Paleoceanography and Heavy Metal Enrichment of Mudstones in the Green Tuff Region, Northeastern Japan

Abstract. A series of mudstones corresponding to N.8 to N.17 of Blow from the Uyashinai Mudstone Member, the Onnagawa Formation and the Funakawa Formation in the Taiheizan area of the central Green Tuff region, northeast Japan, was examined by chemical analysis. According to conventional chemical systematics, the mudstones are analyzed in terms of detrital, biogenic-A (siliceous), biogenic-B (calcareous) and hydrogenous components. The relative contribution of the biogenic-A (siliceous) component increases in upward succession in the Uyashinai and Onnagawa mudstones, whereas the contribution of the biogenic-B (calcareous) component is restricted to the lower Uyashinai mudstones. The contribution of hydrogenous components Zn, Pb, Cu and Ba tends to increase during the Nishikurosawa stage, and decreases near the Nishikurosawa/Onnagawa boundary (Pb and Ba) or in the Onnagawa stage (Zn and Cu). The observed enrichment of heavy metals in the Uyashinai mudstones is attributed to the onset of vigorous upwelling of deep water with higher nutrient and metal content associated with a contemporaneous change in global deep-water circulation.     

Paleoenvironmental significance of a new species of freshwater sponge from the Late Miocene Quillagua Formation (N Chile)

This paper reports the first fossil (Tertiary) occurrence of freshwater sponges of the genus Ephydatia in the southern hemisphere. The sponges appear in diatomite lacustrine sediments of Late Miocene Quillagua Formation (Chile, Atacama region). The investigated specimens represent a new species, Ephydatia chileana sp. nov., which is close to the Recent cosmopolitan E. fluviatilis. On the basis of sedimentological and diatom assemblage data, sponge-bearing diatomites have been interpreted as deposited in open offshore shallow lacustrine conditions with slightly alkaline waters. The sponges show malformations, similar to some diatoms and probably caused by high heavy metal concentrations in a lake water. These concentrations are related to hydrothermal activity, which favored the leaching of volcanic rocks that outcrop extensively in the catchment.     

藏北改则地区鱼鳞山组火山岩同位素年代学

鱼鳞山组火山岩是青藏高原隆升过程中一次重要的碱性钾质火山活动的产物，自发现之日起时代一直定为上新世末至早更新世，对比范围跨羌塘南部到冈底斯地区。通过对鱼鳞山组火山岩同位素测年研究，鱼鳞山组白榴石响岩^40Ar-^39Ar积分年龄为27．8Ma、K－Ar法年龄为30－18Ma,确定鱼鳞山组时代为渐新世至中新世，其分布仅限于班公湖－怒江缝合带以北地区。     

An unconformity in the early Miocene syn-rifting succession, northern Noto Peninsula, Japan: Evidence for short-term uplifting precedent to the rapid opening of the Japan Sea

Abstract   The present paper describes the newly discovered early Miocene unconformity in the northern Noto Peninsula, on the Japan Sea side, central Japan. The unconformity marks the boundary between an early Miocene non-marine to marine succession and a more extensive, late early to early middle Miocene marine succession, and contains a time gap of an order of 1 million years or less from 18 Ma or earlier to 17 Ma. The early Miocene succession likely represents an early phase of marine transgression and initial slow rifting. The overlying early to early middle Miocene succession records the climax of the opening of the Japan Sea at ca  16 Ma with widespread, rapid subsidence of the Japan Arc. The unconformity between the two transgressive successions may represent a global sealevel fall or, more likely, crustal uplifting because no upward-shallowing or regressive facies remains between the two successions. Early Miocene unconformities that are thought to be correlative with this unconformity in the northern Noto Peninsula occur in places along the Japan Sea coast of Sakhalin and Japan. They are likely to have been produced during rifting in response to upwelling of asthenospheric mantle, although more accurate age constraints are necessary to evaluate this idea.     

Geology and characterisation of the Pecket coal deposit, Magellan Region, Chile

The geology, petrography and chemical variation of the Pecket coal sequence, Magellan Region (52°57′S, 71°10′W), the only Chilean coal used for electricity generation on a large scale, has been studied in order to predict their combustion behaviour, especially in coal blends. The depositional environment of formation of the coal seams was a swamp rarely exposed to subaerial conditions and was associated with the development of the folded foreland of the Magellan basin during the Tertiary (Oligo–Miocene). The general tectonic regime of the collision of the Antarctic and South American plates is reflected by a system of joints with 40°N–50°W strike. The maceral composition of all six seams studied indicates high contents of vitrinite (>90%), minor content of liptinite (4.7%) and inertinite (<2%). Occurrence of tonstein horizons altered to kaolinite indicates a distal volcanism during peat accumulation. Coal rank varies between lignite and subbituminous (Ro=0.28–0.42%) with an average dry basis calorific value of 5450 kcal/kg, 17 wt.% moisture, 41 wt.% volatile matter, and sulphur content below 0.5 wt.%. The mineral matter (LTA) associated with the coal shows a dominance of kaolinite with quartz, smectite, and minor basanite. SiO₂/Al₂O₃ and Fe₂O₃/CaO ratios of the ashes diminish towards the lower seams. With respect to the utilisation of Pecket coals in combustion, base/acid ratios (B/A) and silica ratios (SR) indicate potential fouling for seams 1, 2, 5, and 6i, with high fouling indexes (Rf) for seams 2 and 5. Pecket coal is excellent for blend combustion due to its low sulphur content.     

Evolution of the Pearl River and its Implication for East Asian Continental Landscape Reversion

As the link connecting the South China Continent and the northern South China Sea(SCS),the Pearl River is the focus of sedimentology and petroleum geology research.Its evolutionary process and controlling factors are of great significance in revealing the East Asian continental landscape reorganization during the Late Cenozoic.Based on published data,’source-to-sink’provenance analyses allow systematic deliberation on the birth and evolutionary history of the Pearl River.Close to the Oligocene/Miocene boundary,an abrupt shift in the sedimentary composition indicates significant westward and northward expansion of the river’s watershed area,followed by the establishment of a near-modern fluvial network.This sedimentary change generally concurred with a series of regional geological events,including the onset of the Yangtze throughflow,large-scale development of the loess plateau,and formation of the northwestern arid zone and Asian Monsoon system.These major changes in the geology-climate-ecoenvironment system are in close response to the process of the Cenozoic Xizang(Tibetan)Plateau uplift.Consequently,the East Asian continental landscape and most of midCenozoic drainage systems underwent critical reversion into east-tilting,or east-flowing networks.     

浙东中新世菱属果实化石的数量分类

在浙东天台晚中新世嵊县组发现大量菱属果实化石。该化石保存完好,特征丰富。由于其种类多、性状冗杂不明显,菱属植物的鉴定与分类一直存在很大争议。本研究基于菱属果实化石性状特征多、便于测量记录的特点,通过聚类分析和主成分分析等数值统计方法对菱属果实进行鉴别、归类,寻找鉴定分类中的指导性性状。首先,利用上述方法对现生菱属果实进行数量分析,取得了较好结果。然后,采用同样方法对菱属果实化石进行研究,认为聚类分析和主成分分析法能够对化石种进行有效的鉴定分类,可以成功剔除冗余性状。最后,研究得出果体形状、是否有果冠、果冠是否外翻、顶部形态、肩角生长方向、腰角生长方向、腰角长度、瘤状退化腰角数目等特征是菱属果实化石鉴定的关键性状。基于以上性状,嵊县组菱属果实化石可以分为两个类群。     

Magnetochronology of Mid-Miocene mammalian fauna in the Lanzhou Basin,northeastern Tibetan Plateau:Implications for Asian mammal migration

The Quantougou(QTG) Fauna in central Lanzhou Basin is an important late Mid-Miocene fauna on the northeastern Tibetan Plateau margin,but its numerical age remains a matter of debate.Here,we present a new magnetostratigraphic record for a fluvio-lacustrine section to further constrain the age of the QTG Fauna.Results suggest that the studied section spans from polarity chrons C5Cn.2n to C5 n.2n or C5 An.1n,with ages of ca.16.5 Ma to 10 Ma or 16.5 Ma to 12 Ma.The QTG Fauna is located at the top of polarity chron C5r.3 r or C5 Ar.2 r,which corresponds to an age of 11.7 Ma or 12.8 Ma for the fauna.Accordingly,the associated Myocricetodontinae(a subfamily of Gerbillidae,Rodentia) is suggested to have appeared in the Lanzhou Basin at 11.7 Ma or 12.8 Ma,which is the oldest Myocricetodontinae in East Asia but is still much younger than the ～20 Ma appearance of this subfamily in West and South Asia.Our age data support the interpretation that East Asian Myocricetodontinae originated from South Asia.The QTG fauna further suggest a dry and open grassland environment,which is consistent with global cooling after the Mid-Miocene Climatic Optimum.     

新疆塔什库尔干温泉地区花岗岩体侵入与新生代构造变形:对东北帕米尔中新世构造演化的启示

帕米尔高原是受到印度-亚洲大陆碰撞、持续汇聚影响最显著的地区之一,以强烈地壳增厚和缩短、大量断裂和片麻岩穹窿的形成以及广泛的陆内岩浆活动为特征。以往有关帕米尔陆内岩浆岩的讨论多集中于对其地球化学成分及其所指示的构造背景的研究方面,而对岩浆形成与大型新生代构造之间的联系研究较少。本文通过对东北帕米尔塔什库尔干温泉地区新生代花岗岩及其围岩中锆石U-Pb和Ar-Ar年代学研究,结合该地区新生代构造变形分析,揭示岩浆侵入与区域构造变形之间的关系。U-Pb及Ar-Ar测年结果显示温泉地区花岗岩脉形成时代为中新世（11.8±0.2Ma）,其及其围岩在10.8±0.1Ma冷却到300℃左右;中新世花岗岩脉中继承锆石及围岩片岩中碎屑锆石U-Pb的年龄分布特征迥异,它们分别具有类似松潘-甘孜地体以及中帕米尔地体的物质来源。花岗岩内部几乎无变形,围岩片岩变形主要体现为近E-W向的伸展构造,反映其形成于拉张为主的构造应力环境。结合区域构造背景,推测温泉中新世花岗岩脉为公格尔山、慕士塔格峰构造单元岩石部分熔融产物,是在东北帕米尔地壳从挤压增厚向局部伸展转换的过程中形成的,此时,公格尔伸展断裂系可能已经开始发育;此后,直到6~4Ma,公格尔伸展断裂系开始快速运动,与之相伴公格尔-慕士塔格片麻岩穹窿快速折返。     

内蒙古苏尼特左旗中新世晚期孢粉记录干旱事件

对中中新统通古尔组和上覆地层宝格达乌拉组的40个孢粉样品的分析表明通古尔期晚期形成环境较早期温湿,在通古尔期向宝格达乌拉期过渡期间,灌木和草本植物花粉由19·7%增加到46%,而乔木植物花粉总数由69·5%下降为34·7%,松蒿比(A/C)由4突降为0·64,标志着干旱事件的开始。将该地区的古地磁、哺乳类化石和孢粉资料与前人研究进行对比,结果显示干旱事件发生在晚中新世约8·5Ma,这一事件在华北具有广泛的可比性。