Lower carboniferous (Dinantian) stratigraphy and structure in the Kingscourt Outlier,Ireland

Logging of 55 recent boreholes, together with remapping, has resulted in a fundamental reassessment of the stratigraphy and sedimentology of the Dinantian Kingscourt Outlier. Despite the present isolated position of the outlier within the Longford-Down Massif, the Kingscourt rocks are an integral part of the Dublin Basin succession. The newly defined Ardagh Platform marks the most northerly limit to basinal sedimentation in the Dinantian Dublin Basin. The Courceyan is a typical but thinner, north Dublin Basin succession with two new formal units: the Rockfield Sandstone Member and the Kilbride Formation. The latter, a coarse-grained, well washed limestone of latest Courceyan to early Chadian (late Tournaisian) age is the shallow water equivalent of the Feltrim Formation (Waulsortian facies), which is absent in the outlier. The Courceyan interval in the north of the outlier is markedly attenuated. In the succeeding Chadian-Brigantian interval basinal facies predominate in the south, but on the Ardagh Platform an almost complete coeval Viséan shallow water sequence is found. A new platform unit (Deer Park Formation) of latest Asbian to Brigantian age is defined in the Ardagh area. The Dee Member (Chadian) is newly defined for the lower part of the basinal Tober Colleen Formation and the Altmush Shale Member is formally defined for the upper part of the Loughshinny Formation. Two major structures dominate the Kingscourt Outlier: the NE-SW trending Moynalty Syncline in the south and the N-S trending Kingscourt Fault. Both are Hercynian structures, but probably represent reactivated Caledonide basement-controlled structures. Dinantian syn-depositional faulting is indicated in both the Courceyan (‘Kingscourt Sag’) and Chadian-Asbian. The latter period of faulting in the Ardagh area separates platform facies in the north from basinal facies to the south. In the late Asbian, platform facies with carbonate build-ups prograded south into the basin as far south as Nobber, but in the latest Asbian to Brigantian, basinal facies extended northwards over the collapsed platform margin.     

Biostratigraphy of Dinantian limestones and associated volcanic rocks in the Limerick Syncline,Ireland

Rocks of Courceyan to Brigantian age are exposed in the Limerick Syncline. However, a complete Courceyan succession is known only from two boreholes which correlate closely, both faunally and lithologically, with a standard Limerick Province succession in the Pallaskenry Borehole on the Shannon estuary. This is followed by a thick Waulsortian sequence (the newly defined Limerick Limestone Formation) of late Courceyan to early Chadian age and overlying cherty micrites (the newly defined Lough Gur Formation) of early to late Chadian age, whose top is younger to the east. The Lough Gur Formation is succeeded by lavas and tuffs of the Knockroe Volcanic Formation whose upper part is interbedded with and overlain by shallow water oolites and algal-rich bioclastic limestones of the Herbertstown Limestone Formation. The higher part of the latter is in turn interbedded with lavas and tuffs of the Knockseefin Volcanic Formation. The Herbertstown Limestone has rich and diverse coral/brachiopod and foraminiferal assemblages of late Chadian to Asbian age. Its base is markedly diachronous: late Chadian in the west of the syncline and Holkerian in the east. Both the base and top of the Knockroe Volcanic Formation are thus shown to be markedly diachronous and volcanism extends from the Chadian to early Asbian. The Knockseefin Volcanic Formation is entirely of Asbian age. The highest limestones (Dromkeen Limestone Formation) have a diagnostic late Asbian–early Brigantian fauna and are overstepped by mid-Namurian shales.     

Stratigraphy and sedimentology of lower carboniferous (Dinantian) boreholes from West Co. Meath,Ireland

The 2-km deep Athboy Borehole (1439/2) together with the lower part of boreholes EP30 and N915 form a standard type section for strata of Dinantian (Courceyan to Asbian) age in west Co. Meath. Above a thin basal red-bed siliciclastic sequence, the marine Courceyan shelf succession is almost 600 m thick. It comprises the Liscartan, Meath, and Moathill Formations of the Navan Group and the Slane Castle Formation of the succeeding Boyne Group. The shallow-water limestones include micrites, oolites, and sandy bioclastic packstones and grainstones with subordinate skeletal wackestones and shales. Lateral facies changes from north to south in the Navan area suggest deepening across a shelf towards a depocentre further to the south around Trim. The deeper-water Waulsortian Limestones of late Courceyan to Chadian age (Feltrim Formation, ca. 213 m thick) form a series of five sheet-like mudbanks, interbedded with generally thin units of nodular crinoidal limestones and shales. The mudbanks are formed of bryozoan-rich peloidal wackestones and lime-mudstones with phase C and D components. Rare soft-sediment breccias occur at the bottom and top of banks. The succeeding Fingal Group commences with a thin interval (3–20 m) of black shales, laminated packstones, and micritic limestones of Chadian age, the Tober Colleen Formation. This is followed by the Lucan Formation (Chadian to Asbian) predominantly of laminated and graded calciturbidites, laminated sandstones, cherts, and black shales, which is over 1300 m thick. Ten sedimentary units have been informally defined, based on lithofacies and facies associations. The oldest unit, the Tara Member, is characterized by proximal debris-flow breccia deposits and nodular mudstones. A thick bioturbated micrite and shale unit (Ardmulchan Member) in the middle of the formation is overlain directly by a coarse oolitic and crinoidal grainstone unit (Beauparc Member). Near the top of the formation is a distinctive unit of coarse-grained laminated sandstones and shales (Athboy Member). The highest rocks in the Borehole are clean thickly-bedded limestones of the Asbian Naul Formation (>90 m thick). The youngest Dinantian strata in the area, the Brigantian Loughshinny Formation, marks a return to shale-dominant basin sedimentation. The significance of this work lies in the fact that the Athboy borehole is the longest continuously cored borehole in the Carboniferous of Ireland and provides a continuous sedimentary and biostratigraphic record for the northern part of the Dublin Basin. Foraminiferal biozones (Cf2–Cf6) have been recognized in this and in borehole N915, and Stage boundaries identified, which can be applied throughout the Basin. The sedimentary record for the Lucan Formation indicates four tectonic pulses during the Viséan, in the late Chadian/early Arundian, mid-Arundian, Holkerian, and late Holkerian/early Asbian.     

Lower Carboniferous (Dinantian) stratigraphy and structure of the Walterstown-Kentstown area,Co. Meath,Ireland

Stratigraphic units are defined and described for the Lower Carboniferous succession in the Walterstown-Kentstown area of Co. Meath, Ireland. A complete (unexposed) Courceyan succession from the terrestrial red bed facies of the Baronstown Formation to the Moathill Formation of the Navan Group has been penetrated in several boreholes. Although the lower part of the sequence is comparable with the Courceyan succession at Navan and Slane, the middle part of the sequence differs markedly in the Walterstown-Kentstown area and two new members, the Proudstown and Walterstown Members, are defined in the upper part of the Meath Formation. Syndepositional faulting was initiated during the Courceyan, probably in latest Pseudopolygnathus multistriatus or early Polygnathus mehli latus time. Movement on the ENE trending St. Patrick's Well Fault influenced the deposition of the Walterstown Member and the overlying Moathill Formation and was probably associated with the development of the East Midlands depocentre to the south of the area. A second episode of tectonism in the latest Courceyan or early Chadian resulted in uplift and erosion and the development of ‘block and basin’ sedimentation. Subsequent transgression of the uplifted block led to the establishment of the Kentstown Platform, bounded to the north, west and south by rocks of basinal facies. The Milverton Group (Chadian-Asbian), confined to this platform, unconformably overlies Courceyan or Lower Palaeozoic strata and is subdivided into three formations: Crufty Formation (late Chadian), Holmpatrick Formation (late Chadian-Arundian) and Mullaghfin Formation (late Arundian-Asbian). The Walterstown Fault controlled the western margin of the Kentstown Platform at this time. Contemporaneous basinal sediments of the Fingal Group (Lucan and Naul Formations) accumulated to the west of the Walterstown Fault and are much thicker than age-equivalent platform facies. Platform sedimentation ceased in latest Asbian to early Brigantian time with tectonically induced collapse and drowning of the platform; platform carbonates of the Mullaghfin Formation are onlapped northwards by coarse proximal basinal facies of the Loughshinny Formation. A distinct gravity anomaly in the Kentstown area suggests the presence of a granitoid body within the basement. The Kentstown Platform is therefore considered to have formed on a buoyant, granite-cored, footwall high analogous to the Askrigg and Alston Blocks of northern England.     

