Biostratigraphy,microfacies and depositional environments of upper Viséan limestones from the Burren region,County Clare,Ireland     

S.J. Gallagher  C.V. MacDermot  I.D. Somerville  M. Pracht  A.G. Sleeman 《Geological Journal》2006,41(1):61-91

The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Correlation of Mississippian (Upper Viséan) foraminiferan,conodont, miospore and ammonoid zonal schemes,and correlation with the Asbian–Brigantian boundary in northwest Ireland     

P. Czar  I. D. Somerville  W. I. Mitchell  P. Medina‐Varea 《Geological Journal》2006,41(2):221-241

The microbiota of the upper Viséan (Asbian–Brigantian) rocks in the Lough Allen Basin in northwest Ireland is analysed. The Middle Mississippian sequence studied extends from the upper part of the Dartry Limestone/Bricklieve Limestone formations of the Tyrone Group to the Carraun Shale Formation of the Leitrim Group. The rocks have been traditionally dated by ammonoid faunas representing the B_2a to P_2c subzones. The Meenymore Formation (base of the Leitrim Group) also contains conodont faunas of the informal partial‐range Mestognathus bipluti zone. The upper Brigantian Lochriea nodosa Conodont Zone was recognized by previous authors in the middle of the Carraun Shale Formation (Ardvarney Limestone Member), where it coincides with upper Brigantian ammonoids of the Lusitanoceras granosus Subzone (P_2a). Foraminifera and algae in the top of the Dartry Limestone Formation are assigned to the upper Cf6γ Foraminifera Subzone (highest Asbian), whereas those in the Meenymore Formation belong to the lower Cf6δ Foraminifera Subzone (lower Brigantian). The Dartry Limestone Formation–Meenymore Formation boundary is thus correlated with the Asbian–Brigantian boundary in northwest Ireland. For the first time, based on new data, a correlation between the ammonoid, miospore, foraminiferan and conodont zonal schemes is demonstrated. The foraminiferans and algae, conodonts and ammonoids are compared with those from other basins in Ireland, northern England, and the German Rhenish Massif. Historically, the Asbian–Brigantian boundary has been correlated with several levels within the P_1a Ammonoid Subzone. However, the new integrated biostratigraphical data indicate that the Asbian–Brigantian boundary in northwest Ireland is probably located within the B_2a Ammonoid Subzone and the NM Miospore Zone, but the scarcity of ammonoids in the Tyrone Group precludes an accurate placement of that boundary within this subzone. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Early Pragian conodont‐based correlations between the Barrandian area and the Spanish Central Pyrenees     

Ladislav Slavík  Jos Ignacio Valenzuela‐Ríos  Jind&#x;ich Hladil  Peter Carls 《Geological Journal》2007,42(5):499-512

Occurrences and distribution of extremely scarce eognathodontids do not facilitate reliable correlation across the European regions. The correlation of the traditional early Pragian of the Prague Synform (a part of the classical Barrandian area) and the Spanish Central Pyrenees (section Segre 1) is based on conodont taxa of the Icriodus steinachensis and the Pelekysgnathus serratus stocks. This correlation has the potential to be extended to other peri‐Gondwanan regions where this scarcity of eognathodontid faunas exists as well. Application of the morphotype subdivision in I. steinachensis enables approximation of the beginning of the Pragian in the Pyrenees. It is based on the entry of I. steinachensis beta morphotype; it enters together with early eognathodontid taxa in the Barrandian sections. These correlations show that routine application of certain zonal concepts can lead to misleading conclusions. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The eastern margin of the Aberystwyth Grits Formation     

Richard Cave  David K. Loydell 《Geological Journal》1997,32(1):37-44

Structural, lithological and biostratigraphic evidence does not support the existence of the postulated Bronnant Fault previously considered to bound and have had depositional control over the Aberystwyth Grits to the east. The Adail Mudstones Formation is a synonym of the Borth Mudstones Formation; the latter name has priority. Both the type Borth Mudstones Formation and the ‘Adail Mudstones Formation’ in part underlie and in part are lateral equivalents of the lower part of the Aberystwyth Grits Formation. Deposition of the Aberystwyth Grits Formation was confined on its eastern side by a slope enhanced by the prior, and partially contemporaneous, deposition of the Devil's Bridge Formation (largely a slope apron). © 1997 John Wiley & Sons, Ltd.  相似文献   

河套盆地东部第四纪中晚期介形类特征及其沉积环境意义   总被引：1，自引：0，他引：1  

吴利杰  石建省  张翼龙  李政红  王文中  王丽娟  于娟 《地质力学学报》2020,26(1):125-134

根据河套盆地东部DTLC孔介形类组合及其岩性、岩相的分析,着重地探讨了该区第四纪中、晚期介形类的生物地层特征及其沉积古环境意义。研究认为:中更新世早期（Q₂1）,未见介形类,以冲洪积沉积环境为主,兼有河湖交替演化;中更新世晚期（Q₂2）,介形类生物组合为Leucocythere plethora-Eucypris inflate-Limnocyther dubiosa,推测为封闭性的半咸水、咸水湖相沉积环境,气候偏冷;晚更新世早期（Q₃1）,介形类生物组合为Leucocythere plethora-Limnocythere dubios,反映了封闭性的半咸水深湖相沉积环境;晚更新世晚期（Q₃2）,少见淡水介形虫化石,以Ilyocypris manasensis-Candoniella albicans-Cypria luminosa为组合特征,反映了以河流冲洪积环境为主;全新世（Q₄）为河流沉积环境。通过河套盆地区域沉积环境的综合分析认为:中更新世晚期（Q₂2）至晚更新世早期（Q₃1）,河套盆地为封闭性内陆湖盆,黄河为内流河;自晚更新世晚期（Q₃2）以来,黄河逐渐地转为外流河,河套盆地为外流湖盆。   相似文献   

滇东地区奥陶系红石崖组的时代   总被引：2，自引：0，他引：2  

张举  张元动  宋妍妍 《地层学杂志》2013,(1):8-17

红石崖组是分布于滇东和川西南地区的一套红色的奥陶纪粗碎屑沉积地层,含笔石、几丁虫和疑源类等化石,过去通常认为其时代为阿仑尼格期(大致相当于当前国际划分的弗洛期和大坪期)。通过对云南禄劝桂花箐水库岸边、禄劝六江和昆明二村红石崖3条剖面的红石崖组进行了较为详细的化石采集,获得了大量笔石标本,鉴定出了2属15种。根据滇东地区红石崖组的笔石动物群,建立Corymbograptus varicosus笔石带,通过与国内外相关笔石动物群的对比分析,该带可与我国黔北地区的Acrograptus filiformis带、英国湖区的Corymbograptus varicosus带以及阿根廷西北部Acoite组的"Baltograptus deflexus带"进行较好对比,其时代应为早奥陶世弗洛期早中期。据此,红石崖组与其上的巧家组之间很可能缺失大坪期地层。  相似文献   

Acritarchs from the Lower Palaeozoic succession on the south County Wexford coast,Ireland: new age constraints for the Cullenstown Formation and the Cahore and Ribband Groups     

P. M. Brück  M. Vanguestaine 《Geological Journal》2004,39(2):199-224

Lower Palaeozoic sediments crop out on the southern coast of County Wexford, Ireland, comprising three distinctive lithostratigraphical units: from west to east the Cahore Group, the Blackhall Formation of the Ribband Group and the Cullenstown Formation. The three units are largely devoid of macrofossils and thus their ages have to date been uncertain and, in the case of the Cullenstown Formation, speculative. In the Cahore Group, a diverse assemblage of acritarchs composed of seventeen species has been recorded indicating a middle Early Cambrian age. This is similar to the age of the lithologically identical Bray Group to the north, in County Wicklow. In the Ribband Group, two very distinct assemblages have been noted. Both are poorly preserved, but diagnostic species have been determined giving a biostratigrapical range of early Mid‐Cambrian to Llanvirn. Palynomorphs have been recorded for the first time from the Cullenstown Formation allowing comparison with eastern Newfoundland where a similar, less diverse assemblage has been recorded. The age indicated is latest Mid‐Cambrian to early Late Cambrian. Overall, despite generally poor preservation of the organic matter, some 45 acritarch species have been distinguished, among which one new combination is proposed: Retisphaeridium postae instead of Cymatiosphaera postae. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Late Anisian radiolarian assemblages from the Yarlung‐Tsangpo Suture Zone in the Jinlu area,Zedong, southern Tibet: Implications for the evolution of Neotethys     

Dishu Chen  Hui Luo  Xueheng Wang  Bo Xu  Atsushi Matsuoka 《Island Arc》2019,28(4)

Abundant Triassic radiolarian fossils were obtained from varicolored bedded cherts exposed in the Buruocang section near Jinlu village, Zedong, southern Tibet. The radiolarian‐bearing rocks represent fragmented remnants of the Neotethys oceanic sediments belonging to the mélange complex of the east part of the Yarlung‐Tsangpo Suture Zone. Two new middle Late Anisian radiolarian assemblages recognized from this section named Oertlispongus inaequispinosus and Triassocampe deweveri, respectively, are compared with those known from Europe, Far East Russia, Japan, and Turkey. These Anisian radiolarian fossils are the first reported in southern Tibet and the oldest radiolarian record within the Yarlung‐Tsangpo Suture Zone. They improve time constraints for the evolution of Neotethys in southern Tibet.  相似文献   

珠江口盆地BY7—1—1井晚渐新世浮游有孔虫的发现及其地质意义   总被引：6，自引：2，他引：6  

秦国权 《海洋地质与第四纪地质》1992,12(2):21-32

本文系统介绍了珠江口盆地最南的一个探井——BY7—1—1井浮游有孔虫生物地层和海侵层序。通过对该井有孔虫全面系统采样分析,发现了渐新世浮游有孔虫组合。这一重大发现给重新认识该区上、下第三系界线,以及对整个南海北部地层对比提供了新资料。并对有关的一些地质问题进行了讨论。  相似文献   

Pleistocene radiolarian biostratigraphy in the South China Sea*   总被引：4，自引：0，他引：4  

Rujian Wang  Andrea Abelmann 《中国科学D辑(英文版)》1999,42(5):536-543

Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core. 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea. Project supported by the National Natural Science Foundation of China (Grant No. 49291100) and by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as part of a GermadChinese scientific cooperation program. This is Alfred Wegener Contribution No. 1473.  相似文献