川中中侏罗统凉高山组-下沙溪庙组储层特征

以川中地区钻井岩心及露头剖面样品的镜下岩石学特征为基础,对川中中侏罗统凉高山组-下沙溪庙组储层进行了研究,认为储层类型主要为孔隙-裂缝型,而次生溶蚀孔及裂缝提供了最主要的储集空间。储层的发育主要受到沉积微相、物源方向、成岩作用、溶蚀作用以及构造破裂作用等因素控制。其中沉积微相和物源方向是储层发育的物质基础;溶蚀作用及构造破裂作用是储层改善的关键因素;而压实、压溶、胶结、交代等成岩作用则对储层的发育是不利的。     

新疆古伦沟地区古仍格萨拉东岩体的地球化学及锆石U-Pb年龄

古伦沟地区古仍格萨拉东花岗闪长斑岩体位于中天山构造带北缘。地球化学和锆石U-P年龄测定结果显示: 岩石高碱富Na、贫Fe和Mg、弱过铝质(ACNK=0.98~1.11), 稀土总量较低(∑REE=61.28×10-6~99.50×10-6)且分异明显(LaN/YbN=7.82~22.80)、铕弱负异常(δEu=0.72~0.97), 相对富集Rb、Ba、Th、U、K等, 亏损Nb、Ta、P、Ti等, 具火山弧花岗岩的特征。岩体具有较均一的Sr、Nd同位素组成: (87Sr/86Sr)i=0.70677~0.70685, εSr(t)=40.10~41.21, (143Nd/144Nd)i=0.51190~0.51191, εNd(t)= –2.62 ~ –2.30, tDM＝1.31~1.38 Ga。其锆石U-Pb年龄为(488.9±1.7)~(470.5±3.1) Ma。表明古仍格萨拉东岩体形成于早奥陶世陆缘弧环境, 可能是先存的中元古代幔源基性下地壳部分熔融的产物, 其形成与古准噶尔洋向伊犁—中天山板块下的俯冲作用有关, 标志着中天山北缘于早奥陶世时期已进入与俯冲消减有关的活动陆缘演化阶段。此次岩浆活动导致区内发生斑岩型铜矿化。     

A new radiocarbon chronology of Baumkirchen,stratotype for the onset of the Upper Würmian in the Alps

The start of the Upper Würmian in the Alps was marked by massive fluvioglacial aggradation prior to the arrival of the Central Alpine glaciers. In 1984, the Subcommission on European Quaternary Stratigraphy defined the clay pit of Baumkirchen (in the foreland of the Inn Valley, Austria) as the stratotype for the Middle to Upper Würmian boundary in the Alps. Key for the selection of this site was its radiocarbon chronology, which still ranks among the most important datasets of this time interval in the Alps. In this study we re‐sampled all available original plant specimens and established an accelerator mass spectrometry chronology which supersedes the published 40‐year‐old chronology. The new data show a much smaller scatter and yielded slightly older conventional radiocarbon dates clustering at ca. 31 ¹⁴C ka BP. When calibrated using INTCAL13 the new data suggest that the sampled interval of 653–681 m in the clay pit was deposited 34–36 cal ka BP. Using two new radiocarbon dates of bone fragments found in the fluvioglacial gravel above the banded clays allows us to constrain the timing of the marked change from lacustrine to fluvioglacial sedimentation to ca. 32–33 cal ka BP, which suggests a possible link to the Heinrich 3 event in the North Atlantic. Copyright © 2013 John Wiley & Sons, Ltd.     

青海玉树县南洞卡组粗面安山岩地球化学特征：岩石成因与构造背景探讨

青海玉树县南洞卡组粗面安山岩的SiO₂含量为55.92%～57.85%,高Na₂O、MgO和Al₂O₃,低K₂O、TiO₂和 P₂O₅,铝饱和指数A/CNK=0.98～1.08,具有准铝-弱过铝质的特点。岩石K₂O含量低,Na₂O/K₂O=12.60～15.97,显示出钠质粗面安山岩特征。SiO₂-K₂O图解和里特曼指数(2.89～3.25),说明岩石属于钙碱性系列。稀土配分模式为轻稀土弱富集右倾型,铕弱负异常(σEu=0.90～0.96)。微量元素蛛网图显示,岩石富集Rb、Th和U等元素,亏损高场强元素Nb、Ta和大离子亲石元素Ba,样品Ce/Pb、Nb/U 并未随着MgO含量的升高而升高,样品的La/Nb、Zr/Nb、Ba/Nb比值均表现出良好的稳定性,表明岩浆在上升过程中遭受地壳物质混染的可能性不大,可能是其源区特征的反映。研究表明岩浆经历了橄榄石和单斜辉石的结晶分异,且受到俯冲板片熔体对源区的改造作用。结合234 Ma的形成年龄,说明该粗面安山岩是金沙江洋盆向西俯冲消减和斜向碰撞的地质记录,其形成时代和地球化学特征也为江达-维西火山弧的形成演化及成矿作用研究提供依据。     

