Science in China Series D: Earth Sciences

Based on remote sensing information sources including B/W aerial photos of 1983, pseudo-color aerial photos of 1992 and JERS-1/OPS VNIR image of 1996, vegetation types of Yingbazha, in the middle reaches of the Tarim River Basin in Xinjiang, China are mapped using ARC/INFO and related software. The changes in vegetation areas and distribution conditions are analyzed. As a result of natural and human influences, vegetation changes have temporal and spatial characteristics. According to the principles of landscape ecology and geographical information science, the landscape changes are indicated. Moreover, the remote sensing and GIS techniques are integrated to study vegetation and its landscape.

In the region southeast of Okinawa, during May to July 2001, a cyclonic and an anticyclonic eddy were observed from combined measurements of hydrocasts, an upward-looking moored acoustic Doppler current profiler (MADCP), pressure-recording inverted echo sounders (PIESs), satellite altimetry, and a coastal tide gauge. The hydrographic data showed that the lowest/highest temperature (T) and salinity (S) anomalies from a 13-year mean for the same season were respectively −3.0/+2.5°C and −0.20/+0.15 psu at 380/500 dbar for the cyclonic/anticyclonic eddies. From the PIES data, using a gravest empirical mode method, we estimated time-varying surface dynamic height (D) anomaly referred to 2000 dbar changing from −20 to 30 cm, and time-varying T and S anomalies at 500 dbar ranging through about ±2 and°C ±0.2 psu, respectively. The passage of the eddies caused variations of both satellite-measured sea surface height anomaly (SSHA) and tide-gauge-measured sea level anomaly to change from about −20 to 30 cm, consistent with the D anomaly from the PIESs. Bottom pressure sensors measured no variation related to these eddy activities, which indicated that the two eddies were dominated by baro-clinicity. Time series of SSHA map confirmed that the two eddies, originating from the North Pacific Subtropical Countercurrent region near 20°–30°N and 150°–160°E, traveled about 3000 km for about 18 months with mean westward propagation speed of about 6 cm/s, before arriving at the region southeast of Okinawa Island.

The diapirism in the Yinggehai Basin is a combined result of strong overpressure caused by rapid sedimentation of fine-grain sediments and the tensile stress field resulting from right-lateral slip of the boundary-fault. The diapirism showed multiple-stage, episodic nature, and caused intermittent counter-direction onlaps and changes in the thickness of strata. The shallow gas reservoirs in the diapir structural zone displayed obvious inter-reservoir compositional heterogeneities, and their filling history could be divided into 4 stages, with gases injected during different stages having different hydrocarbon gas, CO2 and N2 contents and different stable isotope compositions. The multiple-episode, intermittent activities of the diapirs, multiple-stage, non-continuous injections of fluids, and the transient thermal effect of fluid flow as well as the strong migration fractionation reflected episodic fluid injection and natural gas accumulation.

Through the analyses on sediment lithology,210Pb and137Cs dating, carbonate content, Sr/Ca and Mg/Ca of Ostrocod, and carbon and oxygen stable isotope of carbonate of gravity core from Cuoe Lake in the Naqu area, Tibetan Plateau, the paleolimnology was studied to investigate the environmental variation in the central Tibetan Plateau in the last 200 years. It is inferred that the environmental variation has undergone two stages. The climate was arid in the early 100 years, while it became warmer and more humid in the later 100 years, with a period of 20 years for humidity change.

The 65 whole-rock REE samples studied come from the classic sections of Early Cambrian to Early Silurian in the Yichang area, Hubei Province. REE concentrations tested on ICP-AES are normalized to the North American Shale Composite (NASC), and Ce anomaly values are calculated based on log[3Cen/(2Lan+Ndn)]. With the whole-rock Ce anomaly used as a quantitative index of sea-level changes, 5 prominent eustatic circles are recognized, and a good corresponding relationship is observed between the black shale episodes and the transgressive events. On account of the global distributions of coeval black shales and the specified paleogeographic background of South China, a genetic hypothesis based on the model of O2-minimum zone expansion is suggested for the Early Paleozoic multi-episode black shales in South China.

