Two intriguing pluricolumnals (Crinoidea) from the Lower Palaeozoic of Powys and Shropshire

Complete fossils must be preferred to fragments for most palaeontological studies, but disarticulated specimens are nonetheless potential sources of noteworthy data. Two crinoid pluricolumnals are recorded from the lower Palaeozoic; informed discussion shows each is a basis for palaeobiological interpretation. Both are gracile and are probably belong to disparids. Floricrinus (col.) sp. is from the Silurian of Wenlock Edge, Shropshire, either from the Much Wenlock Limestone Formation (Wenlock) or, more likely, the Lower Elton Formation (Ludlow). This is the first crinoid from the Silurian of the British Isles with a pentapetaloid arrangement of the areola, a geometry common in the Middle-Upper Ordovician and higher in the geologic column. Pluricolumnal gen. et sp. indet. is from the Lower Llanvirn of Powys. One end of the otherwise straight specimen is tightly coiled. This is likely the proxistele, the most flexible region of the column, and the coiling occurred after the crown was lost by autotomy in response to an environmental disturbance.     

Late Wenlock carbon isotope excursions and associated conodont fauna in the Podlasie Depression,eastern Poland: a not‐so‐big crisis?

The middle Silurian ‘big crisis’ refers to a graptolite extinction event and faunal turnover at the onset of a double‐peaked positive carbon isotope excursion. The crisis has been proposed to affect conodonts, giving rise to a sophisticated palaeoecological model of their stepwise extinction, known as the Mulde Event. However, the impact of the event on conodont faunas outside Gotland and the Silurian Baltic Basin remains unknown. Here, it is examined in the Widowo IG‐1 core (E Poland). The middle Silurian succession in this core represents foreshoal, shoal, and lagoonal settings on a tropical carbonate ramp on the shelf of the Eastern European Craton. Three positive δ¹³C_carb excursions have been identified; the two upper excursions correlate with the Mulde isotope anomaly and with two global eustatic regressions. Conodont species proposed to be affected by the extinction event either were not observed or ranged through the extinction interval. Changes in their frequencies are best explained by the sequence stratigraphic architecture of the late Wenlock strata in the Widowo IG‐1 core. The little impact of the ‘big crisis’ may reflect facies homogeneity across the studied interval, supporting the hypothesis that the late Wenlock conodont turnover in epicontinental settings was primarily driven by eustatically controlled facies shifts. Copyright © 2015 John Wiley & Sons, Ltd.     

The farnacht formation along the south side of the clew bay fault zone,Western Ireland: Its chemistry and age of metamorphism

The tectonically isolated Farnacht Formation consists of calc-alkaline dacitic-andesitic lavas of volcanic arc affinity. It is situated immediately to the south of the Clew Bay Fault Zone (western continuation of the Highland Boundary Fault Zone of Scotland) in the northeast corner of the Lower Palaeozoic South Mayo Trough in northwest Ireland. It has been metamorphosed to biotite grade greenschist facies following the development of a pervasive, c-s composite muscovite, quartz, and feldspar schistosity. The Farnacht Formation may comprise a terrane that is directly unrelated to nearby Ordovician and Silurian rocks; its present position was fixed largely by Wenlock times. The age of the Farnacht Formation and the deformational event(s) that produced the schistosity are not known. ⁴⁰Ar/³⁹ Ar step heating from four specimens have dated the crystallization of biotite at from 422 ± 2 to 405 ± 14 Ma with a mean age of 413 Ma. These ages date either the post-D2, pre-D3 metamorphic peak, or a hornfelsing of the same structural age related to an unseen thermal source, and provide a minimum age for the end Silurian - early Devonian Caledonian tectonothermal activity in the northeast part of the South Mayo Trough.     

Stratigraphy and geological history of the Malvern,Abberley and Ledbury Hills

A revised stratigraphy of the Malvern, Abberley and Ledbury Hills is given. The Silurian succession is considered in detail and shows a series of five major sedimentary rhythms or cycles between an initial Llandovery transgression and regression at the close of the Silurian period. The succession exhibits an alternation of shale with either limestones and/or terrigenous clastics, and the rhythmic nature of the sequence suggests a periodic change in base level. A number of different lithological facies can be distinguished in the limestone formations, particularly in the Wenlock limestone. A detailed faunal list is given for most of the Silurian sequence. From the evidence of the stratigraphic succession, an attempt has been made to decipher the complex geological history of the area.     

云南的早期脊椎动物化石研究

我国云南是世界上早期脊椎动物化石的重要产地,古生代中期的鱼类不仅门类齐全,而且大多出现时代早、地区性属种多,其中不少化石材料如今已成为探讨如脊椎动物起源、硬骨鱼类起源、四足动物起源等一系列生命史中重大课题的关键资料。主要对古生代中期云南早期脊椎动物化石的研究做一个系统、全面的回顾与总结,并在此基础上对未来有关研究的重点与方向进行了展望。在探索生物演化格局的同时,不仅要加强对演化机制、环境以及古地理背景的研究,而且更要强调多学科的交叉与融合,充分利用我国古生代中期丰富的鱼类化石资料,在早期脊椎动物系统演化、古地理与古气候等方面做出原创性的成果。     

中国志留纪年代地层学述评

198 4年国际地层委员会志留系分会提出的分统建阶新方案使各国地质学家得以在相同的时间界面上探讨具有全球意义的地质和生物事件。数十年来我国志留纪地层研究进展不小 ,但与国际水平相比 ,研究现状还不能令人满意 ;特别是系内绝大部分的统、阶的界线尚未在全国范围内划定 ,成为当前我国志留系研究最迫切需要解决的问题。本文赞成我国志留纪年代地层框架宜采用“四分统”的方案 ,论述国内志留系顶底界、温洛克统顶底界、罗德洛统顶界的确定并讨论扬子区大部分地区是否发育比兰多维列统更高的志留纪地层的问题。     

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.     

东天山红柳河地区蛇绿岩U-Pb同位素年龄

采用锆石U-Pb方法对东天山红柳河蛇绿岩中辉长岩进行了测试,得到206Pb/238U表面年龄加权平均值为425.5±2·3Ma,代表辉长岩的侵入年龄,说明红柳河蛇绿岩形成于早志留世,相当于文罗克世(Wenlock)哥利顿期(Gleedonian)。这一年龄结果表明早志留世中天山结晶基底已开始从塔里木板块北缘分离出去形成离散地体。     

New British records of Carboniferous lycopod cones

Five species of Carboniferous lycopod cones have been identified from new British localities. Their geographical distributions have been widened and most have had their stratigraphical ranges extended. Comparisons are also made with the ranges of those dispersed spores which appear to be identical to the spores found in the cones.     

Biostratigraphy of Paleozoic Tabulata and Heliolitida of Central Asia

In Soviet Central Asia (Tien Shan and Pamirs) corals are unknown in the Lower Ordovician, rare and unstudied in the Middle Ordovician. The tabulate coral record from the Upper Ordovician, Silurian and Devonian is excellent and numerous common and Key genera and species are enumerated for each stage or substage. Tabulata reached their peak development in the Wenlock, and had markedly decreased in numbers and variety by late Middle Devonian time. Tabulata are rare in Upper Devonian and later rocks but occur through the Carboniferous and into the Upper Permian. -- W. A. Oliver, Jr.     

大地构造对上扬子区志留纪生物礁分布及发育的控制

根据上扬子板块的基底特征，及板块边缘特征等不同大地构造单元演化特征入手，分别对上扬子板块基底地貌、板块边缘构造及板内不同构造单元控制志留纪古沉积环境及生物礁发育演化进行了论述。在上扬子板块的北缘（南秦岭构造带），为被动大陆边缘，沉积环境适于生物礁发育，类型较多。而板块西缘（金沙江构造带）为主动大陆边缘，在岛弧区发育部分点礁以及生物层；板块内部受古隆起影响的地区（川西北、川东南、黔北），形成缓坡沉积环境，在浅缓坡区生物礁十分发育，类型众多；但是板内深断裂（龙门山，二郎山-攀西裂谷带）边缘生物礁不甚发育，仅见生物层-小型点礁组合。志留纪时，上扬子板块受全球海平面变化的影响明显，至Ｗｅｎｌｏｃｋ期后，大部分地区因海平面下降而无沉积。但是在板块边缘凹陷区，因区域构造的影响，全球海平面波动对其影响不大，Ｗｅｎｌｏｃｋ期后继续接受沉积且发育生物礁。     

Age of the peel sandstone group,isle of man

An Early Devonian age for the continental, red‐bed succession of the Peel Sandstone Group can be defined on the basis of: (1) a derived marine fauna of late Wenlock (Homerian) age, (2) a Scoyenia ichnofacies assemblage (including Beaconites and Diplichnites) characteristic of latest Silurian to Early Devonian (Lower Old Red Sandstone magnafacies) sediments in the British Isles, (3) a microflora of late Lochkovian to Pragian age, (4) a detrital palaeomagnetic remanence that pre‐dates local, Acadian palaeomagnetic directions and coincides with a prominent, southerly, Late Silurian to Early Devonian excursion in the local apparent polar wander path, and (5) a mid‐Devonian palaeomagnetic remanence that overprints (?)Acadian, thrust‐related folding. Data presented in this study confirm previous suggestions (Allen and Crowley 1983) that the Peel Sandstone Group represents a rare example of Early Devonian sedimentation preserved on the northern margin of the former Eastern Avalonia microcontinent. Potential correlations and linkages with other Lower Old Red Sandstone successions exposed in the Anglo‐Welsh Basin are developed and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

紫阳文洛克统底界生物地层学新研究

通过对紫阳地区10个文洛克统底界剖面的重新观察,笔者等认为晚兰多弗里期的标准化石Oktavites spiralis(Geinitz)从未进入文洛克统,这与国际上是一致的。过去在紫阳地区所有被鉴定为C．centrifugus Boucek的标本,经详细比较均应改为C．annularis Fu,其层位都产于C．lapworthi带。近年对芭蕉口剖面进行野外调查时,笔者等采到了真正的C．centrifugus Boueek和C．murchisoni Carruthers标本,因此更加完善了C．lapworthi-C．sakmaricus-C．insectus-C．centrifugus-C．murchisoni这一弓笔石演替序列。     

Facies and faunal changes in the Ludlovian rocks of Aymestrey,Herefordshire

The Aymestrey area displays changes in facies, faunas and thicknesses which can be related to its position on the shelf edge during later Silurian times. The Wenlock Limestone becomes an alternation of limestones and mudstones. The Lower and Middle Elton Beds, however, are substantially similar to their development at Ludlow. The Upper Elton Beds and the Bringewood Beds thin westwards within the area, probably due to non-deposition or erosion on a ridge at the hinge between shelf and basin. The most striking change is the rapid westward passage of the Aymestry Limestone facies of the Upper Bringewood Beds into siltstones, which are considered to be shallow-water deposits and not basinal. The Leintwardine Beds exhibit a westward thickening, and slumping is developed in the Lower Leintwardine Beds; the faunas relate more to the basin facies than to the shelf. The Whitcliffe Beds thicken markedly westwards but retain their shallow-water characteristics.     

Excavating eurypterids,giant arthropods of the Palaeozoic

The eurypterids of the Silurian Bertie Group of North America are some of the most striking fossils known, with their dark organic cuticle outlined against a background of light coloured dolomite. Eurypterus is the most abundant genus but the pterygotids with their long grasping claws have fired our imagination as giant extinct predators. Large complete specimens are rarely found—the specimens are dominated by moulted exoskeletons that often disarticulate—but a giant that emerged from the rock more than 50 years ago is being prepared to go on display.     

Middle Paleozoic paleomagnetism of east Kazakhstan: post-Middle Devonian rotations in a large-scale orocline in the central Ural–Mongol belt

In order to test different hypotheses concerning the Paleozoic evolution of the Ural–Mongol belt (UMB) and the amalgamation of Eurasia, we studied Middle Devonian basalts from two localities (11 sites) and Lower Silurian volcanics, redbeds, and intra-formational conglomerates from three localities (20 sites) in the Chingiz Range of East Kazakhstan. The Devonian rocks prove to be heavily overprinted in the late Paleozoic, and a high-temperature, presumably primary, southerly, and down component is isolated at only four sites from a homoclinal section. Most Silurian redbeds are found to be remagnetized in the late Paleozoic; in contrast, a bipolar near-horizontal remanence, isolated from Silurian volcanics, is most probably primary as indicated by positive tilt and conglomerate tests. Analysis of paleomagnetic data from the Chingiz Range shows that southward-pointing directions in Ordovician, Silurian, and Devonian rocks are of normal polarity and hence indicate large-scale rotations after the Middle Devonian. The Chingiz paleomagnetic directions can be compared with Paleozoic data from the North Tien Shan and with the horseshoe-shaped distribution of subduction-related volcanic complexes in Kazakhstan. Both paleomagnetic and geological data support the idea that today's strongly curved volcanic belts of Kazakhstan are an orocline, deformed mostly before mid-Permian time. Despite the determination of nearly a dozen new Paleozoic paleopoles in this study and other recent publications by our team, significant temporal and spatial gaps remain in our knowledge of the paleomagnetic directions during the middle and late Paleozoic. However, the paleomagnetic results from the Chingiz Range and the North Tien Shan indicate that these areas show generally coherent motions with Siberia and Baltica, respectively.     

The Silurian rocks of the Tortworth Inlier,Gloucestershire

The Silurian succession in the Tortworth Inlier includes strata belonging to the three main divisions of the System. The Upper Llandovery, which rests unconformably on Tremadoc beds, consists of about 700 ft. (213 m.) of fine-grained sandstones, mudstones and shales with two igneous bands. The Wenlock Series is represented by some 800 ft. (244 m.) of mudstones, siltstones and calcareous sandstones with impersistent limestone bands at various horizons. The Ludlow succession is incomplete, but at least 300 ft. (91 m.) of mudstones, siltstones and fine-grained sandstones are present, and they pass up conformably into the Downtonian.     

Geology of the Pedwardine district,Herefordshire and Powys

The stratigraphy of the Pedwardine inlier of Precambrian (Longmyndian), Tremadoc, and what are now shown to be upper Llandovery rocks is described. The inlier is surrounded by Silurian rocks, including upper Llandovery (two very small areas), Wenlock, Ludlow and Přídolí (Red Downton Formation). The Ludlow rocks provide a distal record of the mass movement recorded more fully in the Wigmore Rolls area to the east. The Pedwardine area lies along the Church Stretton Fault Zone. Though ill-exposed, it shows evidence of the history of faulting, including thrusting. © 1997 John Wiley & Sons, Ltd.     

The oldest flora of the South China Block, and the stratigraphic bearings of the plant remains from the Ngoc Vung Series, northern Vietnam

Several outcrops of the Late Silurian and Devonian of the Ngoc Vung Series, northern Vietnam, yielded plant remains. The Late Silurian localities delivered the earliest known flora of the South China block. Although the fossils are fragmentary, they complement our knowledge about the global composition of the flora. The major components of the flora are plants with dichotomous habit and terminal bivalvate sporangia, which are close relatives to zosterophylls, and zosterophylls. Plants with possible euphyllophyte affinities and bryophytes are occasionally present. This floral composition is similar to that of the rich, younger South China block assemblages from the Posongchong and Xujiachong Formations of China, considered Pragian in age. The South China block flora is therefore likely to have been dominated by zosterophylls and pre-zosterophylls at least from the Late Silurian to the Pragian (i.e. a 20 million years long period). It also strengthens the hypothesis that more derived plants were present on eastern Gondwana earlier that elsewhere, in the first steps of tracheophyte evolution. The Devonian localities of the Ngoc Vung Series delivered a thick fibrous stem fragment and a basal euphyllophyte. These latter plant remains provide some stratigraphic data. The large stem fragment is consistent with an Eifelian age for the Duong Dong Formation (part of the Ngoc Vung Series), as suggested by the brachiopod fauna. The accompanying basal euphyllophyte displays a combination of characters (axes 3-4 mm wide and lateral branchings) that is also consistent with an Eifelian age, but possibly more characteristic of the Emsian flora. It is therefore suggested that the stratigraphic range of the Duong Dong Formation might be extended down to the Emsian.