Seasonal changes in the flux of individual planktonic foraminifera in the deep ocean have been studied in the western equatorial Pacific warm pool using material collected by sediment traps over a period of 1 yr (1991-1992). Mean total foraminiferal fluxe
The δ13Ccarb record of well preserved carbonates in outcrop and core is here examined from the 2.6 to 1.9 Ga old basins of Western Australia. These data, which are constrained by a well defined stratigraphic and tectonic framework, and by U-Pb zircon age
Sedimentary rocks deposited during the Ediacaran period (∼630542 Ma) contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from +5‰ to - 12‰, followed by a sub-linear recovery to positive �
Carbonates of the 1640 million years (Ma) old Barney Creek Formation (BCF), McArthur Basin, Australia, contain more than 22 different C40 carotenoid derivatives including lycopane, γ-carotane, β-carotane, chlorobactane, isorenieratane, β-isorenieratane
Three planktonic foraminiferal species Globigerina bulloides, Neogloboquadrina pachyderma (d), and Globorotalia inflata collected from core-tops spanning 35° to 65°N in the North Atlantic were used for U/Ca and Mg/Ca and foraminiferal shell weight analy
We explore the use of tetraethoxysilane (TEOS) as a silica source for the formation of carbonate-silica composite materials known as 'biomorphs'. The basic hydrolysis of TEOS furnishes silica in a controllable fashion, allowing a significantly higher repr
The Segwagwa Group of southeastern Botswana, a correlate of the Pretoria Group of the Transvaal Supergroup of South Africa, consists of a major sequence of siliciclastic sedimentary rocks, minor carbonates and basaltic to andesitic lavas and tuffs straddl
Carbonates of ultrahigh-pressure metamorphic (UHPM) origin were discovered in eclogites from western Tianshan, China. In the eclogites, relict magnesite (XMg = 0.79) occurs as rounded to subidiomorphic inclusions (0.01-0.1 mm) within matrix dolomite, and
Silt- to sand-size clay aggregates are absent or relatively rare in unweathered glacial loesses, but dominant in parna where they resist dispersion in particle size analysis (PSA). There are reports that some aggregates in glacial loesses also resist dispersion. However, one would expect freeze-dried aggregates to have mostly edge-to-face orientation of the platy clays and to be easily dispersed in PSA. We test this hypothesis in this paper. We selected Midwest and Alaskan soils formed in late-Pleistocene loess derived from glacial outwash and floodplains beyond the late-Pleistocene glacial boundary. Analytical methods are those in use by the National Soil Survey Laboratory. Soil A and B horizons dispersed well as shown by the 1.5 MPa water to clay ratios of <0.6. In the C horizon, silt-size, rounded, compound particles (aggregates) were few to common and randomly distributed. A few were volcanic glass. Other aggregates consisted of carbonates or layer silicates. Layer silicate aggregates dispersed well in PSA, as hypothesised; Fe and carbonate cemented aggregates did not. Most of these dispersed when given an ultrasonic dispersion treatment.
The Permian of Timor in the Lesser Sunda Islands has attracted the attention of palaeontologists since the middle of the nineteenth century because of the richness, diversity and excellent state of preservation of its fauna. These abundant fossil data have been compiled and updated for the present account. The Permian rocks of Timor were deposited on the northern margin of Australia. At the present time the northern margin of Australia, in the region of Timor, is involved in a continent-arc collision, where Australia is colliding with the Banda Arcs. As a result of this collision. Permian rocks of the Australian margin have been disrupted by folding and faulting with the generation of mud-matrix mélange, and uplifted to form part of the island of Timor. Due to this tectonic disruption, it has proved difficult to establish a reliable stratigraphy for the Permian units on Timor, especially as the classic fossil collections were obtained largely from the mélange or purchased from the local people, and do not have adequate stratigraphic control. Detailed systematic, structural, stratigraphic and sedimentological studies since the 1960s have provided a firmer stratigraphic and palaeogeographic background for reconsideration of the significance of the classic fossil collections. Permian rocks on Timor belong either to a volcanic-carbonate sequence (Maubisse Formation)...
