摘要:

Bergström, S. M.&Cooper, R. A.:Didymograptus bi'usand the trans‐Atlantic correlation of the Lower Ordovician.The co‐occurrence ofDidymograptus bifidus(Hall) andPrioniodus maeLindstrom, and other conodonts of the middle ArenigianP. maeZone in the upper part of the Marathon Limestone, Texas, provides the first non‐graptolitic evidence that at least part of theD. bifidusZone, as recognized in the reference area for the standard graptolite zonal succession of the Ordovician of North America, is as old as the BritisKD. nitidusZone. This has important implications for the correlation of Early Ordovician rocks within North America and across the Atlantic. A regional review of the available evidence from conodonts and shelly megafossils indicates that theD. bifidus—D. artusgraptolite assemblage widely used for identification of theD. bifidusZone in North America ranges in age from the middle Arenigian to, probably, the lower Llanvirnian, and hence is of relatively limited use for precise local and regional correlations. It is also noted that the base of the North American Middle Ordovician falls withinhograptus ‘caduceus’Zone strata that apparently correspond to an interval in the middle to upper part of the BritishD.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01201.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Savage, N. M.: Lower Devonian biostratigraphic correlation in Eastern Australia and Western North America.Correlation of Lower Devonian marine strata of Eastern Australia and Western North America can be attempted using several fossil groups. In general the faunas are similar, with many species common to both areas. Graptolites occur infrequently, but are of great value because of their precise zonal significance. Several of these graptolites occur in the classic type sequences of Bohemia but are absent from the Rhineland stages. For this reason, and because of the Bohemian affinities of the shelly faunas, the Bohemian stage names are preferable to the Rhenish names for use in Eastern Australia and Western North America. Cono‐donts are less precise index fossils than graptolites, but are considerably more abundant and therefore have greater application. Brachiopods are valuable if viewed as assemblages. In terms of the Rhenish stages, most Eastern Australian and Western North American early Lower Devonian formations appear to have been placed too high. Recent evidence from northern Canada throws new light on the problem of correlating Rhenish and Bohemian classic early Lower Devonian stage

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01202.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Bromley, R. G.&Surlyk, F.: Borings produced by brachiopod pedicles, fossil and Recent.Characteristic etching traces are produced in hard calcareous substrates by the pedicles of brachiopods belonging to several groups. It was previously unsuspected that the ability to bore was widespread within the brachiopod phylum. Five species were investigated from the Norwegian Sea:Terebratulina retusaandT. septentrionalis(Terebratulacea),Hemithyris psittacea(Rhynchonellida), andMacandrmia craniumandDallina septigera(Terebratellacea). Fossil traces with closely similar morphology occur in the Cretaceous and are probably also the work of brachiopods. The most characteristic form is designatedPodichnus centrifugalisn. ichnogen., n. ichnosp.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01203.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Broadhurst, F. M.&Simpson, I. M.: Bathymetry on a Carboniferous reef.In the Lower Carboniferous deposits of Castleton, Derbyshire, well bedded shelf limestones, apparently of shallow water origin, pass northwards into a marginal tract of poorly bedded apron‐reef limestones which dip at about 30° downwards and away from the ‘shelf’. Geopetal infillings of shell cavities in the apron‐reef indicate only minor movement since deposition, and the observed dip must be due to deposition on a sloping sea floor. At certain times this sea floor was colonised by stromatolitic algae and corals such asLithostrotionat the apron‐reef crest where there was minimum water depth, followed to progressively increasing depths by (1) a fauna dominated by the coralMichelinia, (2) a fauna of small brachiopods, bryozoa, molluscs, trilobites, and other organisms and (3) a fauna dominated byPseudamussium. At other times crinoidal debris was the dominant component of the apron‐reef, when an alignment of crinoid stems parallel to the dip of the slope occurred at low levels, but a random orientation at the apronreef crest. Other sediments on the apron‐reef are apparently devoid of macrofossils. Volcanic activity occurred during the development of the apron‐reef, and it is suggested that uplift of the shelf area preceded the subaerial flow of a lava tongue which reached and plunged down the apron‐reef slop

