Geochemistry, clay mineralogy and grain size distribution in various sediment cores drilled during ODP Leg 119 on the Antarctic continental shelf off Prydz Bay

Drilling was undertaken at five sites (739-743) on ODP Leg 119 on a transect across the continental shelf of Prydz Bay, East Antarctica, to elucidate the long-term glacial history of the area and to examine the importance of the area with respect to the development of the East Antarctic ice sheet as a whole. In addition to providing a record of glaciation spanning 36 m.y. or more, Leg 119 has provided information concerning the development of a continental margin under the prolonged influence of a major ice sheet. This has allowed the development of a sedimentary model that may be applicable not only to other parts of the Antarctic continental margin, but also to northern high-latitude continental shelves. The cored glacial sedimentary record in Prydz Bay consists of three major sequences, dominated by diamictite: 1. An upper flat-lying sequence that ranges in thickness from a few meters in inner and western Prydz Bay to nearly 250 m in the outer or eastern parts of the bay. The uppermost few meters consist of Holocene diatom ooze and diatomaceous mud with a minor ice-rafted component overlying diamicton and diamictite of late Miocene to Quaternary age. The diamictite is mainly massive, but stratified varieties and minor mudstone and diatomite also occur. 2. An upper prograding sequence cored at Sites 739 and 743, unconformly below the flat-lying sequence. This consists of a relatively steep (4° inclination) prograding wedge with a number of discrete sedimentary packages. At Sites 739 and 743 the sequence is dominated by massive and stratified diamictite, some of which shows evidence of slumping and minor debris flowage. 3. A lower, more gently inclined, prograding sequence lies unconformably below the flat-lying sequence at Site 742 and the upper prograding sequence at Site 739. This extends to the base of both sites, to 316 and 487 mbsf, respectively. It is dominated by massive, relatively clast-poor diamictite which is kaolinite-rich, light in color, and contains sporadic carbonate-cemented layers. The lower part of Site 742 includes well-stratified diamictites and very poorly sorted mudstones. The base of this site has indications of large-scale soft-sediment deformation and probably represents proximity to the base of the glacial sequence. Facies analysis of the Prydz Bay glacial sequence indicates a range of depositional environments. Massive diamictite is interpreted largely as waterlain till, deposited close to the grounding line of a floating glacier margin, although basal till and debris flow facies are also present. Weakly stratified diamictite is interpreted as having formed close to or under the floating ice margin and influenced by the input of marine diatomaceous sediment (proximal glaciomarine setting). Well-stratified diamictite has a stronger marine input, being more diatom-rich, and probably represents a proximal-distal glaciomarine sediment with the glaciogenic component being supplied by icebergs. Other facies include a variety of mudstones and diatom-rich sediments of marine origin, in which an ice-rafted component is still significant. None of the recovered sediments are devoid of a glacial influence. The overall depositional setting of the prograding sequence is one in which the grounded ice margin is situated close to the shelf edge. Progradation was achieved primarily by deposition of waterlain till. The flat-lying sequence illustrates a complex sequence of advances and retreats across the outer part of the shelf, with intermittent phases of ice loading and erosion. The glacial chronology is based largely on diatom stratigraphy, which has limited resolution. It appears that ice reached the paleoshelf break by earliest Oligocene, suggesting full-scale development of the East Antarctic ice sheet by that time. The ice sheet probably dominated the continental margin for much of Oligocene to middle Miocene time. Retreat, but not total withdrawal of the ice sheet, took place in late Miocene to mid-Pliocene time. The late Pliocene to Pleistocene was characterized by further advances across, and progradation of, the continental shelf. Holocene time has been characterized by reduced glacial conditions and a limited influence of glacial processes on sedimentation.

