摘要:

AbstractTwo typical representatives of the Ediacaran biota,Ediacaria booleyin.sp. andNimbia occlusahave been found in deep‐water turbidites within the Upper Cambrian Booley Bay Formation at Booley Bay in Co. Wexford, Eire. The examples ofE. booleyiwere transported over short distances by the turbidity currents and then impacted, in some instances at high angles, into the ocean floor muds where they formed moulds but, as their bodies decayed, these were filled by casting sand from the overlying turbidite. They preserved fine detail during transportation and impaction, thereby indicating the existence of a rigid body wall. The three‐dimensional nature of their preservation allows reconstruction, which shows thatEdiacariahad a discoid form with prominent relief, particularly on its dorsal side, which was divided into three main concentric zones with thin radial features, more evident at the periphery. The ventral side had lower relief, with alternate areas of coarse and fine concentric markings and numerous fine radial lines, some also thicker at the periphery.Nimbia occlusaare disc‐like bodies of low relief and occur in profusion on one sole. Some show a circular outline indicating that they were preserved flat on the bedding plane, but others occur as semicircular reliefs oriented in the palaeocurrent direction. This indicates that they too were moved by the turbidity current, but their abundance and excellent preservation indicate that transport distances were short. There is no evidence in either genus for the coelenterate characteristics of a mouth and a two‐layered body wall enclosing a single cavity. This, and the evidence for a rigid outer wall, adds to recent doubt on the concept of the world‐wide Ediacaran fauna as dominated by soft‐bodied co

ISSN:0072-1050    

DOI:10.1002/gj.3350300202

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAcritarch assemblages have been recovered from the Booley Bay Formation in Duncannon area, Co. Wexford, southeastern Eire. Twelve morpho‐species are described, including the new speciesPolygonium martinae n.sp., and two informal speciesComasphaeridiun. sp. A andHeliosphaeridiumn. sp. B. A new combination,Retisphaeridium brayense(Gardiner and Vanguestaine 1971) comb. nov., is proposed. The relative ages provided by discrete microfossil assemblages and their sequence within the lithological succession suggest that the entire investigated portion of the Booley Bay Formation may be referred to the Upper Cambrian. This biostratigraphic evaluation constrains the age of the recently discovered Ediacaran‐type biota described in Crimeset al.(19

ISSN:0072-1050    

DOI:10.1002/gj.3350300203

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe type species of the Palaeozoic cystoporate bryozoan genusFistuliporaM'Coy, 1849 is redescribed.Fistulipora minorM'Coy, 1849 is the type species, and was the first species described under the genusFistulipora.Quantitative assessment of type and figured specimens ofCalamopora incrustansPhillips, 1836 andF. minorhas shown them to fall within the range of morphological variation exhibited by abundant comparative material collected at several horizons and they are referable to one morphologically variable taxon.F. minoris the junior subjective synonym ofC. incrustansand the form can be quoted asF. minorM'Coy, 1849 =C. incrustansPhillips, 1836 with a valid name ofF. incrustans(Phillips, 1836). However, this does not alter the name of the type species, which isF. minorM'Coy, 1849. The type specimen ofBerenicea megastomaM'Coy, 1844 has also been examined, and this form is also conspecific withF. minorM'Coy, 1849 =C. incrustansPhillips, 1836. Examination of the type specimen ofF. majorM'Coy (1849) has shown it to be referable to the tabulate coral genusChaetetes.A lectotype and paralectotypes are designated forF. minorand the status of the type specimens ofF. incrustansis clarified.

ISSN:0072-1050    

DOI:10.1002/gj.3350300204

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractDetailed mapping and biostratigraphic data provide new evidence of a major break below the base of the Caradoc succession along the northern margin of the Harlech Dome in south central Snowdonia. Within this outcrop the sequence is locally complicated by subsequent tectonic and volcanic events, but undisturbed sections indicate a break of at least 10 Ma between upper Arenig and middle, or upper, Llandeilo strata. The break is greatest between two N‐S trending fracture systems, the Cwm Pennant Fault Zone in the west and Trawsfynydd Fault Zone in the east, which both have a persistent history of reactivation. Between these two fractures neither Llanvirn nor lower Llandeilo strata occur. This contrasts with the thick, and perhaps complete, sequence preserved in the Cadair Idris district on the southern margin of the dome and suggests that, during Llanvirn times, the Harlech Dome formed a major uplifted and tilted block, with a tectonically active northern margin. Subsequently, uplift and tectonism either ceased before, or was overwhelmed by, the ensuing sea‐level rise associated with thegracilis(early Caradoc) transgression. The preservation of ooidal ironstones around the dome suggests that it may have became a large shoal or platformal area at this time. Renewed uplift and erosion along the northern margin of the Harlech Dome during the early Caradoc (gracilistomultidens) led to large‐scale disruption of the stratigraphic succession by mass gravity flow and slumping, overprinting and locally accentuating the effects of the earlier h

ISSN:0072-1050    

DOI:10.1002/gj.3350300205

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA stepped series of sand and gravel terraces on the Lleyn peninsula of North Wales is used to test the magnitude and rate of isostatic depression required by the recently proposed glacimarine model of deglaciation of the Irish Sea Basin. A relative sea‐level fall of 70 m is required while the ice remained pinned at the north Lleyn coast. Even taking the maximum known rate of isostatic uplift, the margin would have to remain stationary for 1400 years. It seems more reasonable to interpret the Lleyn terraces, and similar features around the Irish Sea Basin, as glacifluvial and glacilacustrin

ISSN:0072-1050    

DOI:10.1002/gj.3350300206

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA stratigraphic and structural summary of 5 km of Upper Devonian strata of south‐west Beara, part of the Munster Basin, south‐west Cork is presented. Five formations are recognized on the basis of lithofacies geometries and associations. The lowest Caherkeen Formation comprises rapidly alternating sheet‐like, plane‐bedded, low‐angle, cross‐bedded sandstones and laminated, rippled or desiccated mudrocks. The incoming of thin lenticular sandstone packages, commonly with high‐angle cross‐bedding, distinguishes the overlying Eagle Hill Formation. The succeeding Reen Point Formation comprises thicker bedsets of plane‐bedded, low‐angle and high‐angle cross‐bedded sandstones, separated by thick, massive mudrocks. Intraformational breccias and calcareous nodular siltrocks are distinctive features. The Tholane Formation is characterized by thick massive red‐green mudrocks and a general absence of coarser grained lithologies. This sequence was deposited in a terminal fluvial fan in a basin characterized by decreasing subsidence rates and gradient with time. The overlying Toe Head Formation represents the deposits of a fluvial coastal plain. It has siltrocks that are predominantly green, often with preserved fish and plant debris. There is a relative absence of high‐angled cross‐bedded sandstones and an abundance of flat‐laminated and inclined parallel‐laminated sandstones.The structure of the Beara Peninsula comprises a WSW plunging anticlinorium with a single cleavage formed during the Variscan orogeny. Evidence from locally transecting cleavages and from mapping indicates dextral transpression. Development of the three main fault trends was contemporaneous with the folding. The well‐known copper mineralization of the Allihies area is associated with east‐west fault trends, a pattern observed elsewhere in the western Munster Basin. Basement involvement during both basin development and deformatio

ISSN:0072-1050    

DOI:10.1002/gj.3350300207

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractSmall mudstone diapirs in multi‐layer Ordovician rocks near Llanwrtyd, Wales, match in anatomy those produced experimentally by Ramberg (1981) and Jackson and Talbot (1989). This appears to be the first record of natural examples at this scale, and they cast light on the relative viscosities of the sediments during early diagenesi

ISSN:0072-1050    

DOI:10.1002/gj.3350300208

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300209

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300210

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350300212

出版商:John Wiley&Sons Ltd    

年代:1995

数据来源: WILEY