Biostratigraphy, magnetostratigraphy, granulometry, isotopes and clay mineral composition of ODP Site 188-1165

During Ocean Drilling Program Leg 188 to Prydz Bay, East Antarctica, several of the shipboard scientists formed the High-Resolution Integrated Stratigraphy Committee (HiRISC). The committee was established in order to furnish an integrated data set from the Pliocene portion of Site 1165 as a contribution to the ongoing debate about Pliocene climate and climate evolution in Antarctica. The proxies determined in our various laboratories were the following: magnetostratigraphy and magnetic properties, grain-size distributions (granulometry), near-ultraviolet, visible, and near-infrared spectrophotometry, calcium carbonate content, characteristics of foraminifer, diatom, and radiolarian content, clay mineral composition, and stable isotopes. In addition to the HiRISC samples, other data sets contained in this report are subsets of much larger data sets. We included these subsets in order to provide the reader with a convenient integrated data set of Pliocene-Pleistocene strata from the East Antarctic continental margin. The data are presented in the form of 14 graphs (in addition to the site map). Text and figure captions guide the reader to the original data sets. Some preliminary interpretations are given at the end of the manuscript.

Characteristics and distribution of Neogene turbidites at ODP Site 108-657

Numerous and variable silty-sandy siliciclastic turbidites were observed in Neogene pelagic sediments (late Miocene to Holocene) at Site 657: (1) thick-bedded, coarse-grained and thin-bedded, fine-grained turbidites; and (2) turbidites composed of eolian dune sand and shallow-water bioclasts or of fluvial-sand or mixed sandy component assemblages. The stratigraphic distribution of these turbidites indicates five periods during which climatic conditions and material sources change. Turbidite occurrence prior to 6.2 Ma (late Miocene) is sparse; the deposits contain coarse and fine-grained turbidites with quartz grains of eolian or mixed origin suggesting the existence of arid conditions at about 8.5 and 6.5 Ma. A coarse-grained turbidite of fluvial origin, recording a humid climate, occurs at about 6.2 Ma. During the early Pliocene, turbidites are frequent (15/Ma); they contain only fine-grained sequences comprising material of mixed origin, which indicates a more humid climate perhaps. The late Pliocene starts with rare coarse-grained turbidites of wind-transported sand while the uppermost Pliocene deposits show a higher frequency of fine-grained sequences (10/0.7 Ma) composed mainly of fluvial material. During the early Pleistocene, similar high turbidite frequency was observed (20/1.3 Ma) but with a total lack of eolian supply. During the last 0.7 Ma, the frequency decreases and the sequences are characterized by highly variable sediment components that could be related to strong variations of climatic conditions. The sedimentary characteristics of turbidites are mainly controlled by sediment source and climate. The frequency must be influenced by sea-level variations, by cyclic processes of climatic origin, and possibly by variations in the continental slope morphology. Clay mineral assemblages suggest a south Saharan source of terrigenous material during the late Miocene and the Pliocene and a northwest Saharan source during the Pleistocene.

Mineralogy and geochemistry of aerosols from the Western Pacific

Aerosols collected by net method over the Western Pacific were investigated. Distribution of eolian material, its mineral and chemical compositions are controlled by the climatic and circumcontinental zonalities. It was stated that Fe and Mn were bound with mineral components of aerosols, while trace elements are bound with organogenic matter. Fluxes of aerosols and their components on the ocean surface were determined.

Mineralogy, geochemistry and benthic foraminifera of the Gorrondatxe beach section

A distinctive low-carbonate interval interrupts the continuous limestone-marl alternation of the deep-marine Gorrondatxe section at the early Lutetian (middle Eocene) C21r/C21n Chron transition. The interval is characterized by increased abundance of turbidites and kaolinite, a 3 per mil decline in the bulk d13C record, a >1 per mil decline in benthic foraminiferal d13C followed by a gradual recovery, a distinct deterioration in foraminiferal preservation, high proportions of warm-water planktic foraminifera and opportunistic benthic foraminifera, and reduced trace fossil and benthic foraminiferal diversity, thus recording a significant environmental perturbation. The onset of the perturbation correlates with the C21r-H6 event recently defined in the Atlantic and Pacific oceans, which caused a 2°C warming of the seafloor and increased carbonate dissolution. The perturbation was likely caused by the input of 13C-depleted carbon into the ocean-atmosphere system, thus presenting many of the hallmarks of Paleogene hyperthermal deposits. However, from the available data it is not possible to conclusively state that the event was associated with extreme global warming. Based on our analysis, the perturbation lasted 226 kyr, from 47.44 to 47.214 Ma, and although this duration suggests that the triggering mechanism may have been similar to that of the Paleocene-Eocene Thermal Maximum (PETM), the magnitude of the carbon input and the subsequent environmental perturbation during the early Lutetian event were not as severe as in the PETM.

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.

Clay mineralogy on five NBP cores

During 2006, the SHALDRIL program recovered cores of Eocene through Pliocene material at four locations in the northwestern Weddell Sea, each representing a key period in the evolution of the Antarctic Peninsula ice cap. The recovered cores are not continuous, yet they provide a record of climate change with samples from the late Eocene, late Oligocene, middle Miocene, and early Pliocene and represent the only series of samples recovered from the northwestern Weddell Sea and spanning the Cenozoic and the initial growth of the peninsula ice cap. Late Eocene sediments sampled in the James Ross Basin are typically characterized by very dark greenish-gray muddy fine sand with some preserved burrowing and are interpreted to represent a shallow water continental shelf setting. Rare dropstones, primarily of well-cemented sandstones and minor ice-rafted material consisting of angular grains with glacially influenced surface features record the onset of mountain glaciation, the earliest such evidence in the region. The remaining cores were collected on the Joinville Plateau to the north of the James Ross Basin. The late Oligocene sediments consist of dark gray sandy mud with some clay lenses and many burrows, likely representing a distal delta or shelf setting. This core contains only very few and small dropstones, and the individual grains show decreased angularity and fewer glacial surface features relative to late Eocene deposits. The middle Miocene strata are composed of pebbly gray diamicton, representing proximal glacimarine sediments. The lower Pliocene section also contains many ice-rafted pebbles but is dominated by sandy units rather than diamicton and is interpreted to represent a current-winnowed deposit, similar to the modern contour current-influenced sediments of the region.

Eolian deposition on the Ontong Java Plateau

The record of eolian deposition on the Ontong Java Plateau (OJP) since the Oligocene (approximately 33 Ma) has been investigated using dust grain size, dust flux, and dust mineralogy, with the goal of interpreting the paleoclimatology and paleometeorology of the western equatorial Pacific. Studies of modern dust dispersal in the Pacific have indicated that the equatorial regions receive contributions from both the Northern Hemisphere westerly winds and the equatorial easterlies; limited meteorological data suggest that low-altitude westerlies could also transport dust to OJP from proximal sources in the western Pacific. Previous studies have established the characteristics of the grain-size, flux, and mineralogy records of dust deposited in the North Pacific by the mid-latitude westerlies and in the eastern equatorial Pacific by the low-latitude easterlies since the Oligocene. By comparing the OJP records with the well-defined records of the mid-latitude westerlies and the low-latitude easterlies, the importance of multiple sources of dust to OJP can be recognized. OJP dust is composed of quartz, illite, kaolinite/chlorite, plagioclase feldspar, smectite, and heulandite. Mineral abundance profiles and principal components analysis (PCA) of the mineral abundance data have been used to identify assemblages of minerals that covary through all or part of the OJP record. Abundances of quartz, illite, and kaolinite/chlorite covary throughout the interval studied, defining a mineralogical assemblage supplied from Asia. Some plagioclase and smectite were also supplied as part of this assemblage during the late Miocene and Pliocene/Pleistocene, but other source areas have supplied significant amounts of plagioclase, smectite, and heulandite to OJP since the Oligocene. OJP dust is generally coarser than dust deposited by the Northern Hemisphere westerlies or the equatorial easterlies, and it accumulates more rapidly by 1-2 orders of magnitude. These relationships indicate the importance of the local sources on dust deposition at OJP. The grain-size and flux records of OJP dust do not exhibit most of the events observed in the corresponding records of the Northern Hemisphere westerlies or the equatorial easterlies, because these features are masked by the mixing of dust from several sources at OJP. The abundance record of the Asian dust assemblage at OJP, however, does contain most of the features characteristic of dust flux by means of the Northern Hemisphere westerlies, indicating that the paleoclimatic and paleometeorologic signal of a particular source area and wind system can be preserved in areas well beyond the region dominated by that source and those winds. Identifying such a signal requires "unmixing" the various dust assemblages, which can be accomplished by combining grain-size, flux, and mineralogic data.

Mineralogy and petrographic summary of ODP Leg 198 sites and DSDP Hole 62-463, Shatsky Rise

This petrological study of the lower Aptian Oceanic Anoxic Event (OAE1a) focused on the nature of the organic-rich interval as well as the tuffaceous units above and below it. The volcaniclastic debris deposited just prior to the OAE1a is consistent with reactivation of volcanic centers across the Shatsky Rise, concurrent with volcanism on the Ontong Java Plateau. This reactivation may have been responsible for the sub-OAE1a unconformity. Soon after this volcanic pulse, anomalous amounts of organic matter accumulated on the rise, forming a black shale horizon. The complex textures in the organic-rich intervals suggest a history of periodic anoxia, overprinted by bioturbation. Components include pellets, radiolarians, and fish debris. The presence of carbonate-cemented radiolarite under the OAE1a intervals suggests that there has been large-scale remobilization of carbonate in the system, which in turn may explain the absence of calcareous microfossils in the section. The volcanic debris in the overlying tuffaceous interval differs in that it is significantly epiclastic and glauconitic. It was likely derived from an emergent volcanic edifice.

Grain shape and mineralogy of loess on New Zealands South Island

Infilled fissures are described from the interface between two loess deposits on Banks Peninsula, South Island, New Zealand. Both loesses differ from the other loesses by having a solifluction deposit at their base consisting of angular basalt fragments of the same angularity as fresh frost shattered basalt mixed with the loess. Typically, the fissures are narrow and up to 160 cm deep while the infilling of the overlying loess shows no obvious structure. They occur mainly at higher elevations on south (poleward) facing slopes, and the host loess forms a fragipan of high density. They are most readily explained as being seasonal frost fissures or more probably ice-wedge casts, which would have required either permafrost or deep seasonal frost for their formation. If permafrost had existed, this would imply a cooling of the mean annual temperatures by at least 16 to 18°C.