波斯湾盆地中白垩统Mishrif组碳酸盐岩储层特征及其发育模式

Mishrif组碳酸盐岩储层是波斯湾盆地最主要的储集层之一,储层岩石类型主要为礁滩相生物礁灰岩、生屑灰岩和含生屑泥灰岩,储集空间主要为粒间(溶)孔、晶间(溶)孔、铸模孔、表生期组构选择性溶蚀孔洞和基质微孔。储层多呈层状展布,横向上连续,边界受沉积相带约束; 纵向上发育多套致密隔夹层,呈强非均质性。储层发育与保存主要受沉积作用、成岩作用和构造作用影响。碳酸盐岩缓坡背景下发育的生物礁和生屑滩空间分布受盆地基底古构造格局控制,是优质储层分布相带。相对海平面升降旋回控制相带迁移和成岩作用差异,导致优质孔渗层与致密隔夹层交互发育。构造圈闭发育与油气充注时间的耦合有效抑制压实作用和胶结作用对储层的破坏,是储层得以保存的有利因素。     

Foraminiferal sequence biostratigraphy of the Oligo‐Miocene Janjukian strata from Torquay,southeastern Australia

The foraminiferal fauna from two holes near the coastal section of marls and limestones at Torquay is dominated by inner to mid‐shelf benthic forms, especially the cibicidids, discorbids and miliolids. Planktonic species are rare and rarely age‐diagnostic. A cluster analysis of the species occurrences and relative abundances identified four assemblages, A to D up‐section. These assemblages also closely correspond to lithological changes characterising lithostratigraphic units: Angahook Formation (assemblage A), lower and upper Jan Juc Formation (B, C) and Puebla Clay (D). Biofacies trends based on the relative abundances of inner and outer neritic taxa led to the recognition of third‐order sequences and boundaries equivalent to TB1.1 to TB1.4, confirming a previous identification on sedimentological grounds. They demonstrate that foraminiferal assemblages were directly influenced by third‐order sea‐level fluctuations and can be used to predict third‐order sequences. The long‐uncertain regional Oligocene‐Miocene boundary is placed at the Jan Juc Formation—Puebla Clay contact, across which there was a major faunal change. Several benthic forms disappeared, at least temporarily: Cibicidoides perforatus, Amphistegina lessonii and Pararotalia mackayi. The typical Miocene planktonic taxa Globoquadrina dehiscens and Globoturborotalita brazieri made their first appearance. These events were associated with an increase in inner neritic benthos signalling a low sea‐level, consistent with the contemporaneous global pattern.     

Astronomical Dating of the Middle Miocene Hanjiang Formation in the Pearl River Mouth Basin,South China Sea

The Hanjiang Formation of Langhian age(middle Miocene) in the Pearl River Mouth Basin (PRMB),South China Sea consists of deltaic siliciclastic and neritic shelf carbonate rhythmic alternations,which form one of the potential reservoirs of the basin.To improve stratigraphic resolutions for hydrocarbon prospecting and exploration in the basin,the present study undertakes spectral analysis of high-resolution natural gamma-ray(NCR) well-logging record to determine the dominant frequency components and test whether Milankovitch orbital signals are recorded in rhythmic successions.Analytical results indicate the orbital cycles of precession(～19 ka and～23 ka), obliquity(～41 ka),and eccentricity(～100 ka and～405 ka),which provide the strong evidence for astronomically driven climate changes in the rhythmic alternation successions.Within biochronological constraint,a high-resolution astronomical timescale was constructed through the astronomical tuning of the NGR record to recent astronomically calculated variation of Earth’s orbit. The astronomically tuned timescale can be applied to calculate astronomical ages for the geological events and bioevents recognized throughout the period.The first downhole occurrences of foraminifers Globorotalia peripheroronda and Globigerinoides sicanus are dated at 14.546 Ma and 14.919 Ma,respectively,which are slightly different from earlier estimates in the South China Sea. When compared with the global sea-level change chart,the astronomical estimate for the sequences recognized based on microfossil distributions have the same end time but the different initiation time. This is probably due to the local or regional tectonic activities superimposed on eustatic rise which postponed the effect of global sea-level rising.Astronomical timescale also resolves the depositional evolution history for the Langhian Stage(middle Miocene) with a variation that strongly resembles that of Earth’s orbital eccentricity predicted from 13.65 Ma to 15.97 Ma.We infer that the main factor controlling the variability of the sedimentation rate in the Hanjiang Formation is related to the～405-ka-period eccentricity.     

青藏高原东北部西宁盆地晚渐新世-早中新世沉积物岩石磁学特征及其古环境意义

文章通过对西宁盆地谢家剖面上部(620~819m)厚度190m,有精确年代控制且无明显相变的晚渐新世-早中新世的湖相沉积物样品的磁化率系统测量,建立了该区晚渐新世-早中新世高分辨率的磁化率变化序列,揭示高、低频磁化率在约25Ma和21Ma存在两次明显的台阶式长期增大趋势,并在约23.8Ma,21.6Ma和19.8Ma叠加短期峰值,在时间上可能分别对应全球此时的长期变冷趋势及全球性Mi-1.1事件、Mi-1a事件和Mi-1aa事件短暂快速变冷事件,而频率磁化率记录几乎没有变化。代表性样品的系列岩石磁学分析,揭示出沉积物的载磁矿物主要为假单畴(PSD)的磁铁矿,同时可能还存在赤铁矿和针铁矿;磁化率增大主要由假单畴磁铁矿的含量增多引起,而不是通常情况下的成壤作用形成的超顺磁颗粒的增多引起,推测青藏高原东北部隆升导致的侵蚀增强,或干旱化,或两者兼并,可能是导致西宁盆地上述磁化率增强的原因。