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1.
Charles Hepworth Holland 《Geological Journal》2000,35(1):25-31
The very rare occurrences of cephalopods in the Přídolí Series of the English and Welsh Silurian are recorded and their taxonomy revised. Apart from one derived form, they constitute a typical relict Ludlow fauna, including Cyrtocycloceras ibex, Leurocycloceras whitcliffense, and Polygrammoceras bullatum. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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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. 相似文献
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The disused railway cutting at Ammons Hill, Hereford and Worcester, exposes a sequence of beds belonging to the Devonian St Maughans Formation of Lochkovian (Gedinnian) age. The beds are of Old Red Sandstone facies, but contain brackish water faunas. These faunas occur at a level generally considered to be above the level of marine influence that affected the older Raglan Mudstone Formation of mainly Přídolí Series age. The section, described by King in 1934, is now overgrown, but was excavated in 1986 by the British Geological Survey during its survey of the Worcester 1:50000 sheet. The evidence of the section calls for slight amendment of Allen's (1985) model of an interrupted transition from marine deposition in Ludlow time to freshwater deposition in Gedinnian time that was complete by the time of the formation of a regionally extensive calcrete palaeosol, the Psammosteus Limestone. Subsequent transgressive events took place before the establishment of apparently wholly fluvial and floodplain environments. 相似文献
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Graptolites are recorded for the first time from the Lower Elton Formation of Shadwell Quarry, Wenlock Edge, Shropshire. The presence of Colonograptus colonus (Barrande) indicates that the formation here may be assigned to the lowermost Ludlow, either the nilssoni or lower scanicus graptolite biozone. Copyright © 1998 John Wiley & Sons, Ltd. 相似文献
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海南岛南好组剖析 总被引：9，自引：2，他引：7
南好组是海南岛目前使用最广泛的地层单位之一 ,代表该岛整个下石炭统 ,但其选层型为下志留统而非岩关阶 ,保亭南好地区并不存在下石炭统 ;其副层型原本是青天峡组的层型。据此 ,南好组应予废弃。根据新近发现的吉维特期胞石 Eisenackitina castor、Grahanichitina pilosa、L agenochitina amottensis;法门期牙形刺 Palmatolepisgracilis gracilis、P.gracilis sigmoidalis、Polygnathus germanus;以石燕贝类为主的岩关期腕足动物群 Spirifercf.subgrandis、Fusella cf.fornacensis、Palaeochoristites sp.、Chonetipustula sp.、Marginatia sp.、Rhipidomellaspp.和牙形刺 Siphonodella isosticha- S.cooperi组合 ;以及滑石板期—达拉期牙形刺 Mesogondolella clarki组合 ,岛西北部地区的南好组废弃后可划分出 :中泥盆统吉维特阶 (?) (组名待建 )、上泥盆统法门阶昌江组、下石炭统岩关阶鸡实组 (新名 )、大塘阶青天峡组下段及三棱山组等不同地层单元 相似文献
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《Proceedings of the Geologists' Association. Geologists' Association》2017,128(3):460-479
Fish remains from over 100 localities in the Upper Silurian to Lower Devonian (traditional Lower Old Red Sandstone: LORS: Přidolí–Pragian) of Wales and the Welsh Borderland Anglo-Welsh Basin, southwest Britain have been investigated. Work on microfossils of fish (‘microvertebrates’, generally <5–8 mm) is reviewed, covering agnathan thelodonts, heterostracans, cephalaspids, anaspids, and gnathostomes including acanthodians, placoderms, and chondrichthyans, including the first from Pembrokeshire. Scales of the following taxa are newly identified: acanthodians Euthacanthus sp., Nostolepis musca, Parexus recurvus and Cheiracanthoides sp. cf. C. rarus; early “sharks” including Altholepis sp.; and a (?)radotinid placoderm. Species ranges in space, time and environment reveal interesting patterns, the most significant being a wide geographic distribution, which does not support a wholly freshwater provenance for the Anglo-Welsh Basin; endemic taxa are few. Using the International mid-Palaeozoic Microvertebrate zonal scheme, the presence of a Thelodus parvidens–Paralogania ludlowiensis-osteostracan Assemblage within the Ludlow Bonebed at the base of the former Downton Group (now in part in the new lithostratigraphically defined Daugleddau Group) supports a basal Přidolí age for the member. A mid-Přidolí dearth with few taxa, mainly acanthodians and cephalaspids is followed by an upper Přidolí Trimerolepis–Paralogania kummerowi–Loganellia cuneata-poracanthodid-Toombsaspis pococki Assemblage. The Silurian–Devonian boundary is equated with the appearance of Turinia pagei and associated taxa including Phialaspis symondsi at a level about 30 m below the local Chapel Point Limestone. This biozone can be correlated across the Old Red Sandstone continent. All vertebrate species including newly recognised Lochkovian chondrichthyans indicate marine environments were present in the LORS. 相似文献
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The Downton Bone Bed is a Konzentrat-Lagerstätte deposit located in the Welsh Borderlands, United Kingdom. The Downton Bone Bed is late Silurian, considered to be P?ídolí in age, and occurs within the Platyschisma Shale Member of the Downton Castle Sandstone Formation. The bone bed is exposed at Weir Quarry (Herefordshire), which this study proposes should become established as the type locality for this stratigraphic horizon, due to the destruction of other localities and lack of access to other sites. As Weir Quarry is one of the last remaining exposures of this unit, the objective of this study is to qualitatively describe the sedimentology, ichnology, and invertebrate palaeontology of the bone bed, to enhance the regional understanding of the palaeogeography, depositional environments and depositional processes of the Welsh Borderlands during the late Silurian. Parasequence thickness and frequency, and sedimentary structures such as hummocky cross stratification, observed within the Downton Castle Sandstone Formation, have traditionally been explained to have formed by sea-level oscillations. These are interpreted to have formed entirely by nearshore to shoreface, shallow marine autogenic sedimentary processes, such as storm events (tempestites) and tidal scour. It is interpreted that formation of the Downton Bone Bed occurred as a by-product of these autogenic sedimentary processes, through winnowing and erosion during storm-driven scour and reworking. The low diversity ichno- and invertebrate fauna observed within the Downton Bone Bed is consistent with a nearshore depositional environment and is indicative of a stressed ecosystem due to fluctuating salinity and oxygen levels. 相似文献
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湖南张家界地区志留纪晚期地层新见兼论小溪组的时代 总被引：3，自引：0，他引：3
就华南板块而言,志留纪晚期(Ludlow世—Pridoli世)近岸浅海、非笔石相地层多分布在边缘海湾处,是否在扬子地台内部发育,以往尚无确凿记载。依据来自湘西北张家界—桑植地区新近发现的微体化石(主要指植物碎片),确认志留纪晚期地层在扬子地台内部确实存在。对原小溪组(又称小溪峪组)进行厘定,将它"一分为二":上部仍称小溪组,命名地在桑植瑞塔铺,发育最好的是张家界温塘剖面,岩性为黄绿色碎屑岩,富含大型虫管遗迹化石,时代为Ludlow晚期—Pridoli早期;下部称迴星哨组,归于Llandovery统Telychian阶上部。小溪组与迴星哨组之间为假整合接触,缺失Telychian末期、Wenlock世和Ludlow世早期地层。由此得出结论:在"扬子上升"后,扬子地台内部曾被志留纪晚期的海水侵漫;对其他地区迴星哨组与上覆地层的研究需要细化。 相似文献
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The most southerly exposed Lower Palaeozoic strata in Ireland occur on the southwest coast of County Waterford along a 2.5 km long coastal section at Muggort's Bay where they are surrounded by Devonian rocks. Five formations can be distinguished which, in ascending order, are: the Ballycurreen, Carrickbrean, Rathnameenagh, Moanbrack and Killinoorin formations. The total thickness of the succession is over 1800 m. No macrofossils are present, but the lithologies are largely fine‐grained turbidites and subordinate volcanic rocks which closely resemble the Ribband Group seen elsewhere in southeast Ireland and have previously therefore been classified with it. Palynological analysis was undertaken on 25 samples collected from Muggort's Bay, of which eight were productive. Diagnostic microfossils, comprising acritarchs, chitinozoans and scolecodonts, indicate an Early to Middle Ordovician age for both the Rathnameenagh and the Moanbrack formations. These ages confirm that the strata are part of the Ribband Group which elsewhere has been biostratigraphically dated as ranging from Mid‐Cambrian to Mid‐Ordovician. Reworked mid‐Middle Cambrian acritarchs occur in the Moanbrack Formation and reworked late Middle to early Late Cambrian acritarchs in the Rathnameenagh Formation. Despite generally poor preservation of the organic matter, some 20 acritarch species have been distinguished. Among these, three species belong to the herein revised genus Retisphaeridium for which an emended diagnosis is proposed together with two new combinations, Retisphaeridium capsulatum (Jankauskas, 1976 ) Vanguestaine nov. comb. and Retisphaeridium pusillum (Moczydlowska, 1998 ) Vanguestaine nov. comb. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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调查分析了湖北宜昌龚家冲志留系纱帽组剖面156件样品,在其中95件泥岩、粉砂岩样品中发现大量保存精美的早志留世几丁虫化石。自下而上识别出Conochitina malleus,Plectochitina pseudoaggltinans,Eisenackitinadolioliformis,Eisenackitina causiata等生物带。每一个几丁虫生物带均代表一次几丁虫多样性发展,由新生分子和已知分子所构成的组合特征能很好地与拉脱维亚、爱沙尼亚和沙特阿拉伯等国外同期地层的几丁虫组合进行对比。宜昌地区志留系几丁虫生物带与笔石、牙形石带的关系显示宜昌地区纱帽组的地质延限大致与笔石Stimulograptus sedgwickii带至Oktavites spiralis带相当,特列奇阶底界位于纱帽组第二段底部,与几丁虫Plectochitina pseudoagglutinans生物带的底界位置接近。同期地层,在重庆涪陵焦石坝等地为产大量笔石的富有机质页岩,是页岩气的重要储层,因此,这一研究成果对于深入认识我国南方志留系页岩气储层的分布发育特点具有重要意义。 相似文献
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贵州台江五河剖面灯影组顶部微体动物化石 总被引：2，自引：0，他引：2
贵州台江灯影组白云岩中发现了30～70μm的锥形微体动物化石,它们具有典型的锥管状、似几丁质壳壁和平行纤维结构等生物结构,可能分属软体动物Carinachitids、Arthrochites、Punctatus、Spondylotubus和似几丁虫类化石等5种类型。其中建立了一新属、种Spondylotubus taijiangensis Yang(gen.etsp.nov.)。在灯影组白云岩中这一类群的发现对研究前寒武纪寒武纪界线附近生物的多样性和生物地层,以及寒武纪生物大爆发都具有一定的科学意义。 相似文献
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C. J. Soares S. Guedes R. Jonckheere J. C. Hadler S. M. Passarella A. N. C. Dias 《Geological Journal》2016,51(5):805-810
This work presents fission‐track ages and thermal history modelling of apatite samples from two Brazilian alkaline formations: Alto Paranaíba and Ponta Grossa Arches. The apatite fission‐track ages obtained for Alto Paranaíba Arch agree with those determined by other radiometric dating methods presenting higher closure temperatures. The ages given by the fission‐track thermochronometer suggest that no strong tectonic event has occurred after Alto Paranaíba Formation during Upper Cretaceous. This event is also supported by thermal history modelling of this arch, which is characterized by fast cooling followed by residence at lower temperatures. On the other hand, apatite fission‐track ages from Ponta Grossa Arch are systematically lower than other radiometric ages, suggesting that at least one tectonic event occurred after Ponta Grossa Formation, around 130 Ma. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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20 0 3年的 1∶2 5万地质填图和实测剖面工作中 ,在新疆喀喇昆仑山地区岔路口一带原划二叠纪加温达坂组哑地层中首次采到了大量孢粉化石 ,鉴定为晚二叠世早期。同时 ,对该套地层进行了重新厘定 ,划定为上二叠统早期神仙湾组 ,并对其沉积环境进行了探讨。 相似文献
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Palaeokarst, tidal erosion surfaces and stromatolites in the Silurian Eke Formation of Gotland, Sweden 总被引：1，自引：0，他引：1
LESLEY CHERNS 《Sedimentology》1982,29(6):819-833
Irregular, scalloped erosion surfaces in the shelf carbonate sequences of the lower Eke Formation (Ludlow Series, upper Silurian) in the east of Gotland, Sweden, comprise series of shallow hollows separated by sharp-crested ridges, and cavities with sculptured, undercut walls, cut into lithified sediment. These represent analogues of the solution basins formed in modern coastal and subaerial karst terrains. Discrete erosional cavities merge on enlargement by breaching of the intervening walls to leave remnant, tapering ridges. Sets of the ridges and basins seen in surface view show an average width of basins of 1–2 m, with relief of 40–50 cm and pronounced N-S axes for the ridges; this alignment may reflect the local drainage direction. The lowermost erosion surface passes laterally into a planar, mineralized horizon at the top of the underlying Hemse Group that was resistant to and forms the base level of erosion. Because of restricted exposure of higher Eke Formation sediments the upper limit of erosion remains unknown. There is no evidence of caliche or subaerial diagenetic textures, but solution vugs are common in the eroded limestones. Marine hard-bottom biota attached to some surfaces, and transition from scalloped to planar surfaces indicate erosion in tidal zones, but subaerial karstic erosion is also inferred. The resubmerged karst-eroded topography is overlain by shallow marine carbonates, including small organic buildups. Finely-layered stromatolitic mats developed over the initial infill, in subtidal environments, and grew to form domed mounds within the erosional cavities. They abut sharply against bounding side walls and overhangs. Some emergence is evident from desiccation features in the upper parts of mounds. Biostratigraphical evidence dating the events from initial uplift and karstic erosion to covering of the drowned relief topography places the whole sequence within upper Ludlow times. 相似文献
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María Jos Salas 《Geological Journal》2011,46(6):637-650
The ostracod fauna from the Floian (Lower Ordovician) strata of the Cordillera Oriental, Argentina (Acoite Formation) are documented. One new genus Acoitella and four species are recognized, two of which are new (Nanopsis victoria sp. nov. and Conchoprimitia frequens sp. nov.). The diversity of the Early Ordovician ostracod faunas of the Central Andean Basin is evaluated. Compared with other regions, the ostracod diversity, at generic and specific level, of the Cordillera Oriental was comparatively high during the Tremadocian (nine species recorded) and comparatively low during the Floian (four species recorded). The taxonomic composition of the fauna is similar during the entire Early Ordovician of the Cordillera Oriental, where it displays a high percentage of soanellids. The Floian assemblages are characterized by the dominance of the eridostracan C. frequens sp. nov. with a high percentage of nondimorphic palaeocopids: Nanopsis and two genera of the Soanellidae family (Saltite and Acoitella gen nov.). An ostracod shell bed is described and interpreted to be a parautochthonous assemblage, as a result of transport within the same habitat. The composition of the fauna, with the presence of Saltite and Nanopsis, shows significant affinities with East Gondwana. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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滇东曲靖志留－泥盆系界线研究的新进展 总被引：5，自引：3，他引：5
首次在曲靖玉龙寺组上易剥页岩中发现Ｐｒｉｄｏｌｉａｎ期的化石证据。对多门类大化石及微体化石的分析研究表明，玉龙寺组属晚志留世晚期，下西山村组属早泥盆世早期，志留一泥盆系界线应从它们之间通过。 相似文献
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Krzysztof Birkenmajer Przemys&#x;aw Gedl Ryszard Myczy&#x;ski Jaros&#x;aw Tyszka 《Cretaceous Research》2008,29(3):535-549
This is a critical assessment of the paper by Oszczypko et al. (2004: Cretaceous Research 25, 89–113), in which they tried to prove a mid-Cretaceous age for the Szlachtowa (“black flysch”) and Opaleniec Formations, in the Pieniny Klippen Belt, West Carpathians, both of which had previously been shown to be of Jurassic age. We argue that the mid-Cretaceous age assignment is a misinterpretation, primarily resulting from their field samples having been collected from some Cretaceous lithostratigraphic units, tectonically associated with the Jurassic formations, and/or from tectonic contact-breccias involving Jurassic and Cretaceous strata. In addition, we suggest that they have overlooked a number of significant palaeontological papers, published since 1962, which record the presence of in situ ammonites, aptychi, belemnites, thin-shelled bivalves (Bositra), gryphaeids, foraminifera, and ostracod assemblages, all indicating a Jurassic (mainly Aalenian), and not a Cretaceous, age for the Szlachtowa Formation, and also the in situ Jurassic (Bajocian) ammonites and thin-shelled bivalves (Bositra), Bositra-microfacies, and age-diagnostic foraminiferal assemblages of the Opaleniec Formation.Our presentation here of recently published dinocyst data from well-preserved assemblages further supports the Jurassic ages for the Szlachtowa (“black flysch”) and Opaleniec Formations. 相似文献