ISSN:0072-1050    

DOI:10.1002/gj.3350270102

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe Dalradian succession of central Donegal represents a tectono‐stratigraphic sequence everywhere separated into two distinct successions by the Central Donegal Slide. Each stratigraphic package consistently youngs away from this major D1structure which originated during lower greenschist facies metamorphism and corresponds with the development of locally preserved penetrative S1fabrics. The tectonic slide and associated reversal in the direction of structural facing are commonly marked by mylonites and tectonic schists, which have been subsequently folded and reactivated by kilometric‐scale sheath folds and the Ballybofey Nappe.Structural correlations with northwest Donegal suggest that the Central Donegal Slide relates to the Knockateen Slide, and represents an early thrust with top to the northwest sense of shear. The Central Donegal Slide cuts up‐section through the Middle Dalradian sub‐basin centred on southern Donegal, emplacing younger, anoxic basinal sediments and turbidites over an older, inverted, shelf succession. The location of the Central Donegal Slide adjacent to the margin of this sub‐basin suggests that the siting and form of ductile thrusts may be strongly influenced by the geometry of the pre‐existing sedime

ISSN:0072-1050    

DOI:10.1002/gj.3350270103

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractAbundant and varied trilobite trace fossils are recognized and described in the Cambrian sequence of the Holy Cross Mountains.CruzianaandRusophycusare stratigraphically significant and some of the described traces may be used as local index fossils. The first recognition of theCruziana barbataichnozone in Poland is made and it occurs in the uppermost Middle Cambrian. A new position for the Middle/Upper Cambrian boundary is established. Three new ichnospecies are described:Cruziana magna, C. regularisandRusophycus crebus.

ISSN:0072-1050    

DOI:10.1002/gj.3350270104

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractStratigraphic units are defined and described for the Lower Carboniferous succession in the Walterstown‐Kentstown area of Co. Meath, Ireland. A complete (unexposed) Courceyan succession from the terrestrial red bed facies of the Baronstown Formation to the Moathill Formation of the Navan Group has been penetrated in several boreholes. Although the lower part of the sequence is comparable with the Courceyan succession at Navan and Slane, the middle part of the sequence differs markedly in the Walterstown‐Kentstown area and two new members, the Proudstown and Walterstown Members, are defined in the upper part of the Meath Formation.Syndepositional faulting was initiated during the Courceyan, probably in latestPseudopolygnathus multistriatusor earlyPolygnathus mehli latustime. Movement on the ENE trending St. Patrick's Well Fault influenced the deposition of the Walterstown Member and the overlying Moathill Formation and was probably associated with the development of the East Midlands depocentre to the south of the area. A second episode of tectonism in the latest Courceyan or early Chadian resulted in uplift and erosion and the development of ‘block and basin’ sedimentation.Subsequent transgression of the uplifted block led to the establishment of the Kentstown Platform, bounded to the north, west and south by rocks of basinal facies. The Milverton Group (Chadian‐Asbian), confined to this platform, unconformably overlies Courceyan or Lower Palaeozoic strata and is subdivided into three formations: Crufty Formation (late Chadian), Holmpatrick Formation (late Chadian‐Arundian) and Mullaghfin Formation (late Arundian‐Asbian). The Walterstown Fault controlled the western margin of the Kentstown Platform at this time. Contemporaneous basinal sediments of the Fingal Group (Lucan and Naul Formations) accumulated to the west of the Walterstown Fault and are much thicker than age‐equivalent platform facies.Platform sedimentation ceased in latest Asbian to early Brigantian time with tectonically induced collapse and drowning of the platform; platform carbonates of the Mullaghfin Formation are onlapped northwards by coarse proximal basinal facies of the Loughshinny Formation.A distinct gravity anomaly in the Kentstown area suggests the presence of a granitoid body within the basement. The Kentstown Platform is therefore considered to have formed on a buoyant, granite‐cored, footwall high analogous to the Askrigg and Alston Blocks of

ISSN:0072-1050    

DOI:10.1002/gj.3350270105

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPalaeomagnetic and geochronological data from an Early Palaeozoic high grade metamorphic complex (Jorgina Formation) and Jurassic layered basic intrusion (Moreno Complex) are reported from the Mejillones Peninsula of northern Chile (23–23°30'S).40Ar–39Ar dates from the Lower Palaeozoic Jorgina Formation and the Moreno Complex are between 170 and 158 Ma, coincident with a phase of emplacement of the north Chilean coastal batholith. This suggests that intrusion and magnetization of the Moreno Complex and the metamorphism and remagnetization of the Jorgina Formation were related to batholith emplacement. Extracted stable components of magnetization from all units (17 sites) define site‐mean directions with a scattered distribution. The scatter in site‐mean directions is interpreted as being due to minor, localized, non‐uniform, block‐fault related (normal or strike‐slip, or both) rotation after 158 Ma. The palaeomagnetic and geochronological data indicate that no significant large‐scale latitudinal translation of crustal blocks has taken place in this part of northern Chile since the Late Jurassic. In addition, they indicate that the uniform clockwise rotation after the mid‐Cretaceous which affected the adjacent Cordillera de la Costa either did not extend into the Mejillones Peninsula or took the form of localized block‐fault rotations. The restriction of palaeomagnetically defined styles of rotation to discrete areas within the north Chilean forearc indicates that forearc wide block‐fault rotation models are not applicable to the Pacific ma

ISSN:0072-1050    

DOI:10.1002/gj.3350270106

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractPegmatite dyke swarms are exposed within the easternmost Pyrenees at Cabo de Creus. These dykes were emplaced into high‐grade metamorphosed sedimentary strata of Cambro‐Ordovician age, but lack obvious field relationship to Hercynian intrusive rocks. Together with structural and geochemical data, equilibrium oxygen isotope fractionations at temperatures of ≈ 600°C, the lack of obvious subsolidus exchange, and the H‐ and O‐isotopic signatures of water in equilibrium with pegmatite mica and quartz are interpreted to indicate a derivation from anatexis of a metapelitic source at shallow crus

ISSN:0072-1050    

DOI:10.1002/gj.3350270107

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270108

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270109

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270111

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350270114

出版商:John Wiley&Sons Ltd    

年代:1992

数据来源: WILEY