海相遗迹化石对显生宙生物大辐射事件的响应*

通过系统梳理前寒武纪和显生宙海相遗迹化石记录及笔者自己的研究,发现在寒武纪生命大爆发、奥陶纪生物大辐射、中生代海洋革命共3次里程碑式的生物大辐射过程中,海相遗迹化石的属级多样性变化和歧异度增减均与生物多样性呈正相关,生物扰动强度和深度明显增加,造迹生物的觅食策略和行为习性多样化明显增多。寒武纪生命大爆发时期,最有代表性的生物行为变化是出现了具有垂向分量的潜穴; 奥陶纪生物大辐射期间,海相遗迹化石的分布逐渐从滨、浅海扩展至半深海和深海,表现为造迹生物群落栖息地的扩张; 中生代海洋革命时期,海相和陆相遗迹化石同步增加,生物对生态空间利用的深度、广度和集约性同步增强,遗迹化石面貌表现为深海雕画迹的多样性和歧异度大幅增加、形态类型多样、多种觅食策略共存。地史时期的海相遗迹化石面貌受环境外因和生物内因控制,表现出形态由简到繁、分布范围由小到大的变化趋势,对生态空间的利用表现为由沉积物表层至浅层再到深层、由二维到三维、由局域(浅水)到广域(浅水和深水以及陆地)的发展,印证了生物获取生态机会的过程。     

古生代海洋碳同位素演化

本文给出对中国古生代海相碳酸盐岩地层的系统的碳同位素研究结果。对密集地采自寒武纪、奥陶纪、泥盆纪、石炭纪和二叠纪5个海相碳酸盐岩地层剖面的681个样品作了碳同位素研究。所得到的古生代海相碳酸盐岩地层δ¹³C值长趋势演化的模式表明,从寒武纪(δ¹³C平均为-0.3‰)到石炭纪(3‰)和二叠纪(3.4‰)逐渐富集¹³C.此变化模式与古生代有机碳的埋藏数量有关,或许与大洋中脊体系的体积变化有关。     

山东古生代生物地层单位的划分

本文按照不同生物地层单位的含义,对山东古生代生物地层单位进行了厘定,共划出４１个生物带,其中寒武纪有２１个;奥陶纪１０个,包括３个哑层间隔带;石炭纪３个;二叠纪７个。这些生物地层单位的确立,对统一山东古生代生物地层单位的划分和推动今后的区调工作将起到重要的作用。     

甘肃永昌乌拉尔世Sphenopteris(楔羊齿)新记录: 兼论晚古生代Sphenopteris多样性及古地理演化*

Sphenopteris(楔羊齿属)叶化石在全球晚古生代地层中广泛出现,但该属的系统分类位置及演化特征仍有待深入探讨,而且只有极少数种的表皮及气孔微细构造得到揭示。笔者在甘肃永昌乌拉尔统山西组中发现了2种形态保存较好且具有角质层的楔羊齿,分别是 Sphenopteris yongchangensis sp. nov.(永昌楔羊齿—新种)和Sphenopteris nystroemii (弱楔羊齿)。前者小羽片呈扇形,基部连合,侧脉分叉1次,气孔作椭圆状且为两面生; 后者小羽片呈梭形且顶端钝圆,侧脉分叉1次并达缘,气孔分布于脉间区。经对比,文中报道的2种楔羊齿可能属皱羊齿目(Lyginopteridales)。此外,统计了Sphenopteris在晚古生代的269个化石记录,结合该属的形态学、解剖学特征和分布记录,探讨了其多样性演化和古地理分布,结果表明: 宾夕法尼亚亚纪至乌拉尔世,Sphenopteris广泛分布于全球中低纬度地区,呈现出高度变异和分化; 自晚泥盆世至二叠纪,Sphenopteris型叶化石在中国自华南向华北迁移演化,说明其多样性特征不仅与湿润气候密切相关,而且与其古地理分布相耦合。     

贵州石炭纪遗迹化石—兼论Zoophycos在地史时期的古地理分布

本文是在对贵州石炭系地层岩相古地理研究过程中，采集了大量遗迹化石，共１１属１１种。根据这些遗迹化石的古地理分布特征，建立了贵州石炭纪遗迹化石群落与岩相古地理之间的关系。同时结合石炭系地层中大量的Ｚｏｏｐｈｙｃｏｓ产出层位岩相特征以及国内外已有Ｚｏｏｐｈｙｃｏｓ产出层位岩相古地理情况，总结出Ｚｏｏｐｈｙｃｏｓ的地史时期古地理变迁史，即Ｃ－Ｐ为浅海环境，Ｔ－Ｊ为浅海－深海过渡的半深水环境，Ｋ－Ｅ为深水     

放射状觅食兼停息（或居住）遗迹化石初步研究

本文介绍了8个放射状觅食兼停息(或居住)遗迹化石属的特征,讨论了这类遗迹化石的形成方式、形成环境、与古水流方向的关系及测量分析方法。 通过分析,得出几点初步认识:①这类遗迹是生物停息(或居住)一处,靠身体胀缩或其它方式多次往复运动觅食形成;②这类遗迹多形成于安静、沉积速度缓慢的环境;③这类遗迹化石由停息迹(或居住迹)和觅食迹两部分组成,觅食迹(即放射这部分)迎水流方向上多较发育,因而大量统计觅食迹发育的方向可以判断古水流方向。     

晋东南上石炭统—下二叠统太原组灰岩中遗迹组合及其沉积环境

晋东南陵川地区上石炭统—下二叠统太原组灰岩中遗迹化石发育,已识别出10个遗迹属14个遗迹种,常见遗迹化石包括Zoophycos,Helminthopsis,Planolites,Nereites,Chondrites,Thalassinoides,Rhizocorallium,Ophiomorpha,Palaeophycus和Teichichnus等,其中Zoophycos最为发育。依据遗迹化石的组成、分布及产状特征,可建立4个遗迹组合:(1)Zoophycos-Thalassinoides遗迹组合;(2)Planolites-Helminthopsis遗迹组合;(3)Zoophycos-Teichichnus遗迹组合;(4)Nereites-Chondrites遗迹组合。对这些遗迹化石宿主岩石沉积特征的分析表明,太原组灰岩中的遗迹组合分别产生于海湾—潟湖环境(遗迹组合1)、浅海上部(遗迹组合2)、浅海中部(遗迹组合3)和浅海下部(遗迹组合4)。基于遗迹组合特征和沉积特征的综合分析,提出了研究区太原组遗迹化石组合的沉积环境模式,这一成果可为今后该区太原组中煤与煤层气生成的古环境研究提供生物学信息和基础理论资料。     

遗迹化石的古环境和古地理意义

遗迹化石(或生物成因沉积构造)是原产地环境条件的指示者,是原地埋藏的遗迹群落,因此几十年前即用来研究古环境和古地理。本文从4个方面讨论了利用遗迹化石群落来解释古代环境和古地理条件：①陆相和海相遗迹化石群落的区别;②海陆过渡带环境的遗迹化石群落和海岸线的识别;③遗迹相的古环境和古地理应用,且讨论了Skolithos(石针迹)、Cruziana(克鲁斯迹)、Zoophycos(动藻迹)和Nereites(类砂蚕迹)四个遗迹相研究的新进展;④利用遗迹化石群落对一些地质事件的解释,包括一些沉积事件的解释以及判断缺氧和贫氧环境。     

龙门山地区中泥盆统养马坝组风暴沉积中的遗迹化石及其环境意义

龙门山地区泥盆纪地层中含有种类丰富、数量众多的海相遗迹化石。以野外剖面实测为基础,对北川甘溪石沟里剖面中泥盆统养马坝组风暴沉积中的遗迹化石进行了系统描述,共识别出5种类型的遗迹化石属种,包括Chondrite、Changchengia、Rhizocorallium、Skolithos和Zoophycos。根据遗迹化石的组合特征,将其划分为Chondrites-Zoophycos遗迹化石组合类型,反映了受风暴影响的浅水沉积环境。通过遗迹化石的分布位置、相互间的切割关系,建立了龙门山地区石沟里剖面养马坝组风暴岩中各种遗迹化石形成的先后顺序,依次为Chondrites、Zoophycos、Rhizocorallium、Changchengia和Skolithos。发育于风暴岩中的Chondrites和Zoophycos遗迹化石,具有鲜明的机会种特征,对沉积环境有重要的指示意义。保存于龙门山地区泥盆系养马坝组风暴岩中丰富的具细小分支直径的Chondrites遗迹化石,反应水体氧含量并非控制Chondrites潜穴直径大小的唯一控制因素,可能与造迹生物生活环境的恶劣与否间存在着一定关系;风暴沉积中发育的Zoophycos遗迹化石,指示其在泥盆纪可以沉积于浅海环境。     

辽河断陷古潜山古生界的厘定及其地质意义

辽河断陷以碳酸盐岩和砂页岩为主的古潜山地层一直全部划归中、新元古界。由于在该套地层的部分岩石薄片中发现交代残余的动物化石碎片，因此提出辽河断陷有古生界存在的新观点。通过牙形石、微古植物、动物化石和岩性组合的研究，对这套地层进行了重新厘定，建立了古生代寒武纪、奥陶纪、石炭纪和二叠纪地层层序。研究成果表明，辽河断陷存在古生界储层，古生代潜山并非单斜．而是由被断裂改造的褶皱组成的断块。这一成果为重新认识潜山的内幕构造特征和油气储层分布规律奠定了基础。     

A comparison of the evolution of arc complexes in Paleozoic interior and peripheral orogens: Speculations on geodynamic correlations

We discuss the potential geodynamic connections between Paleozoic arc development along the flanks of the interior (e.g. the Iapetus and Rheic) oceans and the exterior Paleopacific Ocean. Paleozoic arcs in the Iapetus and Rheic oceanic realms are preserved in the Appalachian–Caledonide and Variscan orogens, and in the Paleopacific Ocean realm they are preserved in the Terra Australis Orogen. Potential geodynamic connections are suggested by paleocontinental reconstructions showing Cambrian–Early Ordovician contraction of the exterior ocean as the interior oceans expanded, and subsequent Paleozoic expansion of the exterior oceans while the interior oceans contracted. Subduction initiated in the eastern segment of Iapetus at ca. 515 Ma and Early to Middle Ordovician orogenesis along the flanks of this ocean is highlighted by arc–continent collisions and ophiolite obductions. Over a similar time interval, subduction and orogenesis took place in the exterior ocean and included formation of the Macquarie arc in the Tasmanides of Eastern Australia and the Famatina arc and correlatives in the periphery of the proto-Andean margin of Gondwana. Major changes in the style of subduction (from retreating to advancing) in interior oceans occurred during the Silurian, following accretion of the peri-Gondwanan terranes and Baltica, and closure of the northeastern segment of Iapetus. During the same time interval, subduction in the Paleopacific Ocean was predominantly in a retreating mode, although intermittent episodes of contraction closed major marginal basins. In addition, however, there were major disturbances in the Earth tectonic systems during the Ordovician, including an unprecedented rise in marine life diversity, as well as significant fluctuations in sea level, atmospheric CO₂, and ⁸⁷Sr/⁸⁶Sr and ¹³C in marine strata carbonates. Stable and radiogenic isotopic data provide evidence for the addition of abundant mantle-derived magma, fluids and large mineral deposits that have a significant mantle-derived component. When considered together, the coeval, profound changes in the style of tectonic activity and the disturbances recorded in Earth Systems are consistent with the emergence of a superplume during the Ordovician. We speculate that the emergence of a superplume triggered by slab avalanche events within the Iapetus and Paleopacific oceans was associated with the establishment of a new geoid high within the Paleopacific regime, the closure of the interior Rheic Ocean and the amalgamation of Laurussia and Gondwana, which was a key event in the Late Carboniferous amalgamation of Pangea.     

http://www.sciencedirect.com/science/article/pii/S1674987111001113

The Rheic Ocean was one of the most important oceans of the Paleozoic Era.It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita-Alleghanian -Variscan orogen during the assembly of Pangea.Rifting began in the Cambrian as a continuation of Neoproterozoic orogenic activity and the ocean opened in the Early Ordovician with the separation of several Neoproterozoic arc terranes from the continental margin of northern Gondwana along the line of a former suture.The rapid rate of ocean opening suggests it was driven by slab pull in the outboard lapetus Ocean.The ocean reached its greatest width with the closure of lapetus and the accretion of the periGondwanan arc terranes to Laurentia in the Silurian.Ocean closure began in the Devonian and continued through the Mississippian as Gondwana sutured to Laurussia to form Pangea.The ocean consequently plays a dominant role in the Appalachian-Ouachita orogeny of North America,in the basement geology of southern Europe,and in the Paleozoic sedimentary,structural and tectonothermal record from Middle America to the Middle East.Its closure brought the Paleozoic Era to an end.     

A plate tectonic scenario for the Iapetus and Rheic oceans

The tectonics, dynamics, and biogeographic landscape of the early Paleozoic were dominated by the opening and expansion of one large ocean—the Rheic—and the diminution to terminal closure of another—Iapetus. An understanding of the evolution of these oceans is thus central to an understanding of the early Paleozoic, but their chronicle also presents a rich temporal profile of the Wilson cycle, illustrating continental-scale rifting, microcontinent formation, ocean basin development, arc accretion, and continent–continent collision. Nevertheless, contemporary paleogeographic models of the Iapetus and Rheic oceans remain mostly schematic or spatiotemporally disjointed, which limits their utility and hinders their testing. Moreover, many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios. With the specific aim to resolve some of the uncertainties in the evolution of this early Paleozoic domain, and a broader aim to instigate the application of quantitative kinematic models to the early Paleozoic, I present a new plate tectonic model for the Iapetus and Rheic oceans. The model has realistic tectonic plates, which include oceanic lithosphere, that are defined by explicit and rigorously managed plate boundaries, the nature and kinematics of which are derived from geological evidence and plate tectonic principles. Accompanying the presentation and discussion of the plate model, an extensive review of the underlying geological and paleogeographic data is also presented.     

Highly depleted isotopic compositions evident in Iapetus and Rheic Ocean basalts: implications for crustal generation and preservation

Subduction of both the Iapetus and Rheic oceans began relatively soon after their opening. Vestiges of both the Iapetan and Rheic oceanic lithospheres are preserved as supra-subduction ophiolites and related mafic complexes in the Appalachian–Caledonian and Variscan orogens. However, available Sm–Nd isotopic data indicate that the mantle source of these complexes was highly depleted as a result of an earlier history of magmatism that occurred prior to initiation of the Iapetus and Rheic oceans. We propose two alternative models for this feature: either the highly depleted mantle was preserved in a long-lived oceanic plateau within the Paleopacific realm or the source for the basalt crust was been recycled from a previously depleted mantle and was brought to an ocean spreading centre during return flow, without significant re-enrichment en-route. Data from present-day oceans suggest that such return flow was more likely to have occurred in the Paleopacific than in new mid-ocean ridges produced in the opening of the Iapetus and Rheic oceans. Variation in crustal density produced by Fe partitioning rendered the lithosphere derived from previously depleted mantle more buoyant than the surrounding asthenosphere, facilitating its preservation. The buoyant oceanic lithosphere was captured from the adjacent Paleopacific, in a manner analogous to the Mesozoic–Cenozoic “capture” in the Atlantic realm of the Caribbean plate. This mechanism of “plate capture” may explain the premature closing of the oceans, and the distribution of collisional events and peri-Gondwanan terranes in the Appalachian–Caledonian and Variscan orogens.     

新疆塔里木盆地东北部库鲁克塔格地区寒武─奥陶纪遗迹化石

本文研究的遗迹化石采自新疆塔里木盆地东北部库鲁克塔格山上寒武统和奥陶系．经鉴定计有１６个遗迹属，２１个遗迹种，其中有４个新遗迹种．这个地区丰富的深海Ｎｅｒｅｉｔｅｓ遗迹相遗迹化石在我国首次发现，这些发现对于塔里木盆地的油气勘探，沉积环境分析具有重要的意义．     

新疆塔里木盆地东北部库鲁克塔格地区寒武─奥陶纪遗迹化石

本文研究的遗迹化石采自新疆塔里木盆地东北部库鲁克塔格山上寒武统和奥陶系．经鉴定计有１６个遗迹属，２１个遗迹种，其中有４个新遗迹种．这个地区丰富的深海Ｎｅｒｅｉｔｅｓ遗迹相遗迹化石在我国首次发现，这些发现对于塔里木盆地的油气勘探，沉积环境分析具有重要的意义．     

Palaeozoic structures in the Xayacatlán area,Acatlán Complex,southern Mexico: transtensional rift‐ and subduction‐related deformation along the margin of Oaxaquia

The Xayacatlán area (eastern Mixteca terrane, southern Mexico) was previously inferred to preserve the Ordovician‐Silurian thrust contact between vestiges of the Iapetus Ocean and the para‐autochthon bordering Oaxaquia. Detailed remapping indicates that the rocks occur in four vertically‐bounded, NS fault blocks. The latter record the following tectonothermal events that post‐date Iapetus and occurred along the margins of the Rheic (1) and Pacific (2 and 3) oceans: (1) dextral transtension accompanying intrusion of an NS, tholeiitic dike swarm at ～442 Ma; (2) penetrative, greenschist‐facies deformation during the Mississippian related to extrusion of high‐pressure rocks; and (3) subgreenschist‐facies dextral transtension on NS faults during the generation of Middle Permian fabrics.     

The Anglo-Brabant Massif: Persistent but enigmatic palaeo-relief at the heart of western Europe

The surface geology of central England and Belgium obscures a large ‘basement’ massif with a complex history and stronger crust and lithosphere than surrounding regions. The nucleus was forged by subduction-related magmatism at the Gondwana margin in Ediacaran time. Partitioning into a platform, in the English Midlands, and a basin stretching to Belgium, in the east, was already evident in Cambrian/earliest Ordovician time. The accretion of the Monian Composite Terrane during the Penobscotian deformation phase preceded late Tremadocian rifting, and Floian separation, of the Avalonia Terrane from the Gondwana margin. Late Ordovician magmatism in a belt from the Lake District to Belgium records subduction beneath Avalonia of part of the Tornquist Sea. This ‘Western Pacific-style’ oceanic basin closed in latest Ordovician time, uniting Avalonia and Baltica. Closure of the Iapetus Ocean in early Silurian time was soon followed by closure of the Rheic Ocean, recorded by subduction along the southern margin of the massif. The causes of late Caledonian deformation are poorly understood and controversial. Partitioned behaviour of the massif persisted into late Palaeozoic time. Late Devonian and Carboniferous sequences show strong onlap onto the massif, which was little affected by crustal extension. Compressional deformation during the Variscan Orogeny also appears slight, and was focussed in the west where a wedge-shaped mountain foreland uplift was driven by orogenic indentation, splitting the massif from the Welsh Massif along the reactivated Malvern Line. Permian to Mesozoic sequences exhibit persistent but variable degrees of onlap onto the massif.     

Peri-Gondwanan Ordovician crustal fragments in the high-grade basement of the Eastern Rhodope Massif,Bulgaria: evidence from U-Pb LA-ICP-MS zircon geochronology and geochemistry

Field, geochemical, and geochronologic data of high-grade basement metamafic and evolved rocks are used to identify the nature and timing of pre-Alpine crustal growth of the Rhodope Massif. These rocks occur intrusive into clastic-carbonate metasedimentary succession. Petrography and mineral chemistry show compositions consistent with Alpine amphibolite-facies metamorphism that obliterated the original igneous textures of the protoliths. Bulk-rock geochemistry identifies low-Ti tholeiitic to calc-alkaline gabbroic-basaltic and plagiogranite precursors, with MORB-IAT supra-subduction zone signature and trace elements comparable to modern back-arc basalts. The U-Pb zircon dating revealed a mean age of 455 Ma for the magmatic crystallization of the protoliths that contain inherited Cambrian (528–534 Ma) zircons. Carboniferous, Jurassic, and Eocene metamorphic events overprinted the Ordovician protoliths. The radiometric results of the metamorphic rocks demonstrate that Ordovician oceanic crust was involved in the build-up of the Rhodope high-grade basement. Dating of Eocene-Oligocene volcanic rocks overlying or cross-cutting the metamorphic rocks supplied Neoproterozoic, Ordovician and Permo-Carboniferous xenocrystic zircons that were sampled en route to the surface from the basement. The volcanic rocks thus confirm sub-regionally present Neoproterozoic and Paleozoic igneous and metamorphic basement. We interpret the origin of the Middle-Late Ordovician oceanic magmatism in a back-arc rift-spreading center propagating along peri-Gondwanan Cadomian basement terrane related to the Rheic Ocean widening. The results highlight the presence of elements of Cadomian northern Gondwana margin in the high-grade basement and record of Rheic Ocean evolution. The eastern Rhodope Massif high-grade basement compared to adjacent terranes with Neoproterozoic and Cambro-Ordovician evolution shares analogous tectono-magmatic record providing a linkage among basement terranes incorporated in the Alpine belt of the north Aegean region.