摘要:

AbstractMarine turbidites, tuffs, black mudstones and conglomerates of the Cambro‐Ordovician Clew Bay Group, were deposited in the E–W elongate transtensional Clew Bay Graben that is centred on Clew Bay, NW Ireland. The group is characterized by extensive sedimentary deformation and mass movement on slides; olistostromes, autoclastic breccias and course proximal turbidites are interbedded with apparently less disturbed but often overturned sediments.The Clew Bay Group lies structurally above serpentinized dunite/harzburgite breccias, schistose carbonate peridotites, and other basic and ultrabasic igneous rocks that have ophiolitic geochemical affinities; the sediments may have been in part deposited upon oceanic crust. Ophiolites and sediments that now rest on the Clew Bay Thrust abut Silurian shallow water strata in which the main tectonothermal history, associated with sinistral transcurrent faulting along the thrust zone, is dated at about 410 Ma. The sole thrust dips northward and coalesces with a major deep structure along the Fair Head‐Clew Bay Line (FCL) that is the western continuation of the Highland Border Fault of Scotland. Blueschist relics in the Dalradian immediately to the north of the FCL indicate that subduction was active early in the history of the late Cambrian–early Ordovician Grampian orogeny. The Clew Bay Thrust was a sinistral, transpressional shear zone late in its history, but it probably originated as an obduction complex.The Clew Bay Group cannot be traced into sedimentary, metamorphic or structural continuity with the adjacent Dalradian to the north or Ordovician and Silurian rocks in the South Mayo Trough to the south. It should be considered as a distinct terrane (Clew bay Terrane) or a subterrane of Highland Border‐type rocks along the southern margin of the Grampia

ISSN:0072-1050    

DOI:10.1002/gj.3350240102

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractFragmental carbonate rocks are common in the Mesozoic and Tertiary succession of Mallorca, in the western Mediterranean. On the Formentor peninsula at the northeastern end of the Sierra Norte, two phases of fragmentation post‐date Liassic platform carbonate and its subsequent reworking, and predate deposition of marine Burdigalian sediments. Phase 1 fragmentation resulted in brecciated rocks with angular fragments often little displaced, cemented by coarse calcite. Brecciated rock passes into veined or unbrecciated rock over short distances. These breccias are interpreted as the products of collapse during solution of an evaporite after uplift during the early Tertiary. Phase 2 fragmentation is related to the unconformity with Miocene sediments and is interpreted as a product of karstic processes operating prior to subsidence and deposition of Miocene marine conglomerates. Multiple brecciation is common, yielding complex fragmental rocks, but permitting a relative dating of the two phases and other depositional and structural event

ISSN:0072-1050    

DOI:10.1002/gj.3350240103

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe late Chadian Foel Formation, previously thought to be confined to the Dyserth area of North Wales, forms a poorly exposed but persistent basal unit to much of the Dinantian crop east of the Clwydian Range, necessitating a revision of the local lithostratigraphy. The formation comprises a peritidal heterolith which, together with the lowest few metres of the overlying Llanarmon Limestone, yields microfossil assemblages diagnostic of theEoparastaffella Cf4α Subzone. Succeeding strata, containing the lowest archaediscid foraminifera, provide the first record of Cf4β assemblages from North Wales and establish an early Arundian age for these beds.The Foel Formation was deposited as an aggradational sequence on the northern flank of St. George's Land during a pulsed transgression which began in late Chadian times. The widely recognized basal Arundian transgression is represented by the contact between the Foel Formation and overlying platform carbonates. The latter overlap the Foel Formation in the southernmost part of the Clwydian crop demonstrating, for the first time, southwards onlap on the northern side of the Bala–Bryneglwys Fault Sys

ISSN:0072-1050    

DOI:10.1002/gj.3350240104

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractNew floral and faunal data from the oldest Dinantian limestones (Foel Formation) in the Dyserth area, suggest that these sediments are of Chadian age, rather than the Asbian age concluded by earlier workers. The basal late Chadian limestones rest conformably on Dinantian Basement Beds of ?Chadian age or older.The initial inundation of St. George's Land occurred during Chadian times, when shallow‐water marine limestones accumulated in the Dyserth area and further to the south, together with terrestrially derived siliciclastics, containing drifted plant fragments. Periodically, a restricted hypersaline lagoonal environment was established but an open marine, neritic environment with abundant stenohaline fauna prevailed in this area.These Chadian sediments accumulated on the proximal part of a carbonate ramp and are presumed to have passed laterally downslope into deeper water basinal facies with Waulsortian buildups of the Irish Sea Basin. In the later Arundian, a carbonate ramp–to–platform transition occurred, with widespread deposition of shallow‐water carbonates. In the Asbian this platform developed a rimmed margin, with buildups forming a linear belt between platform and basin.An almost complete Chadian to Brigantian Lower Carboniferous sequence can now be recognized in North Wales. This succession is comparable with the shelf succession in south Cumbria on the northern margin of the Irish Se

ISSN:0072-1050    

DOI:10.1002/gj.3350240105

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240106

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240107

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240108

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240110

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240111

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350240112

出版商:John Wiley&Sons Ltd    

年代:1989

数据来源: WILEY