正在萌芽段的震积地层学

地震是经常发生的,是地球节律的一种反映。震积岩一词是Seilacher A(1969)首先提出的,随后欧美学者掀起了研究高潮。Mutti等(1984)认为浊积岩即震浊积岩,可以作为一个事件地层单元进行填图与追索。我国学者宋天锐(1988)最早提出地震－海啸序列,可以作为燕山地区雾连山组地层划分对比的标志。乔秀夫等(1994．1995) 在华北上震旦统一下寒武坑中建立了“碳酸盐岩液化地震序列”与“萨布哈震积序列”并对华北东部同期地层进行了对比与成因地层学研究。笔者(1991．1994)指出扬子西缘的二叠系震积岩由原地相的地震干扰层与异地相的滑来震积层两部分组成．两者之问被震积不整台面分开 在伸展构造环境下,震积不整合即伸展不整合,它是瞬时间于水下形成的。滑来震积层表现为多旋回的震积序列,其中的化石混积层具有正向有序混积现象,这也与盆地边界正断层多次活动有关。由此,提出“扬子西缘的东吴伸展运动”新认识。将震积岩的研究与构造灾变事件,事件地层学接轨。我国地史上也是一个多震的地区,在我国土地上,完全有可能哺育出现代地层学的一门新分支—— 震积地层学。     

Calcareous Nannofossils and Molecular Fossils in Cobalt-rich Crusts and their Response to the P/E Global Event

A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age.The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous,late Paleocene,(early,middle,late) Eocene,middle Miocene,late Pliocene,and Pleistocene.Gas chromatography(GC) and gas chromatography-mass spectrometry(GC-MS) were used to test the Co-rich crusts,and a variety of molecular fossils were detected,such as chloroform bituminous "A",n-alkane,isoprenoid and sterol.Peak carbon and molecular indices(such as ΣC23 /ΣC24 +,CPI,Pr/Ph,Pr/nC17,Ph/nC18 and δ13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter.Researches on calcareous nannofossils,molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene(P/E) global event is recorded in the cobaltrich crusts from the northwestern Pacific Ocean.A succession of biomes can be observed near the 85 mm boundary(about 55 Ma),i.e.,the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis,and Broisonia parka microbiotas above the P/E boundary,and the bloom of Coccolithus formosus,Discoaster multiradiatus,Discoaster mohleri and Discoaster sp.below the boundary.Typical parameters of molecular fossils,such as saturated hydrocarbon components and carbon-number maxima,Pr/Ph,Pr/C17,Ph/C18,distribution types of sterols,Ts/Tm ratios and bacterial hopane,also exhibit dramatic changes near the P/E boundary.These integrated results illustrate that the biome succession of calcareous nannofossils,relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.     

基于全岩心CT的遗迹化石识别及沉积环境分析:以加拿大麦凯Ⅲ油砂区块为例*

遗迹化石研究对于沉积环境分析具有重要意义。以加拿大麦凯Ⅲ油砂区块下白垩统McMurray组为研究对象,利用高分辨率岩心照片和全岩心CT扫描资料,在确认研究目的层遗迹化石发育属种、单体规模、组合类型及指相特征的基础上,分析了主力油砂层的沉积环境。结果表明: 目的层发育遗迹化石10属12种,包括Asterosoma isp.,Chondrites isp.,Diplocraterion isp.,Ophiomorpha nodosa,Palaeophycus tubularis,Planolites beverleyensis,Planolites isp.,Rosselia isp.,Skolithos verticalis,Skolithos isp.,Teichichnus isp.,Thalassinoides isp.;根据遗迹化石产状与围岩沉积特征,建立了Ophiomorpha-Skolithos、Asterosoma-Chondrites-Rosselia和Teichichnus-Rosselia￣Thalassinoides共3种遗迹组合,分别代表潮间带、潮下带以及浅海陆棚沉积环境中的遗迹化石组成特征。研究区油砂层优质储油砂体为潮间带沉积产物,潮汐砂坝、潮成砂脊为沥青的主要储集体。本研究既体现了全岩心CT资料在遗迹化石研究中的应用,也为潮坪沉积环境分析提供了有益参考。     

Microbial biomineralization processes forming modern Ca:Mg carbonate stromatolites

Modern Ca:Mg carbonate stromatolites form in association with the microbial mat in the hypersaline coastal lagoon, Lagoa Vermelha (Brazil). The stromatolites, although showing diversified fabrics characterized by thin or crude lamination and/or thrombolitic clotting, exhibit a pervasive peloidal microfabric. The peloidal texture consists of dark, micritic aggregates of very high‐Mg calcite and/or Ca dolomite formed by an iso‐oriented assemblage of sub‐micron trigonal polyhedrons and organic matter. Limpid acicular crystals of aragonite arranged in spherulites surround these aggregates. Unlike the aragonite crystals, organic matter is present consistently in the dark, micritic carbonate comprising the peloids. This organic matter is observed as sub‐micron flat and filamentous mucus‐like structures inside the interspaces of the high‐Mg calcite and Ca dolomite crystals and is interpreted as the remains of degraded extracellular polymeric substances. Moreover, many fossilized bacterial cells are associated strictly with both carbonate phases. These cells consist mainly of 0·2 to 4 μm in diameter, sub‐spherical, rod‐like and filamentous forms, isolated or in colony‐like clusters. The co‐existence of fossil extracellular polymeric substances and bacterial bodies, associated with the polyhedrons of Ca:Mg carbonate, implies that the organic matter and microbial metabolism played a fundamental role in the precipitation of the minerals that form the peloids. By contrast, the lack of extracellular polymeric substances in the aragonitic phase indicates an additional precipitation mechanism. The complex processes that induce mineral precipitation in the modern Lagoa Vermelha microbial mat appear to be recorded in the studied lithified stromatolites. Sub‐micron polyhedral crystal formation of high‐Mg calcite and/or Ca dolomite results from the coalescence of carbonate nanoglobules around degraded organic matter nuclei. Sub‐micron polyhedral crystals aggregate to form larger ovoidal crystals that constitute peloids. Subsequent precipitation of aragonitic spherulites around peloids occurs as micro‐environmental water conditions around the peloids change.     

新疆和硕县红山地区中侏罗世地层研究新进展

根据孢粉和植物化石组合面貌 ,结合岩性及岩相特征 ,论述焉耆含油气盆地红山地区长期存有争议的侏罗纪地层的时代归属 ,认为该区仅发育了中侏罗世地层 ,包括西山窑组和头屯河组 ,为本盆地的石油勘探提供了地层划分与对比的时代依据     

Puncoviscana folded belt in northwestern Argentina: testimony of Late Proterozoic Rodinia fragmentation and pre-Gondwana collisional episodes

 Stratigraphic correlations and tectonic analysis suggest that the Puncoviscana fold belt of northwestern Argentina was an intracontinental basin with bimodal igneous suites that formed in connection with the breakup of the Rodinia supercontinent (at ∼800 Ma). Several lines of evidences point to an initial lithosphere rupture, possibly induced by a rising mantle plume. The earliest synrift igneous products are represented by ultra-potassic dykes and alkaline lava flows of high LREE/HREE and low Zr/Nb–Y/Nb ratios. The dyke emplacements and the initiation of rifting were probably synchronous. They pass laterally and upwards (middle part of the Puncoviscana succession) into basalts of alkaline transitional character (OIB-like source). The distinctive chemical feature of these lavas are very similar to the source of oceanic island basalts; thus, they are thought to represent a magmatism associated with the rift and rift-drift transition stage. During this stage of rifting probably true oceanic crust was formed. The upper part of the Puncoviscana sequence, Late Precambrian/Lower Cambrian in age, comprises a thick and monotonous sequence of pillow lavas, massive basaltic flows and minor volcanic breccias and hyaloclastites. These lavas exhibit MORB trace element characteristics with high FeO_t and TiO₂, low K₂O and P₂O₅, flat light REE spectra, little or no depletion in Nb and Ta. This volcanism consists of the major and latest effusive episode from the Puncoviscana basin which was slightly modified by subduction processes. The geodynamical model proposed for the generation of these volcanic rocks could have been developed in two stages. In the first stage the volcanic event is compatible with a progressive opening of a continental rift leading to formation of a mature oceanic basin. In contrast, the second stage shows the effects of a completed Wilson cycle including a primitive volcanic arc which continued until the accreted Cuyania-Arequipa-Belen-Antofalla (CABA) terrane against the proto-Gondwana western borderland of the Amazonian shield (∼535 Ma). Received: 23 December 1997 / Accepted: 9 December 1998     

Microbial fossilization in carbonate sediments: a result of the bacterial surface involvement in dolomite precipitation

ABSTRACT Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria‐like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate‐reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca²⁺ and Mg²⁺ onto the cell surfaces, indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization. The affinity of the cells for Mg²⁺ was related to the capability of the strains to mediate dolomite formation. Combined with sulphate uptake, which dissociates the [MgSO₄]⁰ ion pair and increases the Mg²⁺ availability, the concentration of Mg²⁺ ions in the microenvironment around the cells, where the conditions are favourable for dolomite precipitation, may be the key to overcome the kinetic barrier to dolomite formation. These results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation, implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates.     

东昆仑造山带二叠-三叠系遗迹化石及指相意义

通过对东昆仑造山带二叠－ 三叠系遗迹化石的研究,识别出了滨海Skolithos遗迹相和深海复理石Nereites遗迹相。在造山带地层变形、变质、变位强烈,实体化石稀少,沉积构造受到后期较强烈改造的情况下,遗迹化石的研究对于确定造山带地层的沉积环境、对比地层和研究非史密斯地层构造岩片提供了一种方法。     

山东诸城地区恐龙足迹化石研究综述

山东诸城地区是闻名世界的恐龙化石宝库,这里不仅保存有数量巨大的晚白垩世恐龙骨骼化石,还发现有数量众多的早白垩世恐龙足迹化石。到目前为止,诸城境内共发现的恐龙足迹化石点有3处,分别为南部的皇龙沟与北部的张祝河湾和棠棣戈庄。根据前人对这3处恐龙足迹化石点的研究,对其发现和研究历史、足迹类型(包括非恐龙足迹)、不同类型足迹的大小和特征,以及古地理和古气候等进行了总结,提出了诸城恐龙足迹化石研究中亟待解决的问题。     

Pediculate Brachiopod Diandongia pista from the Lower Cambrian of South China

The Chengjiang Lagerstatte has been celebrated for prolific soft-bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstatte by the Early Life Institute, Northwest University, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods.