Lower and Middle Ordovician conodonts of Laurentian affinity from blocks of limestone in the Rosroe Formation,South Mayo Trough,western Ireland and their palaeogeographic implication

The Middle Ordovician Rosroe Formation consists of some 1350 m of coarse, mainly siliciclastic to volcaniclastic sedimentary rocks, deposited in a submarine fan environment, and is restricted to the southern limb of the South Mayo Trough, western Ireland. Discrete allochthonous blocks, reaching 5 m in size, are present in the formation at several localities. Conodonts recovered from these blocks, collected from two separate locations, are of late Early and mid Mid Ordovician age. The conodonts have high conodont‐alteration indices (CAI 5) indicative of temperatures as high as 300^o to max. 480 °C; some found in the Lough Nafooey area have abnormally high indices (CAI 6), which correspond to temperatures of about 360^o to max. 550 °C. The oldest fauna is dominated by Periodon aff. aculeatus and characterized by Oepikodus evae typical of the Oepikodus evae Zone (Floian Stage; Stage Slices Fl2–3, Lower Ordovician). The younger conodont assemblage, characterized by Periodon macrodentatus associated with Oistodella pulchra, is referred to the P. macrodentatus conodont Biozone (lower Darriwilian; Stage Slices Dw1–2). The Rosroe conodont assemblages are of Laurentian affinity; comparable faunas are well known from several locations along the east to south‐eastern platform margin of Laurentia and the Notre Dame subzone of central Newfoundland, Canada. The faunal composition from the limestone blocks suggests a shelf edge to slope (or fringing carbonate) setting. The faunal assemblages are coeval with, respectively, the Tourmakeady Formation (Floian–Dapingian) and Srah Formation (Darriwilian) in the Tourmakeady Volcanic Group in the eastern part of the South Mayo Trough and probably are derived from the same or similar laterally equivalent short‐lived carbonate successions that accumulated at offshore ‘peri‐Laurentian’ islands, close to and along the Laurentian margin. During collapse of the carbonate system in the late Mid Ordovician, the blocks were transported down a steep slope and into deep‐water by debris flows, mixing with other rock types now found in the coarse polymict clastics of the Rosroe Formation. The faunas fill the stratigraphical ‘gap’ between the Lower Ordovician Lough Nafooey Volcanic Group and the upper Middle Ordovician Rosroe Formation in the South Mayo Trough and represent a brief interval conducive to carbonate accumulation in an otherwise siliciclastic‐ and volcaniclastic‐dominated sedimentary environment. Copyright © 2015 John Wiley & Sons, Ltd.     

Atrypid Brachiopods from the Upper Devonian Wangchengpo Formation (Frasnian) of southern Guizhou, China — Extinction Patterns in the Frasnian of South China

The Wangchengpo Frasnian section of Dushan County contains two atrypid brachiopod assemblages. The lower is characterized by the Atryparia （Costatrypa） dushanensis fauna that appears at the base of the Hejiazhai Member approximately in the falsiovalis to transitans conodont zones： the upper is characterized by the Radiatrypa yangi fauna, which appears in the Lujiazhai Member approximately correspondent with the hassi to Upper rhenana conodont zones. Atrypid brachiopods, together with other brachiopods from the Dushan section show that the Hejiazhai Member is of Frasnian age. Preliminary analyses of Frasnian atrypid brachiopods from sections of South China indicate that there are nine genera and subgenera including Atryparia （Costatrypa）, Kyrtatrypa, Spinatrypa, lsospinatrypa, Spinatrypina, lowatrypa, Desquamatia （Desquamatia）. Desquamatia （Seratrypa）, and Radiatr）pa. Atrypid species diversity did not change much through the Frasnian. On a regional scale in South China, most atrypid species went extinct prior to the Frasnian/Famennian boundary. At any specific locality or section, these atrypids became extinct about 20-40 m below the Frasnian/Famennian （F/F） boundary, within the linguiformis conodont Zone, marking this as the major extinction level. Three new atrypid species are described： Atryparia （Costatrypa） dushanensis, lowatrypa pseudobodini, and Radiatrypa yangi.     

