Impact of mechanical anisotropy and power-law rheology on single layer folding

The infinitesimal and finite stages of folding in nonlinear viscous material with a layer-parallel anisotropy were investigated using numerical and analytical methods. Anisotropy was found to have a first-order effect on growth rate and wavelength selection, and these effects are already important for anisotropy values (normal viscosity/shear viscosity) < 10. The effect of anisotropy must therefore be considered when deducing viscosity contrasts from wavelength to thickness ratios of natural folds. Growth rates of single layer folds were found to increase and subsequently decrease during progressive deformation. This is due to interference between the single layer folds and chevron folds that form in the matrix as a result of instability caused by the anisotropic material behaviour. The wavelength of the chevron folds in the matrix is determined by the wavelength of the folded single layer, which can explain the high wavelength to thickness ratios that are sometimes found in multilayer sequences. Numerical models including anisotropic material properties allow the behaviour of multilayer sequences to be investigated without the need for resolution on the scale of individual layers. This is particularly important for large-scale models of layered lithosphere.     

Late cretaceous Arman’ flora of Magadan oblast: Paleoclimatic interpretation

The Arman’ flora belongs to the formation of the same name in the Arman’ River basin and Nel’khandzha-Khasyn interfluve. It includes about 80 fossil plant species. The similarity of this flora to the reliably dated fossil floras of northwestern Kamchatka and the Pekul’nei Range dates it to being Turonian and Coniacian in age, which is corroborated by isotopic (U-Pb and ⁴⁰Ar/³⁹Ar) dating of the plant-bearing layers. The CLAMP method is used to estimate quantitative climatic variables, according to which the Arman’ flora existed in a temperate humid climate with warm summers and mild winters. This climate is especially similar to the conditions reconstructed from fossil plants of the Turonian Penzhina flora and the Coniacian Kaivayam and Tylpegyrgynai floras of Northeast Asia.     

Oxygen isotope and palaeomagnetic stratigraphy of Equatorial Pacific core V28-238: Oxygen isotope temperatures and ice volumes on a 105 year and 106 year scale

Core Vema 28-238 preserves an excellent oxygen isotope and magnetic stratigraphy and is shown to contain undisturbed sediments deposited continuously through the past 870,000 yr. Detailed correlation with sequences described by Emiliani in the Caribbean and Atlantic Ocean is demonstrated. The boundaries of 22 stages representing alternating times of high and low Northern Hemisphere ice volume are recognized and dated. The record is interpreted in terms of Northern Hemisphere ice accumulation, and is used to estimate the range of temperature variation in the Caribbean.     

Cambrian to Devonian evolution of alluvial systems: The sedimentological impact of the earliest land plants

In present-day alluvial environments, the impact of vegetation on sedimentological processes and deposits is well known. A vegetated catchment may decrease sediment yield, sediment erodibility, Hortonian overland flow, aeolian winnowing of fines, the proportion of sediment transported as bedload, and may increase bank stability, infiltration into substrates, and bed roughness. Vegetation also promotes the production of chemically-weathered clays and soils and the adoption of a meandering style. It is generally understood that, prior to the evolution of terrestrial vegetation during the Early Palaeozoic, ancient alluvial systems were markedly different from modern systems, with many systems adopting a “sheet-braided” style. This understanding has previously informed the interpretations of many Precambrian pre-vegetation alluvial successions, but there has been relatively little work regarding Early Palaeozoic alluvial successions laid down prior to and during the initial colonization of the Earth's surface by plants.A comprehensive review of 144 Cambrian to Devonian alluvial successions documented in published literature was combined with original field data from 34 alluvial successions across Europe and North America. The study was designed to identify changes in alluvial style during the period that vegetation was evolving and first colonizing alluvial environments. An increase in mudrock proportion and sandstone maturity is apparent, along with a decrease in overall sand grain size through the Early Palaeozoic. These trends suggest that primitive vegetation cover promoted the production and preservation of muds from the mid Ordovician onwards and increased the residence time of sand-grade sediment in alluvial systems. The compilation also enables the first stratigraphic occurrence of certain vegetation-dependent sedimentary features to be pinpointed and related to the evolution of specific palaeobotanical adaptations. The first markedly heterolithic alluvial sequences appeared at about the same time as the most primitive terrestrial vegetation in the Ordovician, and prolific pedogenic calcite, charcoal and bioturbated floodplain fines first appeared in the rock record at about the same time as vascular-plant macrofossils became abundant in the late Silurian. Lateral accretion sets in channel deposits appeared near the Silurian–Devonian boundary, at or shortly before the appearance of underground rooting systems, and become progressively more abundant in the record during the Devonian, implying a major expansion of meandering rivers as rooted plants stabilized river banks. Coals become abundant after the development of plant arborescence. The analysis suggests that the evolution of embryophytes had a profound effect on fluvial processes and deposits, and this period of landscape evolution must be considered amongst the most significant environmental and geomorphological changes in Earth history, with profound consequences for all aspects of the Earth system.     

The development of slaty cleavage, fleurieu peninsula, south australia

In low grade, biotite-rich metasiltstones and slates from the western side of Fleurieu Peninsula, the slaty cleavage is defined by elongate deformed old biotites and by the coincident elongate dimensions and (001) planes of thin, well aligned new biotites. Histograms of frequency versus (001)-S₁ angle (S₁ defined by aligned thin muscovite used as the reference plane) were determined in thin section for both populations. The old biotites show a symmetrical bimodal distribution of (001) about S₁, with maxima at around 20° either side ofS₁. This distribution, together with the preserved intracrystalline strain, indicates that these old grains deformed largely by slip on (001) with some modification of grain boundaries by diffusive transfer. The new biotite grains are very well aligned (standard deviation 3.8°) and show no sign of mechanical deformation. They have not been mechanically rotated into alignment but must have nucleated and grown in a specific orientation. The proportion of new to old grains increases with metamorphic grade, causing a rapid strengthening of the crystallographic alignment. In slates and phyllites with similar microstructure, the mica fabric determined by X-ray texture goniometry cannot be used as a quantitative measure of the geometry and magnitude of the bulk strain, as the intensity of the crystallographic fabric will be strongly influenced by the proportion of new mica, which is itself greatly affected by the metamorphic grade during slaty cleavage formation.     

A small-scale spatial analysis system for maritime Australia

Within the field of resource and environmental management, the paramount value of a spatial analysis system is as a tool for regionalising a case-area in diverse directed ways, each being useful for (i) increasing scientific understanding of that area (intellectualisation) or (ii) for allocating operational categories (for example, funding categories, regulatory categories) differentially between parts of the case-area (called operations support or policy support). Success in serving these scientific and administrative values depends in turn upon two primary attributes of the spatial analysis system and a larger number of secondary attributes. These primary attributes are (i) the range and quality of geocoded data sets held in store or able to be accessed and (ii) the range of spatial analysis techniques which can be called upon for operating on stored data sets. Secondary attributes influencing a spatial analysis system's value include its accessibility to potential users, its ease of use, the judgment and experience of its users and the quality of its cartographic and other outputs. The present paper is a status report on the Australian Coastal And Marine Resources Information System, CAMRIS, a spatial analysis system developed as a demonstration for Australia. CAMRIS contains or can access raw and value-added data sets which comprehensively cover both terrestrial and marine components of the Australian maritime estate. Onshore, for the immediate coastal strip, data held or accessible include geocoded data on vegetation, geology, landform, wetland and coastline type, land use, climate and population. For coastal drainage basins, data sets include river networks, river flows, wetland attributes, soils, geology, elevation, vegetation, mineral deposits, beach attributes, population and bird distributions. Nearshore data include geocoded data on estuary attributes, island attributes, seagrass beds and marine protected areas. Offshore (oceanic) geocoded data held or accessible include bathymetry, sea surface temperature and salinity/dissolved oxygen profiles, together with a variety of geophysical records including gravity, magnetics, seismic track lines, substrates, waves, winds, storms, tides and cyclones. While raw data are stored as such whenever available, many of these data sets are in value-added form, held perhaps as a surface or choropleth or as a function of primary data items. A range of spatial analysis techniques is routinely available for application to CAMRIS data sets including those within the SPANS, Arc Info, and Idrisi geographic information systems, the S Plus exploratory data analysis package, and specialist in-house packages such as PATN for multivariate positive classification and LUPIS for resource allocation and normative classification. CAMRIS demonstration studies in various stages of completion address: (1) selection of coastal and marine protected areas; (2) identification of priority areas for the management of land-based marine pollution; (3) planning for coastal population growth; and (4) synoptic impacts of climatic change in the coastal zone. Further candidate studies being considered include mariculture prospects and proactive management of oil spills and leaks. An important indicator of success for the CAMRIS project would be for it to be seen as a prototype for a properly-funded multi-agency national maritime (coastal and marine) spatial analysis system. Australia, with one of the worlds largest and most diverse maritime estates and with a small population imposing increasing pressures on that estate, needs powerful policy and operations support tools.     

The Effects of Hermit Crabs on Hydractiniid Hydroids The effects of hermit crabs on hydractiniid hydroids

Abstract. Hermit crab shells are often encrusted with diverse communities of epibionts. To explore the effects of hermit crabs on the interactions of these encrusting species, two species of hydractiniid hydroids, Hydractinia symbiolongicarpus and Podocoryna carnea , were examined in the presence and absence of Pagurus longicarpus hermit crabs. Colonies growing on Littorina littorea snail shells with hermit crab hosts were compared to those growing on shells without crabs. These experiments suggest that hermit crabs variably affect colony polyp number, colony morphology and the outcome of interspecific competition, according to the size and number of crabs; other factors include water temperature, food availability and hydroid clonal genotype. In order to allow image analysis of perturbations of colony morphology, hydroids were grown on glass surfaces both exposed and unexposed to hermit crabs. Relative to colonies growing on unexposed surfaces, colonies growing on exposed surfaces exhibited larger within-colony patches, thus decreasing the total encrusted surface area and polyp number of colonies. Further, on glass surfaces, hermit crabs accelerated the time to the resolution of interspecific competition ( i.e. , the overgrowth of one colony by the other). While a number of factors may contribute to the relative abundance of these encrusting species, under most circumstances P. longicarpus have large effects on hydractiniid hydroids. Mechanisms underlying these effects likely include hydrodynamics and mechanical disturbance.     

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that ²³⁰Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260–267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed ²³⁰Th carried by bottom currents towards the equator (“focusing”). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25–20.1 Ma but is well developed for the interval 8.55–14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P₂O₅ (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10–25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05–14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P₂O₅ anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10–25 Ma.     

Sensitivity of AUV response to variations in hydrodynamic parameters

The sensitivity of the response of a typical AUV to changes in hydrodynamic parameters is examined. The analysis is primarily performed using a computer model of an axi-symmetric vehicle typical of many AUVs in service today. The vehicle used is the Canadian Self-Contained Off-the-shelf Underwater Testbed (C-SCOUT), designed and built by graduate and work term students. The fully nonlinear computer model is based on Newton–Euler equations of motion, and uses the component build-up method to describe the excitation forces. The hydrodynamic parameters are varied in a series of simulations with the computer model; the response being analyzed for specific performance indicators.     

Upper Carboniferous to Lower Permian transgressive–regressive sequences of central Spitsbergen,Arctic Norway

Investigation of the Upper Carboniferous to Lower Permian sedimentary strata of central Spitsbergen shows that this highly cyclic rock succession is composed of four long-term transgressive–regressive cycles. These long-term cycles are themselves composed of stacked higher order cycles. Transgressive phases are characterized by increasing accommodation space, and include a basal transgressive part of marked retrogradation of facies belts and thickening-upward component cycles. Regressive phases are characterized by decreasing accommodation space, displayed by progradation of facies belts, overall shallowing and increased restriction of the depositional environment, influx of coarse terrigenous sediments and increasing evidence of exposure and/or non-deposition. The oldest transgressive–regressive sequence identified, Sequence 1, is of Serpukhovian to Bashkirian age and represents a syn-rift sequence. Also composed of syn-rift sediments is the transgressive–regressive Moscovian to mid-Gzhelian-aged Sequence 2. The late Gzhelian to late Asselian Sequence 3 is mainly a post-rift sequence. The youngest sequence, Sequence 4, is of Sakmarian to possible Artinskian age, and is also composed of post-rift sediments. The individual transgressive–regressive cycles are defined as second-order cycles, based on lithological signatures, lateral extent of bounding unconformities, and the actual time period the cycles span. Local tectonic activity is believed to control to some extent the development of short-term cycles in the syn-rift succession. However, cyclicity within the long-term cycles is mainly controlled by eustatic sea-level fluctuations, and therefore enables them to be correlated to other Circum-Arctic regions. Copyright © 1999 John Wiley & Sons, Ltd.