摘要:

AbstractLogging 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 col

ISSN:0072-1050    

DOI:10.1002/gj.3350300103

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractCarboniferous rocks in the north Solway onshore outcrop show evidence of hydrocarbon migration. Oil residues occur as intergranular bitumen in sandstones, thoriferous bitumen nodules in sandstones and uraniferous bitumens in fractures associated with the North Solway Fault at the northern margin of the Solway Basin. Oil was emplaced in sandstones after the dissolution of dolomite, calcite and clay cements. The radioelement‐rich bitumens represent deposition following interactions between migrating hydrocarbons and metalliferous fluids. The close proximity of the Caledonian Criffel granodiorite, unroofed by Carboniferous times, suggests that the pluton was the source of uranium and thorium. Hydrocarbon source rocks are identified further east in the more complete succession exposed in the Esk Valley region, along with further oil residues. Time‐temperature modelling suggests that oil was generated from Lower Carboniferous source rocks during the Permo‐Triassic. Chemical age dating of uraninite in bitumen yields early Jurassic ages, which may reflect the time of hydrocarbon migration along the North Solway Fault system, and may be related to a mid‐Jurassic episode of regional uplift. Analyses of thorite in bitumen nodules give a wider spread of data, probably due to the migration of daught

ISSN:0072-1050    

DOI:10.1002/gj.3350300104

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractProgressive thermal demagnetization of samples from the Tan y Grisiau granite defines a coherent easterly positive characteristic remanence (D/I= 124.9/60.3°;, 42 samples,R= 40–51, a95= 4.8°;) residing in magnetite. An ancient reversal of magnetization is recovered in the highest blocking temperature spectrum of a few samples and suggests that a cooling‐related dipolar axis is recorded by this pluton. Only facies of the granite which have been reddened, probably by submagmatic streaming, have recorded a stable remanence. Adjustment for tilt yields a very steep remanence (D/I= 193/88°;) incompatible with any known Early Palaeozoic and younger field direction from Britain. Thein situremanence has a similar declination to the primary magnetization in Late Ordovician dolerites from the Welsh Borderlands and yields a comparable palaeolatitude (41.5°;S). It is concluded that the Tan y Grisiau pluton was magnetized in Late Ordovician times after deformation. Folding in this region is therefore interpreted to be substantially of Taconic (Late Ordovician) origin and not Acadian in age. As bothin situand tilt‐adjusted remanence directions are incompatible with Silurian and younger palaeofield directions from Britain, the pluton is interpreted as a subvolcanic component of the North Wales igneous province. Large anticlockwise rotation of Avalonia is identified between Late Ordovician and Late Silur

ISSN:0072-1050    

DOI:10.1002/gj.3350300105

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe simplest magnetic model for the upper 20 km of crust in central Ireland is of two layers. A thin, weakly magnetic upper layer carrying a number of magnetic bodies that can be related to surface geology overlies a magnetic crustal zone whose gross magnetization increases towards the north. The deeper trace of the lapetus Suture in central Ireland forms the boundary between a more magnetic northern crustal area and a less magnetic southern area. A pre‐Carboniferous major dextral offset of this suture boundary occurs in the Limerick area. The suture is traced beneath the Dingle peninsula in the far south‐west of Ireland.In east‐central Ireland, between the Iapetus Suture and Southern Upland Line, the crust contains a large, south‐dipping magnetic body with no surface expression, which produces the Virginia magnetic anomaly.The development of magnetic bodies — in particular, volcanic rocks of Carboniferous age — has been controlled by regional stress patterns. The major volcanic centre at Limerick lies at the intersection of two major Caledonian block fault systems just to the north of the surface trace of the Herc

ISSN:0072-1050    

DOI:10.1002/gj.3350300106

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe orientations of elongate gutter casts occurring in inner shelf storm deposits of the Proterozoic Bijaygarh Shale Formation, India reveal a modal population oriented roughly parallel to the average trend of the associated wave ripples. Assuming that the wave ripple trend approximately represents the orientation of the contemporary shoreline, the shore‐parallel gutters appear to have been formed by the geostrophic current. Some gutters oriented at high angles to the inferred shoreline presumably represent incision by wave orbital currents in a storm‐induced combined flow regime. The gutters also show variations in the style of incision and infill, which may be useful in distinguishing between gutters formed by wave orbital and geostrophic currents, independently of their orientation pattern with respect to the palaeo‐shor

ISSN:0072-1050    

DOI:10.1002/gj.3350300107

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300108

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300109

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300111

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300112

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300113

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY