RADIOCARBON DATING OF A PEAT DEPOSIT IN THE CUCAMONGA FAULT ZONE,CALIFORNIA*

A sequence of peat beds was deposited in a small sag pond along the Cucamonga fault zone during late Holocene. The stratigraphic section of this deposit is described; several beds have been radiocarbon dated. Comparison of radiometric and stratigraphic chronologies allows reconstruction of the geomorphic history of the sag pond, which extends back 3000 years, and establishes evidence that the fault has been active within the very recent geologic past.     

珠江口盆地恩平凹陷恩平组物源体系分析及未来大洋钻探建议

物源体系分析是沉积盆地特征分析的重要内容，为进一步阐明珠江口盆地恩平凹陷恩平组的沉积特征和物源体系，本文拟利用恩平凹陷的三维地震资料和钻井数据，通过古生物环境分析和锆石U- Pb定年等方法，并借助地震剖面中古沟谷的识别、前积反射结构、地震多属性分析结果和沉积相带平面分布特征，对恩平凹陷恩平组物源体系特征进行综合分析。研究结果表明，恩平组PSQ1～PSQ2时期表现位明显的陆相湖盆特征，物源主要为珠江口盆地内隆起的古生代变质岩和中生代火成岩基底，少量来源于北部华南褶皱带的元古宙变质岩；随着PSQ3时期断层活动逐渐停止，湖平面不断上升，华南褶皱带物源供给能力明显增强，逐渐成为恩平凹陷主要物源。鉴于目前南海北部缺少陆相湖盆地层的完整岩芯剖面，制约了南海北部裂陷期构造- 沉积耦合研究并影响了该地区的油气勘探，建议下一步在南海北部陆相沉积盆地(如珠江口盆地)开展大洋钻探工作，以便获取更连续、时间精度更高，受风化作用影响更小的陆相湖盆地层的完整岩芯剖面。这不仅有利于指导下一步油气勘探，也可通过重建陆相沉积盆地不同地质历史时期的沉积变化过程，为了解古气候状态和预测未来气候变化提供重要依据。     

苏北洪泽凹陷古近系生物地层研究

洪泽凹陷古近系地层发育齐全 ,介形虫、轮藻、孢粉化石丰富 ,根据其属种分布规律 ,建立了 E1 f— E2 s的 12个化石组合序列 ,论述了各门类化石组合特征及对比关系。在此基础上 ,结合岩、电性对比 ,确立了顺河次凹和管镇次凹综合柱状图、地层对比图以及可用于凹陷内地层对比的 7个岩电性特征段。得出本区古近系除三垛运动和吴堡运动造成不整合或假整合外 ,其余组、段间皆为整合接触的结论     

济源凹陷下第三系碎屑岩的成岩作用特征

根据砂岩铸体薄片、扫描电镜和Ｘ－衍射分析资料，研究了济源凹陷下第三系碎屑岩主要的成岩作用特征，并说明了压实作用、胶结作用和溶蚀作用是影响下第三系碎屑岩储集层孔隙结构的主要因素。     

Pressure evolution and hydrocarbon migration in the Baiyun sag, Pearl River Mouth basin, China

The Pearl River Mouth basin is one of the most important offshore basins in China. Petroleum exploration in the deep-water area is to start in the Baiyun sag in the basin. Due to the high cost of exploration in deep-water areas, the hydrocarbon migration and pressure evolution needs to be thoroughly probed before any actual exploration is to be done. Drilling results have indicated that the pore pressure is hydrostatic in shallow-water area. The mud diapirs found in the Baiyun sag indicate that there may be overpressure in the deep-water area. At present, little is known about hydrocarbon migration and pressure distribution in deep-water areas. On the basis of geological data from wells and basin modeling, the research comes to the following conclusions. (1) At least three episodic accumulations and releases of pressure had happened in the Cenozoic, which were closely related to the three regional tectonic movements: the Zhu-Qiong movement in the Late Eocene, the Nanhai movement in the Middle Oligocene and the Dongsha movement between the latest Middle Miocene and Late Miocene. The pressure release and associated hydrocarbon migration occurred primarily during the Dongsha movement, when most of the overpressure was released to hydrostatic pressure except for some overpressure in the deep-water area. (2) Both the measured pressure and the modeling results indicate that the pore pressure is hydrostatic pressure in the shallow-water area. Abnormally high pressure in the deep-water area is noted to be present. The difference of pressure distribution is caused by the lithologies, facies and faults. (3) The diapirs in the deep water cannot be driven by the overpressure because the maximum pressure is less than 9.0 MPa in the course of pressure evolution. (4) The fluids migrated to the shallow-water area and deep-water area along faults. Some faults connected the deep-water fans with the hydrocarbon source. Huge oil and gas fields may be formed in the deep-water area more favourably than in the shallow-water area. Translated from Earth Science-Journal of China University of Geosciences, 2006, 31(2): 229–236 [译自: 地球科学—中国地质大学学报]     

A study on the geochemical characteristics of natural gas and gas sources in the Bozhong sag

Natural gas is composed largely of hydrocarbon gas, especially wet gas in the Bozhong sag. The carbon isotopic composition shows that the gas is of organic origin. The carbon isotopic values of ethane indicate that the natural gas is dominated by mixed gas with minor coal-generated gas and oil-type gas. A gas-source correlation study showed that the source rocks of natural gas are those of the Lower Dongying Formation, the Shahejie Formation and the pre-Tertiary. The natural gas is characterized by multi-source and continuous generation in the study area, indicating that gas exploration potential is good in the Bozhong sag.     

辽河坳陷东部凹陷火山岩构造裂缝形成机制

研究区内最主要的次生裂缝是构造裂缝,是火山岩受构造应力作用后产生的裂缝。按规模构造裂缝可以分为区域构造裂缝与局部构造裂缝。局部构造裂缝包括与纵弯褶皱有关的裂缝、与横弯褶皱有关的裂缝和与断层有关的裂缝。构造裂缝反映出的应力场与区域或局部的应力场是一致的,同时不同级别、不同期次的断层活动过程也是局部或区域裂缝产生和叠加的过程。本区的区域构造裂缝的产生与整个辽河盆地新生代时期,受燕山运动、喜山运动、、幕的强烈影响过程中应力场的变化是一致的。构造裂缝的规模相对较大,在岩体中分布广、研究程度高、规律性强,且成组出现。火山岩要成为良好的储层,必须发育由后期构造作用产生的构造裂缝,将原生的孔隙连通起来,才能成为好的储层。因此,构造裂缝的形成机制对研究裂缝性储层具有十分重要的意义。     

源外鼻状构造区油运移输导通道及对成藏的作用

尚家地区为一鼻状构造,位于三肇凹陷下白垩统青山口组一段油源区之外,其石油的成藏与分布主要受输导通道的控制。能否正确认识该区石油输导通道及对成藏的作用,对于指导该区石油勘探和丰富油气成藏理论均具重要意义。采用油源对比、典型油藏解剖和成藏模式的研究方法,对尚家地区石油输导过程进行了研究,将其划分为以下3个部分：① T2源断裂是三肇凹陷青山口组一段源岩生成石油向下伏下白垩统泉头组四段扶余油层、下白垩统泉头组三段杨大城子油层“倒灌”运移的输导通道;② 被T2—T2-2断裂沟通的砂体是扶余、杨大城子油层石油从三肇凹陷向尚家地区侧向运移的输导通道;③ T2—T1-1断裂是尚家地区扶余、杨大城子油层石油向上覆下白垩统姚家组葡萄花油层运移的输导通道。采用石油输导通道和石油分布之间匹配关系的研究方法,对尚家地区输导通道对石油成藏与分布中的作用进行了研究,得到T2源断裂越发育,三肇凹陷向尚家地区侧向运移的油源越充足;被T2—T2-2断裂沟通的砂体输导通道位置和能力控制着扶余、杨大城子油层和下白垩统泉头组二段石油的分布及富集程度;T2—T1-1断裂输导通道分布控制着尚家地区葡萄花油层的石油富集区域。