蒸馏水中蒙脱石晶层间膨胀压力理论研究

蒙脱石颗粒周围的溶液浓度对其膨胀性有较大影响,传统的双电层模型可以对电解质环境下蒙脱石的膨胀特性做出较好的模拟,但并不适于蒸馏水的情况。针对膨润土在蒸馏水或纯水中已有的膨胀特性试验,本文在前人的研究基础上详细推导了蒸馏水中蒙脱石晶层间的膨胀压力模型,并给出一种简便算法。运用此算法可以避免非线性方程的求解,从而可以较方便的将膨胀力和晶层间距联系起来。     

陕西汉中梁山二叠系乐平统底部吴家坪组王坡页岩新认识

陕西汉中梁山瓜德鲁普统—乐平统界线(GLB)附近的吴家坪组底部王坡页岩段长期以来被认为是古风化壳沉积,代表了茅口期后暴露于地表风化剥蚀的产物。最近对该地层进行了重新研究,采集了系列岩石和化石样品,进行了X射线衍射、古生物学、岩相学和岩石学分析。X射线衍射分析表明该粘土层主要矿物成分为蒙脱石71%,片沸石23%,石英6%,暗示其物质来源于火山玻璃。岩相学分析显示岩石主要由蚀变矿物组成,具有蚀变残留玻屑凝灰质结构,其中蒙脱石、片沸石保留了原岩中的玻屑的塑性形态。粘土层中大量腕足动物化石暗示其为海相环境。研究结果表明王坡页岩是典型的斑脱岩,并非风化壳和长期剥蚀的产物,而是峨眉山大火成岩省火山喷发时火山灰在海相环境下沉积、蚀变的产物。火山灰在正常浅海沉积时对海洋生态系统造成严重破坏,导致了包括腕足动物在内的海洋生物的生存危机。     

Early Ordovician CA-IDTIMS U–Pb zircon dating and conodont biostratigraphy,Canning Basin,Western Australia

A continuously cored section of more than 300 m through the Nambeet Formation and the basal part of the conformably overlying Willara Formation in the Olympic 1 petroleum well, drilled in the Canning Basin of northern Western Australia, yields valuable information that increases by more than 40% the number of precise isotopic ages available to constrain the Ordovician Period. New CA-IDTIMS U–Pb zircon ages for seven bentonite layers in the Olympic 1 core are integrated into a new conodont biostratigraphic framework for the Early Ordovician comprising four biozones recognised in this well. The weighted mean U–Pb dates range from 479.37 ± 0.16 Ma within the late Tremadocian Paroistodus proteus conodont Biozone, to 470.18 ± 0.13 Ma near the boundary between the Floian and Dapingian stages within the Jumudontus gananda conodont Biozone. The intervening Prioniodus oepiki–Serratognathus bilobatus conodont Biozone (early Floian) and succeeding Oepikodus communis conodont Biozone (middle Floian) are similarly well constrained by isotopic dates centred on ca 477 Ma for the early Floian and by three ages of 473–471 Ma for the middle Floian. The seven new isotopic dates significantly increase the precision of dating for the Early Ordovician, where previously only two ages with limited or imprecise biostratigraphic control were known globally.     

The Origin of the Black Shale Series and Bentonites from the Wufeng Formation in the Southwestern Upper Yangtze: Implications for the Convergence of the Yangtze and Cathaysia Blocks in the Late Ordovician

Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary. However, the intimate relationship between their origins and the dynamic mechanisms are unclear, as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition (OST). In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks (i.e., the intracontinental Kwangsian Orogeny), two stratigraphic sections respectively in Zhaotong area (Northeast Yunnan) and Puyi area (Northwestern Guizhou) that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied, on the basis of whole-rock geochemical composition, pyrite δ34S (δ34Spy), total organic carbon (TOC), stable Sr isotope, pyrite framboid size distribution and zircon U-Pb age, trace elements. The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation. These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval. Based on previous research on the genetic relationship between black shale series and plate tectonic movement, a basin-mountain evolution model suitable for South China in the Late Ordovician is presented. The two bentonites in the Wufeng Formation with U-Pb ages of 445.5 ± 0.8 Ma and 441.9 ± 2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician, the provenance region probably being located in the Jiangnan orogenic belt. Thus, we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China, which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.