摘要:

AbstractFor the first time Arundian and Holkerian faunas have been recognized from the lower part of the Dinantian succession in North Wales. These limestones and sandstones, hitherto regarded as Asbian, have a macrofauna and microfauna confirming their older age, and this discovery' has necessitated a revision of the palaeogeography in the North Wales region. Biostratigraphical correlations have been made with contemporaneous platform successions in the Central, Northern, and Southwest Provinces of Britain. A new genus and species of foraminifer,Groessensella moldensis, is described.

ISSN:0072-1050    

DOI:10.1002/gj.3350190202

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe stratotypc of the Arenig Series (Ordovician System) and its boundaries are critically re‐examined. The lithostratigraphy and biostratigraphy of the Tremadoc, Arenig, and Llanvirn age rocks at Arenig Fawr, North Wales that were constructed by Feamsides in 1905 are amended. The Arenig Series at Arenig is represented by the Camedd Iago Formation which was established by Lynas (1973) in the Migneint area. Examination of the sparse graptolite faunas indicates that the type Arenig Series is incomplete,only the extensusZone having been recognized with certainty. There is a possible unconformity at the base and a probable unconformity at the top, and on present knowledge the succession cannot be correlated precisely with what are considered to be Arenig sequences elsewhere.It therefore may prove necessary to redefinethe Arenig Series at a more useful type section. It is suggested that the Carmarthen district may provide a suitable stratotyp

ISSN:0072-1050    

DOI:10.1002/gj.3350190203

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractGlacigenic sediments exposed at Rhosesmor, Clwyd, North Wales, were deposited in a small proglacial lake ponded by the stagnating margin of the Late Devensian Irish Sea icesheet. Three major fades assemblages are identified and show a prograding sequence of topset, foreset, and bottomset deposits associated with two Gilbert‐style deltas stacked one above the other. The lower delta is associated with a lake level at c. 180 m OD. A subsequent ice‐marginal readvance raised the lake to c. 192 m OD, drowned the lower delta and caused the growth of a second delta by an iceward shift of facies. It is estimated that the life of the lake was of the order of 90 years during which average sediment in‐fill amounted to some 4±104m3per

ISSN:0072-1050    

DOI:10.1002/gj.3350190204

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe Mweelrea Group (Llanvirnian) in the South Mayo Inlier, western Ireland, consists mainly of coarse shallow‐water sandstones with minor slates, cobble conglomerates, and ignimbrite tuffs. The Glenummera Formation at the base (up to 600 m), dominantly well‐cleaved slates with some slump features, was deposited in a slope to deep marine shelf environment. A coarsening upward sequence at its top reflects the interaction of fluvial and marine processes, coarse clastic sediments having prograded from the southeast. The rest of the Mweelrea Group (2100 m in the northwest) is dominated by coarse trough cross‐bedded sandstone with little evidence for channelling. Three lenticular marine slates (Glendavock, Uggool, and Glenconnelly Formations), up to 200 m thick, wedge out to the southeast. A humid alluvial fan‐fan‐delta model can explain many features of the Mweelrea Group. Fans built out to the northwest into a relatively small basin with negligible tides and moderate wave energy. Marginal sediments were reworked by waves, occasional storms, and a burrow

ISSN:0072-1050    

DOI:10.1002/gj.3350190205

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe uppermost part of the Ordovician succession in southeastern Murrisk, western Ireland, consists of coarse‐grained sedimentary rocks and tuffs, the Partry Group, hitherto subdivided into the Mweelrea Formation, unconformably overlain by the Maumtrasna Formation. The age of the lower part of the succession is late Llanvirn whilst that of the upper part is unknown. Evidence is presented to show that the two formations are lateral equivalents. Consequently the Mweelrea Formation is redefined and the Maumtrasna Formation becomes redundant. The revision of the stratigraphy enables a coherent sedimentological model for the group to be proposed. The sediments of the Mweelrea Formation were deposited on alluvial fans and distally‐equivalent alluvial plains and delta fans. The direction of sediment transport was towards the north and northw

ISSN:0072-1050    

DOI:10.1002/gj.3350190206

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractContemporaneous trilobite faunas from Rawtheyan rocks forming the local base to the Ashgill Series change in their generic composition along the outcrop between Bala and Corris. The change, although overall a very marked one, is progressive and is held to reflect original ecological control along a depth gradient between a locally elevated area around Bala and the deeper central part of the Welsh Basin. Along this intrabasinal slope three distinctive trilobite generic associations–theCeraurinella‐EncrinuroidesAssociation, theNankinolithus‐OpsimasaphusAssociation and theNovaspis‐cyclopygid Association–succeeded each other in gradually deeper water. Faunas of all three associations differ markedly from contemporaneous faunas of shallower shelf env

ISSN:0072-1050    

DOI:10.1002/gj.3350190207

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190209

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190210

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190211

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190212

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY