The 'Grasses' of the Big Scrub District of North-eastern New South Wales: A sedimentary record of late Holocene grasslands in a subtropical forest landscape

This paper records sedimentary data which indicate that at least part of the Wilsons River floodplain, on the margins of the subtropical rainforest known as the 'Big Scrub', has a long and certainly pre-European history of relative treelessness. Despite a general presumption that this lowland subtropical region was completely forested prior to European settlement, recent historical research has indicated that certain areas were naturally open. While the historical information is clear, the data reported here-a fossil pollen record and one radiocarbon date- reinforces that information for one type of locality, providing an initial indication of time depth.     

Use of deuterated water as a conservative artificial groundwater tracer

Conservative tracers are necessary to obtain groundwater transport velocities at the field scale. Deuterated water is an effective tracer for this purpose due to its similarity to water, chemical stability, non-reactivity, ease of handling and sampling, relatively neutral buoyancy, and reasonable price. Reliable detection limits of 0.1 mg deuterium/L may be obtained in field tests. A field example is presented in which deuterated water, bromide, and pentafluorobenzoic acid are used as groundwater tracers. Deuterated water appeared to be transported conservatively, producing almost identical breakthrough curves as that of other soluble tracers. Electronic Publication     

沈积岩石学

沈积学,在二十世纪初叶始渐起而为地质学中之新支,近数十年来随着石油工业之发达,而日趋蓬勃;一变昔日仅以岩石性质研究为沈积原因之解说,而侧重沈积作用及沈积环境之     

A Pull-Up Shallow Water Seismometer

An inexpensive Pull-Up Shallow Water Seismometer (PUSS) has been designed and built to conduct long range seismic refraction experiments in the North Sea and the continental shelf around Britain, with the particular goal of studying the crustal and lithospheric structure under the epeirogenic basin of the North Sea. Signals from a gimbal-mounted 3-component geophone and a hydrophone are frequency modulated and mixed with clock and flutter correction signals before being recorded on a standard speed cassette tape recorder, with one hour of recording time. A 100 hour programmable timer allows the interval between the time of reset of the clock and each shot window of optional 5 or 10 min duration, to be preselected. The PUSS is launched and recovered using a pull-up technique originally developed for current meters. The replay system is also described.In May 1976 sea trials of 5 PUSSes were conducted along a 200 km refraction line in the North Sea. The encouraging performance of the equipment resulted in the decision to build a further 10 units and to proceed with a 400 km refraction line planned for the summer of 1977.     

A model of ocean current flow and drifter motion

A minor generalization of the theory of random walk is used as a basis for a model of ocean current flow. The model is then applied in a computer simulation of drifter motion. The results of simulation indicate that the geometry of a coastline can have significant impact on the distribution of drifter landings.     

The influence of grain-size analysis methods and sediment mixing on curve shapes and textural parameters: Implications for sediment trend analysis

To this day, deterministic physical models capable of explaining the evolution of grain-size distributions in the course of transport are still lacking. For this reason, various attributes of particle frequency distributions, in particular curve shapes and textural parameters, have for many decades been investigated for potential information about transport behaviour and size-sorting processes of sediments in numerous environments. Such approaches are essentially conceptual and hence rely heavily on the validity of the assumptions on which they are based. A factor which has to date been largely ignored in this context, is the fact that different methods of grain-size analysis (e. g. sieving, laser absorption and diffraction, settling velocity measurements), when applied to the same sample material, produce variable curve shapes, and hence incongruous textural data. This is illustrated by selected examples showing the differences between sieving and settling results, conversion of settling velocities into equivalent settling diameters (psi-phi-transformations), and the influences of particle shape, particle density, and water temperature. It is demonstrated that particle-size distributions are not only method-dependent but also dependent on the adopted post-processing procedure. As a result, only frequency curves generated by the same method and subsequently processed by identical computational procedures can be meaningfully compared. Furthermore, the computation of textural parameters from bi- or multimodal size distributions produces spurious results which are unrelated to the processes leading to the mixing of different size populations frequently observed in nature. In such cases, only the decomposition of such distributions into individual populations and the spatial comparison of such populations makes any sense. Because a physical explanation for the generation of size distributions is lacking, a particular curve shape of a grain-size population has no meaning on its own. Only a systematic comparison of progressively changing curve shapes (and associated textural parameters) of sediments collected on a closely spaced grid can yield data suitable for sediment trend analysis.     

Mathematical modeling of PCB bioaccumulation in Perna viridis

In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (μg g⁻¹ lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (μg g⁻¹ lipid) in the soft tissues of the mussel depends on the competition of the input rate RW and the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k=0.181±0.017 d⁻¹. The critical concentration in water W_c for positive substrate cooperativity was found to be 2.4 ppb. Below W_c, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R=24.0±2.4 μg g⁻¹ lipid ppb⁻¹ d⁻¹. Above W_c, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R=γQ/(Q+δ). This is the case for a water concentration of 5 ppb Aroclor 1254, where γ=15.1 μg g⁻¹ lipid ppb⁻¹ d¹ and δ≈200 μg g⁻¹ lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 μg g⁻¹ lipid, and hyperbolically increasing when the concentration is large compared to 200 μg g⁻¹ lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of the model.     

The Origin of Associated Basic and Acid Rocks in the Lebombo--Nuanetsi Igneous Province, Southern Africa, as implied by Strontium Isotopes

Whole rock Rb–Sr measurements were made on associatedbasic and acid intrusives and extrusives from the northern andsouthern ends of the Lebombo monocline with a view to determineif the acid rocks came from the mantle or from the crust. Inthe south, in Swaziland (now called Ngwame) and Zululand, rhyolitesand granophyres (age 202 14 m.y.) have an initial Si⁸⁷–Sr⁸⁶ratio of 0.7042 0.0005; in the north, in the Nuanetsi syncline,rhyolites (age 206 13 m.y.) and granites from ring complexes(age 177 7 m.y.) have initial ratios of 0.7081 0.0008 and0.7085 0.0007, respectively. The initial ratios of the basicrocks, basalts and gabbros, vary in both areas and have a rangefrom 0.7042 to 0.7125 which can be explained by crustal contamination.The low initial ratios and isotopic homogeneity of the acidmagmas over long distances (160 km) in Swaziland and Zululandare interpreted as implying that they were derived from themantle.     

Rates of iodine remineralization in terrigenous near-shore sediments

Much of the sedimentary geochemistry of iodine has been surmised from analyses of solid phase distributions without direct documentation of reactions or reaction rates. It is shown here that the anoxic production rate of dissolved I in nearshore terrigenous sediments decreases rapidly below the sediment-water interface and is strongly temperature controlled. An apparent activation energy of ~19.3 Kcal/mole comparable to that found for other microbially mediated reactions, describes the temperature dependence of release. Production of dissolved iodide is zeroth order with respect to natural ranges of pore water concentrations and apparently first-order with respect to a reactive I component in the solid phase. First order reaction coefficients in sediments from Mud Bay, South Carolina and Long Island Sound, Connecticut, U.S.A., are strongly depth dependent, varying from ~6.9/yr in the top few centimeters to an average of ~0.011/yr over the upper 70 cm. About 90% of the dissolved I flux comes from the top 10 cm with estimated values of ~ 15 and 29 μmoles/m²/day at 22–23°C in Mud Bay and Long Island Sound, respectively. The I/C net release ratio of decomposing material changes rapidly below the sediment surface. When temperature corrections are made, I remineralization rates from nearshore sediments below the bioturbated zone appear to be similar to those observed in deep water sediments underlying oxygenated waters.