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大同第四纪火山群的活动特点

一、引言大同第四纪火山群位于山西省大同县和阳高县境内(图1),包括近5年来在大峪口,秋林地区首次发现的6个小火山。该火山群大、小火山共计31个。大同火山群南以六棱山北麓断裂为界,分布于大同盆地东部的第四纪沉积区范围。火山群南侧的六棱山和北部的小北山是由前寒武花岗片麻岩组成的山地。     

Strontium isotopic geochemistry of Tianqiao Pb-Zn deposit,Southwest China

Tianqiao carbonate-hosted Pb-Zn deposit, controlled by NW-trending F37 thrust fault and NW-trending Tianqiao anticline, is located in the eastern part of Sichuan-Yunnan-Guizhou （SYG） Pb-Zn metallogenic province, southwestern Yangtze Block, southwest China. Ore bodies in this deposit are hosted in the Devonian-Carboniferous carbonate rocks, and ore minerals include sphalerite, galena and pyrite, while the gangue minerals are dominated by calcite and dolomite. Using high-precision solid thermal ionization mass spectrometry （TIMS）, this paper reports the strontium isotopic compositions （0.7119 to 0.7167） of sulfide samples from the Tianqiao deposit in order to trace the origin of hydrothermal fluids. Compared with the country rocks, the calculated 87Sr/86Sr200 Ma values of sulfide range from 0.7118 to 0.7130, higher than those of the age-corrected Devonian to Permian sedimentary rocks （0.7073 to 0.7101） and the Middle Permian Emeishan flood basalts （0.7078 to 0.7039）, but lower than those of the age-corrected Proterozoic basement rocks （such as the Kunyang and Huili Groups, 87Sr/86Sr200 Ma=0.7243 to 0.7288）. This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Together with geologic and previous isotopic evidences, we considered that the fluids＇ mixing is a possible mechanism for sulfide precipitation in the Tianqiao deposit.     

Influence of Spur Dike on Hydrodynamic Exchange Between Channel and Shoal of Generalization Estuary in Physical Model Test

Widely applied in maintaining estuarial waterway depth, the spur dike has played an important role in currents and sediment exchange between channel and shoal and sediment back-silting in the channel. Through establishing a generalized physical model at a bifurcated estuary and conducting current tests under the joint action of runoff and tide, the influence of the spur dike length on current exchange between channel and shoal is analyzed. Results show that when the spur dike length reaches a certain value, the direction of the flow velocity shear front between the channel and shoal will change. The longer the spur dike, the larger the transverse fluctuating velocity at the peak of flood in the channel shoal exchange area, while the transport of the transverse hydrodynamics is obvious in the process of flood. There is an optimum length of spur dike when the shear stress in the channel and the longitudinal velocity in flood and ebb reach the maximum, and the flow velocity will decrease when the spur dike length is smaller or larger than the optimum. For a certain length of spur dike, the larger the channel shoal elevation difference, the larger the peak longitudinal flow velocity in the middle of the navigation channel in flood and ebb. However, the transverse flow velocity will first decrease and then increase. The transverse transportation is obvious when the channel shoal elevation difference increases.     

古代阶梯状曲流砂坝河流沉积的识别

河流的沉积特征是多样的。实际上，多数河流沉积序列与经典曲流河沉积模式存在一定差别。在松辽盆地茂兴地区泉三段地层中阶梯状曲流砂坝河流较为发育，其特征为：发育２层曲流砂坝沉积，下曲流砂坝厚度较大，一般厚２－５ｍ，发育较完好的正韵律，与经典曲流砂坝沉积模式特征相似；上曲流砂坝亦为正韵律，但泥质含量偏高，层理发育较差。上、下曲流砂坝间多为突变接触，或被紫色或杂色泥质层隔开。     

Paleokarst system development in the San Andres Formation, Permian Basin, revealed by seismic characterization

Paleokarst systems are one of the major factors resulting in carbonate reservoir heterogeneity and compartmentalization. Nevertheless, few effective workflows have been proposed to map the 3D distribution of such systems. We describe a detailed seismic characterization approach integrating core, well log and rock physics analysis, to reveal a complex subsurface paleokarst system in the San Andres Formation, Permian basin, West Texas. In the area of high volume production, the collapsed paleokarst system is characterized by irregularly developed crackle and fracture breccias, mosaic breccias and cave fillings in the Upper San Andres Formation, which are delineated using seismic acoustic impedance. Along the transition from platform to basin, the paleokarst system is marked by a linear collapse including sags and small vertical faults that are recognizable in seismic imaging. Production data indicates that tight paleokarst zones cause reservoir compartmentalization and influence fluid communication between wells. The complex paleokarst system development is explained using a carbonate platform hydrological model, an outcrop analogue similar to modern marine hydrological environments within carbonate islands. Our method of model development for complex subsurface paleokarst systems may be applicable to other paleoenvironments.     

Microseismic and acoustic emission effect on gas outburst hazard triggered by shock wave: a case study

It has a significant and practical meaning for warning precisely gas outburst to reveal microseismic (MS) and acoustic emission (AE) effect of gas outburst precursor. It was thoroughly investigated and discussed on MS and AE effect on an abnormal gas outburst triggered by a strong rockburst using MS- and AE-monitoring systems through spectral analysis technique. We obtained main conclusions are as: (1) MS amplitude prominently decreased prior to outburst, the spectrum significantly moved from extremely low-frequency to high-frequency band, and evolved from “single-peak type” (the center frequency was about 1.5–3.5 Hz) to “multi-peak type” (the peak frequencies were about 25, 50, 75 and 125 Hz, respectively). (2) During the initiative stage of outburst, MS spectrum manifested the broadband distribution, and the predominant frequency was about 20–35 Hz. The high-frequency portion was generated by micro-cracks, and the low-frequency part attributed to macro-fracture for gas outburst channel. (3) The rockburst stimulated micro-fissures formation for gas emission channels, and maintained the event count of MS and AE signals in a relatively higher level, which is a major discrepancy to the common belief that both the total energy and event count should simultaneously and suddenly reduce to the lowest value in a non-outburst coal seam.     

Research Status and Advances in Chert and Permian Chert Event

Cherts are concret research objects for petro-tectonic framework and are widespreadly distributed in special sedimentary environments along orogenic belts and depositional basins. Cherts hold abundant origin related information, which plays important role in palogeographic and paleooceanograpic study. This paper reviewed the history and the advancement of research on chert, especially paying more attention to the research progress about both bedded chert and nodular chert in domestic and international research areas. Combined with Permian cherts distribution in China, we discuss research achivements of silica sources, sedimentary environments and original mechanism from cherts deposited in different sedimentary environments such as oceanic rift, oceanic basin and continent shelf. “Permian Chert Event” (PCE) has been used to discribe the widespread biogenic Permian cherts that occurred around the eastern margins of Panthalassa and Paleotethys Ocean. Research results on Permian cherts in eastern Paleotethys Ocean, particularly the Yangtze areas, are examined here, which suggest Permian cherts are not typically biogenic in origin but severely influenced by hydrothermal sedimentation. The seasonal melting of sea ice is assumed engine for PCE in northwest edge of Pangea Supercontinent, but that dose not work in China. Therefore, a hypothesis different form thermohaline circulation and upwelling is proposed here: there would be a periodical hydrothermal fluid system in the eastern Paleotethys Ocean, providing the source of silica for the development of Permian Chert Event on both south and north continent shelves. What is more, some intensively studied Permian outcrops in the Yangtze areas have the potential to be the typical outcrops for PCE research in China.