Conodont biostratigraphy and paleoecology of the marine sequence of the Tapajós Group,Early-Middle Pennsylvanian of Amazonas Basin,Brazil

This study was undertaken in the south and western regions of the Amazonas Basin to describe the conodont biostratigraphy and paleoecology of Pennsylvanian carbonate rocks of the marine portion of the Tapajós Group comprising the upper Monte Alegre, Itaituba, and lower Nova Olinda formations.The analyzed area includes one outcrop along the Tapajós river (TAP), two carbonate quarries (QI, QII), and 18 wells (dots 1–18). The conodont fauna is dominated by Idiognathoides sinuatus and Neognathodus symmetricus in the Monte Alegre Formation, followed by Idiognathodus incurvus, Diplognathodus coloradoensis and Neognathodus bassleri in the Itaituba and Nova Olinda formations. The conodont association suggests an Early to Middle Pennsylvanian age to the analyzed section. Relative ages attributed to the three lithostratigraphic units using conodonts, palynomorphs, and foraminifers are consistent.Herein are proposed one local taxon-range zone of Idiognathodus incurvus in the Itaituba and lower part of the Nova Olinda Formation and one local taxon-range subzone of Diplognathodus coloradoensis in the Itaituba Formation, suggesting a late Bashkirian – Moscovian (Atokan – early Desmoinesian) age to these strata.The Itaituba Formation marks the establishment of large Pennsylvanian marine conditions in the Amazonas Basin and is composed primarily of marine carbonates of abundant fossil content, tidal flat evaporites and siliciclastic thin intervals. Its lower limit, with the Monte Alegre Formation, is characterized by the predominant occurrence of fluvial-deltaic sandstones superimposed on an extensive sequence of aeolian sandstones, siltstones and shales intercalated with the interdune and lakes. From the upper strata of Itaituba Formation the faunal and lithological characteristics indicate the occurrence of a regressive phase culminating in a restricted environment, arid which indicates the Nova Olinda Formation. This is characterized by the occurrence of evaporites increasingly abundant to the top of carbonates, also shales and siltstones intercalated with the sabkha plain. The carbonate strata have similar marine fossils to those of Itaituba Formation, however, the fauna becomes impoverished in abundance and diversity. The conodont fauna of Early-Middle Pennsylvanian of Amazonas Basin suggests similarities of species with the North American Midcontinent region and the Illinois Basin indicating their probable cosmopolitism; however in a slightly different paleogeographic context, probably due to latitudinal differences, coal deposits are present in North America, whereas widespread evaporitic deposits are registered to the Tapajós Group, Amazonas Basin.     

Selachian fishes from Bhuban Formation,Surma Group,Aizawl, Mizoram

An interesting selachian fish assemblage having stratigraphic and palaeoecological significance is being described from the two intraformational calcareous conglomeratic horizons within the Upper Bhuban unit of Bhuban Formation, Surma Group (Lower to Middle Miocene). The assemblage consists of eighteen species of selachian fishes including two new ones (Carcharhinus bhubanicus and Hemipristis unidenticulata) belonging to thirteen genera and another thirteen forms have been identified up to generic level. It is dominated by the families Carcharhinidae and Lamnidae, and is one of the most diversified Miocene assemblages from the Indian subcontinent. The fish fauna and the associated mega-invertebrates suggest Lower Miocene (Aquitanian - Burdigalian) age for the Upper Bhuban unit of Bhuban Formation. These further suggest that the fish yielding horizons were deposited under a warm shallow marine set-up near to the shoreline in a high-energy environment.     

Late Eocene foraminifers and palaeoenvironment,Cascade Seamount,southwest Pacific Ocean: implications for seamount subsidence and Australia Antarctica Eocene correlation

A Late Eocene foraminiferal fauna of free specimens is recorded from Cascade Seamount, a feature of volcanic origin, whose age and fauna were previously studied only in thin section. The fauna is of Late Eocene (P15) age because of the presence of Globigerapsis index, Globigerapsis rubriformis, Subbotina linaperta, Subbotina angiporoides and Chiloguembelina cubensis. Many typical Eocene indicators, such as Hantkenina, Pseudohastigerina and key globorotaliids, are absent. The age is a little older than that estimated for previous samples from the seamount. The fauna is dominated (78%) by benthic species, especially species of Cibicides that have greater affinities with New Zealand faunas than with coeval southern Australian faunas. The sediment and its fauna accumulated near the lower limits of wave activity, off the coast of a volcano that probably stood at least 400 m above sea level. The location has subsided nearly 1000 m over the past 40 million years to its present water depth of 1000 m, suggesting that the entire East Tasman Plateau was approximately 1000 m above its current depth at the time. Conditions were cool temperate and the fauna lacks any warm water indices, consistent with a palaeolatitude of 55–60°S, but also with cool waters at a time of oscillating conditions in southern Australia and also in Antarctica. There is essentially no infauna and the waters were highly oxygenated in the turbulent zone.     

Detrital provenance,depositional environment,and palaeogeographic implications of Lower Triassic marine sediments in central Tibet

We present our new investigation into the depositional environment and provenance of the Yingshuiquan Formation in the central Qiangtang region of northern Tibet, in order to further our understanding of the environment of the Longmu Co–Shuanghu Palaeo–Tethys during the Early Triassic. The Yingshuiquan Formation is composed of oolitic limestone, calcareous sandstone, calcarenite, thin-bedded ribbon limestone, bioclastic limestone, and coarse oolite limestone that were deposited in a shallow-marine basin and contain abundant Lower Triassic conodont fossils (e.g. Hadrodontina anceps, Pachycladina sp., gen. et sp, Pachyclaina oblique, Hibbardelloides sp). We selected detrital zircons from four calcareous sandstone samples for U–Pb dating, yielding minimum age peaks of 263, 269, 275, and 280 Ma, respectively, and a minimum age of 249 Ma, based on several zircons around the same age. Analysis of the conodont biofacies and zircon LA-ICP-MS dating of calcareous sandstone indicates that the data is consistent with deposition in the Early Triassic. The Yingshuiquan Formation records Early Triassic shallow-water sediment in the Longmu Co–Shuanghu Palaeo–Tethys, and has a Southern Qiangtang and Northern Qiangtang terranes provenance. During the Early Triassic, the carbonate sediments of the Yingshuiquan Formation were deposited in an active environment around the Longmu Co–Shuanghu Palaeo–Tethys, which has became a residual sea basin.     

The upper Viséan–Serpukhovian in the type area for the Serpukhovian Stage (Moscow Basin,Russia): Part 1. Sequences,disconformities, and biostratigraphic summary

The upper Viséan–Serpukhovian strata in the type region for the Serpukhovian Stage is an epeiric‐sea succession ca. 90 m in thickness. The predominantly Viséan Oka Group (comprising the Aleksin, Mikhailov, and Venev formations) is dominated by photozoan packstones with fluvial siliciclastic wedges developed from the west. The Lower Serpukhovian Zaborie Group is composed of the Tarusa and Gurovo formations. The latter is a new name for the shale‐dominated unit of Steshevian Substage age in the studied area. The Zaborie Group is composed of limestones and marls in its lower (Tarusa and basal Gurovo) part and black smectitic to grey palygorskitic shales in the main part of the Gurovo Formation. The Gurovo Formation is capped by a thin limestone with oncoids and a palygorskitic–calcretic palaeosol. The Upper Serpukhovian is composed of a thin (3–12 m) Protva Limestone heavily karstified during a mid‐Carboniferous lowstand. The succession shows a number of unusual sedimentary features, such as a lack of high‐energy facies, shallow‐subtidal marine sediments penetrated by Stigmaria, the inferred atidal to microtidal regime, and palustrine beds composed of saponitic marls. The succession contains many subaerial disconformities characterized by profiles ranging from undercoal solution horizons to palaeokarsts. Incised fluvial channels are reported at two stratigraphic levels to the west of the study area. The deepest incisions developed from the Kholm Disconformity (top of the Mikhailov Formation). This disconformity also exhibits the deepest palaeokarst profile and represents the major hiatus in the Oka–Zaborie succession. The new sea‐level curve presented herein shows two major cycles separated by the Kholm Unconformity at the Mikhailov/Venev boundary. The Lower Serpukhovian transgression moved the base‐level away from falling below the seafloor so that the section becomes conformable above the Forino Disconformity (lower Tarusa). The maximum deepening is interpreted to occur in the lower dark‐shale part of the Gurovo Formation. The base of the Serpukhovian Stage is defined by FADs of the conodont Lochriea ziegleri and the foraminifer Janischewskina delicata in the middle of the sequence VN2. The Aleksinian–Mikhailovian interval is provisionally correlated with the Asbian (Lower–Middle Warnantian) in Western Europe. Based on FODs of Janischewskina typica and first representatives of Climacammina, the Venevian is correlated with the Brigantian in Western Europe. The Tarusian–Protvian interval contains diverse fusulinid and conodont assemblages, but few forms suitable for international correlation. FADs of the zonal conodont species Adetognathus unicornis and Gnathodus bollandensis at several metres above the Protvian base suggest correlation of the entire Zaborie Group and may be the basal Protvian to the Pendleian. Copyright © 2014 John Wiley & Sons, Ltd.     

Characteristics of Albaillella （ Albaillellarian ,Radiolarian） Fauna from Guadalupian to Lopingian Series in Permian, South China

On the basis of establishment of radiolarian biostratigraphy and conodont biostratigraphy,a radiolarian Albaillella fauna in the transitional environment from Guadalupian to Lopingian Series in Permian was found at a pelagic chert section in southeast Guangxi, South China. Radiolarian Albaillella is one of the most sensitive biology to the transitional environment. The Albaillella fauna shows an ecological evolutionary process from Guadalupian to Lopingian: declined stage-recovery stage-flourishing stage. The study of characteristics of the Albaillella fauna in the transitional environment may provide more information, not only for the subdivision and correlation of a high-resolution biostratigraphy, but also for influence of radiolarian Albaillella fauna on the pre-Lopingian mass extinction.     

Reef development on a deepening platform: two Early Cretaceous coralgal patch reefs (Catí, Llàcova Formation, eastern Spain) compared

Two coralgal patch reefs of the Hauterivian Llàcova Formation (Maestrat Basin, eastern Spain), exposed at two consecutive stratigraphic levels within a single section, have been studied to document taxonomic implications of a changing environment. These two reefal palaeocommunities differ substantially in coral taxonomic composition, microbialite formation pattern and in abundance and composition of encrusters and bioeroders. Of a total of 14 coral species, just one (Stylina parvistella) occurs in both reefs, yet is abundant in the (lower) reef A and rare, occurring near the reef base, in the reef B assemblage. Reef A is dominated by a phototrophic fauna and coral species with small corallites and imperforate septa (a stylinid-thamnasteriid-heterocoeniid-actinastreid association), along with an encruster association dominated by Bacinella and Lithocodium. Reef B is characterised by a balanced phototrophic-heterotrophic fauna that gradually passes into a heterotrophic-dominated assemblage. During this latest growth stage, microsolenid corals dominated the assemblage. The encruster fauna is characterised by sponges, polychaetes and bryozoans. Moderate deepening during a transgressive systems tract (TST) depositional sequence and elevated nutrient supply are interpreted to represent the driving environmental parameters that caused faunal compositions to differ between these two reefal palaeocommunities. Nine coral taxa, previously known only from younger (Barremian–Cenomanian) strata, have been identified, namely Dimorphocoenia? rudis, Eocomoseris raueni, Eocomoseris sp., Holocoenia jaccardi, Latusastrea irregularis, Mesomorpha sp., Microsolena kugleri, Polyphylloseris mammillata and Polyphylloseris sp. This observation emphasises the importance of the Hauterivian Stage as a period of evolutionary transition in Late Jurassic–Cretaceous coral faunas.     

上扬子区下志留统四射珊瑚组合带与层序地层序列的关系

摘 要　 根据动物群演替和层序地层的研究‚厘定上扬子区下志留统 （Llandovery） 四射珊瑚 组合带序列：（1） 香树园组 Dinophyllum-Rhabdocyclus 组合带‚时限为 Aeronian 期;（2） 雷家 屯组下部 Stauria-Briantelasma 组合带; （3） 雷家屯组上部 Maikottia-Kodonophyllum 组合带‚ 它们对应于 Telychian 早期;（4） 宁强组 Gyalophylloides -Idiophyllum 组合带‚相当于 Telychian 晚期。上扬子区下志留统可以划分为5个三级层序‚四射珊瑚组合带分别位于三级层序的高 水位体系域内。     

Palaeoenvironmental interpretation of Middle and Late Wisconsinan fossil coleopteran assemblages from western Olympic Peninsula,Washington, USA

Organic sediments exposed in a seacliff near Kalaloch, Washington, contain abundant, well-preserved beetle remains. Fossil assemblages dating from about 48 000 to 40 000 yr BP are dominated by species typical of the lowland and montane forests in the region today. A few species, Micropeplus laticollis, Olophrum consimile, Olophrum boreale, Arpedium cribratum, and Tachinus thruppi are presently not members of the Pacific Northwest fauna. Mean July temperature during this part of the Middle Wisconsinan is estimated to have been about 1°C lower than today. Later Wisconsinan assemblages are dominated by non-arboreal species, indicating a treeless, probably tundra environment. Mean July temperature based mostly on the occurrence of the alpine leaf-beetle species, Asiorestia pallida, is estimated to have been at least 3°C lower than the present day. Palaeoclimatic interpretations based on beetles are in good agreement with those based on pollen.     

Stratigraphy and paleobathymetric interpretation of the Cretaceous Karai shale formation of Uttatur Group, TamilNadu, India

The Karai shale Formation of the Uttatur Group is exposed in a bad land area at the western margin of the Cauvery Basin. This shale has been investigated based on foraminiferal fauna and clay minerals. The foraminiferal assemblages obtained contain predominantly calcareous benthic foraminifera, rare planktic and arenaceous foraminifera. The planktic foraminiferal index taxa Planomalina buxtorfi, Rotalipora reicheli, Praeglobotruncana stephani, and Hedbergella portsdownensis suggest the late Albian to middle Turonian age. The benthic assemblage dominated by Lenticulina, Gavelinella, Osangularia and Quadrimorphina, suggests an outer neritic (100–200 m) environment. The clay mineral content dominated by kaolinite-illite-montmorillonite indicates that the Karai shale was formed from weathering of igneous rocks.     

安徽齐云山晚白垩世兽脚类恐龙足迹点沉积环境

安徽齐云山兽脚类足迹群是目前中国晚白垩世保存最好的恐龙足迹群之一,对其沉积环境的研究为恢复白垩纪末期恐龙动物群的生活环境提供了证据。研究区足迹全部为兽脚类凸型足迹,与无脊椎动物遗迹Palaeophycus tubularis和Scoyenia sp.保存在一起,指示陆相沉积中的浅水沉积。通过薄片鉴定,足迹层位主要为岩屑砂岩,其平均粒径、标准偏差、偏度和峰度4个粒度参数特征与典型的河相砂一致;粒级分布直方图、概率累积曲线图及散点图表明,足迹层位从下到上颗粒逐渐变细,水动力条件变弱,沉积环境由河床沉积转变为边滩沉积。综上,齐云山兽脚类足迹点沉积环境为大型曲流河沉积,足迹保存在边滩沉积的下部,是白垩纪末期干旱气候条件下兽脚类恐龙动物群的水源地。     

α- and β-diversity Change of Late Ordovician Hirnantia Fauna of Changning, Sichuan, Southwest China

A continuous Ordovician-Silurian boundary section from the upper Wufeng Formation through the Kuanyinchiao Formation to the lower Lungmachi Formation has been carefully measured and collected at Shuanghe of Changning, southern Sichuan Province. For the first time, the temporal changes of α- and β-diversities of the Hirnantia fauna have been discussed in great detail. The general trend of brachiopod diversity change, increasing upward, is consistent with the regional trend of the Yangtze Platform, which had been controlled by both intrinsic and extrinsic factors. However, the sudden drop of diversity for a short period in the upper Kuanyinchiao Formation might have been controlled by environmental factors rather than normal faunal turnover. Synecological analysis using numerical methods recognizes two brachiopod-dominated associations of the Hirnantia fauna, the Dalmanella-Kinnella Association and the Mirorthis Association, both living in an offshore, deeper water environment corresponding to BA3-upper BA4, particularly lower BA3.     

浙江长兴煤山二叠-三叠系界线层牙形石序列及其全球对比

在详细研究全球二叠－三叠系界线层候选剖面───中国浙江长兴煤山剖面Ｐ／Ｔ界线层牙形石动物群序列基础上，自下而上识别出４个牙形石带：（１）ＣｌａｒｋｉｎａｃｈａｎｇｘｉｎｇｅｎｓｉｓＣｌａｒｋｉｎａｄｅｆｌｅｃｔａ带；（２）Ｉｓａｒｃｉｃｅｌｌａｐａｒｖａ带；（３）Ｉｓａｒｃｉｃｅｌｌａｉｓａｒｃｉｃａ带；（４）ＣｌａｒｋｉｎａｃａｒｉｎａｔａＣｌａｒｋｉｎａｐｌａｎａｔａ带，并在第一带中划分出３个动物群，从下向上是：ＣｌａｒｋｉｎａｃｈａｎｇｚｉｎｇｅｎｓｉｓＣｌａｒｋｉｎａｄｅｆｌｅｃｔａ－Ｃｌａｒｋｉｎａｓｕｂｃａｒｉｎａｔａ动物群，Ｈｉｎｄｅｏｄｕｓｌａｔｉｄｅｎｔａｔｕｓ－Ｃｌａｒｋｉｎａｍｅｉｓｈａｎｅｎｓｉｓｓｐ．ｎｏｖ．动物群和Ｈｉｎｄｅｏｄｕｓｔｙｐｉｃａｌｉｓ动物群，煤山剖面二叠、三叠系界线层牙形石序列的建立、完善，对确立该剖面在全球二叠、三在系界线高精度对比中的标准地位具重要意义。     

Palaeoenvironment and biogeography of a late MIS 3 fossil beetle fauna from South Taranaki,New Zealand

Fossil beetles from a last glacial landslide‐generated lake‐forest sequence aged 33 480–34 410 cal. yr BP (late Marine Isotope Stage 3 (MIS 3)) are identified from the Waitotara Valley in South Taranaki, North Island, New Zealand. The stratigraphy indicates that the landslide caused changes to local hydrology, resulting in the formation of a lake‐swamp environment and subsequent transition to forest. Fossil leaves suggest a forest dominated by Nothofagus menziesii, and radiocarbon ages indicate the site was forested for around 4000 yr. A fossil beetle‐based temperature estimate using the maximum likelihood envelope method indicates the climate was cooler than present day. The distributions of the fossil beetle taxa are examined and compared with the modern ecological patterns. The fossil fauna is very typical of a modern‐day Nelson (northern South Island) fauna. None of the beetle species is present in the modern South Taranaki fauna and many taxa such as Platypus caviceps, Alema paradoxa, Rhyzobius consors, Syrphetodes ater, Cyclaxyra impressa and species of Grynoma and Pycnomerus are now absent from part or all of the lower North Island. This is important because the lower North Island is currently an area of low diversity and endemism and these results suggest this biogeographical pattern stems from the last glaciation. Copyright © 2008 John Wiley & Sons, Ltd.     

布卡拉曼加拉贝氏牙形石动物群在西藏日土地区的发现及其意义

布卡拉曼加拉贝氏牙形石动物群首次在西藏阿里日土县多玛区脱塔拉剖面的吞龙共巴组底部发现,主要由Rabeignathusbucaramangus,Sweetognathuswhitei,Sweetognathusironatus和Mesogondolellacf.bissilli组成,指示的地层时代为Artinskian中晚期—Kungurian早期。此前,该动物群仅发现于美国犹他州、堪萨斯州、哥伦比亚的布卡拉曼加、帕米尔东南部和中国滇西保山地区。该牙形石动物群的产出地点位于班公湖以北、龙木错以南的喀喇昆仑地层分区,跨越了班公湖-怒江断裂带北界,而这一动物群被认为是冈瓦纳北缘浅海区特有的浅水相类型,因此推测班公湖-怒江缝合带可能不是冈瓦纳大陆的北界。     

Guadalupian （Middle Permian） Conodont Faunas at Shangsi Section, Northeast Sichuan Province

This study recovered the Guadalupian conodont faunas from Shangsi (上寺) Section in Northeast Sichuan (四川). Four genera and nine species were identified, and three conodont zones were recognized and established; they include Jinogondolella nankingensis Zone, J. aserrata Zone, and J. postserrata Zone. The Roadian and Wordian boundary is set in the interval 5 m from the top of Bed 86 by the first appearance of the conodont J. aserrata. The Wordian and Capitanian boundary is set in the interval 2.3 m from the top of the Bed 95 by the first appearance of J. postserrata. Most of the specimens demonstrated low color alteration index (CAI) as 1.5-3, indicating that most part of the Maokou (茅口) Formation may have the suitable thermal conditions for the formation of oil source rocks.     

滇西保山熊洞村栗柴坝组牙形石的发现及其地质意义

针对保山地层区熊洞剖面原属栗柴坝组的灰岩进行了牙形石样品分析,总计建立了5个牙形石带,分别为Pterospathodus pennatus procerus带、Kockelella walliseri带、Ancoradella ploeckensis带、Polygnathoides siluricus带和Polygnathus nothoperbonus带。该剖面第8层原属栗柴坝组,Polygnathus nothoperbonus分子的出现证实其为下泥盆统埃姆斯阶的地层,应归为向阳寺组。剖面总体对应志留系温洛克统底部到下泥盆统埃姆斯阶中部,中间缺失志留系罗德洛统卢德福特阶—下泥盆统埃姆斯阶之间的8～10个标准牙形石带,说明该地区后期可能受构造作用影响,志留系和泥盆系界线为断层接触。该剖面牙形石序列的建立一定程度上完善了滇西保山地层区志留系生物地层的研究程度,为下一步该区生物地层格架的建立奠定了基础。     

Depositional environments in the Telychian Stage (Silurian) of the central Oslo region,Norway

The Telychian succession in the central Oslo region was previously interpreted as deposited in a relatively deep, calm environment showing a continuous transgressive development. A new analysis of fossil assemblages shows that sediments in the central districts were deposited at varying water depths in an environment marked by intense infaunal activity in soft substrates. Two small-scale fluctuations in sea level are attributed to eustasy. The maximum deepening events occurred during the Monograptus turriculatus and Monoclimacis crenulata graptolite zones. Previous depositional models include development of a trough to the north of the Oslo region in early Telychian time, which formed due to isostatic loading caused by an advancing thrust front of the Caledonian Orogeny. Bathymetric analysis shows a deepening in the Ringerike district in the latest Aeronian, which here is interpreted as a distal effect of the loading to the north. The local deepening led to reversal of the epicontinental slope between the northern and western districts and the central districts and the development of an east–west elongate positive area further south. The thrust front acted as a source of siliciclastic material; and when the front halted in mid-Telychian time the trough was filled in gradually by a prograding coast or delta. The diachronous Vik Formation is viewed as a distal development of this progradation. When the east–west oriented positive area subsided the Vik Formation was deposited in Skien to the south.