四川江油-北川地区下石炭统灰岩的古地磁研究

对采于四川北部江油 北川地区 (31.4°N ,10 4 .3°E)下石炭统 39个采点的 334块灰岩标本进行了较为系统的古地磁学研究 ,结果表明 ,标本中剩磁方向具有明显的双分量特征 ,低温 (10 0～ 30 0℃ )分量在地理坐标系下与现代地磁场方向基本一致 ,且不能通过褶皱检验 ,应是现代地磁场的重磁化 ,中温 (30 0～ 4 80℃ )反极性分量在地层坐标系中具有高负倾角的特征 ,其形成可能与早侏罗世岩层的褶皱弯曲有关 .     

豫北早古生代灰岩的岩石磁学研究

对一些可分离出岩石形成时原生剩磁的样品进行深入的岩石磁学研究,发现天然剩磁的特征通常取决于磁铁矿的颗粒度(或单、多磁畴状态),单、多磁畴磁铁矿的含量不同,导致了中温与高温剩磁分量不同程度的叠加,也就造成了不同磁分量分离难易程度的不同     

巴黎盆地下侏罗统的岩石磁学研究及其意义

通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质.     

巴黎盆地下侏罗统的岩石磁学研究及其意义

通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质.     

巴黎盆地下侏罗统的岩石磁学研究及其意义

通过下佛罗统磁性地层学研究,获得了一些能记录岩石形成时的地磁场的样品,根据常规的古地磁方法,等温剩磁和热退磁实验,说明这些岩石的主要载磁矿物为磁铁矿.磁滞回线参数的测量表明多数载磁矿物磁铁矿为假单磁畴,少量样品则可能为假单磁畴与多磁畴的混合物.通过与北美古生代重磁化岩石的磁滞回线参数比值对比,说明重磁化与非重磁化岩五磁滞回线参数比值的分布趋势有明显差别,这一差别可能用于判定岩石的重磁化和非重磁化性质.     

北羌塘盆地雁石坪地区中-上侏罗统岩石磁学特征与沉积环境

羌塘盆地是中国海相中一上侏罗统最为发育的地区.本文对采自北羌塘盆地雁石坪地区侏罗系雁石坪群的沉积岩样品开展了系统热退磁和岩石磁学研究,其结果表明,中侏罗统雀莫错组(上、下段)主要载磁矿物为磁铁矿和赤铁矿;布曲组的主要磁性矿物是细颗粒磁铁矿;夏里组磁性矿物以磁铁矿为主;上侏罗统索瓦组以磁铁矿为主要载磁矿物.布曲组NRM远远高于其余各组(平均值为2.2×10~(-4)A/m)、索瓦组NRM次之(平均值为4.4×10~(-5)A/m)、雀莫错组和夏里组样品的NRM基本相当(平均值为2.2~2.4×10~(-5)A/m).本文认为细颗粒磁铁矿含量的增加可能是布曲组的NRM平均值远远高于索瓦组的主要原因,并且自生磁性矿(如针铁矿、铁的硫化物等)可能是引起布曲组、索瓦组NRM大于的雀莫错组和夏里组的原因之一.通过本研究与古水深和沉积相变化的对比分析,认为雁石坪地区中-上侏罗统磁性矿物组合变化主要受该区沉积环境变化的控制.本研究首次系统报道了羌塘盆地侏罗系雁石坪群各组的磁性矿物组成和组合规律,这将为羌塘盆地侏罗纪高精度磁性地层年代序列的建立以及特提斯沉积一构造演化等研究提供重要的依据.     

