东秦岭东段新发现的沙坡岭细脉浸染型钼矿地质特征、Re-Os同位素年龄及其地质意义

豫西洛宁沙坡岭钼矿床位于华北克拉通南缘东秦岭钼矿带东段,是新近发现的赋存于太古宙太华群变质岩中的细脉浸染型钼矿床。本文对其地质特征进行了研究,并初步测定了1个辉钼矿样品的Re－Os同位素年龄,获得模式年龄为126.8±1.7Ma,表明沙坡岭钼矿形成于燕山期,接近金堆城、雷门沟钼矿的形成时代,Re同位素含量显示其地幔来源的特征。沙坡岭钼矿形成机制错综复杂,有待进一步研究,特别是深部钻孔工程验证工作,对于验证深部是否隐伏着与成矿相关的斑岩体、储量更大的斑岩型钼矿有着重要作用,找矿潜力巨大。     

青藏高原羌塘盆地晚侏罗世索瓦期沉积特征研究

为推进我国石油工业发展丰富石油地质理论,根据野外露头及室内分析化验资料,建立8种相标志,识别出索瓦期沉积相类型有：台地相、台地边缘相、盆地相和海陆过渡相、湖泊相。受北部拉竹龙-金沙江缝合带、中央隆起带和南部班公湖-怒江缝合带的影响,沉积相呈近东西向展布,具南北分带的特点。文章分析了索瓦期的沉积特征,总结了该期的沉积模式。根据研究区的生物特征和沉积特征,推断当时气候是温暖、半干旱的。综合分析认为,索瓦组是羌塘盆地很有潜力的油气勘探目的层,其与上覆雪山组地层可构成有利的含油气组合;而双湖-多涌地区是首选的含油气有利区带。     

Middle pleistocene interglacial sediments at Tye green,Stansted Airport,Essex, England

Interglacial lake deposits at Tye Green, Stansted, resting on unweathered till and overlain by a weathered diamicton are correlated with the temperate Hoxnian Stage. The sediments represent the infilling of an isolated kettle-hole type of lake basin formed at the end of the cold Anglian Stage. Through the temperate period this basin was infilled by inorganic and organic sediments that record the development and decline of deciduous forest. Later periglacial conditions are indicated by the final infilling of the basin by reworked till. The sedimentary sequence and vegetational development recorded in the sediments at Tye Green are compared with other Hoxnian sites in eastern England. Changes in deposition rates are interpreted as representing water-table fluctuations resulting from changes in precipitation. The deposits at Tye Green provide a useful stratigraphical marker in the glacial sequence of the district. Copyright © 1999 John Wiley & Sons, Ltd.     

High-resolution calcareous nannofossil biostratigraphy of the Santonian/Campanian Stage boundary,Western Interior Basin,USA

The base of the Campanian Stage does not have a ratified Global Stratotype Section and Point (GSSP); however, several potential boundary markers have been proposed including the base of the Scaphites leei III ammonite Zone and the base of the paleomagnetic Chron C33r. Calcareous nannofossil assemblages from the Smoky Hill Member of the Niobrara Formation in the central Western Interior Seaway, USA were analyzed from two localities to determine relevant biohorizons and their relationships to these potential boundary markers. In a previous study, the Aristocrat Angus 12-8 core (Colorado) was astrochronologically dated and constrained using macrofossil zonations and radiometric ages. The Smoky Hill Member type area (Kansas) provides an expanded interval with good to excellent nannofossil preservation.Five biohorizons are useful for recognition of the Santonian/Campanian transition within the Smoky Hill Member type area, and three are useful in the Aristocrat Angus 12-8 core. The first occurrences (FOs) of Aspidolithus parcus parcus and Aspidolithus parcus constrictus, as well as the last occurrences (LOs) of Zeugrhabdotus moulladei, Helicolithus trabeculatus specimens larger than 7 μm, and Zeugrhabdotus biperforatus are in close stratigraphic proximity to the base of the Scaphites leei III Zone and the base of Chron C33r.     

考虑弱层置换的岩石边坡稳定性分析

锦屏一级水电站左岸边坡地质结构复杂,岩体存在大量深部裂隙、低波速松弛岩体、煌斑岩脉X及f2、f5断层,严重影响边坡的稳定性。采用基于强度折减法的岩石破裂过程分析RFPA方法对边坡典型部位在开挖后以及其对应弱层置换工况下的破坏全过程进行计算和分析,计算结果表明,f5断层在进行置换加固处理后,边坡安全系数较未置换弱层前提高了0.403,说明在岩质边坡开挖和支护前优先进行深部软弱结构置换处理,可以大大提高工程结构的安全储备。同时,RFPA强度折减法不仅能直观再现边坡潜在滑裂面从萌生到扩展直至贯通导致边坡整体失稳的全过程,而且可以得出边坡安全系数。研究结果对于边坡工程实施前稳定性评价和施工工序具有一定的参考价值。     

昆仑山口西8.1级地震孕育演化的阶段性初步研究

按时间的顺序,将2001年昆仑山口西8．1级地震前的地球物理场转折、中强地震图像演化、周缘动力环境变化、震时的同震变化、震后的地震活动响应与前兆场的调整、5级以上地震的持续平静等过程衔接起来,划分出了该次巨大地震震前、震时、震后的5个不同演化阶段。     

Evolution of sedimentary environments of the middle Jiangsu coast, South Yellow Sea since late MIS 3

An evolutionary model of sedimentary environments since late Marine Isotope Stage 3 （late MIS 3, i.e., ca. 39 cal ka BP） along the middle Jiangsu coast is presented based upon a reinterpretation of core 07SR01, new correlations between adjacent published cores, and shallow seismic profiles recovered in the Xiyang tidal channel and adjacent northern sea areas. Geomorphology, sedimentology, radiocarbon dating and seismic and sequence stratigraphy are combined to confirm that environmental changes since late MIS 3 in the study area were controlled primarily by sea-level fluctuations, sediment discharge of paleo-rivers into the South Yellow Sea （SYS）, and minor tectonic subsidence, all of which impacted the progression of regional geomorphic and sedimentary environments （Le., coastal barrier island freshwater lacustrine swamp, river floodplain, coastal marsh, tidal sand ridge, and tidal channel）. This resulted in the formation of a fifth-order sequence stratigraphy, comprised of the parasequence of the late stage of the last interstadial （Para-Sq2）, including the highstand and forced regressive wedge system tracts （HST and FRWST）, and the parasequence of the postglacial period （Para-Sql）, including the transgressive and highstand system tracts （TST and HST）. The tidal sand ridges likely began to develop during the postglacial transgression as sea-level rise covered the middle Jiangsu coast at ca. 9.0 cal ka BP. These initially submerged tidal sand ridges were constantly migrating until the southward migration of the Yellow River mouth to the northern Jiangsu coast during AD 1128 to 1855. The paleo-Xiyang tidal channel that was determined by the paleo-tidal current field and significantly different from the modern one, was in existence during the Holocene transgressive maxima and lasted until AD 1128. Following the capture of the Huaihe River in AD 1128 by the Yellow River, the paleo-Xiyang tidal channel was infilled with a large amount of river-derived sediments from AD 1128 to 1855, causing the emergence of some of the previously submerged tidal sand ridges. From AD 1855 to the present, the infilled paleo-Xiyang tidal channel has undergone scouring, resulting in its modern form. The modern Xiyang tidal channel continues to widen and deepen, due both to strong tidal current scouring and anthropogenic activities.     

内蒙古西部银额盆地及邻区二叠系隆林阶—冷坞阶层序地层格架

依据露头层序地层学原理,对银额盆地及邻区二叠系隆林阶—冷坞阶露头剖面进行层序界面的识别和层序划分,共划分为2个Ⅲ级层序。在对东西、南北向层序地层对比的基础上,初步建立了研究区的层序地层格架。隆林期—罗甸期全区发生大范围的海侵接受海相沉积,以滨海—浅海陆棚相为主,局部发育碳酸盐岩台地相,盆地边缘发育过渡相沉积,有2个沉积中心,黑鹰山-额济纳旗坳陷带的沉积中心在碧云泉南-芦草井地区,柳园-巴丹吉林坳陷带的沉积中心在卡路山-杭乌拉一带。祥播期-冷坞期继承了前期的沉积格局,只是沉积范围向北西缩小,黑鹰山-额济纳旗坳陷带的沉积中心在芦草井地区,柳园-巴丹吉林坳陷带水体变浅,沉积中心在古硐井地区。     

Stratigraphic records of the dynamic uplift of the Emeishan large igneous province

Abstract

Fluid dynamical and numerical modelling predicts a large-scale regional domal uplift prior to basalt eruptions in large igneous provinces, which can be readily measured when a plume head rises below a shallow marine sedimentary basin. Research on the sedimentology, biostratigraphy, and isotopic chronology of the Emeishan large igneous province demonstrates that the sedimentary environment in the Maokou stage is not uniform carbonate platform facies, but rather sedimentary facies with a north–south linear alignment and west–east different distribution controlled by the syn-depositional normal faulting of the Changhai and Xiaojiang faults, which are the result of underwater dynamic uplift induced by deep mantle activity. The dynamic uplift started in the Maokou stage. Thus, thinning of the Maokou limestone was the product of the difference in the initial depositional thickness caused by the underwater uplift and post-depositional surface uplift and erosion, but post-depositional uplift was much less than kilometre scale. Sedimentary facies differentiation and tectonic–sedimentary evolution in the Maokou stage provide a constraint for the time of the initial eruption and eruption environment before and during the Emeishan basalt eruption. Small-scale magmatic activity might have already begun in the middle of the Maokou stage, whereas submarine and terrestrial sedimentary environments coexisted before and during Emeishan basalt eruption.     

蜀南地区二叠系茅口组古岩溶地区水系分布及岩溶地貌单元特征*

蜀南地区茅口组为一套沉积稳定的巨厚层生物碎屑灰岩,基质致密性脆。中二叠世末的东吴运动使蜀南地区茅口组顶部发育古风化壳岩溶,古岩溶地区水系控制着古岩溶的发育和演化。在研究古地貌恢复方法的基础上,分析研究区地层特征和区域构造背景,采用印模法进行古地貌恢复,进而研究了古岩溶地区的水系发育特征。在此基础上,结合风化壳表面侵蚀溶蚀特征、沉积物性质、地貌组合形态、钻井和地震资料,把研究区划分为岩溶台地、岩溶陡坡、岩溶缓坡及岩溶盆地4种二级地貌单元和溶丘洼地、岩溶槽谷、峰林平原等10种三级地貌单元,进一步分析了各种地貌单元的岩溶特征,为下一步的储集层预测提供了有利的目标。