摘要:

AbstractThis paper describes an unusual occurrence of igneous material as clasts in dyke and pipe breccias associated with late Caledonian minor intrusions. It is shown that the clasts were in a plastic condition when incorporated into the breccia rock. These igneous clasts were derived from magma disrupted at depth and then transported into the fluidized breccia columns where they were mixed with large numbers of clasts derived from the quartzite wall‐rocks. Textures and planar fabrics developed during collapse of the fluidized system are described and shown to be separable from the later compaction associated with extensive pressure solution of the fine matrix. Most Caledonian breccia pipes lack igneous clasts and it is considered that this group of breccias represent the rarely‐preserved boundary zone between active magma and breccia syst

ISSN:0072-1050    

DOI:10.1002/gj.3350190302

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractFor the first time the stratigraphically important brachiopodDavidsonina septosa(Phillips) has been located in thickly bedded pale grey, late Asbian limestones in North Wales. Above these limestones are thinly bedded dark grey Brigantian limestones, which have yielded a rich and diverse coral‐brachiopod fauna, includingLonsdaleia floriformis(Martin). The Girvanella Nodular Bed is recorded for the first time in this region, some distance above the base of the Brigantian. The boundary between the two major lithofacies is marked by a prominent palaeokarstic surface and coincides with a significant faunal change, both in the macrofauna and microfauna that serves to identify the boundary between the Asbian and Brigantian Stages. The discovery within late Dinantian successions of certain diagnostic corals, brachiopods, and algae outside their accepted restricted stratigraphical ranges, casts doubt on their reliable use as Asbian or Brigantian zone fossil

ISSN:0072-1050    

DOI:10.1002/gj.3350190303

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIn the English Lake District lithostratigraphical classification has not kept pace with either the international and national codes or the code of the Geological Society (Hollandet al.1978). Probelms arise, firstly, from acceptance by several of those working in the area, of terms used in by‐gone days, such as ‘Borrowdale Volcanic Series’, and secondly, and more importantly, because individuals have specialized on certain parts of the sequence (the Skiddaw Slates, the Coniston Limestone, etc.), and have erected classifications for these rocks without reference to other parts of the succession. These classifications are examined and modified in such a way that the lithostratigraphical subdivisions are consistent for the whole of the Lower Palaeozoic sequence of the Lake District, and also relate to the international code as it is applied in other regions. The basic Lake District stratigraphical terminology of the last century is, however, retained in allitsessen

ISSN:0072-1050    

DOI:10.1002/gj.3350190304

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractTrace fossils are recorded at two localities from the ‘Armorican Quartzite’ (Lower Ordovician) in the Salamanca area, western Spain. Sixteen ichnospecies, belonging to twelve ichnogenera, are described; all ichnospecies occur in the upper part of the unit, only four in the lower part. The ichnogenera compriseArthrophycus, Cruziana, Daedalus, Didymaulichnus, Diplichnites, Diplocraterion, cf.Gor‐. dia, Monomorphichnus, Muensteria, Palaeophycus, Planolites, andRusophycus.The presence ofCruziana furcifera, C. goldfussi, C. rugosa, andC? cf.imbricataindicate that the upper part of the unit is of Arenig age. The lower part has yielded only the two former ichnospecies and may extend down into the Tremadoc. The species ofCruzianaand their stratigraphical significance are disc

ISSN:0072-1050    

DOI:10.1002/gj.3350190305

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractAround Quebec City the lowest Trenton Group sediments rest directly upon a highly irregular Precambrian surface and represent the deposits of a high‐energy, irregular, rocky shoreline which developed as the Ordovician sea onlapped a major positive topographic feature known as Montmorency Promontory. The complicated lithofacies mosaic developed along this shoreline consists of: (1) Arkosic sandstones, representing reworked regolith and marginal marine elastics; (2)Solenoporagravels, which comprise partly reworked colonies from the bare rock substrate and partly reworked algal maerls; (3) Fine‐grained limestones, which were deposited in low energy environments between and in the lee of numerous islands and shoals; (4) Skeletal limestones, representing island fringing shoals and ephemeral beaches, with extensive thickets of the ramose bryozoanHallopora;(5) Bryozoan liméstones, which represent low‐energy, subtidal deposits with abundant delicate bryozoans; and (6) Coquina limestone lenticles, which accumulated in channels cut into the subtidal Bryozoan limestones. The absence of older Ordovician and Cambrian sediments in the vicinity of Quebec City indicates that Montmorency Promontory at the time of deposition of these Trenton deposits was probably manifested as a rugged archipelago. This represented the remnant of large‐scale topographic highlands which had developed at the continental margin during the late Precambrian in association with extensional rifting, transform faulting, and the inception of the Iapetus Ocean. Gradual subsidence of this topographic high and the development of the rocky shoreline relates to the subsequent development of a compressional system and initiation of ocean closure in the early Middle Or

ISSN:0072-1050    

DOI:10.1002/gj.3350190306

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190308

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190309

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190310

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190311

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350190313

出版商:John Wiley&Sons Ltd    

年代:1984

数据来源: WILEY