Triassic biochronology: State of the art and main problems     

A. A. Shevyrev 《Stratigraphy and Geological Correlation》2006,14(6):629-641

According to known resolution of the IUGS, the International Stratigraphic Commission entrusted its subcommissions with a task to prepare proposals for the official approval of boundaries between Phanerozoic stages. Specially organized working groups were later renamed as special teams for seeking the Global Stratotype Sections and Points (GSSP) for these boundaries. In 2001, the GSSP of lower boundary for the Induan Stage, the basal one in the Triassic System, was officially approved to be in the Meishan section of southern China. The selection appeared to be lame, because the Permian-Triassic boundary layers of the stratotype section are lacking ammonoids. As a result, this boundary is now based only on the first occurrence level (FO) of conodont species Hindeodus parvus. Soon, the proposal of Chinese paleontologists to consider the western Pingdingshan section in the Anhui Province as the GSSP for the lower boundary of the Olenekian Stage may win the official recognition. This boundary between the Olenekian and Anisian stages, which is placed at the FO of conodont species Neospathodus waageni is the least debatable. The Mt. Desli Caira section in northern Dobrogea (Romania) is most appropriate for its global stratotype. In contrast, the Anisian-Ladinian boundary appeared to be most disputable. The Subcommission on Triassic Stratigraphy should select one of three GSSP candidates proposed. The lower Carnian boundary traditionally drawn at the aon Zone base suffered some changes. It is proposed to place it at the FO of the ammonoid genus Daxatina with the GSSP in the Dolomites of Italy. The Norian and Rhaetian boundaries are under discussion.  相似文献   

Molecular implications of hydrophobic organic partitioning theory     

Russell F. Christman  Frederic K. Pfaender 《洁净——土壤、空气、水》2006,34(4):367-374

Recent normal phase silica followed by reverse phase XAD separation has led to the identification of several flavonoid and condensed tannin structures in Suwannee River Fulvic Acid (SFRA) (Leenheer, J. A., Rostad, C. (2004) Scientific Investigations Report 2004–5276, U.S. Geological Survey). We have used the molecular properties of one of these structures to define ideal behavior during partitioning of PAHs assuming that these structures function as an immiscible liquid solvent bound to finely dispersed mineral particles. Existing data for the partitioning of PAHs into NOM compared well to this ideal behavior under Raoult/Henry and Flory‐Huggins treatments, and activity coefficients of pyrene in the hypothetical NOM phase and the free energy of transfer were estimated. If experimental data on partitioning of PAHs into synthesized samples of these structures is similar to NOM uptake data, it will be attractive to assume that, a) much smaller components of the NOM complex than suggested by gross molecular weight may be important in environmental properties such as solubility enhancement, and b) the effective molar volumes within the NOM complex responsible for solubility enhancement may be solute, or solute class dependent.  相似文献   

Magnetostratigraphy of Paleogene deposits in Kamchatka     

P. S. Minyuk  Yu. B. Gladenkov 《Stratigraphy and Geological Correlation》2007,15(1):100-111

Paleomagnetic characteristics of several Paleogene sections in Kamchatka (Il’pinskii Peninsula, Bering Island, Chemurnaut Bay, Mametcha Bay) are considered. The sections are correlated with due account for biostratigraphic data, and possible correlation of magnetic polarity zones distinguished in the sections with the international magnetostratigraphic scale is presented.  相似文献   

Daily Variation of Natural Emission of Methane to the Atmosphere and Source Identification in the Luntai Fault Region of the Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang, China   总被引：1，自引：0，他引：1       下载免费PDF全文

TANG Junhong BAO Zhengyu XIANG Wu GOU Qinghong 《《地质学报》英文版》2007,81(5):771-778

The static flux chamber method was applied to study natural emissions of methane to the atmosphere in the Luntai fault region of Yakela Condensed Oil/Gas Field in the Tarim Basin, Xinjiang Municipality, northwestern China. Using an online method, which couples together a gas chromatography/high-temperature conversion/isotope ratio mass spectrometry （GC/C/MS）, 13^C/12^C ratios of methane in flux chambers were measured and showed that methane gases are liable to migrate from deep oil/gas reservoirs to the surface through fault regions and that a part of the migrated methane, which remains unoxidized can be emitted into the atmosphere. Methane emission rates were found to be highest in the mornings, lowest in the afternoons and then increase gradually in the evenings. Methane emission rates varied dramatically in different locations in the fault region. The highest methane emission rate was 10.96 mg/m^2·d, the lowest 4.38 mg/m^2, and the average 7.55 mg/ m^2·d. The 13^C/12^C ratios of the methane in the flux chambers became heavier as the enclosed methane concentrations increased gradually, which reveals that methane released from the fault region might come from thermogenic methane of the deep condensed oil/gas reservoir.  相似文献   

Production of selected cosmogenic radionuclides by muons 1. Fast muons   总被引：1，自引：0，他引：1  

B. Heisinger  D. Lal  A. J. T. Jull  P. Kubik  S. Ivy-Ochs  S. Neumaier  K. Knie  V. Lazarev  E. Nolte 《Earth and Planetary Science Letters》2002,200(3-4):345-355

To investigate muon-induced nuclear reactions leading to the production of radionuclides, targets made of C₉H₁₂, SiO₂, Al₂O₃, Al, S, CaCO₃, Fe, Ni, Cu, Gd, Yb and Tl were irradiated with 100 and 190 GeV muons in the NA54 experimental setup at CERN. The radionuclide concentrations were measured with accelerator mass spectrometry and γ-spectroscopy. Results are presented for the corresponding partial formation cross-sections. Several of the long-lived and short-lived radionuclides studied are also produced by fast cosmic ray muons in the atmosphere and at depths underground. Because of their importance to earth sciences investigations, calculations of the depth dependence of production rates by fast cosmic ray muons have been made.  相似文献   

华北地台寒武纪沉积层序中关键地层单元──海绿石质凝缩层段   总被引：1，自引：0，他引：1  

陈荣坤 《沉积与特提斯地质》1994,(6)

构成华北古克拉通盆地的中晚寒武世碳酸盐沉积层序及与三级海平面最大海泛期相关的海绿石质凝缩层段是一沉积速率极低、厚度较薄的海相沉积单元。笔者根据凝缩层段中海绿石矿物的Ｋ２Ｏ百分含量和其内部晶体结构划分出其演化级次和形成时限，得出研究区凝缩层段的形成时限为１０４－１０６年。它们与二级、三级海平面最大海泛滞后期相吻合。该成果对区域地层对比、层序划分、海平面升降史和盆地充填史的恢复起极为重要的作用。  相似文献   

中国晚寒武世长山期最大海泛事件及其全球对比意义   总被引：2，自引：0，他引：2  

孟祥化  葛铭  M.E.Tucker 《地质学报》1996,70(2)

在华北地台寒武-奥陶系层序地层研究中发现了不同层序中的海绿石质凝缩层。长山期最大海泛凝缩层系以富钾海绿右的双层结构复合层系为特征,富集多种金属元素和磷、锰、K_2O为特点。长山期海泛事件具有全球对比意义。笔者已在北欧,北美及亚洲26个洲际剖面点发现了长山事件记录。详细的比较沉积学、微相、米级旋回和Fischer图解研究均证明长山期最大海泛事件系起因干二级与三、四级海平面变化周期复合叠加作用,形成时限为1.2-3Ma,最后提出长山期全球海泛事件的洲际模式。  相似文献   

关于地震水平叠加时间剖面二维归位分层作图方法的探讨     

任日春  李朝林  孙成现  赵富有 《吉林地质》2008,27(1)

针对我国东北地区地质构造特征,在煤田地震勘探资料解释工作中,解释后的水平叠加时间剖面,需要进行时深转换;在时深转换作图过程中,依据不同地质模型,采用各自地质模型的综合速度曲线,对水平叠加剖面采用分层作图,使地质层位空间二维归位后,误差小、位置准,从而可提高地震勘探资料解释精度。  相似文献   

Presettlement analogs for Quaternary fire regimes in eastern North America     

James S. Clark  Tristram Hussey  P. Dan Royall 《Journal of Paleolimnology》1996,16(1):79-96

We present a method for identifying analogs for past fire regimes and use it to assess similarity between late Quaternary fire regimes in northern Wisconsin and central New York and a reference set of charcoal series from just prior to presettlement time. The analog method is based on comparisons of distributions of charcoal accumulation rates from annually laminated sediments using a Kolmogorov-Smirnov two-sample D statistic (D). D is a nonparametric statistic expressing the difference between distributions that does not require assumptions concerning the shape of the distributions (e.g. normality, homoscedasticity) and it summarizes differences in a single index. Our study consists of (i) mapping D values obtained by comparisons between pairs of reference charcoal series from the immediate presettlement (calibration) and (ii) identifying possible presettlement analogs from this reference set for Late Quaternary charcoal distributions. Our calibration analysis identified geographic transitions in charcoal transition that were much steeper than apparent from pollen data. Otherwise, geographic patterns in presettlement charcoal and pollen are comparable, including a group of oak/hardwood forest sites in Wisconsin, central Ontario, and New York having similar values, and another group of mostly northern hardwood/hemlock sites in Pennsylvania and Maine. Application to charcoal series dated after 11 000 yr BP at Wisconsin and New York suggests that fire regimes may have been different from those occurring at any of our reference sites. Differences in seasonality of climates and different fuel structures are a possible explanation.This is the 21st in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.  相似文献   

东营凹陷沙一段滩坝-泻湖沉积体系和层序发育的控制特点   总被引：7，自引：0，他引：7  

邬金华  张哲  王柏轩 《地球科学》1998,23(1):3

根据沉积和生物特征可以确认东营凹陷沙一段中的特殊岩性段沉积在滩坝－泻湖体系内．按构成岩性可将滩坝分为砂质和碳酸盐两类．它们的出现反映了凹陷内沙一期相对湖水位上升速率、供屑速率、气候、沉积基底地形等综合背景条件．在演化上,碳酸盐沉积的全面终止意味着滩坝－泻湖体系的终止,终止的根本原因是相对湖水位较大幅度上升所导致的河流注屑速率下降．该沉积体系被认为是湖进体系域的主要构成部分,而且很可能没有典型凝聚层与之伴生．  相似文献