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Outer Shelf (outer + shelf)
Selected AbstractsIchthyoplankton-based spawning dynamics of blue mackerel (Scomber australasicus) in south-eastern Australia: links to the East Australian CurrentFISHERIES OCEANOGRAPHY, Issue 4 2008FRANCISCO J. NEIRA Abstract We describe findings of three ichthyoplankton surveys undertaken along south-eastern Australia during spring (October 2002, 2003) and winter (July 2004) to examine spawning habitat and dynamics of blue mackerel (Scomber australasicus). Surveys covered ,860 nautical miles between southern Queensland (Qld; 24.6°S) and southern New South Wales (NSW; 41.7°S), and were mainly centred on the outer shelf including the shelf break. Egg identifications were verified applying mtDNA barcoding techniques. Eggs (n = 2971) and larvae (n = 727; 94% preflexion) occurred both in spring and winter, and were confined to 25.0,34.6°S. Greatest abundances (numbers per 10 m2) of eggs (1214,7390) and larvae (437,1172) occurred within 10 nm shoreward from the break in northern NSW. Quotient analyses on egg abundances revealed that spawning is closely linked to a combination of bathymetric and hydrographic factors, with the outer shelf as preferred spawning area, in waters 100,125 m deep with mean temperatures of 19,20°C. Eggs and larvae in spring occurred in waters of the East Australian Current (EAC; 20.6,22.3°C) and mixed (MIX; 18.5,19.8°C) waters, with none occurring further south in the Tasman Sea (TAS; 16.0,17.0°C). Results indicate that at least some of the south-eastern Australian blue mackerel stock spawns during winter-spring between southern Qld and northern NSW, and that no spawning takes place south of 34.6°S due to low temperatures (<17°C). Spawning is linked to the EAC intrusion, which also facilitates the southward transport of eggs and larvae. Since spring peak egg abundances came from where the EAC deflects offshore, eggs and larvae are possibly being advected eastwards along this deflection front. This proposition is discussed based on recent data on blue mackerel larvae found apparently entrained along the Tasman Front. [source] Silicified Upper Ordovician trilobites from Pai-Khoi, Arctic RussiaPALAEONTOLOGY, Issue 6 2009ROBERT M. OWENS Abstract:, A collection of silicified trilobites extracted from samples obtained by F. Nansen from the Upper Ordovician of Khabarovo, Pai Khoi, Russian Arctic is dominated by two new species of the proetide Lasarchopyge, a genus known hitherto only from the Argentine Precordillera. Comparison of Lasarchopyge with Scharyia reveals a range of common characters that support inclusion of both genera in the same family. The rest of the fauna comprises a metagnostid (Trinodus elspethi), an asaphid (Isotelus sp.), two remopleuridids (Remopleurides cf. caelatus and R. sp. nov. A), an aulacopleurid (Harpidella triloba), a lichid and an odontopleurid (Apianurus cf. barbatus), the last two being represented by very fragmentary material. T. elspethi, H. triloba, R. cf. caelatus and A. cf. barbatus are common to or closely resemble taxa from the Edinburg Formation, Virginia. Closely related taxa are present also in the Esbataottine Formation, NW Territories, Canada, and in the Albany Group, Girvan district, Scotland. All of these occurrences are of early Caradoc (Sandbian) age, and most lay at palaeolatitudes of 20°,30° south; all are interpreted as having been deposited on the outer shelf, which is consistent with their distribution. [source] EARLY ORDOVICIAN (ARENIG) TRILOBITE PALAEOECOLOGY AND PALAEOBIOGEOGRAPHY OF THE SOUTH CHINA PLATEPALAEONTOLOGY, Issue 3 2005SAMUEL T. TURVEY Abstract:, Faunal composition of South Chinese Arenig benthic trilobite associations is investigated using the multivariate techniques of TWINSPAN, DCA and seriation. Eight fairly distinct benthic associations can be differentiated, organized primarily along a palaeobathymetrical gradient across the Yangtze Platform in southern Shaanxi and western Hubei and the Jiangnan Transitional Belt in northern Hunan: the Taihungshania, Neseuretus, Trinucleid and Asaphid- Pseudocalymene associations (shallow shelf), the Asaphid-Raphiophorid and Nileid-Asaphid associations (< 100 m outer shelf), the Nileid-Illaenid Association (deep outer shelf carbonates) and the Pseudopetigurus Association (deep outer shelf clastics). The highest levels of diversity are displayed by the Asaphid-Raphiophorid Association of western Hubei. Investigation of the biogeographical affinities of this fauna indicates that South China is biogeographically closest to the other Chinese geotectonic units, and displays strong faunal connections to other central and eastern Asian regions as well as to Tethyan and South American regions. Subdivision of the South Chinese trilobite fauna into different depth zones shows a statistically significant correlation between increasing water depth and increasing faunal cosmopolitanism, although taxa endemic to China or Gondwana also occur even in slope faunas. The results of this biogeographical analysis are consistent with a tropical or subtropical peri-Gondwanan association of South China with other Asian terranes. [source] Late Holocene dispersal and accumulation of terrigenous sediment on Poverty Shelf, New ZealandBASIN RESEARCH, Issue 2 2009A. J. Kettner ABSTRACT We use coupled numerical models (HydroTrend and SedFlux) to investigate the dispersal and accumulation of sediment on Poverty Shelf, North Island, New Zealand, during the past 3 kyr. In this timeframe, we estimate that the Waipaoa River system delivered ,10 Gt of sediment to Poverty Shelf, 5,10% of which was transported to the outer shelf and continental slope. The domain of the two-dimensional model (SedFlux) is representative of a 30 km traverse across the shelf. Comparing the model output with seismic reflection data and a core obtained from the middle shelf shows that, without extensively modifying the governing equations or imposing unrealistic conditions on the model domain, it is possible to replicate the geometry, grain size and accumulation rate of the late Holocene mud deposit. The replicate depositional record responds to naturally and anthropogenically induced vegetation disturbance, as well as to storms forced by long-period climatic events simulated entirely within the model domain. The model output also suggests that long-term fluctuations in the amount and caliber of river sediment discharge, promoted by wholesale changes in the catchment environment, may be translated directly to the shelf depositional record, whereas short-term fluctuations conditioned by event magnitude and frequency are not. Thus on Poverty Shelf, as well as in depocenters on other active continental margins which retain a much smaller proportion of the terrigeneous sediment delivered to them, flood-generated event beds are not commonplace features in the high-resolution sedimentary record. This is because the shelf sedimentary record is influenced more by the energy available to the coastal ocean which helps keep the sediment in suspension and facilitates its dispersal, than by basin hydrometeorology which determines the turbidity and velocity of the river plume. [source] Cenozoic stratigraphy and subsidence history of the South China Sea margin in the Taiwan regionBASIN RESEARCH, Issue 4 2003A. T. Lin Seismic reflection profiles and well data are used to determine the Cenozoic stratigraphic and tectonic development of the northern margin of the South China Sea. In the Taiwan region, this margin evolved from a Palaeogene rift to a latest Miocene,Recent foreland basin. This evolution is related to the opening of the South China Sea and its subsequent partial closure by the Taiwan orogeny. Seismic data, together with the subsidence analysis of deep wells, show that during rifting (,58,37 Ma), lithospheric extension occurred simultaneously in discrete rift belts. These belts form a >200 km wide rift zone and are associated with a stretching factor, ,, in the range ,1.4,1.6. By ,37 Ma, the focus of rifting shifted to the present-day continent,ocean boundary off southern Taiwan, which led to continental rupture and initial seafloor spreading of the South China Sea at ,30 Ma. Intense rifting during the rift,drift transition (,37,30 Ma) may have induced a transient, small-scale mantle convection beneath the rift. The coeval crustal uplift (Oligocene uplift) of the previously rifted margin, which led to erosion and development of the breakup unconformity, was most likely caused by the induced convection. Oligocene uplift was followed by rapid, early post-breakup subsidence (,30,18 Ma) possibly as the inferred induced convection abated following initial seafloor spreading. Rapid subsidence of the inner margin is interpreted as thermally controlled subsidence, whereas rapid subsidence in the outer shelf of the outer margin was accompanied by fault activity during the interval ,30,21 Ma. This extension in the outer margin (,,1.5) is manifested in the Tainan Basin, which formed on top of the deeply eroded Mesozoic basement. During the interval ,21,12.5 Ma, the entire margin experienced broad thermal subsidence. It was not until ,12.5 Ma that rifting resumed, being especially active in the Tainan Basin (,,1.1). Rifting ceased at ,6.5 Ma due to the orogeny caused by the overthrusting of the Luzon volcanic arc. The Taiwan orogeny created a foreland basin by loading and flexing the underlying rifted margin. The foreland flexure inherited the mechanical and thermal properties of the underlying rifted margin, thereby dividing the basin into north and south segments. The north segment developed on a lithosphere where the major rift/thermal event occurred ,58,30 Ma, and this segment shows minor normal faulting related to lithospheric flexure. In contrast, the south segment developed on a lithosphere, which experienced two more recent rift/thermal events during ,30,21 and ,12.5,6.5 Ma. The basal foreland surface of the south segment is highly faulted, especially along the previous northern rifted flank, thereby creating a deeper foreland flexure that trends obliquely to the strike of the orogen. [source] | ||||||||||