Early to mid-Viséan shallow water platform buildups,north Co. Dublin,Ireland

A number of carbonate buildups in north Co. Dublin, long assigned to the late Viséan (Asbian), are shown on the basis of coral, foraminiferal and algal evidence to be early to mid-Viséan (late Chadian to Holkerian) in age. They are equivalent in age to beds ranging from the upper part of the Lane Formation to the top of the Holmpatrick Formation. The buildups are poorly exposed and relatively small, probably only a few tens of metres across at most. Buildup sediments are massive to crudely bedded and dominated by peloidal, clotted and dense uniform micrites displaying lime mudstone and bioclastic wackestone textures. Dasycladacean algae are common in the buildups and cryptalgal fabrics are locally important. Cavities in the buildups are generally small (< 5 cm) and lined with inclusion-rich radiaxial calcite cements. Micritization of bioclasts and cements is ubiquitous. Enclosing off-buildup limestones are skeletal and intraclastic grainstones possessing sedimentary structures indicative of deposition in moderate to high energy environments. Fossil and petrographic evidence from the buildups also indicate a shallow water origin for the north Co. Dublin buildups. Compared with the slightly older Tournaisian (Courceyan to early Chadian) Waulsortian buildups which developed extensively in the Dublin Basin, these younger platform buildups are smaller and more isolated and possess a diverse suite of algal components and cryptalgal fabrics. Nevertheless, components in the north Co. Dublin buildups most closely resemble the shallowest phase D Waulsortian buildups, particularly in the presence of abundant peloids and micritized cements. The north Co. Dublin buildups developed on a carbonate platform (the Milverton Platform), adjacent to the Dublin Basin, whereas the Waulsortian developed in a deeper ramp setting. Following the demise of the Waulsortian in early Chadian time carbonate buildups established themselves on the shallow platforms. It is suggested that the microbial communities responsible for these buildups may have ‘evolved’ from older phase D Waulsortian communities and that he north Co. Dublin platform buildups represent the shallow water end of a spectrum of Viséan buildups.     

The carboniferous lithostratigraphy of Southeast County Limerick,Ireland, and the origin of the shannon trough

The Carboniferous succession in southeast County Limerick, on the southeastern margin of the Shannon Trough, is Courceyan to mid-Namurian in age and over 1900 m thick. The lithostratigraphy is described in detail. Its most important aspect is the presence of two thick volcanic sequences, a Chadian one of the alkali basalt to trachyte suite and one of Asbian age dominated by limburgites and ankaramites. The associated Dinantian carbonates are of shelf or ramp facies throughout, and no fundamental division into shelf and basin facies occurs as in the Dublin and Craven Basins in early Viséan times. Rapid differential subsidence between this area and the Shannon Estuary began during deposition of the late Courceyan to early Chadian Waulsortian facies but was less marked in the remaining Viséan when much of the volcanic topography was preserved by rapid basinal subsidence. There was basinal inversion in the late Dinantian to lower Namurian, followed by renewed subsidence in mid-Namurian times. This contrasts with the continuous rapid subsidence of the area further west on the Shannon Estuary. This behaviour, together with a comparison of that of nearby Carboniferous basins such as the Dublin, South Munster, and Craven Basins, which lack substantial volcanic sequences, suggests an origin in a transtensional regime rather than one of simple crustal stretching.     

Chadian faunas and flora from dyserth: Depositional environments and palaeogeographic setting of Viséan strata in northeast wales

New floral and faunal data from the oldest Dinantian limestones (Foel Formation) in the Dyserth area, suggest that these sediments are of Chadian age, rather than the Asbian age concluded by earlier workers. The basal late Chadian limestones rest conformably on Dinantian Basement Beds of ?Chadian age or older. The initial inundation of St. George's Land occurred during Chadian times, when shallow-water marine limestones accumulated in the Dyserth area and further to the south, together with terrestrially derived siliciclastics, containing drifted plant fragments. Periodically, a restricted hypersaline lagoonal environment was established but an open marine, neritic environment with abundant stenohaline fauna prevailed in this area. These Chadian sediments accumulated on the proximal part of a carbonate ramp and are presumed to have passed laterally downslope into deeper water basinal facies with Waulsortian buildups of the Irish Sea Basin. In the later Arundian, a carbonate ramp–to–platform transition occurred, with widespread deposition of shallow-water carbonates. In the Asbian this platform developed a rimmed margin, with buildups forming a linear belt between platform and basin. An almost complete Chadian to Brigantian Lower Carboniferous sequence can now be recognized in North Wales. This succession is comparable with the shelf succession in south Cumbria on the northern margin of the Irish Sea Basin.     

Lithofacies and stratigraphy of the Ordovician Guniutan Formation in its type area,China

The Lower to Middle Ordovician Guniutan (Kuniutan) Formation in the eastern Yangtze Gorges, China has been demonstrated to be similar to the ‘Orthoceratite Limestone’ in Baltoscandia with respect to facies, stratigraphic development and conodont biostratigraphy. Thus the ‘Orthoceratite Limestone’ appears to be a much more widely distributed and characteristically Ordovician facies than has hitherto been assumed. Five lithostratigraphic subdivisions of the Guniutan Formation are here defined in ascending order as the Nanya, Puxi, Wuguixi, Daping and Niangjiafang members. It is shown that these members, which represent considerable spans of time as indicated by their conodont stratigraphy, may be fairly thin but nevertheless regionally extensive. A new conodont zone, with Eoplacognathus crassus as the zonal fossil, is established to accommodate the precise dating of the Wuguixi and Puxi members. Microfacies data from the Guniutan Formation, available for the first time, show that its dominant component particles are sand-sized echinoderm and arthropod debris, as in the Baltoscandian ‘Orthoceratite Limestone’.     

Cryptic exposure horizons in the Carboniferous Limestone of Portishead,Avon

Two unusual subaerial exposure horizons containing fibrous columnar calcite crystals are described from the (early Chadian) Lower Carboniferous of Portishead, near Bristol in southwest Britain. The lower horizon overlies the Courceyan Black Rock Limestone (mid-ramp facies) and is separated from the upper horizon by the Sub-Oolite Bed and is overlain by the Chadian Gully Oolite (both are inner ramp deposits). Regionally the Portishead Palaeosol Beds are interpreted as forming part of extensive emergent surfaces which developed along the southern margin of the Welsh–Brabant Massif. They correlate with similar subaerial exposure horizons in Belgium and southern Germany, and may be the product of a proposed major eustatic sea level fall at the end of the Courceyan.     

New chitinozoans from the historical type area of the Hirnantian Stage and additional key sections in the Wye Valley,Wales, UK

The type locality for several core elements of the Hirnantia brachiopod fauna is a small disused quarry on the western slopes of Cwm Hirnant. There, the Hirnant Limestone Member of the Foel‐y‐Ddinas Mudstone Formation yields a new, well‐preserved chitinozoan assemblage, attributed to the Spinachitina taugourdeaui Biozone. This allows tight correlation with the Hirnantian of Baltica and Laurentia and neatly ties the chitinozoan zonation with the classical brachiopod fauna. Nearby, the chitinozoan assemblage from the Caradoc Cymerig Limestone Member at Gelli‐grîn belongs to the Spinachitina cervicornis Biozone?, and is identical to that recovered from the Burrellian in the Onny Valley, Welsh Borderland. A Silurian assemblage higher up section, discovered in the Cwm‐yr‐Aethnen Formation, is attributed to the globally recognized Eisenackitina dolioliformis Biozone. Attempts to integrate the chitinozoan and graptolite biozonation, in the central Welsh Rhayader area, were less successful. Copyright © 2008 John Wiley & Sons, Ltd.     

湖北宜昌和南漳奥陶系大湾组笔石生物地层

根据宜昌陈家河剖面大湾组的笔石标本,确立笔石序列自下而上为:Didymograptellus eobifidus带、Corymbograptus deflexus带和Azygograptus suecicus带(大湾组下段),Exigraptus clavus带和Undulogr aptusaustrodentatus带(大湾组上段)。对湖北南漳的全家湾和李家湾两剖面的大湾组进行了详细采集测量,其中全家湾剖面大湾组下段自下而上识别出D.eobifidus带、C.deflexus带和A.suecicus带;李家湾剖面大湾组下段自下而上识别出D.eobifidus带和A.suecicus带,证实南漳大湾组的底界与宜昌地区基本一致。     

The shipway limestone of gower: Sedimentation on a storm-dominated early carboniferous ramp

A detailed sedimentary study of the Lower Carboniferous (Courceyan) Shipway Limestone Formation at Three Cliffs Bay on the Gower Peninsula (South Wales) has shown that the bioclastic limestones represent a storm-dominated sequence that contains the storm-related sedimentary structure hummocky cross-stratification (HCS). Conformably overlying the Shipway Limestone is a cross-stratified oolitic sandbody with evidence of subaerial exposure. Six sedimentary lithofacies are identified in these two formations which record a distal to proximal, shallowing-upward trend that passes from beneath mean wave-base to above fairweather wave-base. The shallow marine facies model constructed by Wu (1982) from his study of the Lower Carboniferous limestone sequences of South Wales is re-evaluated. Modifications proposed for the model include the addition of two distal tempestite facies and a proximal oolite sand body. The Shipway Limestone and Brofiscin Oolite record the first major, basin-wide, shallowing-upward phase of the Lower Carboniferous in South Wales.     

新疆柯坪大湾沟剖面柯坪塔格组中段底部笔石生物地层初步分析

新疆塔里木盆地西北缘柯坪大湾沟剖面柯坪塔格组中段底部的泥岩夹白云岩地层中发现有较丰富的笔石、腕足类、三叶虫、双壳类等化石,其中笔石有4属8种及2个比较种和1个未定种,可能属笔石Coronograptuscyphus带至Coronograptusgregarius带。从笔石生物地层看,柯坪塔格组中段底部的时代很可能为志留纪兰多维列世鲁丹期末至埃隆期初。     

Palaeoecological significance of turritelline gastropod-dominated assemblages from the mid-Cretaceous (Albian-Cenomanian) of Texas and Oklahoma,USA

The faunas of three previously poorly known and highly fossiliferous limestones from the upper Lower Cretaceous of Texas are dominated by turritelline gastropods. These faunas consist of turritelline-dominated assemblages in the Whitestone Limestone Member of the Walnut Formation in Travis County (middle Albian), the Keys Valley Marl Member of the Walnut Formation in Coryell County (middle Albian), and the Fort Terrett Formation in Kimble County (middle Albian). A fourth high-spired gastropod assemblage in the Segovia Formation in Pecos County (upper Albian) is not dominated by turritellines. Two other turritelline-dominated assemblages in non-carbonate rocks from the Albian and Cenomanian of Texas and Oklahoma are also described. These turritelline-dominated assemblage occurrences add considerably to our knowledge of the facies occurrence of Cretaceous turritelline-dominated assemblages, and they are consistent with the global facies distribution of these assemblages: i.e., although they are widespread in siliciclastic facies from Cretaceous to Recent, turritelline-dominated assemblages in carbonate facies occur almost exclusively in the Cretaceous and Paleogene.     

The Distribution of Chadian and earliest Arundian strata in North Wales: Implications for Dinantian (Carboniferous) lithostratigraphy and palaeogeography

The late Chadian Foel Formation, previously thought to be confined to the Dyserth area of North Wales, forms a poorly exposed but persistent basal unit to much of the Dinantian crop east of the Clwydian Range, necessitating a revision of the local lithostratigraphy. The formation comprises a peritidal heterolith which, together with the lowest few metres of the overlying Llanarmon Limestone, yields microfossil assemblages diagnostic of the Eoparastaffella Cf4α Subzone. Succeeding strata, containing the lowest archaediscid foraminifera, provide the first record of Cf4β assemblages from North Wales and establish an early Arundian age for these beds. The Foel Formation was deposited as an aggradational sequence on the northern flank of St. George's Land during a pulsed transgression which began in late Chadian times. The widely recognized basal Arundian transgression is represented by the contact between the Foel Formation and overlying platform carbonates. The latter overlap the Foel Formation in the southernmost part of the Clwydian crop demonstrating, for the first time, southwards onlap on the northern side of the Bala–Bryneglwys Fault System.     

Discussion of Jamaican Cenozoic ichnology: review and prospectus: (v. 50, pp. 364–382)

We make two comments on the paper ‘Jamaican Cenozoic ichnology: review and prospectus’ by Donovan et al. (2015). Based on biostratigraphy and new radiometric dates, we recommend the separation of the Richmond Formation (deposited in the Wagwater Graben and onlapping onto the edges of the Clarendon Block and Blue Mountains Block) and the Moore Town Formation (deposited in the John Crow Mountain Graben) which are of early Eocene and early Paleocene age, respectively. The ichnofossils of the Scolicia ichnocoenesis are different in the two basins. We also point out that extensive borings recorded from the late Eocene Somerset Formation of the White Limestone Group most probably came from the late Oligocene Walderston Formation. Copyright © 2015 John Wiley & Sons, Ltd.     

广西百色盆地东部古近系那读组湖相灰岩

百色盆地东部田东坳陷那坤地区古近系那读组三段下部发育一套数米至数十米厚的湖相灰岩,岩石以浅灰色-灰色、含大量的螺蚌化石和具核形石结构为特征,间夹有薄层的泥岩、钙质泥质粉砂岩。本文在实测地表剖面和详细观察岩心的基础上,仔细研究了此套灰岩的岩石学特征。依据丰富的原生沉积构造、古生物化石标志以及沉积地球化学、测井相特征将湖相灰岩的沉积相划分为滨湖、颗粒滩、浅湖三个亚相以及灰泥坪、沼泽、颗粒坪、滩缘、滩核、滩间水道、灰泥浅湖、泥质浅湖等八个微相,并详细地研究了各微相的沉积特征。结合该灰岩的区域分布和沉积相的平面展布格局指出沉积相主体属于浅湖的颗粒滩,并提出了相应的沉积相模式。     

济阳坳陷东营凹陷古近系沙河街组沉积相

济阳坳陷东营凹陷的主要含油层系为古近系沙河街组。沙河街组各段沉积相的展布各具特征,演化序列清楚。沙四段早期主要发育冲积—洪积扇,分布于湖盆的边缘地区;沙四段晚期,受北断南超的箕状构造背景控制,由北向南依次发育了近岸水下扇、滑塌浊积扇、半深湖相和滨浅湖濉坝相沉积。沙三段沉积时期是三角洲发育的鼎盛时期,三角洲的主体主要分布于凹陷的东部和中部地区,伴随着三角洲自东向西的推进及湖盆范围的不断缩小,沉积类型由早期的三角洲—滑塌浊积扇、三角洲—坡移浊积扇体系向晚期的河流—三角洲体系演化。南部斜坡带以河流相沉积为主,北部陡坡带垂向上由近岸水下扇—滑塌浊积扇、三角洲和辫状河三角洲组成。经过沙三段沉积时期三角洲等的填平补齐作用,到沙二段沉积时期以河流相沉积为主,只在凹陷西部的利津洼陷发育小规模的三角洲—浅湖相沉积。沙—段沉积时期湖盆发生大规模湖侵,物源供应减弱,以滨、浅湖相沉积为主,在凹陷南部边缘发育有滩坝相沉积。     

北部湾盆地乌石凹陷东区始新统流三段水进型扇三角洲沉积特征

北部湾盆地乌石凹陷东区流沙港组三段岩性相对复杂,沉积差异大,横向变化快,连通性差,深入研究流沙港组三段沉积物源和沉积特征对油气勘探开发具有一定的指导意义。在系统的岩心观察与精细描述基础上,结合测井、地震和分析化验资料,针对研究区流沙港组三段沉积物源、沉积相类型及展布特征展开研究。综合分析认为,流沙港组三段物源来自于北部高地势地区,发育相对近物源的水进型扇三角洲沉积,砂体厚度较大,相带窄,相变快,其中三角洲前缘可进一步划分为水下分流河道、河口坝、席状砂、分流间湾等4种沉积微相;在物源分析、井震约束的基础上,依据井震结合含砂率等值线,同时结合测井平面相、地震反射结构、地震构型信息等,综合绘制研究区沉积微相平面展布图,确定了研究区流沙港组三段"大前缘小平原"的沉积特征,并最终建立了该区扇三角洲沉积模式,为乌石凹陷东区流沙港组三段油气勘探开发和储量计算提供了借鉴。