Combined flow origin of edgewise intraclast conglomerates: Sellick Hill Formation (Lower Cambrian), South Australia

Unusually thick, coarse grained edgewise intraclast conglomerates occur at eight or more horizons within subtidal nodular and ribbon bedded wackestones and packstones of the Lower Cambrian Sellick Hill Formation, South Australia. The intraclast beds are flat based and laterally discontinuous, forming bar-like structures that must have exhibited bathymetric relief of as much as 1 m. The internal fabrics of these beds are variable. Thinner beds are dominated by flat-lying intraclasts; thicker beds contain both chaotic, randomly oriented, steeply inclined intraclasts and clusters of fan-shaped, vertically stacked edgewise intraclasts. The Sellick Hill Formation intraclast conglomerates are inferred to have been formed by intense, storm-generated combined flows on a broad, subtidal carbonate ramp. Superimposition of wave-induced oscillatory motions on geostrophic bottom flows during large storms generates short-lived, but exceptionally high instantaneous shear stresses in the bottom boundary layer. Entrainment of the relatively large intraclasts occurs through sliding, rather than pivoting. Edgewise fabrics are a product of asymmetric acceleration and deceleration of intraclasts during passage of waves and the chaotic nature of collisions between intraclasts moving within the boundary layer. Collisions between intraclasts impart a rotating moment, causing intraclasts to tip up during maximum fluid shear stress. Lodgement or packing of clasts in vertical or steeply inclined positions occurs within scours, where intraclasts can wedge between other vertically inclined clasts, or where intraclasts are pinned in steep orientations by collisions with shallowly inclined intraclasts. Differential erosional resistance of the intraclast deposits probably led to the development of sharp lateral changes in thickness. The Sellick Hill Formation intraclast conglomerates record erosion and reworking of subtidal, subfairweather wave base environments by exceptionally intense and presumably rare storm flows. The intraclast horizons represent a substantial loss in stratigraphic resolution due to widespread erosion of the ramp.     

A LIMITED-LENGTH-SCALE k-ε MODEL FOR THE NEUTRAL AND STABLY-STRATIFIED ATMOSPHERIC BOUNDARY LAYER

Analytical and numerical models of the neutral and stably-stratifiedatmospheric boundary layer are reviewed. Theoretical arguments andcomputational models suggest that a quasi-steady state is attainable in aboundary layer cooled from below and it is shown how this may be incorporatedwithin a time-steady, one-dimensional model. A new length-scale-limitedk- model is proposed for flows where a global maximum mixing length isimposed by the finite boundary-layer depth or, in stably-stratifiedconditions, by the Obukhov length, whilst still reducing to a form consistentwith the logarithmic law in the surface layer. Simulations compare favourablywith data from the Leipzig experiment and from Cardington airfield inEngland.     

Holocene reef sequences and geochemistry, Britomart Reef, central Great Barrier Reef, Australia

Holocene reef development was investigated by coring on Britomart Reef, a mid-shelf reef, 23 km long and 8 km wide situated 120 km north of Townsville in the central Great Barrier Reef (GBR). Two holes were drilled, Britomart 1 on a lagoon patch reef, and Britomart 2 on the windward reef crest. The Holocene reef (25·5 m) is the thickest yet recorded in the GBR and overlies an uneven substrate of weathered Pleistocene limestone. Mineralogical and geochemical analyses show that magnesian calcite and aragonite were converted to low Mg-calcite below the Holocene-Pleistocene disconformity. Corals above the interface have 7500–8500 ppm Sr, but 1650–1500 ppm just below it, decreasing to 400–800 ppm downwards. The intermediate Sr values could be due to partial replacement of aragonite by calcite or higher original Sr content in the corals. Three units are recognized in the Holocene: (1) coral boundstone unit, (2) coral framestone unit, and (3) coral rudstone unit. The coral boundstone unit forms the top 5 m of both cores and is algal-bound coral rubble similar to the present reef top. The coral framestone unit is composed of massive head corals Diploastrea heliopora and Porites sp., and is currently forming in patch reefs situated in the lagoon and along the reef front. The coral rudstone unit comprises coral rudstone and floatstone with unabraded, and unbound, coral clasts in muddy matrix. This matrix may be up to 30% sponge chips. Radiocarbon dating indicates the reef grew more rapidly under the lagoon than under the reef front from 7000 to 5000 yr BP. The rate of reef growth matched existing estimates of sea-level rise, but lagged approximately 1000 years (5–10 m) behind it. Most of the reef mass accumulated between 8500 and 5000 yr BP as a mound of debris, perhaps stabilized by seagrasses or algae. Accretion of the reef top in a windward direction between 5000 and 3000 yr BP created the present, steep reef-front profile.     

