An Aeronian (Middle Llandovery) graptolite from the Pentamerus Beds near Hillend Farm,Shropshire, UK

A specimen of Clinoclimacograptus retroversus is recorded from the Pentamerus Beds of the A489 road section near Hillend Farm, Shropshire, England. This specimen, combined with the presence of the brachiopod Eocoelia hemisphaerica, demonstrates that the beds here must be of mid to late Aeronian (Mid Llandovery) age. The fossiliferous horizons lie only a few metres above the Precambrian unconformity and thus help to constrain the timing of the transgression here. Copyright © 2002 John Wiley & Sons, Ltd.     

A Rhuddanian (Silurian,lower llandovery) pelmatozoan fauna from south-west Wales

Only two crinoid faunas of Rhuddanian or early Aeronian age have been described hitherto, both from North America. A Rhuddanian pelmatozoan fauna from Haverfordwest, Dyfed, south-west Wales includes the cheirocrinid rhombiferan cystoid Homocystites? sp., plus the following crinoid species: the calceocrinid disparids Calceocrinus turnbulli sp. nov. and Calceocrinus? sp.; the dendrocrinid cladid Dendrocrinus? gasworksensis sp. nov.; the patelliocrinid monobathrid Macrostylocrinus? sp. indet.; columnals of the rhodocrinitid(?) diplobathrid Floricolumnus (col.) sp. cf. F. (col.) girvanensis Donovan and Clark; the rhodocrinitid diplobathrid Chaosocrinus ornatus sp. nov.; and two indeterminate crinoid species. At the familial level this fauna shows strong similarities with coeval, but more diverse, crinoid assemblages from North America, suggesting that endemism did not develop until later in the Silurian.     

Storm-dominated sedimentation along a rocky transgressive shoreline in the Silurian (Llandovery) of Western Ireland

Sedimentation patterns are described from the Kilbride Formation west of the Maam Fault zone, north Galway, Ireland. Seven distinct facies are described using faunal and lithological parameters. Environments of deposition range from marginal marine to deep shelf conditions. Lateral facies distributions were largely controlled by a rocky topographic high which influenced sedimentation until being buried by outer shelf sediments in middle-upper Kilbride Formation times. Four distinct sequences are described: in the lower Kilbride Formation, sequences I and IV are dominated by proximal storm deposits; sequence II was deposited in the lee of the topographic high and is interpreted as barred estuarine deposits; and in sequence III, at the topographic high, no deposition took place. In the upper Kilbride Formation the barrier was buried and uniform outer shelf conditions prevailed throughout the area. Faunal assemblages were strongly controlled by local environmental conditions and do not conform directly with the expected pattern of depth-related brachiopod communities. The Lingula and Eocoelia communities are amalgamated and alloch-thonous, the Pentameroides and Costistricklandia communities are absent, and only the Clorinda community is well represented, though parautochthonous.     

Late Llandovery thelodonts and conodonts from the Kilbride Formation,Co. Galway,western Ireland

Acid etching of a calcareous sandstone horizon within the lower part of the upper Llandovery Kilbride Formation, exposed at Coolin Lough, Co. Galway, has yielded a phosphatic microfauna dominated by conodont elements and thelodont scales. The thelodonts are identified as Loganellia ex gr. scotica and provide the first record of fishes from the Lower Silurian of Ireland; they suggest a Telychian age. The conodont fauna is dominated by Icriodella, indicative of a nearshore environment of deposition. The microfossils were extracted from a shell bed packed with Eocoelia curtisi curtisi Ziegler, confirming a late Telychian age and also suggesting a shallow water depositional environment. This fauna developed marginal to Laurentia and is similar to coeval assemblages from the Anglo–Welsh area and Baltoscandia. © 1996 John Wiley & Sons, Ltd.     

Llandovery Crinoidea of the British Isles,including description of a new species from the Kilbride Formation (Telychian) of western Ireland

