Optical dating of liquefaction features to constrain prehistoric earthquakes in Upper Assam, NE India—some preliminary results

Optical dating of liquefied sand structures formed during major earthquakes in Upper Assam, northeast of India, has been carried out to constrain the timing of prehistoric earthquakes in this seismically active region. The bleaching of source material and of the same material during the creation of a liquefaction feature was tested using quartz extracted from 21 samples associated with two different liquefaction structures in Upper Assam. Due to the poor sensitivity of quartz from this region, a sensitisation procedure was used in our SAR protocol to reduce the scatter in optical ages. Various internal consistency tests of the measurement protocol and the excellent reproducibility of the OSL ages indicate that the dose estimates from the quartz are accurate and the optical ages reliable. The preliminary OSL ages indicate that the liquefaction features were formed between 1430 AD and 1630 AD. This study demonstrates that using OSL, ‘direct dating’ of prehistoric earthquakes may be possible, if sand blows from liquefied dykes are preserved.     

东北地区未来3～5年地震活动趋势预测研究

本文在文献[1]研究成果的基础上,分析了东北地区自上个世纪以来5级以上地震的活动特征,给出了东北地区未来3～5年的地震活动趋势以及最大震级。     

Characteristics of bleaching of sandstone in northeast of Ordos Basin and its relationship with natural gas leakage

Bleaching of sandstone has significant applications to tracing hydrocarbon pathways and evaluating the scale of natural gas seepage. Bleaching of sandstones in the northeast of Ordos Basin is mainly distributed in the Mesozoic Yan'an Formation. Studying on petrology, major elements, REEs and trace elements of bleached sandstones and comparing with adjacent sandstones, combining with geologic-geochemical evidences of gas seepage in the northeast of the basin, the bleached sandstones are formed in the acid environment and reducing fluids. Characteristics of petrology show that the contents of kaolinite are high and the color of margin of ferric oxide minerals is lighter than that of the center. Major elements of sandstone samples show high contents of Al2O3 and low ratio of Fe3 /Fe2 . The TFe2O3 content of the bleached sandstone is lower than that of red rock. REE data show that bleached sandstones have low ∑REE contents and Eu-depleted and slightly Ce-enriched. Trace elements show that the bleached sandstones enrich in Co, deplete in Sr, and slightly enrich in Zr and Hf which are close to the values for the green alteration sandstones, and slightly lower than ore-bearing sandstones. Geochemical characteristics of oil-bearing sandstone in the northern basin suggest that the oil-shows are formed by matured Carboniferous-Permian coal bed methane escaping to the surface, and natural gas in field could migrate to the north margin of the basin. The δ13C (PDB) andδ18O(PDB) values of calcite cement in the study area range from -11.729‰ to -10.210‰ and -14.104‰ to -12.481‰, respectively. Theδ13C (PDB) values less than -10‰ imply the carbon sources part from organic carbon. Comprehensive study suggests that the gas leakage has occurred in the northeastern basin, which is responsible for bleaching of the sandstone on top of the Yan'an Formation.     

桂西北上二叠统及下三叠统古岩溶不整合

文章描述了桂西北乐业、天峨等地区发现于上二叠统顶部、下三叠统顶部的 2个古岩溶不整合面 ,及其暴露、沉积间断特征 ,分析了它们的形成时代。通过这 2个I型层序界面的确认 ,讨论了其与地层划分对比、沉积环境及盆地分析、断裂的发育及与微粒型金矿的关系与意义。     

广西固体矿产钻探工程技术与管理现状及其对策

从钻探设备、工艺技术、生产管理与人员素质等方面，简要分析了广西地矿局固体矿产钻探工程施工技术与管理现状，指出当前存在的突出问题以及解决这些问题的一些建议与对策。     

广西油气资源勘探开发现状与发展前景展望

文章根据广西多年来油气勘探开发的最新成果 ,较全面地介绍和论述了广西境内陆地及海区新生界第三纪盆地、中—上古生代前陆盆地油气勘探开发现状与资源潜力 ,同时依据现代油气勘探地质理论并结合西部大开发的历史机遇 ,提出了广西面向新世纪油气资源勘探发展的战略指导思想、发展方向及发展层次 ,展望了广西油气勘探的发展前景。     

二十世纪广西古人类学研究综述

文章回顾20世纪以来,在广西发现的重要古人类化石和文化遗物,包括4个巨猿化石地点、13个晚期智人化石地点以及一系列旧石器.对柳江人遗址等的地层和年代学进行了综合研究,对国际学术界关于现代人起源的"多地区连续演化说"将提供强有力的证据;百色盆地旧石器的综合研究,将对恢复早中更新世的环境和早期人类迁徙、扩散的模式,有着深远的意义.     

东北和华北东部气温异常特征及其成因的初步分析

采用REOF，SVD分析方法，首先指出东北和华北东部气温异常是全国气温异常的第一主分量，进而分析其异常特征及成因。结果表明：全区年、季气温均呈上升趋势，其中冬季增温最大，极端低温较极端高温升高明显。近百年来，全区增温幅度明显高于20世纪全球平均增暖水平。冬季，对流层中、低层上，当纬向西风偏强时，东北和华北东部易高温；而当经向风强盛时，易低温。夏季，气温异常与东北冷涡活动有关；1980年代以来气温显著变暖与对流层中、低层气压场的年代际突变有关。冬夏季气温与东亚冬夏季风、Nino3区海温的关系并不显著，但在1990年代以前，东北夏季低温与El Nino的对应关系较好。     

粤桂琼交界地区地震趋势综合分析

应用地震活动、台站前兆观测、流动重力、海平面变化和统计分析等多种方法,绘合分析了粤桂琼交界地区近斯的地震活动趋势。认为近３年内或稍长一些时间,该区发生６级以上地震的可能性很小,但有可能发生５级左右地震。     

地下水资源评价中的不确定性因素分析

岩溶蓄水构造（或岩溶含水构造）是固结密实的岩深含水层的组成部份,由于次生构造裂隙和溶蚀形态发育强烈,它们的透水性高于围岩,因而具备在含水层内汇聚和集中传输地下水的功能,新生代以来小平阳地区的岩溶作用在热带气候和新华夏系第二沉降带构造双重背景下发育,对这一地区归纳出８种岩蓄水构造,体积上,它们只占含水层的１％～１０％。通过岩溶水文地质调查找出蓄水构造可以把找水的靶区面积缩小１～２个数量级,半定量地确定其三维几何形状的几部介质结构特征,可为水文物控解释提供地质依据。