Clay mineralogy of ODP Site 188-1165

The Ocean Drilling Program Leg 188 Site 1165 was drilled on the Wild Drift on the Continental Rise off Prydz Bay, East Antarctica to a total depth of 999.1 meters below seafloor (mbsf). It recovered an extensive suite of terrigenous and hemipelagic sediments of early Miocene to Pleistocene age. Of special interest in this study is the sediment column between 0 and 50 mbsf, which consists of a well-preserved section of Pliocene-Pleistocene-age sediments that was sampled at 10-cm intervals. Multiproxy study of this interval could show possible intervals of expansions of the ice-sheet across the continental shelves and express the climatic evolution in Antarctica, particularly during the 'middle' Pliocene warm period (3.15 to 2.85 Ma) which may provide an indication of how the Earth responds to a rise of its surface temperature. According to the existing age model, the upper 50 mbsf stratigraphic sequence of Site 1165 reaches back to ~4.9 Ma. Throughout this interval, the clay-mineral content is characterized by fluctuations of individual clay minerals, particularly smectite and chlorite. The smectite concentration varies mainly between 0% and 30%. Illite fluctuates less between 50% and 80%, and kaolinite varies mainly between 10% and 20%. Chlorite concentrations are mainly 0% to 10%. There is also a noticeable change in magnetic susceptibility at ~34 mbsf that is clearly indicated in the composition of the clay-mineral suite. At this level, smectite decreases and illite, kaolinite and chlorite show some variability. In particular, there is a slight but persistent increase in chlorite. The results from the Plio-Pleistocene transition, with evenly fluctuating smectite and illite contents and the gradually increasing chlorite content, may indicate cooler conditions compared to the mid-Pliocene conditions. Slight increase in illite content and decrease in smectite content towards Pleistocene supports the previous assumption. The results from the mid-Pliocene with the increasing smectite content and decreasing illite content may indicate warmer and possibly interglacial conditions.

Sedimentary facies and clay mineralogy of ODP Site 105-646

The grain-size study and analyses of bulk sediment and clay mineral composition of samples collected from the dominant lithologies recovered at ODP Site 646, located on the northern flank of the Eirik Ridge (Labrador Sea), show variations indicating that contour-following currents, linked to Norwegian Sea Overflow Water (NSOW), have controlled sedimentation since the early Pliocene. These currents were influential until the early Pleistocene, despite the onset of major ice-rafting at about 2.5 Ma. A major mineralogical change occurred during the late Miocene: a decrease in the smectite to illite and chlorite ratio and a decrease of the crystallinity of smectites. This change indicates a renewing of the source rocks, which could result from an important hydrological change at this time. This change also is depicted by grain-size data that suggest the bottom current influence should be set earlier than the Pliocene.

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.

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.

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.

Physical properties and bulk minerals from IODP Holes 308-U1322B, U1322D and U1324B

How the micro-scale fabric of clay-rich mudstone evolves during consolidation in early burial is critical to how they are interpreted in the deeper portions of sedimentary basins. Core samples from the Integrated Ocean Drilling Program Expedition 308, Ursa Basin, Gulf of Mexico, covering seafloor to 600 meters below sea floor (mbsf) are ideal for studying the micro-scale fabric of mudstones. Mudstones of consistent composition and grain size decrease in porosity from 80% at the seafloor to 37% at 600 mbsf. Argon-ion milling produces flat surfaces to image this pore evolution over a vertical effective stress range of 0.25 (71 mbsf) to 4.05 MPa (597 mbsf). With increasing burial, pores become elongated, mean pore size decreases, and there is preferential loss of the largest pores. There is a small increase in clay mineral preferred orientation as recorded by high resolution X-ray goniometry with burial.

(Table 1) Minerals of bulk sediment at DSDP Holes 64-480 and 64-481

This paper provides a brief, descriptive, sedimentological background for the chapters on hydraulic piston core Site 480 in this symposium, and supplements data given in the site chapter for Sites 479-480 (this volume, Pt. 1). Sediments are composed primarily of planktonic diatoms, with minor numbers of silicoflagellates, radiolarians, and varying amounts of both benthic and planktonic foraminifers, along with a large terrigenous component of olive brown, silty clay. The section contains meter-thick intervals of finely laminated facies alternating with nonlaminated zones. A few paleoenvironmental events are documented within the generally uniform sequence by sporadic occurrences of thin turbidites, phosphatic concretions, fish debris concentrations, an ash layer, and a thin layer of diagenetic dolomite. The distribution of nonlaminated and laminated zones is attributed to fluctuations of bottom-water oxygen content caused by variations in circulation, fertility, and productivity. Homogeneous sections are interpreted as coinciding with cooler climatic periods, whereas laminated sections seem to correspond to upwelling conditions during drier periods.

Major elements oxides and mineralogy of primary minerals in ODP Hole 195-1201D basalts

The basement cored at Site 1201 (west Philippine Basin) during Ocean Drilling Program Leg 195 consists of a 91-m-thick sequence of basalts, mostly pillow lavas and perhaps one sheet lava flow, with a few intercalations of hyaloclastite and interpillow sedimentary material. Hydrothermal alteration pervasively affected the basalt sequence, giving rise to a variety of secondary minerals such as K-Fe-Mg-clay minerals, oxyhydroxides and clay minerals mixtures, natrolite group zeolites, analcite, alkali feldspar, and carbonate. The primary minerals of pillow and sheet basalts that survived the intense hydrothermal alteration were investigated by electron microprobe with the aim of characterizing their chemical composition and variability. The primary minerals are mostly plagioclase, ranging in composition from bytownite through labradorite to andesine, chromian-magnesian-diopside, and spinels, both Ti magnetite (partially maghemitized) and chromian spinel. Overall, the chemical features of the primary minerals of Site 1201 basalts correspond to the primitive character of the bulk rocks, suggesting that the parent magma of these basalts was a mafic tholeiitic magma that most likely only suffered limited fractional crystallization and crystallized at high temperatures (slightly below 1200°C) and under increasing fO2 conditions. The major element composition of clinopyroxene suggests a backarc affinity of the mantle source of Site 1201 basement.

Geochemistry of minerals at DSDP Holes 68-501 and 69-504B

The interaction of seawater with basalts in DSDP Hole 501 and the upper part of Hole 504B (Costa Rica Rift) produced oxidative alteration and a zonation of clay minerals along cracks. From rock edges to interiors in many cracks the following succession occurs, based on microscopic observations and microprobe analysis: iron hydroxides (red), "protoceladonite" (green), iddingsite (orange), and saponite (yellow). Clay minerals replace olivines and fill vesicles and cracks. Other secondary minerals are phillipsite, aragonite, and unidentified carbonates. Some glass is transformed to Mg-rich palagonite. Bulk rock chemistry is related to the composition of the secondary minerals. The zonation can be interpreted as a succession of postburial nonoxidative and oxidative diagenesis similar to that described in the Leg 34 basalts.