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01204.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Westermann, G. E. G.: Strength of concave septa and depth limits of fossil cephalopods.Simple septa with spherical curvature are present in the shells of all Endocer‐oidea, Actinoceroidea, Bactritoidea, and most Nautiloidea and Coleoidea. Such septa act as quasi‐hemispherical concave membranes when subjected to hydrostatic pressure. Since the tensile strength of a spherical membrane is directly proportional to the ratio of its thickness and radius of curvature, measurements of these parameters on polished and thin sections of septa can be used to obtain strength of the septum against implosion. Depth limits of fossil cephalopods can be made by calibrating these measurements in terms of recent implosion data on ‘living’SpirulaandNautilus. Estimates of septal strength are augmented by strength estimates for long septal necks and cylindrical to globular connecting rings.Assuming that actual habitats ranged to approximately two‐thirds of the mechanical limits of the shells, the following maximum depth ranges are indicated from this preliminary survey: Endoceroidea 100–450 m; Actinoceroidea 50–150 m; Nautiloidea, Ellesmerocerida 50–200 m, Orthocerida 150–500 m, Oncocer‐ida<150, Discosorida<100 m, Tarphycerida<150 m, Nautilida 200–600 m; Bactritoidea c. 400 m; Coleoidea, Aulacocerida 200–900 m, Sepiida 200–1000 m, Belemnitida 5

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01205.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Jago, J. B.: Cambrian agnostid communities in Tasmania.Two or possibly three different agnostid trilobite assemblages can be distinguished in the late Middle and early Upper Cambrian sequences of northern and western Tasmania. This is significant because in recent years agnostid trilobites have been widely used in local and international correlations of Middle and Upper Cambrian rocks. The three assemblages recognized are (1) an agnostid assemblage in which polymerid trilobites are abscnt, rare or present as thanatocoenotic fossils, (2) a ptychagnostid‐non‐nepeid assemblage, and (3) a nepeid‐clavagnostid‐peronopsid assemblage in which non‐agnostid trilobites are abundant but ptychag‐nostids are absent. It is proposed that assemblage (1) represents an open sea fauna, with assemblages (2) and (3) occurring in progressively shal

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01206.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Henningsmoen, G.: The Cambro‐Ordovician boundary.The Cambrian and Ordovician Systems were established in Britain, and it seems appropriate to define the Cambro‐Ordovician boundary in Britain or where there is a closely related faunal succession at the junction. When Lapworth erected the Ordovician System in 1879, his intention was that its lower boundary should separate the so‐called primordial (or first) and second Palaeozoic faunas. He drew this boundary at the base of the Lower Arenig, but apparently included the Upper Tremadoc in the Lower Arenig. It seems problematic to base the Cambro‐Ordovician boundary on grounds of historical priority, and we seem to be free to decide whether to have the boundary at the base of the Tremadocian, at the base of the Arenigian, or within the Tremadocian (e.g. at the base of the Upper Tremadoc). The alternatives are shortly discussed. Arguments are put forward for placing the boundary not at a break, but preferably in a sequence with cosmopolitan fossils, either in a sequence of uniform facies or perhaps rather in a sequence with frequently alternating

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01207.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

[Anders Martinsson:] Editor's column: Ecostratigraphy.The natural development of biostratigraphy is towardecostratigraphy, i.e. the correlation of fossil ecosystems and their arrangement in a geochronological framework. This stage is not easily attainable and provides far‐reaching systematical and ecological knowledge of the organisms and communities involved. Hence, considerable ecostratigraphical success is hitherto only to be reported from the Quaternary, but the development should be guided towards similar knowledge of earlier intervals of the Phanerozoi

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01208.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1973.tb01209.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY