ISSN:0072-1050    

DOI:10.1002/gj.3350150102

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA recent interpretation of the structural geology and chronology of the northwestern envelope of the Main Donegal Granite by Hutton (1977) is critically examined.Although many aspects of this analysis are sound, there remains serious doubt concerning Hutton's main conclusion that the intense deformation near the granite resulted from its forceful intrusion.

ISSN:0072-1050    

DOI:10.1002/gj.3350150103

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractDrift deposits exposed in a large open cut are described. The basal member of the sequence consists of bedded sandy gravels, and these are overlain by a grey silty sand containing abundant striated pebbles and boulders. The uppermost deposit consists of a brown poorly sorted drift containing silty and sandy lenses. Analysis of the texture, index properties and densities of the sediments, together with the shape, lithology and fabric of the contained pebbles suggests that the basal gravels were deposited by subglacial meltwater, the grey drift is a lodgement till, and the uppermost brown rubbly drift was formed by solifluction of the till, with the addition of frost shattered sandstone from the hilltop above. It is suggested that the glacigenic sediments are of Devensian age, and the solifluction layer Late Devensian.

ISSN:0072-1050    

DOI:10.1002/gj.3350150104

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA geological map of the Caradoc rocks of the Llanuwchllyn to Llanymawddwy area is presented and the geology of the area described in detail. Hitherto unrecorded outcrops provide important stratigraphical evidence which is used to redraw the Caradoc‐Ashgill Series boundary and many of the formational boundaries within the Caradoc Series.The stratigraphy of the area is revised to conform with the standard classification of the Caradoc Series in the Bala region. The only modifications are as follows: the Llaethnant Siltstone is proposed as a formational name for a group of beds which are broadly equivalent to the Glyn Gower Formation but which represent a distinct facies. The greater part of the Nod Glas Formation north of Dinas Mawddwy is shown to be laterally equivalent to the upper part of the Gelli‐grin Formation; it is also subdivided into two members, the Dyfi Mudstone and the Corris Shale, differentiated on lithological and faunal grounds. The stratigraphy of the Dinas Mawddwy area is also amended.Faunal elements (genera) new to the Caradoc Series of this area, and to Wales, are no

ISSN:0072-1050    

DOI:10.1002/gj.3350150105

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractCored boreholes in the central part of the Cheshire‐Shropshire basin form the basis of a sedimentological description of three separate parts of the Keuper Marl succession. The uppermost sequence examined is the lower part of the Middle Keuper Marl within which blocky silty mudstones and well laminated mudstones and siltstones form a rhythmically alternating pattern. Similar alternating patterns are described from the Lower Keuper Saliferous Beds and the top of the Lower Keuper Marl although, in these, the alternations are interrupted to various degrees by halite rock. The blocky and laminated facies are considered to have accumulated in emergent and flooded conditions respectively, the alternations reflecting eustatic variatio

ISSN:0072-1050    

DOI:10.1002/gj.3350150106

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThin beds of pale green and grey ‘claystone’ in the Birkhill Shales (Lower Silurian) of County Down are positively identified as bentonite. In the overlying turbidites, previously regarded as entirely of sedimentary origin, numerous metabentonites demonstrate continuing Silurian vulcanicity.The metabentonites contrast with the enclosing sediments in mineralogy and geochemistry. Illite, with subsidiary chlorite, is the chief alteration product of the primary volcanic glass, and comprises two co‐existing polymorphs. Clay‐grade 1Md mica is derived from montmorillonite, and a coarser 2M variety may be an anchimetamorphic alteration of the former. Some beds additionally contain accessory phenocrysts of orthoclase, oligoclase, biotite or chlorite, and small amounts of apatite and ilmenite. Statistical analysis of the geochemical data indicates that primary alteration of volcanic glass to bentonite was accompanied by relative enrichment of Al, K, Rb, Zr, Nb, and Y, and depletion of Na; additional enrichment of K and Rb occurred with collapse of mixed‐layer clay to illite during Caledonian anchimet

ISSN:0072-1050    

DOI:10.1002/gj.3350150107

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350150109

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350150110

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350150101

出版商:John Wiley&Sons Ltd    

年代:1980

数据来源: WILEY