A new species of cladid(?) crinoid, Segmentocolumnus (col.) clarksoni, based on distinctive, disarticulated stem material, is described from the Upper Llandovery Kilbride Formation. Hitherto, this unit has yielded two taxa based on single, nearly complete crinoids. In contrast, S. (col.) clarksoni is known from numerous specimens, including common long pentagonal, pentameric, heteromorphic pluricolumnals with symplectial articulations, broad pentagonal lumina and narrow claustra. A related morphospecies is known from the Ashgill (Upper Ordovician) of Ireland. The fossil echinoderms of the Llandovery (Lower Silurian) are poorly known globally. Where present in this interval, echinoderms are more commonly preserved as disarticulated ossicles and rarely as complete specimens. Complete crinoids have now been identified from nine horizons in the Llandovery of the British Isles, making this one of the better known pelmatozoan faunas from this time interval. However, only two of these occurrences have yielded as many as five or more identifiable taxa. Seven of the nine occurrences are Upper Llandovery (Telychian). Genera are typical of the Silurian or (Upper Ordovician + Silurian); the only remnant Ashgill taxon that did not survive the Llandovery was the morphogenus Segmentocolumnus (col.) Donovan, an ‘extinction’ that probably owes more to taxonomic method than any evolutionary pattern. Copyright © 2003 John Wiley & Sons, Ltd.     

Graptolite biostratigraphy of the Lower Silurian (Llandovery and Wenlock) of Bohemia

Nearly 50 sections through the Llandovery and Wenlock black shales of the Barrandian area (Bohemia) have been examined bed by bed. This has made possible the compilation of an improved and well defined graptolite zonal scheme with much new biostratigraphic data included. A total of 268 graptolite species and subspecies have been found. Their stratigraphic distribution allows the recognition of 27 graptolite zones: ascensus–acuminatus, vesiculosus, cyphus, triangulatus–pectinatus, simulans, convolutus, sedgwickii, linnaei, turriculatus, crispus, griestoniensis, tullbergi, spiralis, grandis, insectus, centrifugus, murchisoni, riccartonensis, dubius, belophorus, rigidus, ramosus–perneri, lundgreni, parvus, nassa–frequens, praedeubeli–deubeli, ludensis, and several subzones. The biozones are defined by the vertical ranges of their ‘index’ species and are characterized by rich accompanying associations. The zonal scheme is correlated with graptolite sequences elsewhere.     

保山地块下二叠统丁家寨组碳同位素特征

对保山地块的下二叠统丁家寨组碳酸盐岩、含砾钙质杂砂岩及其上、下层位的碳酸盐岩进行了野外剖面实测、钻孔编录和碳、氧同位素分析测试,发现该地区丁家寨组碳同位素表现出一定的变化规律。丁家寨组之下和之上的碳酸盐岩δ¹³C值偏大（均为正值）,而丁家寨组δ¹³C值出现了一至多次负偏移。珊瑚化石和苔藓虫化石分别在铺门前组和丁家寨组中被发现,为其时代的限定提供了新依据。通过与全球其它地区同期碳氧同位素分布的投图对比,发现该时期碳、氧同位素数据因受到冰川的影响而表现出具有较强的线性相关性,这些样品受到了成岩作用的影响。δ¹³C负偏移可能与冰期低水位期沉积和成岩过程中近地表的暴露有关。卧牛寺玄武岩大面积喷发引起的各种效应,包括CO₂含量的升高、全球变暖、风化作用的加强、陆源碎屑输入的增加等多种因素,协同冰川作用共同影响了丁家寨组海洋无机碳同位素的变化。     

Geochemistry and potential correlation of Silurian (Telychian) metabentonites from Ireland and SW Scotland

New occurrences of metabentonites from the Telychian Stage of the Silurian successions in SW Scotland, Co. Down and Co. Mayo, Ireland, are described in terms of their biostratigraphical setting and geochemical characteristics. The Co. Mayo occurrence extends the known distribution of Telychian metabentonites in Europe by 280 km WSW from the coast of Co. Down. Comparisons between samples based on selected trace element ratios suggest three potential correlations. One is between a tuffaceous clay from the Finny School Member, Upper Kilbride Formation of Co. Mayo, and a metabentonite from the Tara Sandstone Formation, Gala Group, Co. Down. One pair of metabentonites from the Carghidown Formation of Kirkcudbrightshire can be related to one pair from the Ardglass Formation of Co. Down. In addition, a unique alkaline chemical composition is identified in two samples from the Kirkmaiden Formation of Kirkcudbrightshire and one sample from the Ballyquintin Formation of Northern Ireland, which implies the existence of a local extensional tectonic regime at that time, consistent with a back‐arc basin. These metabentonites extend across at least two Caledonian suspect terranes and a variety of different sedimentary facies. These data may assist future discoveries and be able to improve stratigraphic correlations across three terranes. Copyright © 2003 John Wiley & Sons, Ltd.     

宜昌地区早志留世（Llandoverian）腕足类一新科Spinochonetidae (fam. nov.)及其意义

腕足类新科Spinochonetidae(fam.nov.)建立在宜昌地区志留系兰多维列统罗惹坪组下段中部(上埃隆阶)的Spinochonetes Rong,Xu et Yang(1974)和Spinolella(gen.nov.)两个属,以及一个属、种未定的分类单元的基础上。新科成员仅有从腹壳喙部伸出一根直的腹喙刺,这与Chonetoidea超科内的Strophochonetidae科以及Chonestrophiidae科众成员的铰合缘刺都是从腹壳铰合缘上伸出来的有着本质差别。另外,本文还对Spinochonetes以及它的属型种S.notata Rong,Xu et Yang(1974)进行重要图解和补充描述。与此同时,对Spinolella(gen.nov),以及S.minuta(gen.et sp.nov.)进行系统描述和对比。据目前所知,新科成员只分布于我国鄂西、黔东北、陕南和川北等地,属于上扬子台地的土族居民。因为Spinochonetidae(fam.nov.)属于腕足类独特的一个类型,演化快,贝体极小,保存精美,因此具有分类学、地层对比,以及恢复古环境等方面的重要意义。     

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.     

大别-苏鲁造山带大理岩碳氧同位素地球化学研究

大别-苏鲁造山带的大理岩分布非常广泛,在三叠纪的陆-陆碰撞中,经受了不同程度的变质作用。本文对分布在大别地区北淮阳、苏家河、桐柏、宿松和苏鲁地区张八岭、五莲和坪上等地区的浅变质大理岩进行了碳氧同位素分析。结果发现,除了张八岭大理岩δ~(13)C值出现明显正异常(1‰～8‰)外,其他地区大理岩的δ~(13)C值均处于0±2‰(PDB)范围之内。所有地区大理岩的δ~(18)O值都有不同程度的降低,最低的δ~(18)O值达到4.5‰(SMOW)。与前人对大别-苏鲁超高压大理岩碳氧同位素研究结果相对比,我们发现大理岩δ~(13)C值分布与岩石是否经过超高压没有联系,而主要反映了其原岩沉积的时代和环境,并且其特征可以与发生在新元古代的冰川事件相关联。区域性的δ~(18)O值降低则说明,大部分岩石都经过了流体交换,并且流体的主要成分是水,含碳很少或者不舍碳,因此流体的来源是大气降水,可能与新元古代冰川溶融有关。     

Carbon isotope records of the early Albian oceanic anoxic event (OAE) 1b from eastern Tethys (southern Tibet,China)

The early Albian Oceanic Anoxic Event (OAE), i.e., OAE1b, is well documented in western Tethys and in the primary North Atlantic Ocean, but has not yet been reported from eastern Tethys. In this paper, we present bulk carbon isotope data of hemipelagites to examine if it was recorded in eastern Tethys. Samples were taken from the upper Chuangdepu Member (nannofossil zone CC8) of the lower Gyabula (former Shadui) Formation at the Bangbu section, Qonggyai, southern Tibet of China. The δ¹³C values mainly range from −0.6‰ to 1.8‰ with a maximum of 1.87‰ and a minimum of −0.69‰. Three stages of carbon isotope evolution were distinguished with three boundaries. By the constraint of the stratigraphic sequence and nannofossil biostratigraphic zone CC8, the rapid δ¹³C change and correlation with western Tethys and Atlantic Ocean together suggest that these three boundaries of the carbon isotope evolution probably correspond to three subevents of the early Albian OAE1b, and the subevent levels of upper Kilian, Paquier, and Leenhardt are recorded in eastern Tethys (southern Tibet). The fact that the amount of δ¹³C shift is less by ∼1.5–2.0‰ in eastern Tethys than in western Tethys and Atlantic Ocean is interpreted as a result of possible cool sea surface (∼14–16 °C) of the southeastern Tethys (northern Indian passive margin of Greater India), which was probably located in a medium–high latitude during the Albian, leading to low primary productivity. The recognition of OAE-1b from Tethys Himalaya can improve our understanding of the Tethys and global paleoclimatic and paleoceanographic changes during the mid-Cretaceous.     

Sedimentary characteristics,formation mechanisms and geological significance of the Shiniulan Formation reefs (lower Silurian) in the Upper Yangtze Platform

The lower Silurian Shiniulan Formation of the Upper Yangtze Platform contains small-scale coral–stromatoporoid reefs, generally from less than 10?km long and from 10 to 30?m in thickness, especially in the middle–upper parts. The reef-building organisms were dominantly tabulate and rugose corals, with fewer stromatoporoids. Reef-inserted organisms include bryozoans, brachiopods, cephalopods, algae, crinoids and bivalves. The Shiniulan Formation is characterised by biohermal limestone, bioclastic limestone, sandstone and mudstone, and is divided into four members according to lithological characteristics. The reefs generally occur in the middle–upper layer, which corresponds to four growth stages: stabilisation, colonisation, diversification and domination. In the reefs, the argillaceous and sandy contents decrease, and the carbonates increase from the base to the top. The growth characteristics, evolution, scale and size of the reefs in the Shiniulan Formation were influenced by three factors: agitation of terrigenous debris, fluctuation of sea level and seawater temperature. The Upper Yangtze region was mainly a shallow marine environment with a warm or torrid tropical and subtropical climate and high salinity in the late Aeronian. However, the Shiniulan Formation has significant differences in growth, evolution and extension scale compared with corresponding reefs in Laurentia and the Siberia and Kazakhstan blocks. Analysis of the geological factors of the Shiniulan Formation and the Menier Formation of Anticosti Island, which has revealed that the two sections have similar reef types, lithology and biology, aims to explain the under-development of large-scale reefs in the Upper Yangtze Platform during the middle–upper Silurian.     

Palaeotopography of the northern portion of the Telychian (Silurian) turbidite basin in central Wales

New palaeocurrent data from the country northeast and southwest of Corris (central Wales) indicate that Telychian sandstones in the Devil's Bridge Formation hereabouts were transported from both the northeast and northwest, consistent with topographical control by down‐to‐southeast movement on the Bala Lineament. This conclusion is supported by considerations of thickness variation and by evidence for listric detachment faulting in the formation at Bwlch y Groes. Towards Plynlimon, flow is broadly southerly and suggests confinement by the northward extension of the Bronnant Fault. A facies and palaeocurrent map is presented for the utilis sub‐Biozone of the Telychian which links with work by the British Geological Survey between Aberyswyth and Rhayader where, by contrast, palaeoflow is to the NNW. Copyright © 2005 John Wiley & Sons, Ltd.     

The biostratigraphy and formational relationships of the upper aeronian and lower telychian (llandovery,silurian) formations of western mid-wales

The stratigraphical relationships of the upper Aeronian-lower Telychian formations in the Aberystwyth area are examined in the light of a new biostratigraphical subdivision of this interval based on graptolites, in which part of the Monograptus turriculatus Biozone is divided into six subzones and the Stimulograptus halli Biozone is resurrected. In the Aberystwyth area (B.G.S. 1:50 000 Sheet 163 (1984)) there is shown to be greater diachroneity of formational —boundaries than previously recognized. Notably, the Cwmsymlog Formation facies persisted in the northeast of the area far longer than anywhere else, due to the persistence of a bathymetric high into the lower Telychian. Also, the basal beds of the Aberystwyth Grits in the west of the area are shown to be of the same age as the uppermost beds of the Devil's Bridge Formation in the east. Thus for a short period the area was subject to turbiditic incursions from two sources. The degree of diachroneity of the base of the Aberystwyth Grits Formation as a whole is less than previously thought — the oldest beds are approximately one subzone older in the south than in the north. The core of the in the clinal pericline responsible for the crescentic outcrop pattern of the Aberystwyth Grits is demonstrated to lie in the vicinity of Llanrhystud, rather than at Aberarth as previously suggested. Four new graptolite species are described and one new genus is erected.     

桂东南志留纪热水沉积成矿的碳氧同位素证据

志留系地层是桂东南博白―岑溪地区铅锌矿床的主要赋矿层位,产出佛子冲和东桃等层状铅锌矿床,其直接赋矿围岩均为下志留统碎屑岩地层中的层状绿色岩和碳酸盐岩夹层。碳、氧同位素测试结果显示,赋矿层位中碳酸盐岩夹层的δ18 O值显著低于正常海相灰岩,在δ18 O-δ13 C图解上碳酸盐岩夹层和矿石中方解石样品投点均集中分布在基性-超基性岩浆岩和花岗岩区及附近。该碳酸盐岩夹层的形成与海底热水沉积作用有关,类似于现代海底烟囱中的低温喷口产物。桂东南志留纪热水沉积成矿作用可以概括为电解成矿机制。     

A New Species of Jiangxialepis (Galeaspida) from the Lower Telychian (Silurian) of Jiangxi and its Biostratigraphic Significance

