How a wet tropical rainforest copes with repeated volcanic destruction

The Holocene Period for the province of West New Britain, Papua New Guinea, is characterised by periodic catastrophic volcanism. The region is mantled in dense wet tropical rainforest, and has been occupied by people since the Pleistocene. Analyses of peat from two nearby sites within a lowland rainforest environment provide us with a macro-level landscape account of the periodic destruction and recovery of the coastal forests during seven periods of volcanic activity in the latter part (2900 yr ago to present) of the Holocene. Radiocarbon dating shows the very close correlation of the peat and tephra layers at both sites, yet the pollen analysis reveals different vegetation communities. These initial results allow us to begin identifying the processes of recovery, and to recognise different ecological pressures placed on vegetation at these neighbouring sites. Evidence of hydrological changes are observed beginning with a marine incursion recorded at Garu Site 3 1360 ¹⁴C yr B.P. The distinct differences in the vegetation re-establishment and community regeneration rates suggest the greater level of disturbance at Garu Site 1 could be related to the depth of the ashfall, although the proximity of a known human settlement may also be a contributing factor. Of note, palynologically, we found that the fern spore flora is particularly rich and believe it will be useful for ecological interpretation.     

中国海相油气田勘探实例(之一) 四川盆地罗家寨大型气田的发现和探明

罗家寨气田发现于2000年,是四川盆地迄今为止发现的储量规模最大的一个气田,2002年探明储量为581.08×108m3。其下三叠统飞仙关组储层由碳酸盐岩蒸发台地边缘优质鲕粒滩白云岩构成,圈闭面积大,构造幅度高,具有一定的埋藏隐蔽性。论述了气田的发现和探明过程,气藏地质的特征,以及对碳酸盐岩气藏勘探的启示。     

The postglacial history of three Picea species in New England, USA

Given the difficulty of separating the three Picea species—P. glauca, P. mariana, and P. rubens (white, black, and red spruce)—in the pollen record, little is known about their unique histories in eastern North America following deglaciation. Here we report the first use of a classification tree analysis (CART) to distinguish pollen grains of these species. It was successfully applied to fossil pollen from eight sites in Maine and one in Massachusetts. We focused on the late glacial/early Holocene (14,000 to 8000 cal yr B.P.) and the late Holocene (1400 cal yr B.P. to present)—the two key periods since deglaciation when Picea has been abundant in the region. The result shows a shift from a Picea forest of P. glauca and P. mariana in the late glacial to a forest of P. rubens and P. mariana in the late Holocene. The small number of P. rubens grains identified from the late glacial/early Holocene samples (<5%) suggests that that species was either absent or rare at most of the sites. The occurrence and distribution of the three species do not reveal any geographic or temporal trend during late glacial time, but the data suggest that they were distributed in local patches on the landscape. The results of this study indicate that the recent population expansion of Picea (1000 to 500 cal yr B.P.) was likely the first time since deglaciation that P. rubens was abundant in the region.     

台湾恒春半岛的隆起珊瑚礁台地

台湾本岛南端的恒春半岛,出露隆起珊瑚礁石灰岩和现代珊瑚礁海岸。隆起珊瑚礁石灰岩在地貌上的表现是多阶的台地。最高的公园面可达海拔300m,依次向下,是海拔约100～160m的笼仔埔面,海拔70～80m的埔顶面以及海拔10～20m的垦丁面。在恒春半岛的西侧,珊瑚礁台地面已经倾斜,因此高度的表现不同。ESR及14C定年表明,抬升的更新世珊瑚礁台地形成于0.5Ma B.P.前后及0.13Ma B.P.两时期;海拔10～20m的全新世珊瑚礁台地约形成于6 000a B.P.的时期。这些证据显示了地质时期里全球变迁的蛛丝马迹。     

秦岭祁连山昆仑山构造发展史与南北中国板块的拼合

按秦岭祁连山昆仑山发展演化，中国大陆的形成可总结为3阶段板块拼贴“焊合”模型即：中元古代至新元古代早期，原始秦昆洋俯冲—消减，塔里木—华北古陆（北中国板块）与华南洋域新生陆壳（南中国板块）拼贴增生，形成原始中国古陆；震旦纪至志留纪，原始中国古陆裂解，秦祁海洋扩张—俯冲—消减，阿拉善—华北板块（北中国板块）与塔里木、柴达木、华南组成的联合板块（南中国板块）缝合统一，形成古中国板块，泥盆纪至三叠纪早期，古特提斯洋俯冲—消减，藏滇板块（基梅里大陆一部分）与古中国板块碰撞拼贴，滨邻古特提斯洋的中国大陆西南缘（秦祁昆地区）全面皱起，造就中国大陆轮廓；中生代以来，板内超长期继承性汇聚和滨西太平洋边缘构造带、新特提斯—喜马拉雅构造叠加、改造，造就现令中国大陆构造、地势。     

碧口地块东-北缘中、新生代构造隆升及演化：来自磷灰石和锆石裂变径迹的证据

青藏高原具有复杂的构造演化特征,该地区自中、新生代以来的构造隆升和构造演化机制一直是地质研究的热点。为精细刻画青藏高原板块、华北板块和华南板块之间的拼合关系及差异性隆升特征,对位于青藏高原东北端的碧口地块进行了磷灰石和锆石裂变径迹测试,以及热史模拟和岩石冷却速率计算。结果锆石和磷灰石裂变径迹年龄分别在（118±5～265±29）Ma和（29.0±2.7～54.0±7.0）Ma之间;碧口地块东北缘及北缘冷却速率接近,在3.125～3.448 ℃/Ma之间,东缘冷却速率相对较低,为2.041～2.273 ℃/Ma。结果表明,中、新生代以来,碧口地块及其周缘总体上经历了持续隆升过程,但不同地区隆升特征具有差异性：碧口地块北侧在早、中侏罗世（151±7）Ma经历了构造挤压和隆升过程;东部相对较晚,在晚侏罗世（143±11）Ma经历了构造隆升阶段;东北端在早白垩世才与华北板块拼接并进入持续构造隆升阶段。进入古近纪（54.0±7.0）Ma隆升阶段,即始新世早期后,碧口地块东缘在始新世中后期（44 Ma）开始发生构造隆升,北缘自渐新世中晚期（29～32 Ma）开始发生显著的构造隆升。上述区域在10 Ma（中新世晚期）共同进入快速隆升阶段。     

湖相沉积物与全球变化的研究

为预测未来全球的气候变化，必须了解在过去水圈、气圈与生物圈的各自作用以及它们是如何相互影响的。为此，ＩＧＢＰ（国际地圈－生物圈计划）组织了过去全球变化项目（ＰＡＧＥＳ）。湖相沉积物保存着与ＰＡＧＥＳ有关的不同时空尺度的丰富的地球系统历史信息，特别是湖相沉积物包含着可以说明全球气候变化的水圈与生物圈的陆源组分的反应。这种信息对了解影响气候变化的流域是如何发展的至关重要。笔者应用西伯利亚贝加尔湖与中国西北部青海湖作为两个实例，叙述了多学科研究湖相沉积物物理与化学参数，并利用这些参数测定了晚更新世湖区及其流域对过去气圈的变化以及日幅射分布的影响     

The Evolutionary History of Ore-forming Processes of Metallic Ore Deposits in Northern Guangxi1

Abstract The northern Guangxi region is an important rare metal, rare earth metal and polymetallic metallogenic province. In the region there exist five metallogenic series and two metallogenic subseries, whose metallogenesis shows features of polycyclic spiral evolution throughout the geological history. As far as various cycles are concerned, mantle-derived ore substances were reduced while crust-derived ore substances increased from early to late times; in the whole geological evolutionary history, mantle-derived substances decreased gradually while crust-derived ones increased. Meanwhile ore element associations became more and more varied. In terms of space, mineralization migrated from the old basement outwards, i.e. from west to east during the Precambrian, and from north to south during the Phanerozoic, and again from east to west during the Yanshanian.     

鄂尔多斯盆地东北部构造热演化史的磷灰石裂变径迹分析

运用磷灰石裂变径迹(AFT)分析的构造热年代学研究方法,系统探讨鄂尔多斯盆地东北部不同区段中新生代以来的热演化历史,为盆地东北部石油和天然气等多种沉积能源矿产的勘探预测提供新的约束条件。模拟结果表明:盆地东北部经历了250~150 Ma缓慢埋藏增温过程,平均增温速率为0.9℃/Ma;150~120 Ma为快速增温阶段,平均增温速率高达2.1℃/Ma,地层温度达到最高,且均大于130℃。之后不同区段经历差异降温过程:北缘露头区经历了120~65 Ma快速降温,平均冷却速率约1.3℃/Ma;65~10 Ma缓慢降温,平均冷却速率约为0.4℃/Ma。南缘露头区及盆地沉降区则经历了120~30 Ma缓慢降温,平均冷却速率约为0.9℃/Ma;30~10 Ma快速降温,平均冷却速率约为1.5℃/Ma。10 Ma以来,盆地东北部整体抬升冷却,平均冷却速率约6.5℃/Ma。分析结果认为燕山中期构造热事件之最高热增温作用的关键时刻为(120±10)Ma,促成鄂尔多斯盆地东北部主要烃源岩层系的成熟生烃和大规模油气成藏。在后期的差异抬升冷却过程中,北缘露头区在65 Ma±通过了110℃等温面,南缘露头区及盆地的沉降区在30 Ma±通过了110℃等温面,有利于相邻地区原生油气藏的积聚和保存,古近纪晚期(30 Ma)尤其是新近纪晚期近10 Ma以来的强烈构造抬升作用有可能是引发原生油气藏调整—改造和次生成藏的关键因素。     

http://www.sciencedirect.com/science/article/pii/S1674987111000594

A new model is suggested for the history of the Baikal Rift,in deviation from the classic two-stage evolution scenario,based on a synthesis of the available data from the Baikal Basin and revised correlation between tectonic-lithological-stratigraphic complexes(TLSC) in sedimentary sections around Lake Baikal and seismic stratigraphic sequences(SSS) in the lake sediments.Unlike the previous models,the revised model places the onset of rifting during Late Cretaceous and comprises three major stages which are subdivided into several substages.The stages and the substages are separated by events of tectonic activity and stress reversal when additional compression produced folds and shear structures.The events that mark the stage boundaries show up as gaps,unconformities,and deformation features in the deposition patterns. The earliest Late Cretaceous-Oligocene stage began long before the India-Eurasia collision in a setting of diffuse extension that acted over a large territory of Asia.The NW-SE far-field pure extension produced an NE-striking half-graben oriented along an old zone of weakness at the edge of the Siberian craton.That was already the onset of rift evolution recorded in weathered lacustrine deposits on the Baikal shore and in a wedge-shaped acoustically transparent seismic unit in the lake sediments.The second stage spanning Late Oligocene-Early Pliocene time began with a stress change when the effect from the Eocene India-Eurasia collision had reached the region and became a major control of its geodynamics.The EW and NE transpression and shear from the collisional front transformed the Late Cretaceous half-graben into a U-shaped one which accumulated a deformed layered sequence of sediments.Rifting at the latest stage was driven by extension from a local source associated with hot mantle material rising to the base of the rifted crust.The asthenospheric upwarp first induced the growth of the Baikal dome and the related change from finer to coarser molasse deposition.With time,the upwarp became a more powerful stress source than the collision,and the stress vector returned to the previous NW-SE extension that changed the rift geometry back to a half-graben. The layered Late Pliocene-Quaternary subaerial tectonic-lithological-stratigraphic and the Quaternary submarine seismic stratigraphic units filling the latest half-graben remained almost undeformed.The rifting mechanisms were thus passive during two earlier stages and active during the third stage. The three-stage model of the rift history does not rule out the previous division into two major stages but rather extends its limits back into time as far as the Maastrichtian.Our model is consistent with geological, stratigraphic,structural,and geophysical data and provides further insights into the understanding of rifting in the Baikal region in particular and continental rifting in general.