Grain entrainment and transport rates of magnetic minerals of coastal sediment samples from the Bay of Plenty, New Zealand

Heavy (magnetic & non-magnetic) minerals are found concentrated by natural processes in many fluvial, estuarine, coastal and shelf environments with a potential to form economic placer deposits. Understanding the processes of heavy mineral transport and enrichment is prerequisite to interpret sediment magnetic properties in terms of hydro- and sediment dynamics. In this study, we combine rock magnetic and sedimentological laboratory measurements with numerical 3D discrete element models to investigate differential grain entrainment and transport rates of magnetic minerals in a range of coastal environments (riverbed, mouth, estuary, beach and near-shore). We analyzed grain-size distributions of representative bulk samples and their magnetic mineral fractions to relate grain-size modes to respective transport modes (traction, saltation, suspension). Rock magnetic measurements showed that distribution shapes, population sizes and grain-size offsets of bulk and magnetic mineral fractions hold information on the transport conditions and enrichment process in each depositional environment. A downstream decrease in magnetite grain size and an increase in magnetite concentration was observed from riverine source to marine sink environments. Lower flow velocities permit differential settling of light and heavy mineral grains creating heavy mineral enriched zones in estuary settings, while lighter minerals are washed out further into the sea. Numerical model results showed that higher heavy mineral concentrations in the bed increased the erosion rate and enhancing heavy mineral enrichment. In beach environments where sediments contained light and heavy mineral grains of equivalent grain sizes, the bed was found to be more stable with negligible amount of erosion compared to other bed compositions. Heavy mineral transport rates calculated for four different bed compositions showed that increasing heavy mineral content in the bed decreased the transport rate. There is always a lag in transport between light and heavy minerals which increases with higher heavy mineral concentration in all tested bed compositions. The results of laboratory experiments were validated by numerical models and showed good agreement. We demonstrate that the presented approach bears the potential to investigate heavy mineral enrichment processes in a wide range of sedimentary settings.

Holocene sedimentation in the Strait of Otranto, Mediterranean Sea

An extensive radiograph study of 24 undisturbed, up to 206-cm long box and gravity cores from the western part of the Strait of Otranto revealed a great variety of primary bedding structures and secondary burrowing features. The regional distribution of the sediments according to their structural, textural, and compositional properties reflects the major morphologic subdivisions of the strait into shelf, slope, and trough bottom (e.g., the bottom of the northern end of the Corfu-Kephallinia Trough, which extends from the northeastern Ionian Sea into the Strait of Otranto): (1) The Apulian shelf (0 to -170m) is only partly covered by very poorly sorted, muddy sands without layering. These relict(?) sands are rich in organic carbonate debris and contain glauconite and reworked (?Pleistocene) ooids. (2) The slope sediments (-170 to -1,000 m) are poorly sorted, sandy muds with a high degree of burrowing. One core (OT 5) is laminated and shows slump structures. An origin of these slumped sediment masses from older deposits higher on the slope was inferred from their abnormal compaction, color, texture, organic content, and mineral composition. (3) Cores from the northern end of the Corfu-Kephallinia Trough (-980 to -1,060 m) display a few graded sand layers, 2-5 cm (maximum 30 cm) thick with parallel and ripple-cross-laminations, deposited by oceanic bottom or small-scale turbidity currents. They are intercalated with homogeneous lutite. (4) Hemipelagic sediments prevail in the more southerly part of the Corfu-Kephallinia Trough and on the "Apulian-Ionian Ridge", the southern submarine extension of the Apulian Peninsula. Below a core depth of 160 cm, these cores have a laminated ("varved") zone, representing an Early Holocene (Boreal-Atlanticum) "stagnation layer" (14C age approximately 9,000 years). The terrigenous components of the surface sediments as well as those of the deeper sand layers can be derived from the Apulian shelf and the Italian mainland (Cretaceous Apulian Plateau and Gargano Mountains, southern Apennines, volcanic province of the Monte Vulture). Indicated by the heavy mineral glaucophane, a minor proportion of the sedimentary material is probably of Alpine origin. If this portion is considered to be first-cycle clastic material it reaches the Strait of Otranto after a longitudinal transport of 700 km via the Adriatic Sea. The lack of phyllosilicates in the coarse- to medium-grained shelf samples might be explained by the activity of the "Apulian Current" (surface velocities up to 4 knots) which in the past possibly has affected the bottom almost down to depths of the shelf edge. The percentage of planktonic organisms, and also the plankton: benthos ratio in the sediments is a useful indicator for bathymetry (depth zonation).