The Murray canyons are a group of deeply incised submarine canyons on a steep 400 km section of the continental slope off Kangaroo Island, South Australia. Some of the canyons are amongst the largest on Earth. The canyons, some 80 km long, descend from the shelf edge to the abyssal plain 5200 m deep. Sprigg Canyon, the deepest and one of the largest, has walls 2 km high. The thalwegs of the larger canyons are concave in profile, steepest on the upper continental slope (15-30°), with about 4° gradient on the mid slope, then level out on the lower slope to merge with the 1° continental rise. Between canyons, the continental slope is slightly convex to linear with a gradient of about 5-6°. Canyon walls commonly slope at 15-22°. The passive continental margin narrows to 65 km at the Murray canyons and links the Bight and Otway Basins. West-northwest-trending Jurassic-Cretaceous rift structures control the irregular shape of the central canyons. At the western end, large box canyons, 1 km deep, are incised into thick sediments of the Ceduna Sub-basin. Formed by headscarp erosion, some of these canyons have coalesced by canyon capture. The upper parts of most canyons are cut into Cretaceous sediments and in some places are floored by basement rocks. Large deep-water holes...
Geochemical anomalies and stable isotope ratios (δ18O, δ13C) in authigenic carbonates and organic matter (δ13C) from a 660-year sediment core from Lake Chenghai, southern China, provide a continuous history of recent lake eutrophication. The multi-prox
Oblique convergence since the Early Cenozoic between the northward-moving Australian plate, westward-moving Pacific plate and almost stationary Eurasian plate has created a world-ranking tectonic zone in the eastern Indonesia-New Guinea- Southwest Pacific region (Tonga-Sulawesi megashear) that is notorious for its complex mix of tectonic styles and terrane juxtapositions. Unlike an ancient analog - the Mesozoic-Cenozoic Cordillera of North America - palaeomagnetic constraints on terrane motions in the zone are few. To improve the framework of quantitative control on such motions and therefore our understanding of the development of the zone, results of a palaeomagnetic study in the Highlands region of Papua New Guinea (PNG), in the southern part of the New Guinea Orogen, are reported. The study yields new insights into terrane tectonics along the Australian craton's active northern margin and confirms the complexity of block rotations to be expected at the local scale in tectonically intricate zones. The study is based on more than 500 samples (21 localities) collected from an interior and an exterior zone of New Guinea's central cordillera. The two zones are separated by the Tahin and Stolle-Lagaip-Kaugel Fault zones and collectively represent the para-autochthonous northern margin of the Australian craton. Samples from the interior zone...
Willemite (zinc silicate) is the main zinc mineral in some carbonate-hosted ore deposits (e.g., Franklin, New Jersey; Vazante, Brazil; Beltana, South Australia; Kabwe, Zambia). Recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent, relatively low environmental impact of ore processing owing to the lack of acid-generating sulfides in the waste, and advances in ore processing technologies. In the past, most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits. However, recent data on the Vazante, Beltana, and Kabwe deposits indicate willemite crystallization at temperatures in excess of 150°C, raising the possibility of primary precipitation from hydrothermal fluids. We use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions. Activity-activity diagrams reveal that, in the presence of dissolved sulfur and quartz, willemite instead of sphalerite will precipitate under oxidizing (e.g., hematite-stable, sulfate-predominant) and alkaline (pH higher than K feldspar-muscovite-quartz) conditions. Willemite also becomes more stable, relative to sphalerite...
South of Byrd Glacier, central Transantarctic Mountains, Antarctica, Lower Cambrian Shackleton Limestone (Byrd Group) is divided into four informal members. The transition from Shackleton carbonates to clastics of Starshot Formation is conformable, with alternating units of limestone and argillite, and a thick succession of pillow basalt. Douglas Conglomerate is interbedded with and overlies Starshot Formation, and overlies folded Shackleton Limestone unconformably. Lower amphibolite-grade Selborne Group is composed of Madison Marble and Contortion Schist. The contact between the two formations is interbedded marble and schist, and includes metabasalt. We correlate Byrd Group with Selborne Group, Shackleton Limestone with Madison Marble, and Starshot Formation and Douglas Conglomerate with Contortion Schist. These correlations and the lack of equivalent lithologies to the north of Byrd Glacier imply that Byrd Glacier is the northern boundary of the Byrd depositional basin, and reinforces the notion that it marks a major tectonic discontinuity crossing the Ross Orogen.
New U-Pb radiometric dates for K-bentonite horizons within the Lower Cambrian to Middle Ordovician platform carbonates from the Precordillera terrane of NW Argentina provide further constraints on models for the allochthonous or parautochthonous accretion of this terràne. Two K-bentonite layers from the Talacasto section yield indistinguishable sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dates of 469.5 + 3.2 Ma and 470.1 ± 3.3 Ma respectively. These are within uncertainty of the U-Pb SHRIMP zircon date of 468.3 = 3.4 Ma for a porphyritic rhyolite from the Famatinian magmatic arc, Sierra de las Planchadas, near Rio Chaschuil. Geochemical and isotope data also demonstrate the similarity of the K-bentonite and Chaschuil rhyolite parent magmas. Thus, it is highly probable that the Famatinian arc volcanoes. provided the ash for the K-bentonite horizons, suggesting proximity to the Precordillera terrane during the deposition of the Lower Cambrian to Middle Ordovician platform carbonates. This implication supports a mid-Ordovician collision model, but could also be compatible with a parautochthonous model for docking of the Precordillera terrane, by movement along the Pacific margin of Gondwana, rather than across the Iapetus Ocean.
The use of copper-based fungicides by Victorian vinegrowers has increased the total copper concentration in some vineyard soils to 250 mg/kg compared to background levels of approximately 10 mg/kg. The Australian and New Zealand guidelines for the assessment of contaminated sites recommend that total copper concentrations in soil exceeding 60 mg/kg require environmental investigation, and this level is exceeded in 8 of the 14 vineyards investigated. The focus of this paper is to measure the accumulation, distribution and fractionation of copper in contaminated and uncontaminated soils as a step towards understanding copper existence in soils and its potential for availability to flora and fauna. Physical and chemical properties and total copper concentrations were measured in soil samples from four selected wine-producing regions of Victoria, including vineyard soils and adjacent background soils. Copper fractionation in soils with high total copper concentrations was measured using a selective extraction procedure. Copper in surface soils (0-1 cm) and throughout soil profiles (maximum depth of 50 cm) was separated in the following fractions: water soluble (WS), exchangeable (E), sorbed (S), easily reducible Mn (ERMn), bound to carbonates (CA)...
U-series microanalysis and dating is providing new insights into the timing and rates of formation of different minerals, including opals, authigenic iron oxides, zircons, and pedogenic carbonates, during the late Pleistocene. However, the low natural abundance of U and its decay chain isotopes, makes in situ U-series isotope analysis difficult. Using a state-of-the art excimer laser-ablation system coupled to a second generation MC-ICP-MS (Finnigan Neptune), we demonstrate the ability to measure [ 234U/238U] and [230Th/ 238U] activity ratios with in-run precision of l%0 and 3%0, respectively, at a spatial resolution of 90 μm in materials containing 100-500 μg g-1 U. To verify the accuracy and precision of our approach we have prepared and thoroughly assessed two new 'in-house' reference materials (Al-Ca-Si glass and α-Fe2O3) for U-series isotopic composition and micro-scale homogeneity. Together with NIST 610, these reference materials allow us to monitor and correct for Th/U elemental fractionation and to accurately determine 230Th/U isotopic ratios. We show that calibration using silicate glasses imparts a small but significant (∼3%) matrix bias for U-series analysis of iron oxides, and highlights the need for matrix matched materials to obtain accurate U-series chronologies by laser-ablation MC-ICP-MS.
Joseph Bonaparte Gulf is a large embayment on the northwestern continental margin of Australia. It is approximately 300 km east-west and 120 km north-south with a broad continental shelf to seaward. Maximum width from the southernmost shore of Joseph Bonaparte Gulf to the edge of the continental shelf is 560 km. Several large rivers enter the gulf along its shores. The climate is monsoonal, sub-humid, and cyclone-prone during the December-March wet season. A bedrock high (Sahul Rise) rims the shelf margin. The sediments within the gulf are carbonates to seaward, grading into clastics inshore. A seaward-thinning wedge of highstand muds dominates the sediments of the inner shelf of Joseph Bonaparte Gulf. Mud banks up to 15 m thick have developed inshore. Coarse-grained sand ridges up to 15 m high are found off the mouth of the Ord River. These overlie an Upper Pleistocene transgressive lag of mixed carbonate and gravelly siliclastic sand. Four drowned strandlines are present on the inner shelf at depths of 20, 25, 28 and 30 m below datum. These are interpreted as having formed during stillstands in the Late Pleistocene transgression. Older strandlines at great depths are inferred as having formed during the fall in sea-level following the last highstand. For the most part the Upper Pleistocene-Holocene marine sediments overlie an erosion surface cut into older Pleistocene sediments. Incised valleys cut into this erosion surface are up to 5 km wide and have a relief of at least 20 m. The largest valley is that cut by the Ord River. Upper Pleistocene sediments deposited in the incised valleys include interpreted lowstand fluvial gravels...
A reservoir carbonate core plug has been imaged in 3D across a range of length scales using high resolution X-ray microtomography (μ-CT). Data from the original 40-mm diameter plug was obtained at the vug scale (42 μm resolution) and allows the size, sh