Effects of copper exposure on the scope for growth of the clam Ruditapes decussatus from southern Portugal

The clam Ruditapes decussatus L. was collected from Ria Formosa, Faro, southern Portugal, and exposed to a sublethal copper concentration of 0.01 mg l⁻¹ for 20 days. Physiological measurements, respiration rates, clearance rates and absorption efficiency, were undertaken initially and after 2, 5, 9, 14 and 20 days and used to calculate Scope for Growth. Copper accumulation rate was calculated through the analysis of copper in the tissues at the same sampling times. The experiment showed two phases. Initially, copper was rapidly accumulated (1.95 μg Cu g⁻¹ dw day⁻¹ in the first 48 h), clearance rates declined markedly (lowest value 13.5% of control) and respiration rates increased (116% of control), resulting in a rapid decline of Scope for Growth, which showed a negative value after 5 days. In the second phase, (from day 9 on), the rate of copper uptake declined to 0.55 μg Cu g⁻¹ day⁻¹ and physiological responses were more stable. After 20 days, copper concentration in the tissues was 38.4 μg Cu g⁻¹ dw (bioconcentration factor 3840). Clearance rates were 50% of control rates and respiration rates were still high, 145% of control rates. Therefore, Scope for Growth and performance of the clams was still greatly affected (ca. 23% of the control values), indicating that though animals partially recovered through detoxifying mechanisms, excess copper caused sustained impairment of physiological functions. This experiment confirms that the physiological energetics approach and the integrated Scope for Growth measurement is a sensitive methodology to detect deviations from normal performance and assess stress at environmental realistic copper concentrations.     

Evidence of fluid inclusion for thermal fluid-bearing hydrocarbon movements in Qiongdongnan Basin, South China Sea

Diagenetic research and inclusion observance indicate that there are seven types of inlcusion in the reservoirs in the Qiongdongnan Basin. Based on the fluorescence color, ratio of gas/liquid, formation temperature, salinity and organic component of fluid inclusions, three events of thermal fluid movement were found, and only the second and third events are relative to hydrocarbon migration and accumulation with the temperatures of 140–150°C and 170–190°C., respectively.The mechanism of gas migration in aqueous phase suggests that the discharging site of thermal fluid is the favourable location for natural gas accumulation. Project supported by the Natlonal Natural Science Foundation of China.     

The sedimentation history of Lake Huron and Georgian Bay: results from analysis of seismic reflection profiles

An extensive seismic reflection profile survey conducted concurrently with a sediment coring program in northern Lake Huron, Georgian Bay, and the North Channel revealed a detailed Holocene lake level history. Seven acoustic sequences were identified in the seismic stratigraphy, and these sequences show great variation in both the character and the spatial distribution of sediment deposition through time. The depths to the acoustically-defined sequence boundaries were digitized from the analog seismic records and merged with Loran-C navigation records from the cruise, yielding a three-dimensional record of the location of each sequence boundary. Thicknesses of the sequences were calculated from these depths, and a minimum-curvature spline surface was fit to the thickness data. These surfaces were used to construct isopach maps which show the trends in thickness of sediment accumulation throughout the lake basins for each of the sequences. ¹⁴C-AMS dates of materials from the cores fixed the dates of the sediment sequence boundaries, allowing sediment accumulation rates to be calculated. The distribution of sedimentation in the basins as shown on the isopach maps allowed assessment of sediment transport and water flow through the basins over time, which when combined with the work of Lewis & Anderson (1989), provides a detailed record of the transport and drainage of water through these basins as the Wisconsinan ice sheet retreated and isostatic rebound opened and closed outlets. Reversals of flow direction through the Straits of Mackinac and through the channels connecting Lake Huron and Georgian Bay and the North Channel are indicated by changes in sediment thickness distributions.     

A radiocarbon-dated gelifluction lobe in the Nachvak Fiord area,northern Labrador,Canada

Radiocarbon dates obtained on organic materials overridden by a gelifluction lobe allow some estimate of past gelifluction rates for a site near sea level in northern Labrador. The calculated mean gelifluction rate for the last 400 years is in the order of 8 mm yr^?1, somewhat higher than the average gelifluction rate described from other locations in the Canadian Arctic. The lobe contains two lithostratigraphic units: an inner diamicton, probably representing a buried gelifluction lobe, overlain by a silt/clay unit which may have been emplaced abruptly as a solifluction sheet. Mean creep rates for these units were in the order of 5 mm yr^?1 and 15 mm yr^?1 respectively. The area is presently subsiding, and transgressive beach material overlies terrestrial organics which are approximately 300 years old.     

Regional variation of mechanical and chemical denudation,upper Colorado River Basin,U.S.A.

The variation of mechanical and chemical denudation is investigated using discharge and sediment yield data from the Upper Colorado River System. Annual precipitation ranges from approximately 150 mm to 1500 mm. Mean specific yield ranges from 0-2 1/s km² ( = 6 mm p a) to 151/s km² ( = 475 mm p a). The hydrological-geomorphological system adjusts itself to these varying climatic conditions; in some areas, however, the effects of lithology or land use seem to override the climatic controls. It is demonstrated that the increase in the absolute and particularly the relative amount of suspended sediment is closely related to a decrease in annual runoff and to an increase in the importance of high magnitude/low frequency events. This indicates that in areas of low annual runoff and high runoff variability, soluble rocks are more resistant than in more humid areas. During high magnitude/low frequency events, suspended sediment concentrations and loads are very high in semiarid areas due to sparse vegetation cover and dominance of direct runoff. Events of moderate magnitude and frequency, which in more humid areas transport most of the dissolved load, seldom occur. The trend towards increasing mechanical denudation is even observed in areas of very low runoff (0-221/s km² = 7 mm p a). The peak of sediment yield in dry areas seems to approximate the point of no runoff very closely. Mechanical and chemical denudation are of equal importance at a runoff of about 300 mm per year.     

A numerical compaction model of overpressuring in shales

A one-dimensional model of sediment compaction is presented to relate pressure, porosity, permeability, and fluid and solid-particle velocities in an evolving sedimentary basin. The burial history of a sedimentary package is followed and incorporated into rate models for diagenetic reactions to predict clay compositions with depth. The governing set of nonlinear, partial differential equations constitutes a moving boundary problem and is solved by a finite difference scheme. Sedimentation rates and a permeability-porosity function for shales are required to implement the model. Additional factors are incorporated to mimic the effect of increased fluid volume generated by dehydration from clay mineral transformations and by thermal expansion. We demonstrate that the major cause of overpressuring in sediments accumulating along passive margins is nonequilibrium compaction. Sedimentation rates and strata permeability are the most important geologic factors in the formation of overpressured zones. Smectite dehydration and aquathermal pressuring play secondary roles in the development and sustenance of overpressures.     

油气充注对成岩作用的影响

油气充注对成岩作用的影响有三个方面 :抑制石英和伊利石的胶结作用、油气中所有机酸对深部孔隙的溶蚀改造作用、油气超压对压实的缓冲作用。英国北海Miller油气藏等的资料显示 ,油气充注较早时 ,油区的石英胶结速率比水区的明显要低 ,石英的胶结丰度比一般预测值低 ,而孔隙度比一般的预测值要高。我国渤海湾盆地东营凹陷油田资料显示 ,无论浅部或深部 ,凡是含油砂岩 ,其长石类及碳酸盐类矿物的溶解都十分强烈 ,次生孔隙很发育 ,而不含油的砂岩 ,其矿物溶解及次生孔隙发育一般较差 ;油层的方解石、白云石含量一般比水层低 ,深层尤为明显。干酪根生成油气时的流体体积增加 ,可大大增加孔隙流体压力 ,产生超压 ,并可传递到储集层 ,因而大大增加对压实作用的抵抗能力。上述三方面实质上都为深部油气成藏改善了储层基础 ,对深部油气勘探具有非常现实的意义。     

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured ¹⁰Be concentrations has been modelled using a χ² inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.     

克拉通盆地基底结构特征及油气差异聚集浅析

克拉通盆地分布广泛，面积巨大，油气资源潜力和富集程度差异性也很大。把世界主要克拉通盆地按照其基底不均一特性划分为4种类型：裂谷拉张型（北美密歇根和伊利诺斯盆地）、拼接缝合型（中国塔里木和俄罗斯东西伯利亚盆地）、褶皱造山型（北美威利斯顿盆地）和稳定结晶型（澳洲卡奔塔里亚湾盆地等）。在对各类盆地深部基底结构和油气富集规律比较分析的基础上，初步认为发育在活动构造基底（裂谷、褶皱带、缝合线）上的克拉通盆地油气资源远远好于稳定结晶基底上形成的盆地，各类盆地的油气丰度排序为：裂谷型＞褶皱型＞拼接型＞稳定结晶型，不同类型的克拉通盆地油气成藏的主控因素也各有差异。