The Jurassic of the Northern Calcareous Alps and its Global Boundary Stratotype Section and Point (GSSP)
Hisashi SuzukiHans‐Jürgen GawlickTetsuji OnoueTeiji MikamiHonami SatoDaisuke YamashitaKeisuke Ishida
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Abstract:
ジュラ系の国際境界模式層序・位置がオーストリア国チロル州のクーヨッホ層序断面に置かれることが2010年に正式に決まった.それはジュラ紀最古のアンモナイトPsiloceras spelae tirolicumが初産出する層準で,ケンドゥルバッハ層の基底から5.8 m上位に位置する.筆者らは2012年に行われた国際堆積学会の巡検でクーヨッホ層序断面を訪れたので,その概要を紹介する.ジュラ系の国際模式境界が置かれた北部石灰アルプスでは,近年の研究でオリストリスの基質をなす珪質堆積岩からジュラ紀の放散虫化石が数多く報告され,年代決定に有効なことが示された.本稿では特に研究が進んでいるザルツカンマーグート地方の代表的なジュラ紀層を紹介し,北部石灰アルプスの地質構造発達史を概観する.Keywords:
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这份报纸简短为寒武纪的系统的全球阶段总结正式批准的全球标准 Stratotype 节和点和建议 GSSP (GSSP ) 。Luoyixi 镇附近的 Luoyixi 节， Guzhang，西北的湖南为全球 Guzhangian 阶段的底作为边界 stratotype 被批准，它是一个未命名的系列的最高的阶段作为寒武纪的系列 3 暂时地称为。GSSP 位置谎言在在节的 Huaqiao 形成的底上面的 121.3 m，与大都会的 agnostoid 三叶虫 Lejopyge leavigata 的第一外观与一致。在 Duibian 村庄的 Duibian B 节， Jiangshan，西方的浙江，为是 Furongian 系列的第二个阶段的建议全球 Jiangshanian 阶段的底作为边界 stratotype 被建议。建议 GSSP 位置谎言在在节的 Huayansi 形成的底上面的 108.12 m，与大都会的 agnostoid 三叶虫 Agnostotes orientalius 的第一外观与一致。这根地平线也与大都会的 polymerid 三叶虫 Irvingella angustilimbata 的第一外观。
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Cenomanian
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Abstract Sections exposing the Cambrian–Ordovician Boundary interval at Broom Point in western Newfoundland have been proposed earlier for a global systemic boundary stratotype. These lie within the Cow Head Group, a late Middle Cambrian to early Middle Ordovician allochthonous unit of limestone, shale, and conglomerate deposited at the toe of the ancient continental slope and on the adjacent continental rise. Several recent studies have further investigated the stratigraphy, sedimentology, and palaeontology of the Cow Head Group and others are under way on magnetostratigraphy and chemostratigraphy. These aspects are reviewed for six key boundary sections representing proximal to distal facies: Cow Head Ledge, Broom Point South, Broom Point North, St Pauls Inlet Quarry, Martin Point, and Green Point. In particular, new data are presented from 260 conodont samples that yielded 15500 conodonts. This intense sampling has allowed the discrimination of minor hiatuses in the proximal to intermediate facies where conglomerates have eroded and cannibalized underlying strata. New conodont data from Broom Point North have lowered the base of the C. lindstromi Zone into unit 74 conglomerates, thereby making this section unsuitable as a boundary stratotype. New collections from Green Point have yielded abundant conodonts and over 9400 conodonts have been recovered from 77 samples. The conodont, graptolite, and trilobite biostratigraphy through the boundary interval is documented allowing accurate correlation between sections and more precisely revealing small hiatuses in the proximal and intermediate facies. The sequence of conodont zones is: Eoconodontus notchpeakensis, Cordylodus proavus, C. caboti, C. intermedius, C. lindstromi and C. angulatus. These can be correlated with trilobite zones established from both in situ and clast faunas from the proximal to intermediate facies and with graptolite assemblages (of Cooper 1979) especially in the intermediate to distal facies. Three new species of Cordylodus are described ( C. andresi, C. hastatus and C. tortus ) and the full apparatus of Iapetognathus preaengensis is illustrated. The criteria for selecting a global boundary stratotype and point (GSSP) are reviewed in terms of the Cow Head sections. The Green Point section is shown to meet, and largely surpass, the prerequisites required of a stratotype. The Green Point section is proposed to be the global boundary stratotype with the base of the Ordovician System defined at the base of unit 23, which is the base of the Broom Point Member, Green Point Formation, at a level coincident with the base of the Cordylodus lindstromi Zone. In addition to an abundant and superbly preserved conodont fauna, this section preserves the best sequence of earliest planktic graptolites through a 40 m interval; the first nematophorous graptolites (of Assemblage 1) occur in unit 25, 6.9 m above the base of the C. lindstromi Zone. This level can be readily correlated into the proximal facies where both deep and shallow water trilobites ( in situ and in clasts, respectively) show the base of the C. lindstromi Zone to lie within the Symphysurina brevispicata trilobite Subzone.
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The Global Stratotype Section and Point (GSSP) for the boundary between the Capitanian and Wuchiapingian stages, also the boundary between the Guadalupian and Lopingian Series is defined at the First Appearance Datum (FAD) of the conodont Clarkina postbitteri postbitteri at the base of Bed 6k in the Penglaitan Section along the Hongshui River in Guangxi, South China. This point is within a chronomorphocline from Clarkina postbitteri hongshuiensis to C. dukouensis and nearly coincides with the Middle-Upper Absaroka Megasequence boundary and as such is documented within a continuously deposited carbo-nate lowstand succession with deep-water facies of the Maokou Formation below and deep-water facies of the Heshan Formation above. Furthermore, this point also coincides with a major extinction of various Permian fossils including ammonoids, brachiopods, corals, and fusulinaceans. The proximity to an appa-rently global major sequence boundary and extinction event will serve as a means of correlation of this GSSP into other regions in which the defining taxon is not present because of profound provincialism du-ring the Middle and Upper Permian. Carbon isotopic trends and magnetostratigraphic signatures are also provided to help correlate this GSSP into other regions, including those with continental facies successions. The Tieqiao Section near the county town of Laibin is also described as a supplementary reference section.
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Permian–Triassic extinction event
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The biostratigraphic Permian/Triassic (P/T) boundary is defined by the first appearance of H. parvus. The first appearance of H. parvus within the cline H. latidentatus-H. parvus is a globally recognizable event in the conodont evolution. The first appearance of H. parvus is not facies related and can be observed both in ammonoid-free shallow-water deposits and in ammonoid-bearing pelagic deposits. H. parvus is a common, easily determinable species known so far from the entire Tethys, Japan, western North America, Boreal realm (Greenland) and the Tethyan margin of Gondwana. H. parvus is the first species with world-wide distribution to appear after the absolute minimum in the faunal diversity indicated by the minimum in δ13C. The Meishan section (South China) contains a continuous, pelagic sedimentary record across the P/T boundary without stratigraphic gaps. It is nearly unaltered thermally (CAI = 1-1.5). Its fossil content (ammonoids, conodonts, foraminifers, bivalves, brachiopods, sporomorphs etc.) and event succession have been thoroughly studied. Absolute age and magnetostratigraphy have also been subjected to intensive studies. The section is readily accessible and under protection of the government. This section is best suitable as a global stratotype section and point (GSSP) for the base of the Triassic. No other section in the world is known to be qualified for defining the P/T boundary in a GSSP. H. parvus made its earliest appearence in the middle part of Boundary Bed 2 (Bed 27) at Meishan. It evolved within Bed 27 from H. latidentatus within a phylomorphogenetic continuum in a continuous and monofacial stratum. The biostratigraphic P/T boundary lies very close to the event boundary (15cm above the event boundary at the base of Boundary Bed 1 = Bed 25, and a few centimetres above the minimum in δ13C in the lower Boundary Bed 2).
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The Early-Middle Permian(Cisuralian-Guadalupian) boundary is marked globally by tremendous changes in terms of the development of ammonoid faunas.At that time the new Order Ceratitida appeared and their first known representatives are found in the lowest part of the Middle Permian Roadian Stage.The earliest Ceratitida therefore serve as reliable markers for the boundary between the Lower and Middle Permian in the Tethyan region and North America in terms of ammonoids.In other biogeographic regions,how-ever,where Ceratitida have not been found,representatives of the families Pseudogastrioceratidae and Spirolegoceratidae play an important role in biostratigraphical subdivision.The GSSP(Global Stratotype Section and Point) between the Lower and Middle Permian is defined in the Glass Mountains of Texas based on the first appearance of the conodonts species Jinogondolella nanking-ensis.However,the first Middle Permian representatives ammonoids appear slightly below this level in the Texas section.As the Roadian Stage was originally defined by Furnish based on ammonoid data.Many ammonoid experts do not agree with a definition based on conodonts in view of a fact that a typical set of Middle Permian ammonoids existed in the Early Permian based on the conodont definiton.Ammonoid experts therefore strongly suggest that the ceratitid Paraceltites elegans and other ceratitid ammonoids should all be attributed to Middle Permian.In this study,characteristic ammonoid faunas around the boundary between the Lower and Mi-ddle Permian in China are re-identified and reviewed.Based on a number of ammonoid occurrences materials near the Kungurian-Roadian boundary previously reported,I consider that ammonoid faunas near the Lower-Middle Permian boundary mainly occur in South and northwest China.Compared with the coeval ammonoid faunas in Russia,it can be concluded that endemic elements including Pseudohaloritinae and Shou-changoceratinae dominate the ammonoid faunas near the boundary.Based on a new study of a number of the ammonoid faunas,the lower part of the Shuangbaotang Formation is assigned to the Kungurian,the middle to upper part of the formation to the Roadian;the Fanjiatun Formation to the Roadian or Wordian;the Jiala Formation from Xigaze,Tibet and the Urulung Formation at Duilongdeqing,Tibet,to Roadian.The Shuangbaotang Section in Gansu Province and the Dongwuli Section in Zhejiang Province are considered the most promising localities to solve the problem of the Kunguian-Roadian boundary in terms of ammonoids.
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Fusulinacean foraminifera have been described from several localities and horizons within the Upper Pennsylvanian and Lower Permian of the North American midcontinent (Beede, 1916; Dunbar and Condra, 1927; Skinner, 1931; Newell, 1934; Newell and Keroher, 1937; Merchant and Keroher, 1939; Dunbar and Henbest, 1942; Burma, 1942; Thompson, 1954, 1957; Thompson et al., 1956; Douglass, 1962; King, 1988; Sanderson and Verville, 1988), but surprisingly, a comprehensive account of fusulinacean biostratigraphy of the stratotype of the Upper Pennsylvanian Virgilian Stage has never been published. This report summarizes fusulinacean biostratigraphic data from the Virgilian section in the stratotype region of southeastern Kansas. The publication of this dataset is particularly important because of the current efforts to standardize global Pennsylvanian chronostratigraphy (Metcalfe, 1997), and related efforts and debates concerning the definition and correlation of stages in the Upper Pennsylvanian and Lower Permian succession of North America.
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