The Upper Devonian orbital cyclostratigraphy and numerical dating conodont zones from Guangxi,South China

The hierarchically organized laminae, bundles, bundlesets and superbundlesets which correspond to a sub-Milankovitch, obliquity or precession, eccentricity and long eccentricity cyclothems, respectively, have been distinguished from the Upper Devonian Fras-nian-Famennian (F-F) transitional carbonate successions deposited in the carbonate-basin and slope facies of Guangxi, South China. The durations of cyclothems are 8000-10000a, 16667a or 33333a, 100000a and 400000a, respectively. The ratio of eccentricity to precession, eccentricity to obliquity, and long eccentricity to eccentricity is 1 : 6, 1 : 3 and 1 : 4 in the Devonian, respectively. Orbital cyclostratigraphical studies show that the durations of the conodont falsio-valis Zone, transitans Zone, punctate Zone, Lower hassi Zone, Upper hassi Zone, jamieae Zone, Lower rhenana Zone, Upper rhenana Zone, linguiformis Zone, Lower triangularis Zone, Middle triangularis Zone and Upper triangularis Zone are 0.4, 0.4, 0.4, 0.3, 0.4, 0.2, 0.8, 0.6, 0.8, 0.3, 0     

The discovery of Neoproterozoic extensional structures and its significance for gas exploration in the Central Sichuan Block,Sichuan Basin,South China

The Central Sichuan Block(CSB) is the hardest block between the deep faults of Pujiang-Bazhong and Huaying Mountain in the central part of Sichuan Basin, which lies in the northwestern part of the upper Yangtze Craton. The CSB has long been considered as the oldest and most stable core area of Yangtze Craton, with the uniform basement and high level of hardening. Here we present a detailed interpretation of deep structures in the CSB by integrating high-resolution seismic data(approx. 50000 km2) with large-scale aeromagnetic data. Results show that eight Neoproterozoic extensional structures of different scales are nearly EW-, NEE-, and NW-trending in the CSB. Discovery of these extensional structures changes previous understanding of the CSB as a unified block. The extensional structures experienced one or two stages of extension in the longitudinal section, and filled with 3000–5000-m-thick weakly magnetic materials. Development of basal A-type granite in Weiyuan, Sichuan Basin and bimodal volcanic rocks of the Suxiong Formation, Western Sichuan confirms the CSB's Neoproterozoic extensional tectonic setting. The newly discovered Neoproterozoic extensional structures are of great significance for source rock and favorable sedimentary facies distribution, reservoir development, and gas accumulation.     

Magnetic susceptibility variations of carbonates controlled by sea-level changes--Examples in Devonian to Carboniferous strata in southern Guizhou Province, China

This paper presents magnetic susceptibility results of 578 samples from three Devono-Carboniferous carbonate successions in the Yangtze Block. They indicate that the magnetic susceptibility variations in carbonates are controlled by ancient sea-level changes. It is particularly so if the supply of detrital materials was low, when the magnetic susceptibility was mainly controlled by the content of authigenic minerals. If the supply of detrital materials was high, the average susceptibility value would be higher, but there is still a correlation between susceptibility and sea-level curves. A sea level rise would lead to a decrease in the content of the detrital materials, and therefore to a decrease in the susceptibility values. On the top of HST, the uplift and exposure events may lead to elevated magnetic susceptibility values. Carbonate susceptibilities can therefore be considered as one of the environmental proxy data for the research of sequence stratigraphy.     

Diagenetic fluids evolution and genetic mechanism of tight sandstone gas reservoirs in Upper Triassic Xujiahe Formation in Sichuan Basin,China

The reservoirs of the Upper Triassic Xujiahe Formation in Sichuan Basin have the characteristics of low compositional maturity, low contents of cements and medium textural maturity. The general physical properties of the reservoirs are poor, with low porosity and low permeability, and there are only a few reservoirs with medium porosity and low permeability in local areas. Based on the diagenetic mineral association, a diagenetic sequence of cements is established: early calcites (or micrite siderites) →first quartz overgrowth→chlorite coatings→dissolution of feldspars and debris→chlorite linings→ second quartz overgrowth (quartz widen or filled in remain intergranular pores and solution pores)→dissolution→third quartz overgrowth (quartz filled in intergranular and intragranular solution pores)→intergrowth (ferro) calcites→dolomites→ferro (calcites) dolomites→later dissolution→veins of quartz and calcites formation. Mechanical compaction is the main factor in making the reservoirs tight in the basin, followed by the second and third quartz overgrowth. In a long-term closed system, only feld-spars and some lithic fragments are dissolved by diagenetic fluids, while intergranular cements such as quartz and calcit are not dissolved and thus have little influence on the porosity of the Xujiahe Formation. This is the third factor that may have kept the sandstones of Xujiahe Formation tight finally. The hydrocarbon was extensively generated from organic materials after the second quartz overgrowth, and selectively entered favorable reservoirs to form tight sandstone gas reservoirs.     

