摘要:

AbstractSedimentation patterns are described from the Kilbride Formation west of the Maam Fault zone, north Galway, Ireland. Seven distinct facies are described using faunal and lithological parameters. Environments of deposition range from marginal marine to deep shelf conditions. Lateral facies distributions were largely controlled by a rocky topographic high which influenced sedimentation until being buried by outer shelf sediments in middle‐upper Kilbride Formation times. Four distinct sequences are described: in the lower Kilbride Formation, sequences I and IV are dominated by proximal storm deposits; sequence II was deposited in the lee of the topographic high and is interpreted as barred estuarine deposits; and in sequence III, at the topographic high, no deposition took place. In the upper Kilbride Formation the barrier was buried and uniform outer shelf conditions prevailed throughout the area. Faunal assemblages were strongly controlled by local environmental conditions and do not conform directly with the expected pattern of depth‐related brachiopod communities. TheLingulaandEocoeliacommunities are amalgamated and alloch‐thonous, thePentameroidesandCostistricklandiacommunities are absent, and only theClorindacommunity is well represented, though parautochth

ISSN:0072-1050    

DOI:10.1002/gj.3350290302

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDiatomite associated with the Kolubara Coal Basin was studied to better understand early stage silica diagenesis of shallow water deposits. The Kolubara Basin consists of Neogene siliciclastic rocks, diatomite, marlstone and rare carbonates. Palaeozoic metamorphic and Mesozoic sedimentary and igneous basement rocks are transgressively overlain by Upper Miocene sandstone, siltstone, shale and mudstone. This Upper Miocene section is transgressively overlain by the Pontian section, which contains diatomite and coal beds.White and grey diatomite forms beds 0.7‐2.2 m thick that are continuous over an area of about 2 km2. Siliceous rocks vary in composition from diatomite (81‐89 per cent SiO2) to diatom‐bearing shale (58‐60 per cent SiO2). Siliceous deposits are laminated in places, with the laminae defined by variations in clay minerals, organic matter and diatoms. Diatomite shows only incipient diagenesis characterized by the fragmentation of diatom frustules, the minor to moderate corrosion of frustules and the formation of minor amounts of opal‐A' (X‐ray amorphous inorganic opal) cement. The low degree of diagenesis results from the young age of the deposits, low burial temperatures and possibly also from the presence of abundant organic matter and the dissolution of kaolinite. The presence of only weak diagenesis is also reflected by the characteristically poor consolidation of the rocks and low rank of the asso

ISSN:0072-1050    

DOI:10.1002/gj.3350290303

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA formal lithostratigraphy is erected for the Late Ordovician and Silurian rocks of northern England. The scheme presented herein emphasizes natural depositional sequences within the supergroup and defines new type sections or cites existing definitions where appropriate. It is intended to be sufficiently flexible and comprehensive to apply to all the inliers, and to bear some rational relationship to lithostratigraphical usage in other British Lower Palaeozoic inliers.

ISSN:0072-1050    

DOI:10.1002/gj.3350290304

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Pirin‐Pangaion Structural Zone occupies the south‐western part of the Rhodope Massif. It consists of Proterozoic amphibolite facies metamorphic rocks of the Rhodopian Supergroup, and granitoids of Hercynian, Late Cretaceous and Palaeogene age.The pre‐Hercynian structure of the zone is dominated by an interference pattern of three superimposed fold generations of NE‐SW and NW‐SE trends. These structures are cut by Hercynian granitoids, and the entire complex is affected by late Hercynian or early Alpine conical folds. The zone was overthrusted by the Ogražden and Kroussia Units (Serbo‐Macedonian ‘Massif’) along the north‐east vergent Mid‐Cretaceous Strimon overthrust, and by the Central Rhodope Zone of the Rhodope Massif, along the south‐west vergent Meso‐Rhodopean Overthrust. With this thrusting event, the Pirin‐Pangaion Structural Zone was brought together with the Serbo‐Macedonian ‘Massif’ and the Central Rhodope Zone to form the Late Cretaceous Morava‐Rhodope Zone, which acted as a ‘plateau’ along the southern edge of the Eurasian plate. Late Cretaceous granitoid magma of crustal origin intruded this zone, whereas north of it the Srednogorie volcanic island arc was the site of igneous activity with magmas originating in the upper mantle.The West Thrace Zone developed as a Palaeocene to Oligocene depression superimposed over the older basement obliquely to the southern periphery of the Rhodope Massif. In the Late Eocene and Early Oligocene, this depression represented a volcanic island arc with mantle‐derived basic to intermediate magmas; contemporaneous granitoid magmas formed through crustal melting in the thickened crust of the Rhodope Massif (Pirin and Pangaion Units included). Early Miocene thrusting was most intense in the Pangaion Unit, and was followed

ISSN:0072-1050    

DOI:10.1002/gj.3350290305

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDolerites of the Obudu Plateau of south‐eastern Nigeria occur predominantly as dykes cutting Precambrian basement gneisses. Minor dolerite sills have also been mapped. The dolerites are dominantly olivine tholeiites and are geochemically of the oceanic basalt type. They were emplaced in a within‐plate tectonic setting and yield a40Ar/39Ar plateau age of 140.5 ± 0.7 Ma, which is interpreted as the age of their emplacement. This age indicates that the Obudu dolerites are the products of basic magmatism related to the early stages of rifting along the Benue Trough of Nigeria. The Obudu dolerites are comparable with Mesozoic tholeiitic dykes of the northern Amazon craton, whose intrusion preceded the break‐up of Africa and South A

ISSN:0072-1050    

DOI:10.1002/gj.3350290306

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290307

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290308

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290310

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290311

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350290312

出版商:John Wiley&Sons Ltd    

年代:1994

数据来源: WILEY