A new species of Shuyuidae (Eugaleaspiformes, Galeaspida), Jiangxialepis jiujiangensis sp. nov., is described from the lower Telychian (Llandovery, Silurian) Qingshui Formation in Jiujiang, Jiangxi Province, China. The new species differs from the type species J. retrospina from Wuhan, Hubei Province in its sharp and posteriorly positioned median dorsal spine and narrow spine-shaped inner cornual processes. The Silurian strata in Xiushui–Wuning area has provided a standard framework for the correlation of Silurian shallow marine red beds in South China. Thus, the finding of J. jiujiangensis from the Silurian Lower Red Beds (LRBs) in Jiangxi Province bears very important biostratigraphic significance. It can directly compare to Jiangxialepis retrospina from the Fentou Formation in Wuhan, Hubei Province in the genus level. This indicates that the age of the fish-bearing strata in Wuhan is most likely to be the early Telychian rather than middle Telychian as previously assumed.     

Origin of the Silurian Crude Oils and Reservoir Formation Characteristics in the Tazhong Uplift

<正>The Silurian stratum in the Tazhong uplift is an important horizon for exploration because it preserves some features of the hydrocarbons produced from multi-stage tectonic evolution.For this reason,the study of the origin of the Silurian oils and their formation characteristics constitutes a major part in revealing the mechanisms for the composite hydrocarbon accumulation zone in the Tazhong area.Geochemical investigations indicate that the physical properties of the Silurian oils in Tazhong vary with belts and blocks,i.e.,heavy oils are distributed in the TZ47-15 well-block in the North Slope while normal and light oils in the No.Ⅰfault belt and the TZ16 well-block,which means that the oil properties are controlled by structural patterns.Most biomarkers in the Silurian oils are similar to that of the Mid-Upper Ordovician source rocks,suggesting a good genetic relationship. However,the compound specific isotope of n-alkanes in the oils and the chemical components of the hydrocarbons in fluid inclusions indicate that these oils are mixed oils derived from both the Mid-Upper Ordovician and the Cambrian-Lower Ordovician source rocks.Most Silurian oils have a record of secondary alterations like earlier biodegradation,including the occurrence of UCM humps in the total ion current(TIC) chromatogram of saturated and aromatic hydrocarbons and 25-norhopane in saturated hydrocarbons of the crude oils,and regular changes in the abundances of light and heavy components from the structural low to the structural high.The fact that the Silurian oils are enriched in chain alkanes,e.g.,n-alkanes and 25-norhopane,suggests that they were mixed oils of the earlier degraded oils with the later normal oils.It is suggested that the Silurian oils experienced at least three episodes of petroleum charging according to the composition and distribution as well as the maturity of reservoir crude oils and the oils in fluid inclusions.The migration and accumulation models of these oils in the TZ47-15 well-blocks,the No.Ⅰfault belt and the TZ16 well-block are different from but related to each other.The investigation of the origin of the mixed oils and the hydrocarbon migration and accumulation mechanisms in different charging periods is of great significance to petroleum exploration in this area.     

中国东部橄榄岩包体和榴辉岩中CO_2流体包裹体的碳同位素组成

应用阶段加热技术 ,对中国东部新生代玄武岩中的橄榄岩包体和大别造山带超高压榴辉岩进行了包裹体 CO2 的碳同位素组成测定。结果表明 ,橄榄岩的δ1 3C值变化较大 ,从 - 2 2 .8‰到 0 .7‰ ,明显不同于前人报道的低δ1 3C值 (- 2 8‰～- 2 0‰ )特征 ,指示中国东部地幔流体中 CO2 的碳同位素组成是不均一的 ,反映了地壳有机碳与原生地幔碳的混合特征。大别造山带榴辉岩的 δ1 3C变化从 - 18.5‰到 4 .6‰ ,同样明显不同于前人报道的低 δ1 3C值 (- 30‰～ - 2 0‰ )特征。榴辉岩的低δ1 3C值指示了板块俯冲前其玄武岩原岩受到地表含有机碳流体蚀变后的碳同位素特点 ,而较高的δ1 3C值反映了板块折返过程中榴辉岩受淋滤大理岩的富 CO2 流体叠加的退变质效应。橄榄岩包体和超高压榴辉岩的轻碳同位素共同特点反映了板块俯冲引起的壳—幔物质相互作用和碳同位素地球化学再循环 ,指示中国东部岩石圈地幔含有丰富的地壳有机碳组分