摘要:

AbstractThe Fishguard Volcanic Complex represents an important volcanic episode which occurred within the Welsh sector of the British Caledonide region during early Ordovkian times. A variety of extrusive and contemporaneous intrusive rocks are present, ranging in composition from basic, through intermediate to acidic. Mineral and whole‐rock chemical analyses have been determined on a representative suite of rocks from the complex and, despite secondary alteration effects, the original tholeiitic characteristics of the suite can be discerned. The variation observed is considered to result largely from low‐pressure crystal fractionation, although the origin of the acidic magma remains speculative in view of subsequent extensive recrystallization. The rocks of the Fishguard Volcanic Complex formed in the Welsh Basin, which has been likened by earlier workers to a marginal basin. Comparison of the geochemical characteristics of the Fishguard Volcanic Complex with that of documented marginal basin rocks appears to favour this content

ISSN:0072-1050    

DOI:10.1002/gj.3350170102

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe numerous coal clasts in the late‐Pleistocene fluvioglacial Lleiniog Gravels of eastern Anglesey contain a varied assemblage of Westphalian A (and possibly also early Westphalian B) spores. Directional sedimentary structures indicate that the meltwater currents which deposited the gravels came mainly from the north and east, while glacial striae and erratic trains indicate that the parent (? Devensian) glacier flowed from the northeast. Consideration is given to the possibility that the coal clasts were derived from the breaking‐up, fairly locally, of far‐travelled rafts of Coal Measures. It is concluded, however, that the most probable explanation is still Greenly's (1919) postulate that the source is a yet‐to‐be‐identified submarine outcrop situated only a few kilometres northeast

ISSN:0072-1050    

DOI:10.1002/gj.3350170103

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractOn the southwest‐facing slopes of a bedrock ridge lying between Cardigan Bay to the north and the Afon Teifi to the south stands a group of hills in which 30‐35 m of cross‐laminated and parallel‐laminated sands with lenticular upward‐fining gravel sequences are overlain by 10‐12 m of gravel in a single foreset bed. The sediments mantle a surface of till sloping gently toward the southwest, were transported toward the southwest (across one margin of the Afon Teifi valley), and were cut by a system of densely arranged conjugate normal faults striking northwest‐southeast.The lenticular gravels and fault system suggest that the deposits accumulated as a glaciofluvial outwash spread, and on top of an ice‐lobe that became isolated in the Teifi valley during the downwasting of a glacier which had occupied Cardigan Bay and much of the country to the south. The large gravel foresets capping the succession are the only indication at Banc‐y‐Warren of the former existence of a lake, but neither a large nor deep body of wate

ISSN:0072-1050    

DOI:10.1002/gj.3350170104

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractTraditional methods of studying natural folds are reviewed. A new method of describing cleavage attitude in folds is presented; the β plot. The combined graph of dip isogon angle ϕ (Hudleston 1973) and cleavage angle β is proposed as a linked classification of fold and cleavage geometry. Plots of β and βϕ are given for three natural fold examples. The classification is extended to the geometry and strain attitude (βϕ5) of two finite‐element models and the classical folding models. Results are compared and some tentative conclusions drawn on the relationship of cleavage, theXYplane of strain and di

ISSN:0072-1050    

DOI:10.1002/gj.3350170105

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350170106

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350170108

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350170101

出版商:John Wiley&Sons Ltd    

年代:1982

数据来源: WILEY