Both the Jinding and Baiyangping ore deposits developed in the Lanping basin, which is a Mesozoic-Cenozoic terrestrial clastic sedimentary basin. Their occurrences can easily lead many people to compare them with the Pb-Zn deposit hosted in sedimentary rocks, such as Mississippian Valley-, Sedex- and sandstone-type Pb-Zn deposits. However, the Lanping basin developed in the settings of strong tectonic activity of the continental crust, which could cause an effective material exchange between the lower crust and the upper mantle. The orebodies are clearly tectonically controlled without syngenetic features, which probably represents a new type of the sedimentary rock-hosted Pb-Zn deposit. The isotopic compositions of noble gases in ore-forming fluids indicate that 2%–32% of helium (3He/4He = 0.19 Ra–1.97 Ra) is derived from the mantle, 50.1% of neon (20Ne/22Ne = 10.45–10.83;21Ne/22Ne = 0.03) from the mantle, and considerable amount of xenon (129Xe/130Xe = 5.84–6.86;134Xe/130Xe = 2.26–2.71) from the mantle, which show that mantle fluids played an important role in the ore formation. The ore-forming age of 67—60 Ma obtained by Re-Os and40Ar−39Ar dating methods is later than the host rock, which is coeval with the Himalayan alkali magmatism of the mantle source and mantle-crust source. In this paper, the mineralization of the Jinding and Baiyangping ore deposits is considered to be related to the mantle fluids which move upward with the magma or along the deep faults, and mix with the meteoritic brine in the crust to result in large-scale deposition.

Porosity is a basic parameter for evaluating reservoir, and NMR logging is an effective method to obtain the porosity. However, we have often found that there exist significant differences between NMR porosities and formation core porosities in the complex reservoir. In this paper, we list the factors which affect the NMR porosity response in the complex reservoir, such as longitudinal relaxation time (T 1), transverse relaxation time (T 2), hydrogen index (HI) and borehole environment. We show how these factors affect the NMR porosity response and suggest methods to correct them. This should improve the accuracy of NMR logging porosity in complex reservoirs for the terrestrial formation.

Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data, the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM, the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the teleconnection mode which is from the northwest of India via the Tibetan Plateau to northern China. The former mode is defined as the “south” teleconnection of the Asian summer monsoon, forming in the period of ISM onset; while the latter mode is called the “north” teleconnection, mainly occurring in the Asian monsoon culminant period. During the process of the “south” teleconnection’s formation, the Asian monsoon circulation has experienced a series of important changes: ISM onset, the northward movement of the south Asia high (SAH), the onset vortex occurrence, the eastward extension of the stronger tropical westerly belt, and the northeastward jump of the western Pacific subtropical high (WPSH), etc. Consequently, since ISM sets up over Kerala, the whole Asian continent is covered by the upper SAH after about two weeks, while in the mid-and lower troposphere, a strong wind belt forms from the Arabian Sea via the southern India, BOB and the South China Sea (SCS), then along the western flank of WPSH, to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams, the upper westerly jet stream and the low level jet have been coupled vertically over east Asia, while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet stream and the low level jet, i.e. right of the entrance of the upper jet stream and left of the low level jet. Such a structure of the vertical circulation can trigger the Meiyu onset over the Yangtze River Valley.

Accurately determining the age of the Tuchengzi Formation has direct influence on confirming the boundary between the Jurassic and the Cretaceous systems in northern Hebei-western Liaoning, and on related geological problems in China. However, the Tuchengzi Formation mainly consists of sedimentary rocks, with a poor fossil record and especially lack of index fossils. The Tuchengzi Formation is also lack of the type of volcanic rocks that can provide an isotopic age. Therefore, the age of the Tuchengzi Formation has been uncertain. Based on our systematic dating of the tuff interbedded in the Tuchengzi Formation of Chengde and Jinlingsi-Yangshan basins in northern Hebei-western Liaoning, combined with the dating results of previous researchers, here we suggest that the age range of the Tuchengzi Formation in northern Hebei-western Liaoning is from 147 Ma to 136 Ma. It implied that the Tuchengzi Formation was mainly formed in the Early Cretaceous.