摘要:

AbstractThree hornblende‐bearing intrusive masses consisting mainly of cumulate rocks derived from a water‐rich, alkali‐basalt magma are described. They probably all belong to one Lower Palaeozoic 'sill‐like' intrusion with an original sloping floor. The sequence is divided into nine zones, and three major, and numerous minor units are recognized. Deuteric activity produced important alteration sequences, while Caledonian regional metamorphism only caused substantial alteration to the mineralogy in the marginal zones of the in

ISSN:0072-1050    

DOI:10.1002/gj.3350070102

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThree interstratified pyroclastic deposits in the Caradocian marine sequence around Bala (N. Wales) are investigated. Their petrology is used for identification and correlation.The Cefn Gwyn Ash is a vitric tuff, locally indicating subaerial deposition. The Frondderw Ash is the product of subaqueous pyroclastic flows, giying evidence of very short‐lived volcanic activity. The Pont‐y‐Ceunant Ash is a waterlaid vitric crystal tuff. Lateral changes in lithology allow a north‐easterly source‐area to be inferred for the former two members. Sedimentary structures show partial emergence of the area during Soudleyan times.The highest member, the Pont‐y‐Ceunant Ash, is restricted to the south‐w

ISSN:0072-1050    

DOI:10.1002/gj.3350070103

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractTrace fossils are recorded from eight localities within Upper Cambrian (Ffestiniog Stage) strata in North Wales. Trilobite furrows (Cruziana), resting impressions (Rusophycus), walking and striding tracks (Diplichnites), sideways grazing tracks (Dimorphichnus) and swimming grazing marks (Monomorphichnus, gen. nov.) are described, largely on the basis of over 500 collected specimens, and are figured together with examples of other trace fossil genera includingRouaultia, PhycodesandMonocraterion.The trilobite traces are used to investigate the varied methods of locomotion of the animais. They also indicate the morphology of some of the trilobite hard and soft parts from which it is inferred that most of these traces were probably made by a population consisting of a small number of closely allied species of trilobites belonging to the Olenid family.

ISSN:0072-1050    

DOI:10.1002/gj.3350070104

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractStructural lineations of varying orders have been mapped for the full extent of the Welsh uplands where in some areas their clear impress in the micro‐relief has revealed minor structures not previously described in geological literature. Although significant variations in the strike of these structurally induced breaks of slope may be noted they display the more typical Caledonoid alignments (NE—SW or NNE—SSW) in nearly 60 per cent of the total area of the country. The dominance of these trends has been somewhat accentuated by the fact that even along the northern edge of “Armorican” South Wales, where low dips are a feature, a NE–SW grain is also evident in extensive tracts of the prevalent

ISSN:0072-1050    

DOI:10.1002/gj.3350070105

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractNodules enriched in hydrocarbon occur sparingly in a subarkose bed of Namurian (?Kinders‐coutian) age near Heysham, Lancashire. The nodules are commonly spheroidal to ellipsoidal (1‐9 cm across) and are composed of alternating shells of hydrocarbon‐rich and hydrocarbon‐poor sandstone. Irregular impregnations and pellets are also formed from hydrocarbon. The hydrocarbon is infusible, insoluble in CCl4, CS2and petroleum naphtha, and is classified as a pyrobitumen. Ash content averages 22.1% and the ash contains major V; subordinate Fe, U, Ca; minor Pb, Ti; traces of Ba, Mn, Zr, Ga, Y, Sr, Ni and Th. Sulphide inclusions in the hydrocarbon are comprised of chalcopyrite and pyrite. Hydrocarbon, commonly with illite, replaces primary sandstone matrix and clastic grains. The nodules may have formed as periodic structures (cf. Liesegang rings) with precipitation from thixotropic hydrocarbon compounds. The available evidence is insufficient, however, to postulate with any certainty the origin of the hydrocarbon. It may have formed syngenetic accretions with clastic detritus or alternatively it may have been introduced after deposition of the sandstone, although no feeders have been o

ISSN:0072-1050    

DOI:10.1002/gj.3350070106

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractStrata ranging from Arvonian to Llanvirnian are described. These rocks outcrop in a number of cylindrical or periclinal folds trending NE‐SW. The lowest rocks are voicanic and pass upwards into mainly coarse marine sedimentary rocks intercalated with thin turf bands and ignimbrites. These lowest Cambrian rocks must have been deposited in vcry shallow water while the ignimbrites would have been laid down on land. The slates of the Nantlle slate belt are overlain, in part conformably, by the Cymmffyrch (Bronllwyd) Grit of upper Lower Cambrian‐Middle Cambrian age, and this is overlain by thick Upper Cambrian slates and quartzites in the east of the area. No Arenig rocks are exposed as the Ffestiniog slates are immediately overlain by Llanvirnian.Two sets of folds are seen: the first (F1) phase includes mainly cylindrical or periclinal folds with steep limbs and an associated axial planar cleavage (S1) which are the basis of the regional structure. Later (F3) small‐scale folds produced flexure of the (F1) folds and associated with the later movements is an S3crenulation cleavage. The riebeckite microgranite of Mynydd Mawr is briefly desc

ISSN:0072-1050    

DOI:10.1002/gj.3350070107

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe secondary flow and transverse changes of water depth in curved stream channels are exploited to develop a quantitative, partly empirical model of the way lithology varies vertically in deposits accumulated through processes of lateral deposition. According to the model, grain size decreases upward in a lateral deposit and the sedimentary structures change from those denoting large stream powers upward to kinds indicative of small powers. The model also shows that the proportion of flat‐bedded sand‐grade material in a lateral deposit is essentially independent of stream power but controlled by channel curvature and hence general sinuosity. The predictions of the model compare satisfactorily with the characteristics of selected coarse members in fining‐upwards cycles of fluviatile origin from Devonian strata in Britain and North America. The model is thought to have value as a tool for environmental interpreta

ISSN:0072-1050    

DOI:10.1002/gj.3350070108

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe metamorphic rocks forming the area are divided into four groups separated by easterly dipping shear zones. The two western groups are orthogneisses and the eastern two are metasediments. The structures indicate movements from east to west with the most westerly group of gneisses having been a stable block during the movements. The metamorphic and structural events in the area are considered to be part of the Caledonian Orogeny. A Devonian granophyre is intruded into the metamorphic rocks. Small areas of Devonian type sediments occur overlying the metamorphic rocks.

ISSN:0072-1050    

DOI:10.1002/gj.3350070109

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThe Borrolan Complex comprises earlier and later rock suites which are separated by an intrusive junction. The earlier suite forms a conformable sheeted complex which has been punched through by a later plug‐like body and includes several distinct magma types; while the later suite differentiated gravitationally in place. Field and microscopic evidence suggests that some of the earlier rocks were emplaced prior to the principal movements on the Assynt Thrust Plane, while the later suite post‐dates the development of the Assynt Thrust, although it is affected by a deformation. It is suggested that the emplacement of the greater bulk of the Borrolan rocks after movement on the Assynt Thrust Plane had ceased excludes the possibility of the Borrolan, and nearby Loch Ailsh, intrusions being the trigger mechanism which set off the great duplication of strata in the Assynt Culminat

ISSN:0072-1050    

DOI:10.1002/gj.3350070110

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY

摘要:

AbstractThis magnalithofacies, which forms the bulk of two formations, the Bunter Pebble Beds and the Lower Keuper Sandstone, is described and interpreted as the deposits of former low‐sinuosity, largely braided, streams which flowed across a regional palaeoslope inclined to the north‐west. Arid blocks of the Welsh and Pennine Massifs lay to the west and east. Lithofacies A, conglomerate breccia and gravel, is interpreted as a deposit of former channel floors and sometimes bars. Lithofacies B crossbedded pebbly coarse sandstone, formed from large‐scale ripples developed on channel (? braid) bars of flood courses, whilst lithofacies C, argillaceous finer sandstone, represents the large‐scale ripples of quieter channels at lower stage and discharge. Lithofacies D, interbedded fine sandstone and shale, formed a riverplain topstratum deposit and, rarely, a levee. Lithofacies E is similar to D except that the sandstone is coarser and injects the mudstones repeatedly. Lithofacies F, red shales and mudstones (largely the ‘marl’ bands of former authors), may be laterally restricted or extensive. The former bands represent deposits of bar swales and abandoned cut‐off channels of varying stage: the latter suggest the development of a riverplain topstratum. Lithofacies X, soft fine sandstone, is aeolian. These lithofacies are arranged in vertical repetitions of varying thicknesses which are often asymmetric. Allocyclic climatic influence, reflected in varying discharge and sediment load under conditions of net accretion and steady subsidence, is regarded as a dominant factor in the origin of miocycles, megacycles and magna‐cycles, though in smaller repetitions the possibility of channel wandering, and in magnacycles the influence of tectoni

ISSN:0072-1050    

DOI:10.1002/gj.3350070111

出版商:John Wiley&Sons Ltd    

年代:1970

数据来源: WILEY