Petrology and geochemistry of the Izu-Bonin Forearc tephras

Numerous marine tephra layers cored at Sites 792 and 793 in the Izu-Bonin forearc region offer additional information about the timing and spatial characteristics of arc volcanism and the evolution of island arcs. Explosive volcanism along the Izu-Bonin Arc, with maxima just before rifting of the arc at ~40 and 5-0 Ma, produced black and white tephras of variable grain sizes and chemical compositions. Most of the tephras belong chemically to low-K and low-alkali tholeiitic rock series with a few tephra of the high-K and alkalic rock series. Most of the tephras (low-K series) were derived from the Izu-Bonin Arc, although a few were produced far to the west of the Izu-Bonin Arc (e.g., from the Ryukyu Arc). Black tephras may have come from nearby sources, such as Aogashima, Sumisu, and Torishima islands. The high-K series of tephras, within the sediments younger than 3 Ma, may reflect thickening of the island-arc crust.

Mineralogical and grain size analysis of ODP Hole 119-745B from the Southern Ocean

The upper Miocene to Pleistocene sediments recovered at ODP Sites 745 and 746 in the Australian-Antarctic Basin are characterized by cyclic facies changes. Sedimentological investigations of a detailed Quaternary section reveal that facies A is dominated by a high content of siliceous microfossils, a relatively low terrigenous sediment content, an ice-rafted component, low concentrations of fine sediment particles, and a relatively high smectite content. This facies corresponds to interglacial sedimentary conditions. Facies B, in contrast, is characteristic of glacial conditions and is dominated by a large amount of terrigenous material and a smaller opaline component. There is also a prominent ice-rafted component. The microfossils commonly are reworked and broken. The clay mineral assemblages show higher proportions of glacially derived illite and chlorite. A combination of four different processes, attributed to glacial-interglacial cycles, was responsible for the cyclic facies changes during Quaternary time: transport by gravity, ice, and current and changes in primary productivity. Of great importance was the movement of the grounding line of the ice shelves, which directly influenced the intensity of ice rafting and of gravitational sediment transport to the deep sea. The extension of the ice shelves was also responsible for the generation of cold and erosive Antarctic Bottom Water, which controlled the grain-size distribution, particularly of the fine fraction, in the investigated area.

Age determination, sedimentological, biogeochemical, and plant macrofossils analyses of outcrop PG2038-1

Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene-Kyuele in the NE Siberian Arctic (latitude 71°17'N, longitude 125°34'E). The water-body displays thaw-lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5-m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ~7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ~0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin.

Grain size analyses of ODP Leg 178 sites

Sites 1095, 1096, and 1101 were drilled on the continental rise west of the Antarctic Peninsula (Fig. F1) to recover a continuous high-resolution record of Antarctic glaciation. Site 1095 is the subject of a short paper in this volume (Pudsey, 2001, doi:10.2973/odp.proc.sr.178.214.2001), whereas mass accumulation rates at the three sites are described by Wolf-Welling (2001, doi:10.2973/odp.proc.sr.178.223.2001) and ice-rafted debris at Site 1101 is discussed by Cowan (2001, doi:10.2973/odp.proc.sr.178.206.2001) This report documents grain-size data (sand and fine fraction) and the proportion of biogenic silica for the upper 300 m at Site 1095, the upper 250 m at Site 1096, and the whole 220 m at Site 1101.

Grain size analyses of ODP Leg 116 holes

Ocean Drilling Program (ODP) Leg 116 cored the distal part of the Bengal Fan at three closely spaced sites (717-719). The recovered sediments consisted dominantly of turbidites that varied in thickness between a few centimeters and 2 m or more. A number of different facies have been identified in the sequence and are described by Stow et al. (1990, doi:10.2973/odp.proc.sr.116.110.1990). Representative examples of these facies types were selected and sampled for grain-size analysis. The results of these analyses are tabulated in this data report.

Dust flux in the Arabian Sea

Eolian grain size and flux were measured on samples from 11 Arabian Sea sediment traps deployed 200-1250 km offshore. The timing of increased grain size is coincident with the onset of strong summer monsoon winds and dust storm activity over the Arabian Peninsula and Middle East. Data spanning a full annual cycle show that eolian grain size is highly correlated with barometric pressure (r=-0.91) and wind speed (r=0.84), enabling calibration of the downcore record in terms of these primary meteorological variables. Eolian flux is highly correlated with organic carbon flux (r=0.80); both increase 6-8 weeks after the grain size increase and summer monsoon onset. This lag, and the low correlation between eolian grain size and eolian flux (r=0.36), likely result from the differential sinking rates of large and small dust particles in the surface waters as well as biological scavenging associated with monsoon-induced productivity.

Grain-size distribution and Folk's statistics at DSDP Leg 64 Holes

Grain size of 139 unconsolidated sediment samples from seven DSDP sites in the Guaymas Basin and the southeastern tip of the Baja California Peninsula was determined by sieve and pipette techniques. Shepard (1954) classification and Inman (1952) parameters correlation were used for all samples. Sediment texture ranged from sand to silty clay. On the basis of grain-size parameter, the sediments can be divided into three broad groups: (1) very fine sands and coarse silts; (2) medium- to very fine silts; and (3) clays and coarse silts.

Sediment organic matter, grain size, and results of prediction models from northern North Atlantic and Arctic Seas

Sediment samples and hydrographic conditions were studied at 28 stations around Iceland. At these sites, Conductivity-Temperature-Depth (CTD) casts were conducted to collect hydrographic data and multicorer casts were conductd to collect data on sediment characteristics including grain size distribution, carbon and nitrogen concentration, and chloroplastic pigment concentration. A total of 14 environmental predictors were used to model sediment characteristics around Iceland on regional geographic space. For these, two approaches were used: Multivariate Adaptation Regression Splines (MARS) and randomForest regression models. RandomForest outperformed MARS in predicting grain size distribution. MARS models had a greater tendency to over- and underpredict sediment values in areas outside the environmental envelope defined by the training dataset. We provide first GIS layers on sediment characteristics around Iceland, that can be used as predictors in future models. Although models performed well, more samples, especially from the shelf areas, will be needed to improve the models in future.

Physical properties, compressional-wave velocity and consolidation characteristics of ODP Holes 133-815B and 133-817B

Sites 815 and 817 were drilled near the Townsville Trough during Leg 133 of the Ocean Drilling Program. The physical properties, compressional-wave velocity, and consolidation characteristics indicate that the periplatform carbonate sediments maintain more water content and lower compressional velocity near the Queensland Plateau than the clayey hemipelagic sediments, which have a clay content of up to 60%. Bulk density, void ratio or porosity, water content, and compressional-wave velocity are shown to have a linear relationship with burial depth. Between 3.5 and 5 Ma (about 100-500 mbsf), these physical properties maintained a constant rate vs. the depth in core because of the fast sedimentation-rate effect at Site 815. However, compressionalwave velocity still increases downward in this section. The clay content in this section causes an increase of bulk modulus and compaction effect. At Site 817, scarce terrigenous mud content and abundant carbonate content (88%-97%) cause a straight line relationship between physical properties and burial depth. During the consolidation test, we show that dominant micritic particles may cause faster acoustic velocity than sediments composed mainly of coccoliths. The bulk modulus ratio increasing rate in the clay-rich carbonate sediments is almost 4.5 times higher than in the clay-free periplatform carbonate sediments.