Benthic foraminifera and bottom water evolution in the middle-southern Okinawa Trough during the last 18 ka

A piston sediment core E017 from the middle-southern Okinawa Trough was investigated. A preliminary study of the deep-water evolution since 18 cal. ka BP was performed based on the quantitative census data of benthic foraminiferal fauna, together with planktonic foraminiferal oxygen and carbon isotope, AMS(14)C dating, and the previous results achieved in the southern Okinawa Trough. The result shows that the benthic fauna was dominated by Bulimina aculeata (d'Orbigny), Uvigerina peregrina (Cushman), Hispid Uvigerina and Uvigerina dirupta (Todd) during the glaciation-deglaciation before 9.2 cal. ka BP, while Epistominella exigua (Brady), Pullenia bulloides (d'Orbigny), Cibicidoides hyalina (Hofker), Sphaeroidina bulloides (d'Orbigny) and Globocassidulina subglobosa (Brady) predominated the fauna in the post-glacial period after 9.2 cal. ka BP. The benthic foraminifera accumulation rate (BFAR), paleoproductivity estimates and benthic foraminiferal assemblage conformably indicate that surface water paleoproductivity and organic matter flux during the glaciation-deglaciation were higher than those of the post-glacial period in the middle-southern Okinawa Trough, and gradually enhanced from the southern to the central Okinawa Trough during the glaciation-deglaciation, which could be caused by the discrepancy of the terrigenous nutrients supply. High abundances of E exigua, an indicator of pulsed organic matter input, after 9.2 cal. ka. BP may indicate that the intensity of seasonally riverine pulsed flux during the post-glacial period was stronger than that of the glaciation-deglaciation period, and the seasonal influx in the central trough might be stronger than in the south. The temporal distributions of the typical species indicating bottom water oxygen content and ventilation condition show that the ventilation of the bottom water during the post-glacial period is more active than the glaciation-deglaciation, which reflects that the evolution of the intermediate and deep waters of the northwestern Pacific during the last glaciation has no evident influence on the deep-water of the middle-southern Okinawa Trough. Additionally, the variations in agglutinated benthic foraminiferal abundance and other carbonate dissolution proxies indicate that carbonate dissolution gradually increased since the last 18 ka in the Okinawa Trough and rapidly enhanced at 9.2 cal. ka BP. The modern shallow carbonate lysocline could form at 3 cal. ka BP.

Paleoceanographic records in the sedimentary cores from the middle Okinawa Trough

Two gravity piston cores (Cores 155 and 18) involved in this study were collected from the middle Okinawa Trough. Stratigraphy of the two cores was divided and classified based on the features of planktonic foraminifera oxygen isotope changes together with depositional sequence, millennium-scale climatic event comparison, carbonate cycles and AMS(14)C dating. Some paleoclimatic information contained in sediments of these cores was extracted to discuss the paleoclimatic change rules and the short-time scale events presented in interglacial period. Analysis on the variation of oxygen isotope values in stage two shows that the middle part of the Okinawa Trough may have been affected by fresh water from the Yellow River and the Yangtze River during the Last Glacial Maximum (LGM). The oxygen isotope value oscillating ranges of the cores have verified that the marginal sea has an amplifying effect on climate changes. The delta(13)C of benthic foraminifera Uvigerina was lighter in the glacial period than that in the interglacial period, which indicates that the Paleo-Kuroshio's main stream moved eastward and its influence area decreased. According to the temperature difference during the "YD" period existing in Core 180 and other data, we can reach the conclusion that the climatic changes in the middle Okinawa Trough area were controlled by global climatic changes, but some regional factors had also considerable influence on the climate changes. Some results in this paper support Fairbanks's point that the "YD" event was a brief stagnation of sea level rising during the global warming up procession. Moreover, the falling of sea level in the glacial period weakened the exchange between the bottom water of the Okinawa Trough and the deep water of the northwestern Pacific Ocean and resulted in low oxygen state of bottom water in this area. These procedures are the reasons for carbonate cycle in the Okinawa Trough area being consistent with the "Atlantic type" carbonate cycle.

