摘要:

AbstractHydrocarbon shows occur in Cambrian sandstones in the Welsh Borderland. In Shropshire, sandstones of the Upper Comley Group in particular contain hydrocarbons infilling residual primary porosity and secondary porosity after leaching of feldspars. In the Malvern Hills, the Hollybush Sandstone is locally black due to an impregnation by hydrocarbons. Evidence from the distribution of hydrocarbons in other Lower Palaeozoic rocks and in Precambrian rocks in Shropshire suggests that they have migrated from hydrocarbon‐bearing Carboniferous sandstones. However, the source of hydrocarbons for the Hollybush Sandstone may be the immediately superjacent Upper Cambrian black shale

ISSN:0072-1050    

DOI:10.1002/gj.3350220302

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe Lower Carboniferous Pen‐y‐Holt Limestone of South Wales comprises about 300m of interbedded wackestones and lime mudstones.The wackestones are interpreted as relatively distal ‘turbidite‐like’ storm‐generated deposits and the lime mudstones as background deposits. The storms had a periodicity of about one per 9000–18000 years. They were deposited in a deep‐ramp carbonate environment at least 20–30km from the ancient shoreline and in about 100m water depth, and therefore probably below wave base. The ramp is estimated to have had an average slope angle of 0·5–1·0 degree.Unlike other previously described carbonate or siliciclastic storm deposits, the Pen‐y‐Holt Limestone storm deposits are totaly mud‐supported and generally lack internal sedimentary structures, yet contain large bioclasts such as crinoid ossicles. The simultaneous deposition of lime mud and crinoid ossicles from a storm‐generated turbidity current is hydrodynamically untenable. Thin‐section evidence however, suggests that the lime mud may have originally been deposited as peloids which have since been largely destroyed during diagenesis. Peloids and crinoid ossicles, it is suggested, could have been

ISSN:0072-1050    

DOI:10.1002/gj.3350220303

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractBoreholes recently drilled by the British Geological Survey provide the first extensive collection of fossil plants from the Newent Coalfield, Gloucestershire. They belong to theLobatopteris vestitaBiozone, indicating a late Westphalian D age. The Newent sequence is thus homotaxial with part of the Forest of Dean Coalfield, and supports the view of Wills (1956) that there was a ‘strait’ extending across St George's Land during the late Westphal

ISSN:0072-1050    

DOI:10.1002/gj.3350220304

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractPossible causes for the outflow of Windermere through the Leven valley instead of the Cartmel valley are discussed. An earlier seismic investigation of the problem by Coster and Gerrard (1947) is reviewed and shown to be inconclusive. Further geophysical surveying and mapping demonstrate a rock bar in the Cartmel valley, 3km southeast of Newby Bridge. This barrier is 21m above the present water level in Windermere. Blockage by glacial deposits is disproved and the probable history of the outflow discussed. It is concluded that the outflow from Windermere has used the Leven valley from an early stage.

ISSN:0072-1050    

DOI:10.1002/gj.3350220305

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThroughout most of its geological evolution Etna has been characterized by the eruption of lava flows of a predominantly hawaiitic composition, but within the stratigraphical record there are four major sequences of pyroclastic materials: the Acireale tephra and lahars (˜100000 B.P.); the ‘lower tephra’ and Milo lahars (both ˜26000 B.P.); the Biancavilla ignimbrites (15–15500 B.P.) and the ‘upper tephra’ (˜5000–6000 B.P.). This paper reports investigations carried out on these deposits in order to determine their stratigraphy, petrology, sedimentology, and likely origins. Whereas the Biancavilla ignimbrites were generated when a more evolved, gas‐charged magma (benmoreite) was being produced by the volcano, the other suites of pyroclastic deposits were erupted from hawaiitic magmas—similar to those that have characterized the volcano during historical times. These deposits resulted from two processes: violent strombolian activity producing lapilli‐rich. coarse, but well‐sorted sediments, and hydrovolcanism when the mixing of water and magma in the conduit, brought about more violently explosive activity, giving rise to highly fragmented, poorly sorted, airfall tephra and lahars. Conditions favouring hydrovolcanism occurred at times in the volcano's history when palaeoenvironment and palaeogeography were conducive to the retention of large amounts of surface and subsurface water. Although climates favouring the retention of water at high levels on the volcano have occurred on many occasions in the history of the volcano, at ˜26.000 and ˜5000‐6000 B.P. these occurred in conjunction with a construct of sufficient height and suitable configuration to allow storage of water and give rise to hydrovolcanic activity. The nature of the mechanisms responsible for the emplacement of these hydrovolcanic deposits is considered and it is concluded that airfall is the most probable process. Finally, the implications of this research for the assessm

ISSN:0072-1050    

DOI:10.1002/gj.3350220306

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe External Sierras of the southern Pyrenees represent the frontal thrust complex of a south Pyrenean thrust sheet which was active from the late Eocene to early Miocene. Triassic, Cretaceous and Eocene limestones, sandstones and mudstones involved in this thrusting can be divided into eight mappable units. Mapping and the construction of serial sections across the Western External Sierras show that the amount of southward translation of the thrust sheet increases eastwards from the thrust tip. There is an increased slip of at least 5km along 30km of the External Sierras. Structures show a progressive development from a “primitive” form in the west to a more complex thrust and fold geometry in the east. The general pattern is one of thrust and fold development in response to compression from the north. Backthrusting has occurred on the forward side of the frontal thrust complex. These backthrusts cut up section towards the north and form triangle zones where they intersect thrusts which cut up sections towards the south. The latest thrust movements deformed early Miocene fanglomerates and were out‐of‐sequence reactivations of earlier

ISSN:0072-1050    

DOI:10.1002/gj.3350220307

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractRegional and detailed gravity surveys over Carboniferous rocks in northeast Wales have revealed an elongated Bouguer anomaly low over part of the outcrop of the Cefn‐y‐Fedw Sandstone Group. The anomaly has a pronounced gradient over the boundary of these sediments with the limestones of the underlying Viséan Series, but downdip, to the east, the anomaly merges with the general decrease of Bouguer anomaly values. The anomaly can be explained if the thickness of the lower density Cefn‐y‐Fedw Sandstone Group increases abruptly along the margin of the outcrop of these rocks. Various explanations for this are considered including faulting, a syncline. and channel‐like deposits. The interpretation is further complicated by the presence of sandstones with densities varying between 2·2 Mg m−1and 2·6 Mg m−3Although a full explanation is not possible without further evidence, the existence of the Bouguer anomaly low necessitates a review of the nature of the Cefn‐y‐

ISSN:0072-1050    

DOI:10.1002/gj.3350220308

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350220301

出版商:John Wiley&Sons Ltd    

年代:1987

数据来源: WILEY