Tasman Geosyncline greenstones and ophiolites   总被引：1，自引：1，他引：0  

K. A. W. Crook  E. Anne Felton 《Australian Journal of Earth Sciences》2013,60(1):117-131

Palaeozoic greenstones lying at the base of stratigraphic sequences or in fault blocks in the Tasman Geosyncline are compared with the Penrose Conference definnition of an ophiolite by using tabulated petrological, structural, and metallogenic data. Of 45 occurrences, only 9 are recognizably ophiolites: 4 are in rift zones adjoining Precambrian continental crust at the ends of the geosyncline; and away from the margins, in that part of the geosyncline most typically of West Pacific‐type, only 5 of the 33 greenstone occurrences are recognizably ophiolites. Ophiolites are rare in the Tasman Geosyncline, in contrast to several Atlantic‐type geosynclines. This may be a characteristic of West Pacific‐type geosynclines in general.

Alpine‐type serpentinites are rather common in the Tasman Geosyncline. The metallogeny of some shows affinities with ophiolites, suggesting a common origin as oceanic crust. Their relative abundance suggests that West Pacific‐type geosynclines, such as the Tasman Geosyncline, may have developed on oceanic crust of unusual composition. Alternatively, it may reflect differences of deformation style between Atlantic‐ and West Pacific‐type geosynclines.

The term ophiolite has been used uncritically in plate tectonic analyses of the Tasman Geosyncline, calling in question the objectivity of these analyses. If objectivity is to be maintained, some indication should be given of the quality of the data used in plate tectonic analyses.  相似文献   

The influence of wind forcing on across-shelf transport in the Florida Keys     

Ned Philip Smith 《Continental Shelf Research》2009

Acoustic Doppler current profiles and current meter data are combined with wind observations to describe the transport of water leaving Florida Bay and moving onto the inner shelf on the Atlantic side of the Florida Keys. A 275-day study in the Long Key Channel reveals strong tidal exchanges, but the average ebb tide volume leaving Florida Bay is 19% greater than the average flood tide volume entering the bay. The long-term net outflow averages 472 m³ s⁻¹. Two studies in shelf waters describe the response to wind forcing during spring and summer months in 2004 and during fall and winter months in 2004–2005. During the spring–summer study, southeasterly winds have a distinct shoreward component, and a two-layer pattern appears. Surface layers move shoreward while near-bottom layers move seaward. During the winter study, the resultant wind direction is parallel to the Keys and to the local isobaths. The entire water column moves in a nearly downwind direction, and across-shelf transport is relatively small. During the summer wet season, Florida Bay water should be warmer, fresher, and thus less dense than Atlantic shelf waters. Ebbing bay water should move onto the shelf as a buoyant plume and be held close to the Keys by southeasterly winds. During the winter dry season, colder and saltier Florida Bay water should leave the tidal channels with relatively high density and be concentrated in the near-bottom layers. But little across-shelf flow occurs with northeasterly winds. The study suggests that seasonally changing wind forcing and hydrographic conditions serve to insulate the reef tract from the impact of low-quality bay water.  相似文献   

异常地层压力声波衰减分析及地层压力地震数据外推反演   总被引：1，自引：0，他引：1       下载免费PDF全文

张冰  符力耘  魏伟  管西竹 《地球物理学报》2014,57(10):3373-3388

澳大利亚西北大陆架卡拉汶盆地含有丰富的油气资源, 但其地质条件复杂, 普遍存在异常地层高压分布,特别是该区区域盖层-中深层巨厚的Muderong页岩层内存在局部异常高压带,给石油钻井带来巨大困难.本文根据卡拉汶盆地北部地区10余口井的实测地层压力资料、声波测井数据和联井地震剖面, 研究该页岩层内异常压力千赫兹尺度声波响应的衰减特征,及其与地层有效压力之间的关联计算模型.通过联井地震数据的井-震相关性分析进行井-震过渡,研究井旁地震数据在异常高压带的衰减特征,及其与地层有效压力之间的关联计算模型,从而实现井震资料联合进行地层压力地震外推反演.研究表明,Muderong页岩层地层有效压力与井中声波速度/阻抗品质因子和井旁地震阻抗品质因子具有良好的正向相关性,根据二者交汇数据拟合经验公式反算得到的各井有效压力结果基本反映出实测有效压力曲线的变化特征.卡拉汶盆地北部地区地震数据具有良好的井-震相关性,地震资料品质相对可靠,确保了声-压相关分析的井-震过渡.最后,通过地震阻抗品质因子与地层有效压力之间的关联计算模型,进行该区异常地层压力地震外推反演,预测结果与钻井证实的异常压力分布特征基本符合.本研究为卡拉汶盆地中深部区域盖层局部异常高压带的地层压力外推反演提供了一种有效途径.  相似文献   

Changes of Paleo-precipitation on the Sunda Shelf Since the Last Glacial Maximum Revealed by Hydrogen and Oxygen Isotopes     