Coherent slumping of early postglacial lake sediments at Hall Lake, Ontario, Canada

Cores of organic postglacial sediment from Hall Lake, southern Ontario, Canada, are described. The laminated, calcareous sediments deposited between 9,000 and 8,000 B.P. have coherently slumped into the deep part of the lake, causing overturning and replication of parts of the sequence. This process may be considered as a mechanism for sediment focusing, since it involves reworking of marginal sediments into deeper areas. Unlike previously described mechanisms, it may be a source of error in the interpretation of diagrams of pollen percentages as well as accumulation rates. The slumping has only been recognized through the distortion of the laminae. It might not be possible to recognize slumping in unstratified sequences.     

Stegosaur tracks and the persistence of facies — the Lower Cretaceous of Western Australia

Sometimes between January and June 1996, the only known stegosaur tracks were stolen from Broome in north-western Australia (Fig. 1). Vandalism or loss of any type material is always to be lamented, yet there is good cause to suspect that the trackmaker at Broome was not a stegosaur. The reasons why this should be so relate to some of the factors involved in the formation of dinosaur trace fossils and the difficulties encountered in their interpretation. The stratigraphy at Broome is notable for preserving evidence of potential Wealden-type deposition in Australia.     

The ice-dammed lakes of Ossian Sarsfjellet (Svalbard): their geomorphology and significance

The tidewater glacier complex of Kongsvegen/Kronebreen, at the head of Kongsfjorden in north-west Spitsbergen, has advanced rapidly several times since its Neoglacial maximum. Two such advances, 1869 and 1948, are well constrained in time and space and are widely interpreted as glacier surges. During the 1869 advance an ice-dammed lake formed on the western side of Ossian Sarsfjellet. This ice-dammed lake is associated with a thrust moraine complex. Four lake levels are identified, two of which are associated with rock-cut shorelines implying a degree of lake stability. The history of this lake, the nature of the ice dam and its relationship to the thrust moraine complex are discussed. The lake history spanning 28 to 35 years is used to assess the ice-marginal dynamics of the Kongsvegen/Kronebreen glacier. It is concluded that, contrary to previous suggestions, the rapid advance of this tidewater glacier may simply be an example of a non-climatic ice-marginal fluctuation, of the type common to tidewater glacier, as opposed to a glacier surge. A second ice-dammed lake, to the east of Ossian Sarsfjellet, formed sometime after 1869 as the ice retreated, and still exists today. This largely supraglacial lake is associated with a very different geomorphological assemblage, which has a poor long-term preservation potential. The geomorphological characteristics of the two lakes on Ossian Sarsfjellet are compared and used to discuss the problems associated with the recognition of ice-dammed lakes within the Pleistocene record. On the basis of the evidence presented here, ice-dammed lakes may be more common during deglaciation than currently suggested.     

Regional dynamics in the globalising wine industry: the case of Marlborough, New Zealand

The rapid expansion of the New Zealand wine industry has rested largely on a specific wine commodity form, Marlborough Sauvignon Blanc. Global demand for a specialised product has provided the impetus for substantial development at the regional level, an increasingly complex industry structure, and for the intrusion of international capital. This paper explores the contests and relations within the industry through attention to the commodity's value-added chain, wherein recent developments are interpreted as a contest over the brand rents. The contemporary situation therefore may be explained through overlapping organisational and geographic framings of these relations: producer versus buyer-driven dynamics; regional–national and global interests; and inter- and intra-corporate strategies. The commercial contest for control of the region-varietal commodity reveals some paradoxical outcomes in which the region is reaffirmed as a site of investment in an evidently globalised industry, and the significance of who controls what fraction of the value chain is re-asserted.