Sedimentary facies and biofacies of the Torinosu Limestone in the Torinosu area,Kochi Prefecture,Japan

The Torinosu Limestone represents carbonate platform deposits in a foreland basin, the sedimentary setting of which is highly different from those of well‐known Late Jurassic reefs in the western Tethys that developed on shelf areas of continental margins and intra‐Tethyan platforms. Sedimentological and paleontological analyses were conducted on a 55.5 m‐thick Upper Jurassic–Lower Cretaceous (Tithonian–Berriasian) carbonate sequence (Torinosu Limestone) at the Eastern Hitotsubuchi Quarry, Kochi Prefecture, Southwest Japan. The carbonate sequence is composed of two sections that are separated by a subaerial exposure surface. Two and three depositional units have been defined in the lower and upper sections, respectively, based on changes in lithology and the biotic composition of the carbonates; they are numbered from 1 to 5, in ascending order. Calcified demosponges (stromatoporoids and a chaetetid Chaetetopsis crinita) are abundant in three units (2, 3, and 5), in which microencrusters (mostly Lithocodium aggregatum and Bacinella irregularis) and microbialites are also common to abundant. Although most of them are para‐allochthonous, in‐situ branching stromatoporoids are found on and above the subaerial exposure surface (unit 3). Corals are less common, poorly diverse, and primarily represented by the family Microsolenidae. Siliciclastic grains occur in all units, but they are particularly common in units 1 and 4. The co‐occurrence of the Lithocodium–Bacinella association, which is typical of oligotrophic or moderately mesotrophic shallow‐water environments, with microsolenids, which are indicative of high nutrient levels and/or low‐light intensity due to high turbidity, suggests repeated changes in nutrient levels associated with terrigenous input. Based on lithology, biotic composition, and succession, we infer that sea‐level changes and related terrigenous input controlled the sedimentary environment of the studied carbonate sequence.     

Discovery and significance of microspherules at Lower-Middle Devonian boundary of Guangxi, South China

Microspherules are found in different facies at the Lower-Middle Devonian boundary, Guangxi, South China. There are more than 20 grains per kilogram rock sample. Composition and form of the microspherules are very similar to those of the microtektites from modern deposits of South Pacific Ocean and F-F boundary (Devonian). This may indicate that the microspherules from Guangxi are most likely the products of an extraterrestrial impact event that occurred at the end of Early Devonian Epoch. The event may be responsible for the biomass reduction and extinction of benthic organisms at the end of Early Devonian. The impact products (ejecta) can be used as a potential tool for stratigraphic correlation.     

Carbon isotope composition of the Lower Triassic marine carbonates, Lower Yangtze Region, South China

The Early Triassic is a critical period in earth his- tory. A series of events such as volcano eruptions[1,2], sea-level fluctuations, changes in environmental con- ditions[3], mass extinctions[4,5] as well as global negative carbon isotope excursions[6-9] have been discovered in the uppermost Permian or across the Permian-Triassic boundary. Large scale sea-level rise[10-12], restoration of environment conditions, re- covery of ecosystem[13], including gradual carbon iso- tope rise[14] occur…     

2008年5月12日汶川地震谱震级及相关问题研究

基于P波和S波的谱震级特征对汶川地震进行了定量研究,可以看出P波和S波的最大谱震级出现在不同的周期上。对这一现象的构造物理意义进行了讨论,推测相对于P波而言,地震发生期间辐射的S波能量来自异常大的震源体积。选择部分全球地震的谱特征为背景,对汶川地震的体波谱震级特征进行了分析,结论是汶川地震的特征与其所处的周边环境是一致的。