On the recent warming of the southeastern Bering Sea shelf   总被引：1，自引：0，他引：1  

P.J. Stabeno  N.A. Bond  S.A. Salo 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2599

During the last decade, the southeastern Bering Sea shelf has undergone a warming of 3 °C that is closely associated with a marked decrease of sea ice over the area. This shift in the physical environment of the shelf can be attributed to a combination of mechanisms, including the presence over the eastern Bering Sea shelf of a relatively mild air mass during the winter, especially from 2000 to 2005; a shorter ice season caused by a later fall transition and/or an earlier spring transition; increased flow through Unimak Pass during winter, which introduces warm Gulf of Alaska water onto the southeastern shelf; and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter. While the relative importance of these four mechanisms is difficult to quantify, it is evident that for sea ice to form, cold arctic winds must cool the water column. Sea ice is then formed in the polynyas during periods of cold north winds, and this ice is advected southward over the eastern shelf. The other three mechanisms can modify ice formation and melt, and hence its extent. In combination, these four mechanisms have served to temporally and spatially limit ice during the 5-year period (2001–2005). Warming of the eastern Bering Sea shelf could have profound influences on the ecosystem of the Bering Sea—from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species.  相似文献   

黔东南凯里-榕江-从江前寒武系甚低级变质作用研究   总被引：1，自引：0，他引：1  

安佳丽  王河锦  苑蕾 《岩石学报》2018,34(3):669-684

根据碎屑岩甚低级变质作用原理,运用伊利石结晶度、绿泥石结晶度、伊利石-白云母多型、伊利石(白云母)b_0值、绿泥石温度计等碎屑岩低温变质研究的方法,分析研究了黔东南前寒武系67个2μm的粘土样品,得到黔东南凯里-榕江-从江一带下江群伊利石结晶度为0.221~0.607°Δ2θCu Kα、绿泥石结晶度为0.239~1.393°Δ2θCu Kα,变质带伊利石-白云母多型均为2M_1型,伊利石(白云母)b_0值为0.9001~0.9048nm,平均0.9021nm。根据伊利石(白云母)b_0值的累积频率曲线得出研究区下江群遭受的变质作用为典型的中压变质类型。由Cathelineau(1988)绿泥石温度计估算出下江群浅变质带峰期变质温度为362~382℃。以上结果表明凯里-榕江-从江一带下江群经历了成岩-高近变质-浅变质作用,基于Warr和Rice标样的成岩/变质界限,剖面可划分为一个成岩带、两个近变质带、一个转变带和一个浅变质带。结合华南地区新元古代构造运动,推断新元古界下江群经历的成岩-变质作用与晋宁运动引起的扬子地块与华夏地块碰撞拼贴有关。  相似文献   

中亚造山带东南部晚古生代-早中生代地壳增生和古亚洲洋演化:来自内蒙古东南部林西-东乌旗地区岩浆岩的证据SCIEI北大核心CSCD     

刘建峰  李锦轶  赵硕  张进  郑荣国  张文龙  吕前露  郑培玺 《岩石学报》2022,(8):2181-2215

本文在系统收集内蒙古林西-东乌旗地区晚古生代-早中生代岩浆岩的年代学、岩石地球化学以及锆石Hf同位素资料基础上,通过分析岩浆岩岩石组合随时空的变化规律,并结合区域地质资料,探讨了中亚造山带东南部洋盆演化和地壳增生等重要地质问题。研究结果表明,二连浩特-贺根山蛇绿岩带南、北两侧晚古生代-早中生代岩浆岩在年代学上显示不同的活动期次,具有不同岩石组合和地球化学特征,指示它们分属于不同的构造岩浆岩带。蛇绿岩带以北晚泥盆世-中二叠世岩浆活动在时间上呈连续分布的特征,并在晚石炭-早二叠世时期达到活动峰值。火成岩构造组合分析表明,晚泥盆世-石炭纪和早-中二叠世岩浆活动分别与二连浩特-贺根山洋盆向乌里雅斯太大陆边缘之下的俯冲和洋盆闭合后俯冲板片断离引起的软流圈上涌造成的区域伸展背景有关。蛇绿岩带以南岩浆活动时间上呈现石炭纪、早-中二叠世、晚二叠世-三叠纪幕式分布特征,各期岩浆活动前锋有随时间向南迁移的趋势。这三期岩浆活动分别与古亚洲洋板片向宝力道岛弧之下的俯冲、板片后撤以及洋盆消失之后古板块的碰撞造山作用有关。锆石Hf同位素分析表明,中亚造山带东南部晚古生代至早中生代时期存在显著的地壳增生;其中二连浩特-贺根山蛇绿岩带以北表现为地壳的垂向增生,以南表现为地壳的侧向增生。  相似文献   

Deep-sea reef fish assemblage patterns on the Blake Plateau(Western North Atlantic Ocean)     

Steve W. Ross  & Andrea M. Quattrini 《Marine Ecology》2009,30(1):74-92

Deep‐water coral habitats are scattered throughout slope depths (360–800 m) off the Southeastern United States (SEUS, Cape Lookout, North Carolina, to Cape Canaveral, Florida), contributing substantial structure and diversity to bottom habitats. In some areas (e.g. off North Carolina) deep corals form nearly monotypic (Lophelia pertusa) high profile mounds, and in other areas (e.g. off Florida) many species may colonize hard substrata. Deep coral and hard substrata ecosystems off the SEUS support a unique fish assemblage. Using the Johnson‐Sea‐Link submersible (in 2000–2005, 65 dives), and a remotely operated vehicle (in 2003, five dives), fishes were surveyed in nine deep reef study areas along the SEUS slope. Forty‐two benthic reef fish species occurred in deep reef habitats in these study areas. Species richness was greatest on the two coral banks off Cape Lookout, North Carolina (n = 23 and 27 species) and lowest on the two sites off Cape Canaveral, Florida (n = 7 and 8 species). Fish assemblages exhibited significantly (ANOSIM, Global R = 0.69, P = 0.001) different patterns among sites. Stations sampled off North Carolina (three study areas) formed a distinct group that differed from all dives conducted to the south. Although several species defined the fish assemblages at the North Carolina sites, Laemonema barbatulum, Laemonema melanurum, and Helicolenus dactylopterus generally had the most influence on the definition of the North Carolina group. Fish assemblages at three sites within the central survey area on the Blake Plateau were also similar to each other, and were dominated by Nezumia sclerorhynchus and L. melanurum. Synaphobranchus spp. and Neaumia sclerorhynchus differentiated the two southern sites off Cape Canaveral, Florida, from the other station groups. Combinations of depth and habitat type had the most influence on these station groups; however, explicit mechanisms contributing to the organization of these assemblages remain unclear.  相似文献   

Origin of the hydrocarbon gases carbon dioxide and hydrogen sulfide in Dodan Field (SE-Turkey)     

《Marine and Petroleum Geology》2014

Gas occurrences consisting of carbon dioxide (CO₂), hydrogen sulfide (H₂S), and hydrocarbon (HC) gases and oil within the Dodan Field in southeastern Turkey are located in Cretaceous carbonate reservoir rocks in the Garzan and Mardin Formations. The aim of this study was to determine gas composition and to define the origin of gases in Dodan Field. For this purpose, gas samples were analyzed for their molecular and isotopic composition. The isotopic composition of CO₂, with values of −1.5‰ and −2.8‰, suggested abiogenic origin from limestone. δ³⁴S values of H₂S ranged from +11.9 to +13.4‰. H₂S is most likely formed from thermochemical sulfate reduction (TSR) and bacterial sulfate reduction (BSR) within the Bakuk Formation. The Bakuk Formation is composed of a dolomite dominated carbonate succession also containing anhydrite. TSR may occur within an evaporitic environment at temperatures of approximately 120–145 °C. Basin modeling revealed that these temperatures were reached within the Bakuk Formation at 10 Ma. Furthermore, sulfate reducing bacteria were found in oil–water phase samples from Dodan Field. As a result, the H₂S in Dodan Field can be considered to have formed by BSR and TSR.As indicated by their isotopic composition, HC gases are of thermogenic origin and were generated within the Upper Permian Kas and Gomaniibrik Formations. As indicated by the heavier isotopic composition of methane and ethane, HC gases were later altered by TSR. Based on our results, the Dodan gas field may have formed as a result of the interaction of the following processes during the last 7–8 Ma: 1) thermogenic gas generation in Permian source rocks, 2) the formation of thrust faults, 3) the lateral-up dip migration of HC-gases due to thrust faults from the Kas Formation into the Bakuk Formation, 4) the formation of H₂S and CO₂ by TSR within the Bakuk Formation, 5) the vertical migration of gases into reservoirs through the thrust fault, and 6) lateral-up dip migration within reservoir rocks toward the Dodan structure.  相似文献   

桂东南那卜地区古生代变质岩系的构造演化序列     

覃小锋  李锦诚 《南方国土资源》2001,14(2):7-13

桂东南那卜地区古生代变质岩系 ,主要由花岗质岩石 (宁潭超单元 )和古生界组成。岩石构造变形强烈 ,构造形迹复杂 ,根据不同尺度上观察到的各种构造要素的几何学、运动学、构造应力场以及相互叠加关系等特征 ,可将其组成不同的构造组合 (群落 )。依据各构造组合之间的相互关系、同位素年龄 ,并结合相应的变质事件和岩浆活动事件等 ,建立起 2个旋回和 4个世代的构造变形序列。并初步探讨了古生代变质岩系的构造演化过程。  相似文献   

Rare-earth elements as source indicators of Pan-African granites from Obudu Plateau,Southeastern Nigeria   总被引：1，自引：1，他引：0  

V. U. Ukaegbu  F. T. Beka 《中国地球化学学报》2008,27(2):130-134

The rare-earth element （REE） concentrations of representative granite samples from the southeast of the Obudu Plateau, Nigeria, were analyzed with an attempt to determine the signatures of their source, evolutionary history and tectonic setting. Results indicated that the granites have high absolute REE concentrations （190×10^-6-1191×10^-6; av.=549×10^-6） with the chondrite-normalized REE patterns characterized by steep negative slopes and prominent to slight or no negative Eu anomalies. All the samples are also characterized by high and variable concentrations of the LREE （151×10^-6-1169×10^-6; av.= 466×10^-6）, while the HREE show low abundance （4×10^-6-107×10^-6; av.=28×10^-6）. These are consistent with the variable levels of REE fractionation, and differentiation of the granites. This is further supported by the range of REE contents, the chondrite-normalized patterns and the ratios of LaN/YbN （2.30-343.37）, CeN/YbN （5.94-716.87）, LaN/SmN （3.14-11.68） and TbN/YbN （0.58-1.65）. The general parallelism of the REE patterns, suggest that all the granites were comagmatic in origin, while the high Eu/Eu＊ ratios （0.085-2.807; av.=0.9398） indicate high fo2 at the source. Similarly, irregular variations in LaN/YbN, CeN/YbN and Eu/Eu＊ ratios and REE abundances among the samples suggest behaviors that are related to mantle and crustal sources.  相似文献   

东非鲁伍马盆地深水区构造-沉积演化过程及油气地质特征   总被引：1，自引：0，他引：1  

陈宇航  姚根顺  吕福亮  唐鹏程  鲁银涛 《海相油气地质》2016,(2):39-46

利用深水区的二维、三维地震资料开展构造-沉积演化研究,鲁伍马盆地二叠纪—早侏罗世为冈瓦纳陆内—陆间裂谷活动期,发育河流—湖泊沉积;中侏罗世—早白垩世为马达加斯加漂移期,位于剪切型大陆边缘,发育海陆过渡相沉积;晚白垩世—渐新世为被动大陆边缘期,深水沉积广泛发育,重力流沉积延伸至戴维隆起带;中新世—第四纪为东非裂谷海域分支活动期,陆坡和凯瑞巴斯地堑发育深水重力流沉积。盆地垂向上形成"断—坳—断"结构,二叠纪—早侏罗世及中新世—现今发育两期明显的裂谷活动。马达加斯加漂移期的海相泥岩为深水区的主力烃源岩,古近纪的陆坡深水浊积砂体为主要储层。东非裂谷海域分支的断层活动沟通了下伏烃源岩,晚期断层不发育的西部陆坡成为主要的油气聚集区。  相似文献   

滇东南安那金矿床成矿流体地球化学研究   总被引：1，自引：1，他引：0  

董文斗  沈能平  苏文超  蔡佳丽 《岩石学报》2016,32(11):3321-3330

云南安那金矿床位于右江盆地南缘,产于二叠纪辉绿岩侵入体之中,广泛发育乳白色石英网脉,蚀变辉绿岩体即为金矿体。与右江盆地以沉积岩为容矿岩石的卡林型金矿床类似,具有硅化、粘土化、碳酸盐化和硫化物化等热液蚀变特征。本文对安那金矿床石英中的流体包裹体岩相学、显微测温学、激光拉曼光谱以及氢氧同位素组成进行了分析,发现成矿期石英中的流体包裹体主要为富含CO_2气-液两相或三相流体包裹体,其均一温度范围为208~312℃(平均254℃),盐度很低,变化范围为0~2%Na Cleqv,成矿溶液的密度为0.88~0.98g/cm~3,表明形成安那金矿床的成矿流体属于中温、低盐度、中-低密度的流体。激光拉曼光谱分析显示,石英中包裹体的气相成分富含CO_2、N_2以及微量CH_4等挥发分。成矿流体的氢氧同位素组成显示变质流体成因,结合矿石显微岩相学结构,认为流体溶蚀交代辉绿岩中的含Ti-Fe辉石或者钛铁矿,溶解Fe的硫化作用过程是含Au黄铁矿和毒砂沉淀富集的重要机制。成矿作用可能与右江盆地南缘印支期造山事件有关。  相似文献   

The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria     

V. Fischer  A. ClémentM. Guiomar  P. Godefroit 《Cretaceous Research》2011,32(2):155-163

A complete ichthyosaur rostrum, with 124 associated teeth, was recently discovered in Laux-Montaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. This specimen also represents the first occurrence of Aegirosaurus outside the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Tooth morphology and wear pattern suggest that Aegirosaurus belonged to the “Pierce II/ Generalist” feeding guild, which was hitherto not represented in post-Liassic ichthyosaurs. Most Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary.  相似文献