孙吴-嘉荫盆地白垩系淘淇河组-太平林场组砂岩主量元素的地球化学特征

沉积盆地中砂岩的地球化学特征主要受物源区控制,碎屑岩的地球化学成分可揭示沉积物的地质信息.笔者通过对孙吴-嘉荫盆地白垩系淘淇河组-太平林场组砂岩的主量元素地球化学特征分析,结合砂岩薄片碎屑成分统计表明:淘淇河组-太平林场组时期物源区的大地构造背景主要为活动大陆边缘,包括大陆岛弧和大洋岛弧.物源区母岩类型主要为花岗岩,中酸性火山岩及低级变质岩.盆地不同位置物源区的大地构造背景和母岩类型有所不同.结合区域地质资料综合分析认为:在淘淇河组-太平林场组沉积时期,小兴安岭仅在太平林场组时期不是盆地主要物源区,而佳木斯地块一直是盆地东部的一个主要物源区.     

Early Cambrian radiation of brachiopods: A perspective from South China

Brachiopods, a group of benthic suspension-feeding marine invertebrates, made their first appearance in the Lower Cambrian. In the Yangtze Platform (South China), well-exposed Lower Cambrian stratigraphic succession represents shallow to deeper water environments. Strata from eastern Yunnan, southern Shaanxi and the Yangtze gorges areas of western Hubei Province, deposited in muddy-siltstone and carbonate lithofacies, contained an abundant variety of brachiopods, including all the representatives of the subphylum Linguliformea and the calcareous-shelled genera of Kutorgina and Nisusia from the subphylum Rhynchonelliformea. Thus the fossil assemblage bears witness to the first major phase of evolutionary radiation of brachiopods during the ‘Cambrian explosion’ interval of metazoans. Brachiopods from the celebrated Chengjiang fauna have exquisitely preserved soft-tissues, which reveal the body plans and evolutionary acquisition of morphological novelties of the early stocks, and also provide a good opportunity for testing the analogies with the stem groups from the extant representatives. These fossils have corroborated the view that brachiopods developed complex organization of tissues, and achieved considerable evolutionary success already by the onset of ‘Cambrian Explosion’. Thus it is not improbable that a large part of this radiation occurred within, or only just before early Cambrian time. Studies of Chengjiang brachiopods suggest that attachment by a pedicle to the substrate was probably the most common relationship of Cambrian brachiopods with the substrate where they inhabited.     

Cretaceous transformation from passive to active continental margin in the Western Carpathians as indicated by the sedimentary record in the Infratatric unit

The Cretaceous orogen of the Western Carpathians comprises fragments of the destructed northern Centrocarpathian domain, which is defined as Infratatric unit and formed a continental margin facing the Penninic Ocean in Jurassic and Cretaceous times. The breakup event and opening of the Penninic Ocean occurred in the Early Jurassic (Pliensbachian), which is recorded by an abrupt deepening event from shallow-water sediments to deep-water nodular limestone in the Infratatric sediment succession. The transformation of the passive into an active continental margin by the onset of subduction of the Penninic oceanic crust occurred in Santonian times and is reflected by the beginning of flysch deposition in the Infratatric Belice domain, which took the position of a forearc basin in the convergent margin setting. The forearc basin was supplied by clastic material from the more internal part of the Infratatric unit, which experienced nappe stacking, metamorphism, and subsequent exhumation in Late Cretaceous times. In the frontal part of the forearc basin an accretionary wedge was built up, which formed an outer-arc ridge and delivered detrital material into the forearc basin in Maastrichtian time. Final collision between the European and the Adriatic plate occurred in the Eocene period and is responsible for weak metamorphism in the Infratatric unit.     

Upper Cretaceous depositional environments and bivalve assemblages of far-east Asia: the Himenoura Group, Kyushu, Japan

The depositional environments and bivalve assemblages are determined for the Upper Cretaceous Hinoshima Formation of the Himenoura Group, Kamishima, Amakusa Islands, Kyushu, Japan. The Hinoshima Formation is characterized by a thick transgressive succession that varies from incised-valley-fill deposits to submarine slope deposits with high aggradation rates of depositional systems. The incised valley is filled with fluvial, bayhead delta, brackish-water estuary, and marine embayment deposits, and is overlain by thick slope deposits.Shallow marine bivalves are grouped into five fossil assemblages according to species composition: Glycymeris amakusensis (foreset beds of a bayhead delta), Nippononectes tamurai (foreset beds of a bayhead delta), Ezonuculana mactraeformis–Nucula formosa (central bay), Glycymeris amakusensis–Apiotrigonia minor (slope), and Inoceramus higoensis–Parvamussium yubarensis (slope). These bivalve assemblages all represent autochthonous and parautochthonous conditions except for a Glycymeris amakusensis–Apiotrigonia minor assemblage found in debris flow and slump deposits. The life habitats of these bivalves and the compositions of the assemblages are discussed in terms of the ecological history of fossil bivalves of the mid- to Late Cretaceous.     

Cretaceous climate, volcanism, impacts, and biotic effects

Cretaceous volcanic activities (LIPs and CFBPs) appear to have had relatively minor biotic effects, at least at the generic level. Major biotic stress during the Cretaceous was associated with OAEs and related to nutrient availability largely from weathering, greenhouse warming, drowning of platform areas, and volcanism. The biotic effects of OAEs were often dramatic at the species level, causing the extinction of larger specialized and heavily calcified planktonic foraminifera (rotaliporid extinction) and nannoconids (nannoconid crises), the temporary disappearances of other larger species, and the rapid increase in r-selected small and thin-walled species, such as the low oxygen tolerant heterohelicids and radially elongated taxa among planktic foraminifera and thin walled nannofossils. Biotic diversity increased during cool climates, particularly during the late Campanian and Maastrichtian, reaching maximum diversity during the middle Maastrichtian. High biotic stress conditions began during greenhouse warming and Deccan volcanism about 400 ky before the K-T boundary; it reduced abundances of large specialized tropical planktic foraminiferal species and endangered their survival. By K-T time, renewed Deccan volcanism combined with a large impact probably triggered the demise of this already extinction prone species group.Evidence from NE Mexico, Texas, and the Chicxulub crater itself indicates that this 170 km-diameter crater predates the K-T boundary by 300,000 years and caused no species extinctions. The Chicxulub impact, therefore, can no longer be considered a direct cause for the K-T mass extinction. However, the K-T mass extinction is closely associated with a global Ir anomaly, which is considered too large, too widespread, and too concentrated in a thin layer to have originated from volcanic activity, leaving another large impact as the most likely source. This suggests that a second still unknown larger impact may have triggered the K-T mass extinction.     

海拉尔盆地查干诺尔凹陷下白垩统层序地层格架及沉积体系研究

依据岩芯、测井、录井和地震资料,以层序地层学理论为指导对海拉尔盆地查干诺尔凹陷下白垩统的扎赉诺尔群进行层序地层划分。扎赉诺尔群可划分为1个超层序,形成于凹陷断陷发育期,自下而上可划分为5个三级层序(Sq1、Sq2、Sq3、Sq4、Sq5)。进而在层序框架内对沉积体系类型和时空展布特征进行了分析。凹陷主要发育冲积扇、扇三角洲、湖底扇、滨浅湖和半深—深湖沉积体系,并且层序地层格架对各沉积体系分布具有控制作用。     

东昆仑南缘早三叠世洪水川组的源区特征:来自碎屑组成、重矿物和岩石地球化学的证据

分布于东昆仑南缘的早三叠世洪水川组系一套由砾岩、砂岩、页岩和鲕粒灰岩等浅海相和河流相沉积物构成的弧前盆地沉积组合.砂岩碎屑组成、重矿物组合、岩石地球化学和古水流综合研究结果表明,洪水川组砂岩物源主要来自于北侧的岛弧带,同时南侧的阿尼玛卿蛇绿混杂带也为其形成提供了部分物源;源区主要出露长英质岩石、变质岩和硅质岩.     

浙江白垩系两种掌鳞杉科化石微细结构及其古环境意义

利用扫描电镜和生物光学显微镜对采自浙江新昌镜岭馆头组的两种已绝灭的松柏类掌鳞杉科植物Pseudofrenelopsis papillosa Chow and Tsao和Pseudofrenelopsis parceramosa Watson细微结构进行了观察研究。其中P.papillosa无论从宏观形态还是表皮构造都与模式标本完全一致;而定为Pseudofrenelopsis parceramosa的标本节间角质层较为光滑,气孔排列规则,副卫细胞上未见乳突,此外该标本气孔器大小、自由叶大小、节间长度等方面都与Pseudofrenelopsis中的其他种不太相同。并利用化石P.parceramosa的气孔比率通过最近现生亲缘种法恢复了早白垩世晚期大气CO2浓度为861~1047ml/L,得出用本种恢复早白垩世晚期CO2浓度时应用石炭纪标准较为准确,说明本种可以作为环境指标。     

Ti-in-zircon thermometry: applications and limitations

The titanium concentrations of 484 zircons with U-Pb ages of ∼1 Ma to 4.4 Ga were measured by ion microprobe. Samples come from 45 different igneous rocks (365 zircons), as well as zircon megacrysts (84) from kimberlite, Early Archean detrital zircons (32), and zircon reference materials (3). Samples were chosen to represent a large range of igneous rock compositions. Most of the zircons contain less than 20 ppm Ti. Apparent temperatures for zircon crystallization were calculated using the Ti-in-zircon thermometer (Watson et al. 2006, Contrib Mineral Petrol 151:413–433) without making corrections for reduced oxide activities (e.g., TiO₂ or SiO₂), or variable pressure. Average apparent Ti-in-zircon temperatures range from 500° to 850°C, and are lower than either zircon saturation temperatures (for granitic rocks) or predicted crystallization temperatures of evolved melts (∼15% melt residue for mafic rocks). Temperatures average: 653 ± 124°C (2 standard deviations, 60 zircons) for felsic to intermediate igneous rocks, 758 ± 111°C (261 zircons) for mafic rocks, and 758 ± 98°C (84 zircons) for mantle megacrysts from kimberlite. Individually, the effects of reduced or , variable pressure, deviations from Henry’s Law, and subsolidus Ti exchange are insufficient to explain the seemingly low temperatures for zircon crystallization in igneous rocks. MELTs calculations show that mafic magmas can evolve to hydrous melts with significantly lower crystallization temperature for the last 10–15% melt residue than that of the main rock. While some magmatic zircons surely form in such late hydrous melts, low apparent temperatures are found in zircons that are included within phenocrysts or glass showing that those zircons are not from evolved residue melts. Intracrystalline variability in Ti concentration, in excess of analytical precision, is observed for nearly all zircons that were analyzed more than once. However, there is no systematic change in Ti content from core to rim, or correlation with zoning, age, U content, Th/U ratio, or concordance in U-Pb age. Thus, it is likely that other variables, in addition to temperature and , are important in controlling the Ti content of zircon. The Ti contents of igneous zircons from different rock types worldwide overlap significantly. However, on a more restricted regional scale, apparent Ti-in-zircon temperatures correlate with whole-rock SiO₂ and HfO₂ for plutonic rocks of the Sierra Nevada batholith, averaging 750°C at 50 wt.% SiO₂ and 600°C at 75 wt.%. Among felsic plutons in the Sierra, peraluminous granites average 610 ± 88°C, while metaluminous rocks average 694 ± 94°C. Detrital zircons from the Jack Hills, Western Australia with ages from 4.4 to 4.0 Ga have apparent temperatures of 717 ± 108°C, which are intermediate between values for felsic rocks and those for mafic rocks. Although some mafic zircons have higher Ti content, values for Early Archean detrital zircons from a proposed granitic provenance are similar to zircons from many mafic rocks, including anorthosites from the Adirondack Mts (709 ± 76°C). Furthermore, the Jack Hills zircon apparent Ti-temperatures are significantly higher than measured values for peraluminous granites (610 ± 88°C). Thus the Ti concentration in detrital zircons and apparent Ti-in-zircon temperatures are not sufficient to independently identify parent melt composition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cenomanian-lower coniacian radiolarian assemblages from the Naiba reference section (Sakhalin)

Reexamination of radiolarians from the Naiba and Bykovo formations of the Naiba reference section (West Sakhalin Mountains) is carried out. Distinguished in the section are the Cromyomma (?) nodosa-Amphipyndax sp. A (terminal early Cenomanian), Cuboctostylus kasinzovae-C. sakhalinensis (Middle Cenomanian), Cuboctostylus trifurcatus-Cassideus yoloensis (terminal middle-late Cenomanian), and Spongodiscus concentricus-Multastrum robustum (late Turonian to early Coniacian probably) assemblages. According to results of comparative analysis for North Pacific regions, concurrent radiolarian assemblages from the Naiba section and California contain up to 40% of species in common, whereas taxonomic similarity with assemblages from Japan is insignifican in contrast.