Paleoenvironmental change in the middle Okinawa Trough since the last deglaciation: Evidence from the sedimentation rate and planktonic foraminiferal record

Well-dated, high-resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores, A7 and E017, in the middle Okinawa Trough reveal strong and rapid millennial-scale climate changes since similar to 18 to 17 thousand years before present (kyr B.P.). Sedimentation rate shows a sudden drop at similar to 11.2 cal. kyr B.P. due to a rapid rise of sea level after the Younger Dryas (YD) and consequently submergence of the large continental shelf on the East China Sea (ECS) and the retreat of the estuary providing sediment to the basin. During the last deglaciation, the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly, consistent with the timing of sea surface temperature (SST) variations determined from Mg/Ca measurements of planktonic foraminifera from one of the two cores. These fluctuations are coeval with climate variation recorded in the Greenland ice cores and North Atlantic sediments, namely Heinrich event 1 (H1), Bolling-Allerod (B/A) and YD events. At about 9.4 kyr B.P., a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the Kuroshio Current in the Okinawa Trough, which was synchronous with a rapid sea-level rise at 9.5-9.2 kyr B.P. in the ECS, Yellow Sea (YS) and South China Sea (SCS). The abundance of planktonic foraminiferal species, together with Mg/Ca based SST, exhibits millennial-scale oscillations during the Holocene, with 7 cold events (at about 1.7, 2.3-4.6, 6.2, 7.3, 8.2, 9.6, 10.6 cal. kyr BP) superimposed on a Holocene warming trend. This Holocene trend, together with centennial-scale SST variations superimposed on the last deglacial trend, suggests that both high and low latitude influences affected the climatology of the Okinawa Trough. (c) 2006 Elsevier B.V. All rights reserved.

Seismic profiles across the middle Tan-Lu fault zone in Laizhou Bay, Bohai Sea, eastern China

The stratigraphic architecture, structure and Cenozoic tectonic evolution of the Tan-Lu fault zone in Laizhou Bay, eastern China, are analyzed based on interpretations of 31 new 2D seismic lines across Laizhou Bay. Cenozoic strata in the study area are divided into two layers separated by a prominent and widespread unconformity. The upper sedimentary layer is made up of Neogene and Quaternary fluvial and marine sediments, while the lower layer consists of Paleogene lacustrine and fluvial facies. In terms of tectonics, the sediments beneath the unconformity can be divided into four main structural units: the west depression, central uplift, east depression and Ludong uplift. The two branches of the middle Tan-Lu fault zone differ in their geometry and offset: the east branch fault is a steeply dipping S-shaped strike-slip fault that cuts acoustic basement at depths greater than 8 km, whereas the west branch fault is a relatively shallow normal fault. The Tan-Lu fault zone is the key fault in the study area, having controlled its Cenozoic evolution. Based on balanced cross-sections constructed along transverse seismic line 99.8 and longitudinal seismic line 699.0, the Cenozoic evolution of the middle Tan-Lu fault zone is divided into three stages: Paleocene-Eocene transtension, Oligocene-Early Miocene transpression and Middle Miocene to present-day stable subsidence. The reasons for the contrasting tectonic features of the two branch faults and the timing of the change from transtension to transpression are discussed. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.

Sea surface temperature reconstruction for the middle Okinawa Trough during the last glacial-interglacial cycle using C-37 unsaturated alkenones

C-37 unsaturated alkenones were analyzed on a core retrieved from the middle Okinawa Trough. The calculated U-37(K') displays a trend generally parallel with those of the oxygen isotopic compositions of two planktonic foraminiferal species, Neogloboquadrina dutertrei and Globigerinoides sacculifer, suggesting that in this region, SST has varied in phase with global ice volume change since the last glacial -interglacial cycle. The U-37(K')-derived SST ranged from ca. 24.0 to 27.5 degrees C, with the highest value 27.5 degrees C occurring in marine isotope stage 5 and the lowest similar to 24.0 degrees C in marine isotope stage 2. This trend is consistent with the continental records from the East Asian monsoon domain and the marine records from the Equatorial Pacific. The deglacial increase of the U-37(K')-derived SST is similar to 2.4 degrees C from the Last Glacial Maximum to the Holocene. (c) 2007 Elsevier B.V. All rights reserved.

南海大陆边缘地壳结构与盆地形成机制--以珠江口－琼东南盆地为例

South China Sea is located in the convergence of Eurasian plate, the Pacific Ocean plate and Indian Ocean-Australia plate. The total area is about 3,500,000 km2, the geologic structure is complicated, and the structure line cut off reciprocal is the marginal sea taking form by that the seafloor spreads during the middle Oligocene. South China Sea continental margin have developed more than 10 large oil-gas bearing basins and a number of medium-small sized basins. These basins contain abundant mineral resources such as oil & gas. The marginal deepwater area in the north part of South China Sea has become our country’s strategic energy prospecting frontier. The deepwater area of Zhujiangkou and Qiongdongnan basins is the research target in this thesis. The thesis studied deep structure and the earth dynamics of the north part of South China Sea margin, and these researches provide scientific basis for oil-gas resources strategic investigation and valuation in deepwater sea area of north part slope of South China Sea. In order to develop the research of rebuilding velocities and density architecture of earth shell in region of interest, in marginal deepwater area in the north part of South China, we adopted 14 long-cable seismic reflection profile data of 3556.41 kilometers in total, the gravity measurement data along profiles (3851.44 kilometers in total), the magnetic observation along profiles (3838.4 kilometers in total) and depth measurement along profile, the logging data of 11 wells in project, the interpreted fault parameter and preexisting geologic and geophysical research achievement. This thesis has carried out concretely studying research as follows: 1. Overlay-velocity data sampling and analysis, interval velocity calculation, time-depth conversion, model building of earth shell velocity and layering character of earth shell are studied on 14 deep sections. Velocity structure in region of interest has revealed: Changchang is the sag with thinnest crust in Qiongdongnan basin; the sedimentary thickness lowers gradually from north to south, and the thickness change from west to east is milder. The sags’ sedimentary velocities in Qiongdongnan basin have obvious demarcation. The velocity of the 8000 meters sedimentary rocks is 4700 m/s in Shunde sag and Baiyun sag, and is the lowest; at that depth, the velocity very different in Liwan sag and Baiyun sag, which is about 800m/s. 2. Extracting gravity data and building of initial crust density model along the section; With Bouguer gravity anomaly data as constraint, revising density distributes of initial model, and building the crust density model. 3. With crust velocity and density as constraint, correcting the effect of thermobaric field and constructing constitution structure of rock in region of interest. By this research, we known that rocks in Zhujiangkou upper crustal layer are chiefly granite-gneiss, quartzite, granodiorite and basalt, however, rocks in Qiongdongnan basin upper earth shell are chiefly composed of granite-gneiss, quartzite, granodiorite, diorite and basalt. 4. Synthetically crust velocity and density structure, gaining expanding factor on crust and entire crust along section. The result is indicated: the expanding factor in every sag rises from northwest to southeast, which have reflected thinning characteristic of crust from continent to ocean. Intra-crustal deformation degree in Changchang and Ledong-Lingshui sag is bigger than that in Songnan-Baodao sag. Entire crust extension factor in Changchang and Songnan-Baodao sag is greater than that in Ledong-Lingshui sag, which can make an explanation of frequently event and longer heating process in middle-east of Qiongdongnan basin. 5. Synthesize multidisciplinary information to discuss the earth dynamics significance of discordogenic seismic profile in deepwater area of Zhujiangkou and Qiongdongnan basins.

青藏高原横波速度与各向异性结构及其壳幔形变印迹

As the most spectacular and youngest case of continental collision on the Earth, to investigate the crust and mantle of Tibetan plateau, and then to reveal its characters of structure and deformation, are most important to understand its deformation mechanism and deep process. A great number of surface wave data were initially collected from events occurred between 1980 and 2002, which were recorded by 13 broadband digital stations in Eurasia and India. Up to 1,525 source-station Rayleigh waveforms and 1,464 Love wave trains were analysed to obtain group velocity dispersions, accompanying with the detail and quantitative assessment of the fitness of the classic Ray Theory, errors from focal and measurements. Assuming the model region covered by a mesh of 2ox2o-sized grid-cells, we have used the damped least-squares approach and the SVD to carry out tomographic inversion, SV- and SH-wave velocity images of the crust and upper mantle beneath the Tibetan Plateau and surroundings are obtained, and then the radial anisotropy is computed from the Love-Rayleigh discrepancy. The main results demonstrate that follows, a) The Moho beneath the Tibetan Plateau presents an undulating shape that lies between 65 and 74 km, and a clear correlation between the elevations of the plateau and the Moho topography suggests that at least a great part of the highly raised plateau is isostatically compensated. b) The lithospheric root presents a depth that can be substantiated at ~140 km (Qiangtang Block) and exceptionally at ~180 km (Lhasa Block), and exhibits laterally varying fast velocity between 4.6 and 4.7 km/s, even ~4.8 km/s under northern Lhasa Block and Qiangtang Block, which may be correlated with the presence of a shield-like upper mantle beneath the Tibetan Plateau and therefore looked as one of the geophysical tests confirming the underthrusting of India, whose leading edge might have exceeded the Bangong-Nujiang Suture, even the Jinsha Suture. c) The asthenosphere is depicted by a low velocity channel at depths between 140 and 220 km with negative velocity gradient and velocities as low as 4.2 km/s; d) Areas in which transverse radial anisotropy is in excess of ~4% and 6% on the average anisotropy are found in the crust and upper mantle underlying most of the Plateau, and up to 8% in some places. The strength, spatial configuration and sign of radial anisotropy seem to indicate the existence of a regime of horizontal compressive forces in the frame of the convergent orogen at the same time that laterally varying lithospheric rheology and a differential movement as regards the compressive driving forces. e) Slow-velocity anomalies of 12% or more in southern Tibet and the eastern edge of the Plateau support the idea of a mechanically weak middle-to-lower crust and the existence of crustal flow in Tibet.

山西堡子湾金矿角砾岩带控矿规律、成矿时代及隐伏矿体定位预测

The Puziwan gold deposit is located at the northern boundary of the North China platform where there are very favorable ore-forming conditions. The deposit is a medium-sized gold deposit associated with silver and copper polymetallic minerallization which were closely related to cryptoexplosive processes and fluidization and underwent multi-epoch superposition of mineralization. The mineralization consists of cryptoexplosive breccia-type, fluidizing-type, porphyry-type, quartz vein-type, etc. The ore-controlling law of ore-bearing brecciated zone is systematically studied in the paper. The shape, scale and attitude of ore bodies are dominat in the upper, the ore bodies of fluidizing breccia-type are dominant in the upper and the middle part, the porphyry-type ore bodies are dominant in the bottom. The quartz vein-type ore bodies are impenetrated in all the brecciated zone. The metallogenic epoch of Puziwan gold deposit is collated and stipulated. The Rb-Sr isochron age of quartz porphyry (wall rock) is 233 Ma, refering to the Ar-Ar age of gold-bearing quartz, excluded the former conclusion that the so-called metallogenic epoch (245.9Ma) is in Indosinian epoch. The nonage metallogenic age of Buziwan gold deposit shoule be in the Yanshanian epoch (142.5Ma). By applying the sub-specimen sampling technique, the Rb-Sr isochron age of gold-bearing pyrites in late mineralization epoch is dated to be 64 Ma. In conclusion, the metallogenetic epoch of Puziwan gold deposit is in late Yanshanian-early Himalayan epoch. On the above basis, the metallogenic model of the "train type" and new texture model of ore deposit are established. by applying the methods of geology, shallow seismic exploration, remote sensing, partial geochemical extraction and the study of inclusions in the late granite porphyry, the author has made the metallogenic progosis in the depth and the prephery of Puziwan gold deposit and eight prospecting targets are proposed.

黄骅坳陷高尘头地区储层非均质性及成藏研究

Gaochentou region is located in the southwest direction of Gaochentou village in Huanghua city of Hebei province. In regionally structural position, It lies in Qikou sag In the middle part of Huanghua depression, which belongs to the east part of the south Dagang structure zone in the middle part of Huanghua depression. Its' very beneficial at regional structure in Gaochentou , and It becomes the advantage area for oil and gas gathered and preserved, Sandstone reservoir of Dongying Formation is main bearing bed .Dongying Formation in Gaochentou region of Huanghua depression is consisted of set of mudstone and sandstone interbeds by deposited delta fades . Dongying Formation can be divided into 3 members from above to below: the first member of Dongying Formation (FMDF), the second member of Dongying Formation (SMDF), and third member of Dongying Formation (TMDF). The lithology of the upper part of FMDF was consisted of mostly middle-grained and fine-grained sandstone, and it is small for the oil-bearing area of the sand bodies .The lithology of the lower part is coarse-grained sandstone bodies which are well connected between sandstone bodies of wells, and the lower part was main bed of oil production in Dongying Formation; SMDF and TMDF are consisted of larger scale set of mudstone, in which the sandbodies are lenticular and pinch out quickly, and the lithology was mostly fine sandstone and silt stone, in which there are little oil and gas .Because the reservoirs in this area are largely influenced by the factors such as lithology, fault and others, and the reservoirs have the strong,heterogeneity , there exists the problem of oil-down and water-up for vertical distribution of oil and gas bearing. It is not very clearly for the three dimension distribution of sandstone , and the geology researchs is not enough. So, it can't satisfy the need of further development and production for Gaochentou oilfield.Having the key problem of oil-down and water-up and the mechanism of the reservoir for Gaochentou area, There are as follow study works, the first, is study of the high-resolution correlation of sequence stratigraphy and sedimentary microfacies. Dongying Formation was divided into three parasequence sets and each parasequence set was divided into different amount of parasequences. FMDF, as the main oil and gas producing bed, can be divided into seven parasequences. Oil and gas are discovered in six parasequences except the seventh. On the basis of study of sedimentary microfacies, the sediments of Dongying Formation are considered deposited mainly in delta front subfacies. The microfacies types of Dongying Formation are sub-water distirbutary channel, sub-water natural bank, inter distributary channel bay, distributary channel mouth dam, and delta front mat sand.Seismic facies analysis and logging-constrained inversion technique were applied by Author for transverse prediction of sandstone reservoir. Having 4 modes of interwell single sandbodies correlation technique, Author have described distribution characteristics of sandbodies, and established geological reservoir model of Gaochentou reservoir.Author presented that the reservoirs characteristic have very strong heterogeneity ,and In the section of sandstone interlayed with mudstone,the folium sandstone interlayed with each other, and the wedge shaped sandbodies pinched out in the mudstone. So the pinch-out up sandstone trap and lenticular sandstone trap are easily formed. They are most small scale overlying pinches out in the place of slope. This article applies the concept of deep basin oil to resolve reasonably the problem of which the oil is below the water in Gaochentou area. Combined with the study of sedimentary facies, reservoir and other aspects, the mechanism and patterns of deep basin oil are studied on the basis of characteristics in Gaochentou area.On the basis of the above study, the mechanism of the oil and gas' migration and accumulation in isotropic sandstone and heterogeneous sandstone are thoroughly analyzed through experiments on physical modeling. Experiments on physical modeling show that the discrepancy between sand layers with different permeability and thickness has important influence on the direction, path, and injection layer of oil's migration. At the beginning of the injection of oil and gas in high permeability sand layer, the pressure is low, the migration resistance is small, and the oil and gas are more easily displacing the water in sand. So it can act as good transformation layer or reservoir. But at the beginning of the injection of oil and gas in sand layer with low permeability, the pressure is high, the migration resistance is big, and the oil and gas are more difficultly displacing the water in sand. So it can only act as bad or worse transformation layer or reservoir. Even if it cannot act as transformation layer or reservoir, it can act as water layer or dry layer. The discrepancy between sand layers on permeability and thickness can make discrepancy in injection of oil and gas between different layers. Consequently it leads to small amount of oil and gas injection in sand layers with low permeability. Ultimately it affects the oil's accumulation and distribution in different sand layers.At Last, combining analysis of the structure and pool forming condition, The thesis has established models of reservoir formation to predict the advantage distribution of oil and gas bearing , and put forward the prospective target It is not only of theoretical signification for explosion and importance, but also has realistic value in guiding the progressive petroleum exploration and exploitation.

中国粮食生产的区域演进研究

Grain is one of the primary material conditions of the human survival and the grain production concerns the stability and development of the society directly. The regional patterns influence greatly on the grain production and the rational production distribution the regional comparative advantages and promotes grain production. This thesis starts with summarizing of the characteristics of changes and the overall trend of regional pattern of grain production of our country since 1949. Then it carries on network analyses to the factors, which influences the evolvement of regional grain production patterns of our country. And finally it gives some proposals to the grain production distribution in the future. The main content includes: Firstly, Reviewing the regional evolvement of grain production in our country, and analyzing the changes of the regional pattern of grain production of our country on the provincial scale and county scale separately, since 1949, especially since the reform and opening up policy. The main grain production areas are acting an important position in ensuring the national grain security, so this thesis analyses the main matter of the main grain production areas, forecasts the grain production situation in the future, and selects the Northeastern main grain production areas as the typical area to carry on the positive research. Secondly, this thesis analyzes the origin causes from two respects of natural and social economy of the regional evolvement pattern of grain production in China. Thirdly, based on the summarizing to the status of the regional pattern of the grain production, this thesis proposes the precept of the grain production distribution in the future in our country. Therefore, the areas of three major cereal crops, rice, wheat and corn, are confirmed on the basis of the comparative advantages. Finally, this thesis puts forward the security system of guaranteeing the grain production progressing steady in China. According to the above analysis, some conclusions have been achieved as follows: (1) The grain gross production gets on extricating itself from awkward position frequently while fluctuating greatly annually since 1949 in China. (2) Since the reform, its traditional regional pattern of grain production, the most of which was concentrated in the south area, has changed rapidly. China's center of gravity of grain production has shifted from the south to the north, and on the belts of latitude, the grain production has represented a trend of focusing to the middle area in China. (3) The main grain production areas play a very important role in ensuring China's food security. With their relative severe situation of the problems of agriculture, rural area and peasant, China has carried out a series of measures, which aim at improving the food-producing conditions of the main grain production areas, and enhancing the grain yields there. Under this condition, a forecast of the producing amount of the main grain production areas under the nation's self-supplying rate of over 95% shows that the increasing provision production in these areas can meet the demand of the country. (4) The natural and social economic factors influence together on the changes of the grain production regional pattern. Along with the state system transition and progress of agricultural science and technology, the regional pattern of grain production is affected heavier by the agricultural policy and technological elements. (5) The grain production will be concentrated to the middle province in the future, which economic development level being medium-sized; According to crop allocation, although the rice superiority production area located in the South, its comparative advantage index is little in some degree. Meanwhile, the wheat and corn superiority production areas are in the North mainly and its scale superiority and production level advantage are all comparatively obviously.