Preface

Evolutionary palaeoecology and palaeobiogeography: year 4 of the IGCP-591 project 'The Early to Middle Palaeozoic Revolution - Bridging the Gap between the Great Ordovician Biodiversification Event and the Devonian Terrestrial Revolutio

Preface

Evolutionary palaeoecology and palaeobiogeography: year 4 of the IGCP-591 project 'The Early to Middle Palaeozoic Revolution - Bridging the Gap between the Great Ordovician Biodiversification Event and the Devonian Terrestrial Revolutio

Preface

Evolutionary palaeoecology and palaeobiogeography: year 4 of the IGCP-591 project 'The Early to Middle Palaeozoic Revolution - Bridging the Gap between the Great Ordovician Biodiversification Event and the Devonian Terrestrial Revolutio

Silurian sequence stratigraphy of the Carnic Alps, Austria

Sequence stratigraphy provides an alternative approach to correlation that may also serve as a predictive framework for the interpretation of sea-level and sedimentological change. The main aim of this study is to apply sequence stratigraphic concepts to the biostratigraphically well constrained shallow to moderately deep shelf carbonates and basinal graptolitic shale facies of the Silurian successions in the Carnic Alps of Austria in order to correlate the sequence packages and sea-level changes established there with those identified in other areas of North America and Europe. Documenting local sea-level curves is essential for determining global eustasy. The sea-level curve for the Silurian of the Carnic Alps has been elaborated within a refined stratigraphic framework for the Silurian based on conodont and graptolite biozonation [Melchin, M.J., Cooper, R.A., Sadler, P.M., 2004. The Silurian Period. In: Gradstein, F.M., Ogg, J.G., Smith, A.G. (Eds), A Geologic Time Scale. Cambridge University Press, Cambridge, pp. 188–201.]. In particular, the minor and frequent sea-level changes within the Silurian of the Carnic Alps are of special interest as these stratigraphic intervals are poorly preserved and not well studied in other Silurian localities. The interpretation of the field and microfacies analysis indicates major sequence boundaries in the Llandovery (3), Wenlock (3), Ludlow (3) and Přídolí–Lochkovian (2) which may be correlated with coeval disconformities in the Appalachian Foreland Basin of eastern North America and/or in the Welsh Basin of the British Isles. The following times appear to represent relative sea-level highstand maxima in the Silurian of the Carnic Alps, as indicated by dark, graptolitic shales in deep shelf to basinal carbonate-dominated sections: a) early Aeronian, approximately the Coronograptus cyphus graptolite Zone/Demirastrites triangulatus graptolite Zone), b) the early Telychian (Oktavites spiralis graptolite Zone; Pterospathodus celloni conodont Superzone), c) late Telychian (lower Pterospathodus a. amorphognathoides conodont Zone); d) early to middle Sheinwoodian (Kockelella ranuliformis to Ozarkodina sagitta rhenana conodont Zones; Monograptus riccartonensis graptolite Zones); e) mid-Wenlock ((?upper Kockelella walliseri conodont Zone; Cyrtograptus rigidus graptolite Zone); f) mid Homerian (Ozarkodina bohemica conodont Zone; Gothograptus nassa graptolite Zone); g) near the Wenlock–Ludlow boundary (Neodiversograptus nilssoni graptolite Zone); h) Polygnathoides siluricus conodont Zone; i) near the Ludlow–Přídolí boundary (upper Ozarkodina snajdri Interval Zone); j) lower Přídolí (Monograptus parultimus graptolite Zone) and k) at the Silurian–Devonian boundary (earliest Lochkovian: Icriodus woschmidti woschmidti conodont Zone. Of these, the earlier (at least b–e) are well represented in the Appalachian Basin, as in Avalonian sections in Great Britain and in Baltica. Johnson [Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events. GFF 128, 115–121.] documented eight major highstands in global sea-level during the Silurian. The temporal resolution obtained in the Carnic Alps for local sea-level changes allows for refinement of the Telychian to Přídolí sea-level curve, as the stratigraphic successions are chronologically well-defined using both conodont and graptolite biostratigraphy and K-bentonite levels. Nearly all inferred deepenings in the Carnic Alps section, with the exception of that in the Polygnathoides siluricus conodont Zone, approximately match highstands recorded on the Silurian sea-level curves of Johnson [Johnson, M.E., 1996. Stable cratonic sequences and a standard for Silurian eustasy. In: Witzke, B.J., Ludvigson, G.A., Day, J. (Eds.), Paleozoic sequence stratigraphy – Views from the North American Craton. Geol. Soc. Am. Spec. Pap. vol. 306, Boulder, pp. 203–212., Johnson, M.E., 2006. Relationship of Silurian sea-level fluctuations to oceanic episodes and events. GFF 128, 115–121.]; however, the two Telychian highstands are not distinguished but rather are combined as highstand 4 on the Johnson curve, although they are recognized by Loydell [Loydell, D.K., 1998. Early Silurian sea-level changes. Geol. Mag. 135 (4), 447–471.], and the upper Kockelella walliseri conodont Zone deepening is not explicitly numbered by Johnson. These similarities suggest pervasive and probably eustatic events that are manifested in the Apulia Terrane [Cocks, L.R.M., Torsvik, T.H., 2002. Earth geography from 500 to 400 million years ago: a faunal and palaeomagnetic review. J. Geol. Soc. Lond. 159 (6), 631–644.], Laurentia and Avalonia during these time intervals

Nautiloid cephalopods – a review of their use and potential in biostratigraphy

In terms of their use as biostratigraphical tools, nautiloid cephalopods are the poor relations of ammonoids. Nevertheless, in certain situations, they may provide useful biostratigraphical data, particularly where other biostratigraphically valuable taxa are not present; or in certain situations demonstrate a resolution as great as, or greater than ammonoids, trilobites, graptolites or conodonts. Nautiloid cephalopods are of especial value in palaeobiogeographical studies, but their use for this purpose may be hampered by the poor understanding of the stratigraphical ranges of individual taxa. The biostratigraphical value of nautiloid cephalopods is demonstrated here through a number of case studies of Ordovician taxa, combined with a review of their biostratigraphical use in Palaeozoic and Mesozoic successions. These both demonstrate the potential of this group and indicate great scope for further research.Fil: Evans, Daniel H.. Natural England; Reino UnidoFil: King, Andy H.. Geckoella; Reino UnidoFil: Histon, Kathleen.Fil: Cichowolski, Marcela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Time-specific aspects of facies: State of the art, examples, and possible causes

The term “time-specific facies” (TSF) was introduced to the scientific community by the late Otto H. Walliser to refer to unique facies typical of particular narrow intervals, some of which were related to bioevents. In some senses, however, the concept was recognized much earlier and is even engrained in the very names of some geologic periods. The concept of time-specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time. The recognition of time-specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale. These range from very short-term, but widespread facies that overlap with event deposits, to general facies types that may persist for intervals up to 10s of millions of years in duration. This paper briefly summarizes the history of development of the TSF concept, provides examples to illustrate a few of the key aspects of time-specific facies and offers a few tentative explanations for this phenomenon. Among the factors that control TSFs, abrupt changes in redox conditions and early diageneticmineralization, sedimentary condensation, often associated with abrupt sea level change, altered climate and paleoceanography, and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of TSFs. Inevitably, however, many TSFs reflect multiple effects and some remain largely unexplained