Clay mineralogy of sediments from the Bengal Fan

We have measured the relative abundances of smectite, illite, chlorite, and kaolinite in a composite section of the distal Bengal Fan. Two sources of sediment appear to dominate, a smectite-poor, illite-rich source associated with rapid denudation of the Himalayas and a smectite-rich, illite-poor source probably on the continental margin of the Indian sub-continent. Changes in source appear to be related to uplift in the Himalayas and Tibetan Plateau both directly and through the climatic and oceanographic consequences of uplift.

Stable isotopes, sedimentology and geochemical analyses of Middle Eocene to early Miocene sediments of ODP Site 177-1090

During Leg 177 of the Ocean Drilling Program (ODP), a well-preserved middle Eocene to lower Miocene sediment record was recovered at Site 1090 on the Agulhas Ridge in the Atlantic sector of the Southern Ocean. This new sediment record shows evidence of a hitherto unknown late Eocene opal pulse. Lithological variations, compositional data, mass-accumulation rates of biogenic and lithogenic sediment constituents, grain-size distributions, geochemistry, and clay mineralogy are used to gain insights into mid-Cenozoic environmental changes and to explore the circumstances of the late Eocene opal pulse in terms of reorganizations in ocean circulation. The base of the section is composed of middle Eocene nannofossil oozes mixed with red clays enriched in authigenic clinoptilolite and smectite, deposited at low sedimentation rates (LE 2 cm/ka). It indicates reduced terrigenous sediment input and moderate biological productivity during this preglacial warm climatic stage. The basal strata are overlain by an extended succession (100 m, 4 cm/ka) of biosiliceous oozes and muds, comprising the upper middle Eocene, the entire late Eocene, and the lowermost early Oligocene. The opal pulse occurred between 37.5 and 33.5 Ma and documents the development of upwelling cells along topographic highs, and the utilization of a marine nutrient- and silica reservoir established during the pre-late Eocene through enhanced submarine hydrothermal activity and the introduction of terrigenous solutions from chemical weathering on adjacent continents. This palaeoceanographic overturn probably was initiated through the onset of increased meridional ocean circulation, caused by the diversion of the Indian equatorial current to the south. The opal pulse was accompanied by increased influxes of terrigenous detritus from southern African sources (illite), mediated by enhanced ocean particle advection in response to modified ocean circulation. The opal pulse ended because of frontal shifts to the south around the Eocene/Oligocene boundary, possibly in response to the opening of the Drake Passage and the incipient establishment of the Antarctic Circumpolar Current. Condensed sediments and a hiatus within the early Oligocene part of the section possibly point to an invigoration of the deep-reaching Antarctic Circumpolar Current. The mid-Oligocene to lower Miocene section on long time scale exhibits less pronounced lithological variations than the older section and points to relatively stable palaeoceanographic conditions after the dramatic changes in the late Eocene to early Oligocene.

Mineral quantification of a Jordan Cretaceous outcrop (Section GM3, Ghawr Al Mazar, Ghor al Mazrar)

Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic, because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio-eustatic forcing. An alternative concept suggests that the water-bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge, as a function of the temperature-related intensity of the hydrological cycle, may have driven eustasy during warm climates. However, this idea has long been neglected for two reasons: 1) the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2) empirical data were missing that document past variations in the hydrological cycle in relation to eustasy. In the present study we present the first empirical evidence for changes in precipitation, continental weathering intensity and evaporation that correlate with astronomically (long obliquity) forced sea-level cycles during the warmest period of the Cretaceous (Cenomanian-Turonian). We compare sequence-stratigraphic data with changes in the terrigenous mineral assemblage in a low-latitude marine sedimentary sequence from the equatorial humid belt at the South-Tethyan margin (Levant carbonate platform, Jordan), thereby avoiding uncertainties from land-ocean correlations. Our data indicate covariance between cycles in weathering and sea level: predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products (clays) in deposits that represent sea-level fall (aquifer charge > discharge). Conversely, preservation of weathering-sensitive minerals (feldspars, epidote and pyroxenes) in transgressive sediments reflects decreased continental weathering due to dryer climate (aquifer discharge > charge). Based on our results we suggest that aquifer-eustasy represents a viable alternative to glacio-eustasy as a driver of cyclic 3rd-order sea-level fluctuations during the middle Cretaceous greenhouse climate, and it may have been a pervasive process throughout Earth history.

Grain size distribution and clay mineralogy of upper Miocene sediments of ODP Hole 107-652A

The upper Miocene sedimentary sequence of Site 652, located on the lower continental margin of eastern Sardinia, was cored and logged during Ocean Drilling Program (ODP) Leg 107. Geophysical and geochemical logs from the interval 170-365 m below seafloor (mbsf), as well as various core measurements (CaCO3, grain size, X-ray diffraction), provide a mineralogical-geochemical picture that is interpreted in the framework of the climatic and tectonic evolution of the western Tyrrhenian. The results indicate the presence of short- and long-term mineralogical variations. Short-term variations are represented by calcium-carbonate fluctuations in which the amount of CaCO3 is correlated to the grain size of the sediments; coarser sediments are associated with high carbonate content and abundant detrital material. Long-term variation corresponds to a gross grain-size change in the upper part of the sequence, where predominantly fine-grained sediments may indicate a gradual deepening of the lacustrine basin towards the Pliocene. Regional climatic changes and rift-related tectonism are possible causes of this variability in the sedimentation patterns. The clay association is characterized by chlorite, illite, and smectite as dominant minerals, as well as mixed-layers clays, kaolinite, and palygorskite. Chlorite, mixed-layers clays, and illite increase at the expense of smectite below the pebble zone (335 mbsf). This is indicative of diagenetic processes related to the high geothermal gradient and to the chemistry of the evaporative pore waters, rather than to changes in the depositional environment.

Clay mineralogy of the Cenozoic Pagodroma Group, East Antarctica

The Cenozoic Pagodroma Group in the northern Prince Charles Mountains, East Antarctica, is a glaciomarine succession of fjordal character, comprising four uplifted formations of different ages. The composition of the <2 µm fraction of sediments of the Pagodroma Group was analysed in order to help identify source areas, past weathering conditions and glacial regimes. Both clay and non-clay minerals have been quantified. The assemblage of the upper Oligocene to lower Miocene Mount Johnston Formation is characterised by the dominance of illite and intermediate concentrations of chlorite. Similar to that assemblage is the clay mineral suite of the middle Miocene Fisher Bench Formation, where illite and chlorite together account for 95% of the clay minerals. The middle to upper Miocene Battye Glacier Formation is the only formation with significant and persistent smectite concentrations, although illite is still dominant. The kaolinite concentration is also high and is even higher than that of chlorite. The clay fraction of the upper Pliocene to lower Pleistocene Bardin Bluffs Formation is characterised by maximum kaolinite concentrations and relatively low illite and chlorite concentrations. The bulk of the clay fraction in each formation can be explained by the physical weathering and erosion of a nearby source under glacial conditions. In the case of Mount Johnston Formation and Fisher Bench Formation this source may be situated in the metavolcanic and gneissic rocks of Fisher Massif. The sediments of the Bardin Bluffs Formation indicate a local source within the Amery Oasis, where Proterozoic granitoid rocks and gneisses, and Permo-Triassic fluvial rocks of the Amery Group are exposed. These results suggest a strong local imprint on the glacial sediments as northwards flowing ice eroded the bedrock in these areas. The origin of the clay fraction of the Battye Glacier Formation is a matter of debate. The smectite and kaolinite content most easily can be explained by erosion of sources largely hidden beneath the ice upstream. Less likely, these clay minerals reflect climatic conditions that were much warmer and wetter than today, facilitating chemical weathering.

Chemical and mineral composition of rocks and sediments from the Amirante Arc

New geological and geophysical data on the Amirante Arc, which locates to the south of the Seychelles Islands, are presented. These data were obtained by Pacific Oceanological Institute during the 33-rd cruise of R/V Professor Bogorov in 1990. The Amirante Arc represents a seamount chain, which has submeridional strike and total length about 400 km. To the west of the Amirante Arc there are a deep sea trench and a back-arc basin, i.e. this area is characterized by structural elements associated with the subduction zone of Western Pacific type. According to our data the Amirante Arc is composed by tholeiites of ocean plateau type. This facts are evidences that the Amirante Arc differs from typical Pacific island arcs. This gives an opportunity to distinguish a special type of oceanic structures, i.e. non-volcanic (amagmatic) ridges. The Amirante Ridge has been probably formed as a result of oceanic crust heaping due to horizontal displacements of its blocks in the process of spreding ridge formation in the Indian Ocean during Cretaceous-Paleogene.

Grain characteristics and XRD raw data of ODP Sites 162-981 and 162-984

Multisensor track data, including magnetic susceptibility, gamma-ray attenuation porosity evaluator (GRAPE) wet bulk density, and natural gamma emission, were collected on all cores recovered during Ocean Drilling Program Leg 162. Data from the upper Pliocene and lower Pleistocene of Sites 981 and 984 are here compared to results from analyses of a limited set of discrete samples, including benthic foraminiferal isotopic composition, grain size, carbonate content, abundance of foraminifers and lithic particles, and clay mineralogy. Natural gamma emission most closely monitors the input of felsic terrigenous material to these two sites. Magnetic susceptibility also tracks felsic terrigenous input at Site 981 but appears to reflect a separate, more mafic, terrigenous component at Site 984. The GRAPE record does not correlate well with any discretely measured variable at Sites 981 or 984.

Clay mineralogy of Cape Roberts sediment cores

The clay mineral assemblages of the ca. 1600 m thick Cenozoic sedimentary succession recovered at the CRP-1, CRP-2/2A and CRP-3 drill sites off Cape Roberts on the McMurdo Sound shelf, Antarctica, were analysed in order to reconstruct the palaeoclimate and the glacial history of this part of Antarctica. The sequence can be subdivided into seven clay mineral units that reflect the transition from humid to subpolar and polar conditions. Unit I (35-33.6 Ma) is characterised by an almost monomineralic assemblage consisting of well crystalline, authigenic smectite, and therefore does not allow a palaeoclimatic reconstruction. Unit II (33.6-33.1 Ma) has also a monomineralic clay mineral composition. However, the assemblage consists of variably crystallized smectite that, at least in part, is of detrital origin and indicates chemical weathering under a humid climate. The main source area for the clays was in the Transantarctic Mountains. Minor amounts of illite and chlorite appear for the first time in Unit III (33.1-31 Ma) and suggest subordinate physical weathering. The sediments of Unit IV (31-30.5 Ma) have strongly variable smectite and illite concentrations indicating an alternation of chemical weathering periods and physical weathering periods. Unit V (30.5-24.2 Ma) shows a further shift towards physical weathering. Unit VI (24.2-18.5 Ma) indicates strong physical weathering under a cold climate with persistent and intense illite formation. Unit VII (18.5 Ma to present) documents an additional input of smectite derived from the McMurdo Volcanic Group in the south.

Chemical and mineral compositions of bottom sediments from the Sea of Japan

Physical properties (water content, bulk density, magnetic susceptibility, natural remanent magnetization, nature of magnetization, and composition of ferromagnetic fraction), chemical, and (optionally) mineral composition of bottom sediments from the north-west Sea of Japan have been studied. Their stratigraphic subdivision based on composition of diatoms has been carried out. Obtained data have allowed to find out some aspects of influence of paleogeographic conditions and diagenetic processes on change of physical properties of the sediments, as well as on their composition in Holocene and Late Pleistocene.

Geochemistry and mineralogy of sediments from the Atlantis II Fracture Zone

Thirteen sediment samples, including calcareous ooze, sandy clay, volcanic sand, gravel, and volcanic breccia, from Ocean Drilling Program (ODP) Sites 732B, 734B, 734G and Conrad Cruise 27-9, Station 17, were examined. Contents of major and trace elements were determined using XRF or ICP (on samples <0.5 g). Determinations of rare earth elements (REE) were performed using ICP-MS. Mineralogy was determined using XRD. On the basis of the samples studied, the sediments accumulating in the Atlantis II Fracture Zone are characterized by generally high MgO, Cr, and Ni contents compared with other deep-sea sediments. A variety of sources are reflected in the mineralogy and geochemistry of these sediments. Serpentine, brucite, magnetite, and high MgO, Cr, and Ni contents indicate derivation from ultramafic basement. The occurrence of albite, analcime, primary mafic minerals, and smectite/chlorite in some samples, coupled with high SiO2, Al2O3, TiO2, Fe2O3, V, and Y indicate contribution from basaltic basement. A third major sediment source is characterized as biogenic material and is reflected primarily in the presence of carbonate minerals, and high CaO, Sr, Pb, and Zn in certain samples. Kaolinite, illite, quartz, and some chlorite are most likely derived from continental areas or other parts of the ocean by long-distance sediment transport in surface or other ocean currents. Proportions of source materials in the sediments reflect the thickness of the sediment cover, slope of the seafloor, and the nature of and proximity to basement lithologies. REE values are low compared to other deep-sea sediments and indicate no evidence of hydrothermal activity in the Atlantis II Fracture Zone sediments. This is supported by major- and trace-element data.

Grain-size and bulk and clay mineralogy of ODP Leg 204 sediments

We present grain size, granulometric statistical parameters, and calcium carbonate content of sediment samples from the summit and east and west flanks of southern Hydrate Ridge (Sites 1244-1250). These data are compared with magnetic susceptibility measurements from the same intervals. Bulk and clay mineralogy from Sites 1244 (east flank), 1247 (west flank), and 1250 (summit) are also presented. The integration of these data allows us to characterize the main sedimentary facies and composition of the Quaternary age sediments from southern Hydrate Ridge.

Mineral composition and geochemistry of sediments from ODP Leg 127 sites

The lithostratigraphy of Neogene hemipelagic sediments recovered from the Japan Sea during Leg 127 was revised to improve intersite consistency and to remove confusion stemming from diagenetic modification of the lithology through the opal-A to opal-CT transformation. Special emphasis was put on the presence and nature of dark-light cycles in revising the lithostratigraphy. Mineral composition analysis was conducted for samples from Sites 794, 795, and 797. In addition, major element chemical composition analysis was conducted for these same sample sets from Site 794. The result of mineral composition analysis suggests that the detrital component, which consists of such minerals as quartz, plagioclase, illite, and kaolinite plus chlorite, is diluted to various degrees by biogenic silica (opal-A) and its diagenetic equivalents (opal-CT and quartz). Smectite, on the other hand, may be a diagenetic or hydrothermal alteration product of volcanic material, although more study is necessary to confirm its origin. As a whole, vertical variation in the sediment composition is consistent with the revised lithostratigraphy and helps to characterize the redefined lithologic units quantitatively.