Juan He 《地球科学进展》2017,32(11):1137-1146

The Sunda Shelf, owing to its unique geographical location and roles, has attracted much attention on its changes during the glacial cycle. At present, there is a consensus about the change of temperature in the region, but the reconstruction of paleo precipitation has been disputed. The hydrogen and oxygen isotope records since the last glacial in the Sunda Shelf were collected, combining with other paleo climate record, we roughly divided the precipitation records in the region into the Northern and Southern areas. During the glacial, the precipitation changed little and climate remained moist in the northern area, while precipitation decreased greatly,and the climate became dry in the southern. Difference in the precipitation isotopes between the northern and southern areas might be related to the different controlling factors of the precipitation isotopes in the two areas and large-scale atmospheric circulation in the region. Limited by the collected hydrogen and oxygen records, the precise mechanism of division in regional hydrological changes of the region still needs more work to confirm.  相似文献   

Fast accurate computation of shelf waves for arbitrary depth profiles     

G. Kaoullas  E.R. Johnson 《Continental Shelf Research》2010

A simple fast and straightforward, accurate numerical method is proposed for calculating barotropic non-divergent continental shelf waves, above general shelf profiles. The problem is reduced to a linear eigenvalue problem for the along-stream wavenumber k, that can be solved directly with exponential accuracy, using any standard linear eigenvalue package.  相似文献   

OSL chronology of a sedimentary sequence from the inner-shelf of the East China Sea and its implication on post-glacial deposition history     

《Quaternary Geochronology》2015

Sedimentary records from the inner-shelf of the East China Sea (ECS) are unique for the reconstruction of post-glacial palaeoclimate and sea-level changes. So far, the chronology of sediment succession from this region has mainly been based on radiocarbon dating, which might be problematic due to reworked deposition or old carbon contamination. In this study we tested the applicability of optically stimulated luminescence (OSL) dating to a drilling core (ECS-DZ1) taken from the northern ESC. A total of 20 OSL samples and two radiocarbon samples were collected from the upper 58 m of this core. The results indicate the likely sufficient reset of OSL signal of fine-grained (4–11 μm) quartz before burial, and thus reliable chronology for the studied core sediments. For one sample, however, the extracted coarse-grained (100–200 μm) quartz overestimated the deposition age significantly, presumably resulting from partial bleaching prior to deposition. The fine-grained quartz ages are generally consistent with the stratigraphical order, and the reliability of these OSL ages are further validated by two selective robust ¹⁴C dates. The chronological framework of core ECS-DZ1 reveals striking sedimentation-rate changes. By comparison with other chronostratigraphical records, we infer that post-glacial deposition history (since ∼15 ka) of the study site is likely related to regional sea-level rise and delta-estuary environment evolution, as well as strengthened human activities and/or coastal currents.  相似文献   

Sandwaves on the Southeast Vietnam Shelf recorded by high resolution seismic profiles: formation and mechanism   总被引：1，自引：0，他引：1  

Viet Dung Bui  Alex Schimanski  Karl Stattegger  Phach Van Phung  The Tiep Nguyen  Tien Hai Nguyen  Trung Thanh Nguyen  Truong Thanh Phi 《Frontiers of Earth Science》2009,3(1):9-20

The application of high resolution seismic data using boomer sound source has revealed a wide distribution of large-scale bedforms (sandwaves) on the Southeast Vietnam continental shelf. Bedforms that are a few meters high in wave height and hundreds of meters long in wavelength are primarily developed in the inner shelf (20–40 m) and considered to be formed under the present-day marine hydrodynamic conditions. Those bedforms developed in the deeper water (120 m) of the northernmost part of the continent can be interpreted as the relict morphological features formed during the latest sea-level lowstand of the late Pleistocene period. Two sediment transport paths have been identified on the basis of the bedform’s leeward orientation: northeast-southwest (along-shore) and north-south (cross-shore). A quantitative bottom current map is constructed from sandwave dimensions, surface sediments and measurement data. The strongest current velocities that gradually decrease toward the southwest are indicated by large sandwaves in the north (field B). Water depth, surficial sediment composition and bottom current are three factors that control the development of bedforms.  相似文献   

Setting sediment quality guidelines: a simple yet effective method     

Bjørgesaeter A  Gray JS 《Marine pollution bulletin》2008,57(6-12):221-235

Deriving sediment quality guidelines (SQGs) for marine sediments is a difficult task. It will often be a trade off between reproducibility and relevance. One of the fundamental questions in ecotoxicology is to decide what one should measure to detect response in ecosystems exposed to human disturbance. In this paper we use field data to estimate threshold levels eliciting effects on soft bottom macrobenthos collected at different sediment types and depths on the Norwegian Continental Shelf and test these against natural levels occurring levels in reference conditions. SQGs are presented from multivariate analyses based on 121 gradients (represented with Ba, THC, Cd, Cu, Pb and Zn) incorporating more than 2000 species. Clear clusters with slightly disturbed communities related to contamination loadings were evident in 35% of the gradients. We found large variations in naturally occurring contamination concentrations and in the threshold levels electing effects on the fauna at different sediment types and depths. For example, an increase in depth of only 100 m can triple the Cu and Zn concentrations that elicit effects. Lowest background and threshold levels were found in shallow, sandy sediment. Our results suggest that current SQGs are too high. We hypothesised that setting a SQG of 4-times background concentrations will give sufficient protection for the fauna from metal contamination. The overall background concentration eliciting effects on metal was 3.6x.  相似文献   

Nutrient availability in support of Karenia brevis blooms on the central West Florida Shelf: What keeps Karenia blooming?     

Gabriel A. Vargo  Cynthia A. Heil  Kent A. Fanning  L. Kellie Dixon  Merrie Beth Neely  Kristen Lester  Danylle Ault  Susan Murasko  Julie Havens  John Walsh  Steven Bell 《Continental Shelf Research》2008

Identifying nutrient sources, primarily nitrogen (N) and phosphorus (P), sufficient to support high biomass blooms of the red tide dinoflagellate, Karenia brevis, has remained problematic. The West Florida Shelf is oligotrophic, yet populations >10⁶ cells L⁻¹ frequently occur and blooms can persist for months. Here we examine the magnitude and variety of sources for N and P that are available to support blooms. Annual average in situ or background concentrations of inorganic N in the region where blooms occur range 0.02–0.2 μM while inorganic P ranges 0.025–0.24 μM. Such concentrations would be sufficient to support the growth of populations up to ∼3×10⁴ cells L⁻¹ with at least a 1 d turnover rate. Organic N concentrations average 1–2 orders of magnitude greater than inorganic N, 8–14 μM while organic P concentrations average 0.2–0.5 μM. Concentrations of organic N are sufficient to support blooms >10⁵ cells L⁻¹ but the extent to which this complex mixture of N species is utilizable is unknown. Other sources of nutrients included in our analysis are aerial deposition, estuarine flux, benthic flux, zooplankton excretion, N₂-fixation, and subsequent release of organic and inorganic N by Trichodesmium spp., and release of N and P from dead and decaying fish killed by the blooms. Inputs based on atmospheric deposition, benthic flux, and N₂-fixation, were minor contributors to the flux required to support growth of populations >2.6×10⁴ cells L⁻¹. N and P from decaying fish could theoretically maintain populations at moderate concentrations but insufficient data on the flux and subsequent mixing rates does not allow us to calculate average values. Zooplankton excretion rates, based on measured zooplankton population estimates and excretion rates could also supply all of the N and P required to support populations of 10⁵ and 10⁶ cells L⁻¹, respectively, but excretion is considered as “regenerated” nutrient input and can only maintain biomass rather than contribute to “new” biomass. The combined estuarine flux from Tampa Bay, Charlotte Harbor, and the Caloosahatchee River can supply a varying, but at times significant level of N and P to meet growth and photosynthesis requirements for populations of approximately 10⁵ cells L⁻¹ or below. Estimates of remineralization of dead fish could supply a significant proportion of bloom maintenance requirements but the rate of supply must still be determined. Overall, a combination of sources is required to maintain populations >10⁶ cells L⁻¹.  相似文献   

Variability of the subtropical shelf front off eastern South America: Winter 2003 and summer 2004     

Alberto R. Piola  Osmar O. Möller Jr.  Raúl A. Guerrero  Edmo J.D. Campos 《Continental Shelf Research》2008

Hydrographic data collected during surveys carried out in austral winter 2003 and summer 2004 are used to analyze the distributions of temperature (T) and salinity (S) over the continental shelf and slope of eastern South America between 27°S and 39°S. The water mass structure and the characteristics of the transition between subantarctic and subtropical shelf water (STSW), referred to as the subtropical shelf front (STSF), as revealed by the vertical structure of temperature and salinity are discussed. During both surveys, the front intensifies downward and extends southwestward from the near coastal zone at 33°S to the shelf break at 36°S. In austral winter subantarctic shelf water (SASW), derived from the northern Patagonia shelf, forms a vertically coherent cold wedge of low salinity waters that locally separate the outer shelf STSW from the fresher inner shelf Plata Plume Water (PPW) derived from the Río de la Plata. Winter T–S diagrams and cross-shelf T and S distributions indicate that mixtures of PPW and tropical water only occur beyond the northernmost extent of pure SASW, and form STSW and an inverted thermocline characteristic of this region. In summer 2004, dilution of Tropical water (TW) occurs at two distinct levels: a warm near surface layer, associated to PPW–TW mixtures, similar to but significantly warmer than winter STSW, and a colder (T∼16 °C) salinity minimum layer at 40–50 m depth, created by SASW–STSW mixtures across the STSF. In winter, the salinity distribution controls the density structure creating a cross-shore density gradient, which prevents isopycnal mixing across the STSF. Temperature stratification in summer induces a sharp pycnocline providing cross-shelf isopycnal connections across the STSF. Cooling and freshening of the upper layer observed at stations collected along the western edge of the Brazil Current suggest offshore export of shelf waters. Low T and S filaments, evident along the shelf break in the winter data, suggest that submesoscale eddies may enhance the property exchange across the shelf break. These observations suggest that as the subsurface shelf waters converge at the STSF, they flow southward along the front and are expelled offshore, primarily along the front axis.  相似文献