-ash layers of the Shikoku Basin overlain by silty and sandy trench-wedge deposits. Past investigations of clay mineralogy and sand petrography within this region have led to the hypothesis that most of the detritus in the Nankai Trough was derived from the Izu-Honshu collision zone and transported southwestward via axial turbidity currents. Shipboard analyses of paleocurrent indicators, on the other hand, show that most of the ripple cross-laminae within silty turbidites of the outer marginal trench-wedge facies are inclined to the north and northwest; thus, many of the turbidity currents reflected off the seaward slope of the trench rather than moving straight down the trench axis. Shore-based analyses of detrital clay minerals demonstrate that the hemipelagic muds and matrix materials within sandy and silty turbidites are all enriched in illite; chlorite is the second-most abundant clay mineral, followed by smectite. In general, the relative mineral percentages change relatively little as a function of depth, and the hemipelagic clay-mineral population is virtually identical to the turbidite-matrix population. Comparisons between different size fractions (<2 µm and 2-6 µm) show modest amounts of mineral partitioning, with chlorite content increasing in the coarser fraction and smectite increasing in the finer fraction. Values of illite crystallinity index are consistent with conditions of advanced anchimetamorphism and epimetamorphism within the source region. Of the three mica polytypes detected, the 2M1 variety dominates over the 1M and 1Md polytypes; these data are consistent with values of illite crystallinity. Measurements of mica bo lattice spacing show that the detrital illite particles were eroded from a zone of intermediate-pressure metamorphism. Collectively, these data provide an excellent match with the lithologic and metamorphic character of the Izu-Honshu collision zone. Data from Leg 131, therefore, confirm the earlier interpretations of detrital provenance. The regional pattern of sediment dispersal is dominated by a combination of southwest-directed axial turbidity currents, radial expansion of the axial flows, oblique movement of suspended clouds onto and beyond the seaward slope of the Nankai Trough, and flow reflection back toward the trench axis.

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.