摘要:

AbstractThe uppermost Whitcliffian strata of the Welsh Borderlands record the final phase of marine sedimentation in the Silurian basin and shelf environments. They give way transitionally to the succeeding non‐marine Lower Old Red Sandstone. As a contribution to the understanding of the change from marine to continental facies, the magnetic fabric method was used to obtain palaeocurrent data for the uppermost Whitcliffian. The results confirm that the uppermost Whitcliffian palaeocurrent pattern is essentially “Silurian” in character and does not foreshadow the deltaic and littoral patterns of sediment distribution observed in the basal Old Red Sand

ISSN:0072-1050    

DOI:10.1002/gj.3350080201

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThree gravity traverses across the eastern half of the South Wales Coalfield indicate a local, elongate, negative Bouguer anomaly of a few milligals amplitude bordering the southern rim. The anomaly has a maximum amplitude of 4 mgal near Maesteg and attenuates eastward, dying out in the vicinity of the East Crop. Two possible geological causes of the anomaly are examined, namely a local thick sequence of normal Upper Carboniferous strata and a discrete, low‐density body of Carboniferous age with no apparent surface expression. The former, uncontroversial explanation requires rock densities at variance with measured values. In the case of the hypothetical low density body which can explain the anomaly, a variety of possible ages and configurations are discusse

ISSN:0072-1050    

DOI:10.1002/gj.3350080202

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe Pleistocene rock‐stratigraphic record is accorded more or less traditional time‐stratigraphic interpretation which was held widely before application of an Irish developmental model in 1960. The following sequence of events are recognised: (1) Complete glaciation, of indeterminate age, which antedated the raised beach interglacial. (2) The raised beach episode which is shown to be the last (Ipswichian) interglacial. (3) The last (Devensian/Weichselian) glaciation, followed by possible readvance in northwest and northeast Wales; prior and subsequent to glaciation periglacial conditions obtained. It is shown that the Irish model, relying heavily as it does on the equation of rock and time stratigraphy, is inapplicable in Wa

ISSN:0072-1050    

DOI:10.1002/gj.3350080203

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractLocal developments of the Upper Ordovician Sholeshook Limestone are briefly described and inter‐correlated on the basis of their trilobite faunas. The base of the formation is diachronous and overlies the Mydrim Shales unconformably. The base of the normally succeeding Slade and Redhill Mudstones is also diachronous and to the north and west of Haverfordwest this formation contains strata laterally equivalent to the main part of the Sholeshook Limestone.It is suggested that the Sholeshook Limestone falls within the Cautleyan Stage of the Ashgill Series. This extends the range of several trilobite species normally regarded as Middle Ashgill (Rawtheyan) indice

ISSN:0072-1050    

DOI:10.1002/gj.3350080204

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractThe Aymestrey area displays changes in facies, faunas and thicknesses which can be related to its position on the shelf edge during later Silurian times. The Wenlock Limestone becomes an alternation of limestones and mudstones. The Lower and Middle Elton Beds, however, are substantially similar to their development at Ludlow. The Upper Elton Beds and the Bringewood Beds thin westwards within the area, probably due to non‐deposition or erosion on a ridge at the hinge between shelf and basin. The most striking change is the rapid westward passage of the Aymestry Limestone facies of the Upper Bringewood Beds into siltstones, which are considered to be shallow‐water deposits and not basinal. The Leintwardine Beds exhibit a westward thickening, and slumping is developed in the Lower Leintwardine Beds; the faunas relate more to the basin facies than to the shelf. The Whitcliffe Beds thicken markedly westwards but retain their shallow‐water characteri

ISSN:0072-1050    

DOI:10.1002/gj.3350080205

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractSeventy‐three new exposures of Upper Silurian rocks along forestry roads in the Ludlow area are recorded and an indication is given of their stratigraphical significance and of their potential research valu

ISSN:0072-1050    

DOI:10.1002/gj.3350080206

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractEvidence from 1,450 boreholes and coastal seismic profiles adds further precision to the form of the sub‐drift channels of South Lancashire and North Cheshire. These channels resemble sub‐aerial valleys, but commonly have ungraded profiles locally reaching at least 289 ft (87 m) below O.D. In some places they are still below present sea level, 40 miles (64 km) inland. It is suggested that previous views of origin can be reconciled by considering them to be river valley Systems, partly rejuvenated by low Pleistocene sea levels, and locally modified by sub‐glacial melt

ISSN:0072-1050    

DOI:10.1002/gj.3350080207

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractSix species of Bryozoa, three new, of Upper Visean age are described from Tullaghoge, County Tyrone, Ireland. The assemblage suggests shallow water conditions subject to wave action. The new species areDyscritella tyronei, Stenophragmidium incrustans, andSulcoretepora? ramosa.

ISSN:0072-1050    

DOI:10.1002/gj.3350080208

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractSize sorting of shells and valves of transported death assemblages ofMytilus edulisis shown to have taken place, and greatly affected size‐frequency distributions of shell accumulations deposited in a beach environment. Selective transport and deposition of different size grades gives histograms which may be strongly skewed or multimodal, and include numerous small shells. The usually predicted bell‐shaped distributions for sorted assemblages are not always produced. Little evidence of growth and mortality rates can be deduced with confidence from the transported assembla

ISSN:0072-1050    

DOI:10.1002/gj.3350080209

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY

摘要:

AbstractA review of certain late‐stage textures in subaerial, submarine and lunar extrusive rocks is presented, together with a genetic classification of vesicles. The term paravesicle is introduced for hollows in lavas caused by the introduction of a gaseous phase into the lava after extrusion. Examples taken from the andesitic lavas of the Borrowdale Volcanic Series are used to illustrate the usefulness of studying such feature

ISSN:0072-1050    

DOI:10.1002/gj.3350080210

出版商:John Wiley&Sons Ltd    

年代:1973

数据来源: WILEY