摘要:

AbstractThe Ordovician‐Silurian rocks at Garth, 30 km northeast of Llandovery, have been remapped. Within the siltstone‐dominated succession, the coarser Cwm Clŷd Formation is regarded as stratigraphically equivalent to the A1sandstone of Llandovery and has yielded a single specimen ofEostropheodonta hirnantensisfrom near the base in the northernmost exposures. The Formation rests with a stratigraphical break on fossiliferous Rawtheyan siltstones in the south but is underlain by later Rawtheyan and abundantly fossiliferous Hirnantian sediments (Wenallt Formation) further north where the succession appears continuous. Sedimentary and faunal evidence demonstrates the shallowing of the Ashgill sea before a transgression and deepening started in late Hirnantian times. The implications of the sequence in determining the systemic boundary are discu

ISSN:0072-1050    

DOI:10.1002/gj.3350160102

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350160103

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe riebeckite‐bearing rhyolite of Winkston Hill, Peebles, is shown to be peralkaline and may be named a pantellerite. Trace element comparison with other more altered members of the Tweeddale lavas from Wrae Hill suggests that the whole suite is peralkaline. It is thought most unlikely that the suite was developed in association with an Upper Ordovician subduction zone, and it was perhaps erupted on an oceanic islan

ISSN:0072-1050    

DOI:10.1002/gj.3350160104

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractJoints, minor faults and mineral veins were recorded at 334 stations between Kidwelly and Black Mountain, S. Wales. A systematic pattern occurs with joint sets striking at 360°, 340°, 290°, 250°, and 210°. Minor faults and shear planes exhibit both strike and dip‐slip displacements. The jointing is considered to have formed quite early during folding, and both joints and faults can be attributed to a principal compression acting almost N‐S and subparallel to bedding. Phases of dilation are recorded by sets of mineral veins. All the deformational structures are considered to be of Armor

ISSN:0072-1050    

DOI:10.1002/gj.3350160105

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractIn recent years the folding and cleavage seen in the Aberystwyth Grits has been ascribed to downslope movement in soft unlithified sediment, not to tectonic forces. A detailed examination of folded beds in a small part of the outcrop was undertaken to test this theory. It is concluded that the folding and cleavage was initiated by movement from a rising tectonic ridge, but that the sediments may not have been completely lithified at the time of folding.

ISSN:0072-1050    

DOI:10.1002/gj.3350160106

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractNew road cuttings have exposed a large part of the Merioneth Series. The rocks are low‐grade thinly layered metasediments which have undergone extensive buckling resulting in tectonic ripples, mullions, and crenulations. It is suggested that the periclinal form of these structures may be the result of buckling layered sequences with longitudinal and transverse zones of constraint (heterogeneities). The process is analogous to ‘quilting’ of thin metal sheets and the heterogeneities are perhaps due to layer thickness variation. There are two foliations; which may form a progressive sequence of cleavage development during the evolution of the fold

ISSN:0072-1050    

DOI:10.1002/gj.3350160107

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractSeabed samples, consisting of shale of Lower Liassic age and limestones of Upper Liassic age, have been recovered from the northwest flank of the St. George's Channel basin. These data have made possible the calibration of parts of lines 6 and 11 of the I.G.S. deep seismic survey. An updated and refined version of the geology of the south Irish Sea is presented which incorporates the new information and indicates the extent of the Precambrian and Lower Palaeozoic basement that is now thought to subcrop beneath the Pleistocene cover southwest of the Lleyn Peninsula. In addition the offshore extension of the Bala Fault is suggested to be an intra‐basin fault across Cardigan Bay and St. George's Channe

ISSN:0072-1050    

DOI:10.1002/gj.3350160108

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350160109

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350160110

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350160112

出版商:John Wiley&Sons Ltd    

年代:1981

数据来源: WILEY