摘要:

AbstractRocks 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 s

ISSN:0072-1050    

DOI:10.1002/gj.3350270302

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractArundian mudbank complexes at Pollower and Carrickbaun in north‐west Ireland are described in detail. The two bank complexes developed on different fault blocks controlled and separated by the Curlew Mountain Fault system which was active during the Dinantian. The two mudbank complexes are composed predominantly of lime mudstone and wackestone textures with abundant peloids and intraclasts. Stromatactoid cavity systems in the banks are extensive and have multiple generations of geopetal internal sediment and radiaxial and bladed cryptofibrous calcite cements. These mudbanks are comparable with earlier Courceyan‐Chadian deep water Waulsortian mudbanks which accumulated on carbonate ramps. Components in the Pollower bank most closely resemble those in subphotic Phase C Waulsortian banks, whereas the Carrickbaun mudbank, which possesses dasycladacean algae, intraclasts and micritized fragmented bioclasts, indicates a much shallower environment ofin situcarbonate mud accumulation, comparable to the photic Phase D assemblages of Waulsortian banks. The difference in depositional setting is also reflected by their respective enclosing lithologies. The Pollower bank is surrounded by deep water black argillaceous wackestones and shales, whereas at Carrickbaun shallower water crinoidal packstones and grainstones are developed on the flanks and bank top. The Arundian mudbank complexes have many similarities with the Asbian mudbanks of north‐west Ireland and as such appear to represent an important ‘stratigraphic’ link in the continuum of deep water mudbanks between the two main periods of development in the early Dinantian (Waulsortian) and late Dinantian (Asbian/Br

ISSN:0072-1050    

DOI:10.1002/gj.3350270303

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe Broadford Beds comprise a basal carbonate‐dominated unit overlain by dark muddy sandstones and an upper cross‐bedded sandstone unit. The limestones include coralliferous and oolitic lithologies and the sandstones include pisolitic berthierine ironstones and abundant phosphate nodules. The Broadford Beds have a maximum thickness of 140 m and can be subdivided into 17 parasequences, each initiated by an approximately 20 m rise in relative sea level. Marine flooding surfaces are most readily recognized in the lower parts of the succession, where diagenetic data can be utilized to locate emergence surfaces. There is no diagenetic evidence of early emergence in the upper parts of the sequence, but a variety of sedimentological data can be used to identify parasequence boundaries. Deposition of the Broadford Beds occurred largely around the shores of a number of islands in the northern Hebridean area. These islands partly isolated the Skye–Applecross area from a deeper marine basin to the west, and this may have enhanced the formation of authigenic phosphates and iron silicates. It is possible to use the regional variability of parasequence thicknesses to investigate the role of active local tectonism in governing differential subsidence and sediment s

ISSN:0072-1050    

DOI:10.1002/gj.3350270304

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractInternal regions of orogenic belts may be characterized by an alignment of fold axes with mineral elongation lineations. This relationship is commonly interpreted as representing progressive tightening and rotation towards the shear direction of early buckle folds, the hinges of which were initiated orthogonal to this direction. Detailed structural analysis of lower amphibolite facies Dalradian metasediments of the Ballybofey (fold) Nappe, north‐west Ireland, shows that an intense S3schistosity is developed axial planar to mesoscopic and minor F3folds. In areas of low D3strain, F3fold axes plunge gently towards the north‐east, whereas in regions of greater strain plunges are towards the south‐east subparallel to the constant mineral lineation. Minor folds which initiated at angles of 70–80° from the mineral lineation subsequently rotated towards the shear direction in a consistent clockwise sense. Progressive and variable non‐coaxial deformation oblique to the original mean F3orientation has resulted in a unimodal distribution pattern of fold axes. Analysis of the angular rotation of fold axes enables estimates of the bulk shear strain to be evaluated and models of progressive deformation to b

ISSN:0072-1050    

DOI:10.1002/gj.3350270305

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractIn Volume 26, 7‐26 of the Journal, Dr D. M. D. James described the stratigraphy, sedimentology and structure of the late Ordovician to earliest Silurian succession in the core of the Tywi Anticline between the Sugar Loaf and the Wye Valley. He has used these new data to consolidate his previous model of a non‐depositional slope, established by Ashgill progradation of the shelf margin, separating basinal from shelf facies during the latest Ashgill and early Silurian (James 1983).Over the past four years, we have mapped the northern region of the Tywi Anticline, north‐east of the Chwefru Valley, as part of the survey of the 1:50000 Sheet 179 (Rhayader) (British Geological Survey (a) in press). Our results (Barronet al.1989; Davieset al.1991; Smithet al.1991; Waterset al.in press; Wilsonet al.in press) lead us to question aspects of James's Ashgill stratigraphy and the viability of his non‐depositional slop

ISSN:0072-1050    

DOI:10.1002/gj.3350270306

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270307

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270308

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270310

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270311

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270301

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY