摘要:

AbstractTwenty‐six form‐species of plant macrofossils occur in the Coal Measures exposed in the Howgill Head Quarry, Whitehaven, Cumbria, UK. They belong to theNeuropteris semireticulataSubzone in the lower part of theParipteris linguaefoliaZone, indicating the uppermost Duckmantian. They confirm that the sandstones exposed in this part of the West Cumberland Coalfield are part of the Whitehaven Sandstone Formation, and not a stratigraphically lower unit as previously suggested. The Howgill head fossils represent the only well documented example of aN. semireticulataSubzone assemblage in Britain, although comparable assemblages are known from coeval strata in northern France, Belgium, northern Germany and Pol

ISSN:0072-1050    

DOI:10.1002/gj.3350280202

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe West Spitsbergen Fold Belt, together with the Eurekan structures of northern Greenland and Ellesmere Island, are suggested to be the result of Late Cretaceous‐Palaeocene intracontinental compressional tectonics. The Late Palaeozoic –Mesozoic rocks of western Spitsbergen are characterized by near‐foreland deformation with ramp‐flat, top‐to‐the east thrust trajectories, whereas structurally higher nappes involving Caledonian complexes are typified by more listric thrusts and mylonite zones. A minimum of 40 km of shortening is estimated for the northern part of the West Spitsbergen Fold Belt. The axial trends in the West Spitsbergen and the North Greenland Eurekan fold belts parallel the principal fault zones which accommodated the separation of Greenland and Svalbard after Chron 25/24. In northern Greenland, north directed Eurekan thrusts associated with mylonites and cleavage formation represent at least 10 km of shortening. Between 50 and 100 km of shortening is estimated for the markedly arcuate Eurekan Fold Belt of Ellesmere Island, but the principal tectonic transport is eastwards. Kinematic reconstructions suggest that Svalbard was linked to North America before the opening of the Eurasian Basin and Norwegian — Greenland Sea. In the Late Cretaceous — Palaeocene interval, the relative motion between Greenland and North America was convergent across the Greenland — Svalbard margin, giving rise to the West Spitsbergen Fold Belt and the Eurekan structures o

ISSN:0072-1050    

DOI:10.1002/gj.3350280203

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Sierra Grande Formation (Silurian‐Early Devonian) consists of quartz arenites associated with clast supported conglomerates, mudstones, shales and ironstones. Eight sedimentary facies are recognized: cross‐stratified and massive sandstone, plane bedded sandstone, ripple laminated sandstone, interstratified sandstone and mudstone, laminated mudstone and shale, oolitic ironstone, massive conglomerate and sheet conglomerate lags. These facies are interpreted as shallow marine deposits, ranging from foreshore to inner platform environments. Facies associations, based on vertical relationships among lithofacies, suggest several depositional zones: (a) beach to upper shoreface, with abundant plane bedded and massive bioturbated sandstones; (b) upper shoreface to breaker zone, characterized by multistorey cross‐stratified and massive sandstone bodies interpreted as subtidal longshore‐flow induced sand bars; (c) subtidal, nearshore tidal sand bars, consisting of upward fining sandstone sequences; (d) lower shoreface zone, dominated by ripple laminated sandstone, associated with cross‐stratified and horizontal laminated sandstone, formed by translatory and oscillatory flows; and (e) transitional nearshore‐offshore and inner platform zones, with heterolithic and pelitic successions, and oolitic ironstone horizons. Tidal currents, fair weather waves and storm events interacted during the deposition of the Sierra Grande Formation. However, the relevant features of the siliciclastics suggest that fair weather and storm waves were the most important mechanisms in sediment accumulation.The Silurian‐Lower Devonian platform was part of a continental interior sag located between southern South America and southern Africa. The Sierra Grande Formation was deposited during a second order sea level rise, in which a shallow epeiric sea flooded a deeply weathered low rel

ISSN:0072-1050    

DOI:10.1002/gj.3350280204

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractContacts within nested plutons are crucial for constraining the relative timing of pluton emplacement and the internal geometry of composite plutons. Exposures in orogenic belts are commonly discontinuous, however, disguising these contacts. In this paper, the Merrimac plutons in the northern Sierra Nevada of California are used as an example of how composition and foliation patterns can allow the definition of unexposed contacts and identify nested plutons.Image analysis techniques were used to determine modal compositions of a total of 52 samples from the Merrimac plutons. The integrated analysis of compositional data and foliations patterns reveals a critical contact within the plutons, and suggests that the Merrimac plutons indicate way‐up towards the north‐east at the time of emplacement 142 ± 3 Ma ago. This paper provides guidelines for recognizing nested plutons in poorly exposed areas and shows that consistent structural and compositional assymmetries within nested plutons can be used as regional top‐direction indi

ISSN:0072-1050    

DOI:10.1002/gj.3350280205

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractIn south Cumbria, Permo‐Triassic breccias and conglomerates (‘brockram’) are exposed only at Rougholme Point on the Cartmel peninsula. In 1973 the Institute of Geological Sciences Humphrey Head borehole penetrated 257 m of brockram before entering probable Upper Carboniferous sediments. The brockram consists of pebbles of carbonate, chert and basalt in a matrix of haematite‐stained quartz sand. Carbonate and chert fragments were derived from the upper part of the Carboniferous Limestone sequence exposed today nearby. Basalt clasts were derived from lavas, which appear to have cooled in a subaqueous environment, at least in part. They were locally derived and are the only certain evidence for Carboniferous volcanic activity in south Cumbria. As volcanic fragments increase in abundance towards the base of the borehole they must have been derived from the top of the succession being eroded and are probably of Brigantian age.Carbonate fragments were dolomitized soon after incorporation in the brockram, probably by saline fluids derived from the evaporative Zechstein Sea. The dolomitization was incomplete, leaving remnant limestone cores to clasts which were subsequently dissolved. The resultant vugs were infilled by dolomite, calcite and gypsum cements, which have been partially weathered from outcropping brockram, leaving hollow

ISSN:0072-1050    

DOI:10.1002/gj.3350280206

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA range of colour alteration index (CAI) values between 3.0 and 6.0 is recorded for conodont elements recovered from the Arundian to Brigantian (Dinantian, Lower Carboniferous) sequence around Castletown, Isle of Man. Mantle‐derived heat, channelled through the Caledonian South Barrule pluton, is proposed as the major cause of these elevated values. A lower CAI of 2.5 is obtained from elements recovered from a borehole sunk into the concealed Namurian (Upper Carboniferous) deposits near Shellag Point; the Glen Mona pluton acted as the medium for mantle‐derived heat in this instance. The CAI values which may have been established during a late Dinantian volcanic episode around Castletown were overprinted by the greater effects of heat emanating from the South Barrule pluton. The record of CAI 6.0 for a sample taken from the immediate vicinity of a dyke indicates a high level of very localized CAI elevation in the early Terti

ISSN:0072-1050    

DOI:10.1002/gj.3350280207

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractNew mapping has better defined the well known arc in Acadian (late Caledonian) structures centred in the Berwyn Hills. This arc, convex to the north‐west and about 20 km across, is defined by the strikes of bedding and cleavage and the trends of fold hinges. In contrast, a mineral lineation within the cleavage has a north‐north‐westerly plunge throughout the arc. It approximates to the long (X) axes of measured strain ellipsoids. A primary origin for the arcuation is implied by this consistency, by the absence of secondary cleavages and by opposing senses of fold transection across the arc. The new data favour the hypothesis of shortening of the Lower Palaeozoic cover against and over a pre‐existing basement high inferred from geophysical data and from metamorphic and sedimentary

ISSN:0072-1050    

DOI:10.1002/gj.3350280208

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Bicester magnetic anomaly is one of several high wavenumber features superimposed on the magnetic anomaly associated with the London Platform. Seismic reflection data suggest that the source of the Bicester anomaly is a body of basaltic rocks of Carboniferous age that can be traced from the Steeple Aston borehole. Three‐dimensional interpretational techniques indicate that the magnetic source has a total magnetization vector dipping at 60°, azimuth 170°, with an intensity of 1.39 A m−1and this has been used to derive a three‐dimensional model of the source. The nature of the magnetic remanence contributing to this vector is discussed. A detailed two‐dimensional magnetic model has been constructed using the seismi

ISSN:0072-1050    

DOI:10.1002/gj.3350280209

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350280210

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350280212

出版商:John Wiley&Sons Ltd    

年代:1993

数据来源: WILEY