Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 Correlation of the early Paleogene in northwest Europe: an overview R. W. O'B. KNOX British Geological Survey, Keyworth, Nottingham NG12 5GG, UK The last two decades have seen a major resurgence Rockall area (Legs 12, 48, 81), and the volcanic of interest, both commercial and scientific, in the successions of British Tertiary Igneous Province early Paleogene stratigraphy of northwest Europe. (BTIP) and the North Atlantic Igneous Province The commercial interest has arisen primarily as a (NAIP). Five, largely independent, areas of study result of major oil and gas finds in the central and can thus be identified: Northern North Sea, mostly in deep-water sand- (1) the onshore sections of the southern margin of stones of late Paleocene to mid Eocene age. the North Sea Basin, restricted to inner shelf, Increased interest in the onshore sections has been littoral and terrestrial facies; stimulated partly in response to the offshore hydro- (2) the offshore sections of the North Sea Basin carbon exploration, but largely through the and West of Shetlands area, dominated by activities of international (IUGS/IGCP) working outer shelf, slope and basinal facies, but groups, whose primary concern is the establishment including inner shelf to terrestrial facies around of a globally standardized system of series and the Scottish landmass; stages. The onshore sections of the southern North (3) the offshore sections of the Goban Spur area, Sea Basin area are of particular importance in restricted to bathyal facies (largely calcareous these investigations, because they include nannofossil oozes); the historical stratotypes for the Paleocene and (4) the offshore sections of the Rockall area, repre- Eocene series and for their constituent stages. senting inner shelf to bathyal facies; Unfortunately, these historical stratotypes are (5) the onshore and offshore stratified sections inappropriate as global stratotypes because of their of the BTIP and GFIP, dominated by lavas stratigraphic incompleteness, and their limited and tufts, but with intercalations of non- representation of the standard Paleogene biozones. volcanogenic sediments. Only through the fullest understanding of these historical stratotype sections, however, can we ensure that the standard stages are defined in a way that ensures the maximum compatibility with traditional assignments in NW Europe (Knox 1994; Schmitz 1994). For a long time the commercially driven and scientifically driven lines of investigation proceed- ed more or less independently, partly because of the !tI confidential nature of the offshore investigations _ and partly because of difficulties in correlating widely separated sections of strongly contrasting lithofacies and biofacies. For these reasons, the earlier stratigraphic compilations for the Paleogene of northwest Europe were concerned almost exclusively with the onshore areas (e.g. Curry et al. 1978; Cavelier & Pomerol 1986; Pomerol 1989). A notable exception is the compilation of data collected in relation to IGCP Project 124 (Vinken et al. 1988), which represents a remarkable achievement in the field of multidisciplinary and multinational stratigraphic collaboration. Fig.1. Distribution of early Paleogene sedimentary and Other areas that have been the subject of detailed igneous successions in NW Europe, with locations of the analysis are the oceanic successions of the eastern Bay of Biscay, Goban Spur and Rockall DSDP sites Atlantic (Fig.l), encountered during DSDP drilling (Legs 12, 48, 80, and 81) and central North Sea well in the Goban Spur area (Legs 48, 80) and in the 22/10a-4. From Knox, R. W. O'B., Corfield, R. M. & Dunay, R. E. (eds), 1996, Correlation of the Early Paleogene in Northwest Europe, Geological Society Special Publication No. 101, pp. 1-11. Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 2 R.W. O'B. KNOX A broad stratigraphic framework has now been SE England provide a more or less continuous tran- established for each of these areas. For example, sect from sublittoral facies in the historical extensive studies have now been carried out on Thanetian stratotype sections of Kent to outer shelf all aspects of biostratigraphy, such that regional 'North Sea'facies in northern parts of East Anglia. zonation schemes are firmly established for the The major challenges for the future are (i) inter- more important fossil groups. Similarly, comp- regional correlation within northwest Europe, and rehensive magnetic polarity zonations have been (ii) calibration of the northwest European established for the onshore areas of the BTIP and sections in terms of the standard biozones and the the southern North Sea Basin, providing not only a geological timescale. Because it is clear that no one means of correlation, but also a direct link to the discipline can solve all these problems, a multi- geological timescale. It is only now that these disciplinary approach is paramount. The purpose of comprehensive stratigraphic frameworks have been this overview is to provide a brief assessment of established that correlation betweeen the individual how the different disciplines have contributed areas (referred to as 'interregional correlation' in towards interregional correlations, and how the this account) can be realistically attempted. ultimate aim of a chronologically calibrated, Problems in interregional correlation arise integrated stratigraphy for the entire northwest primarily from differences in the type and nature European region might be achieved. of the available stratigraphic data. Examples of limitation due to data type are seismic data, which Essential elements of an interregional are available only for offshore sections, and magnetic polarity data, which can be obtained only correlation from cored sections or outcrops. Even within a The geological timescale single discipline, interpretation can be hampered by different methods of data acquisition. Thus bio- The publication of a new Paleogene timescale stratigraphic data for the offshore hydrocarbons (Cande & Kent 1995) is a welcome development basins are largely based on cuttings, and thus in view of the significant discrepancies between dependent on first downhole occurrences (FDOs), earlier timescales, especially over the late whereas for the onshore sections they are based on Paleocene to early Eocene interval. The incor- the standard criteria of first and last appearance poration of a radiometric date obtained from a datums (FADs, LADs). A more serious limitation tephra layer of early NP10 age puts the new on interregional correlation is the effect of facies on timescale on a much firmer footing. This is the nature and diversity of fossil assemblages. Thus especially important for assessing the influence of while the Goban Spur sections in the eastern 'Atlantic' tectonism on stratigraphic events, as it Atlantic possess rich calcareous microfaunas and allows an improved correlation between the bio- nannofaunas, allowing assignment to the standard stratigraphically dated sedimentary successions and Paleogene biozones, equivalent strata in central the radiometrically dated lava successions of the parts of the North Sea Basin are commonly North Atlantic borderlands. However, as cautioned devoid of calcareous fossils. Conversely, whereas by Berggren & Aubry (1996), timescales are con- palynomorphs are ubiquitous in the North Sea structed on a series of assumptions that will be Basin, they are reported to be absent from the subject to continuous reassessment, and the new Goban Spur sections. Under such circumstances, Paleogene timescale is no exception. The Cande & correlation between the two successions must rely Kent (1995) timescale is nevertheless considered to on a combination of techniques, with particular provide a much improved overall chronological emphasis on those that are less facies dependent calibration of the standard biozones and magnetic (e.g. magnetostratigraphy and tephrostratigraphy). polarity zones (see Berggren et al. in press). Its Fortunately, not all of the correlation problems adoption by the lUGS Subcommission on are so severe. For example, the early Paleogene Paleogene Stratigraphy should ensure that it succession of Denmark, accessible through outcrop becomes the common standard until such time as sections and cored boreholes, is of deep-water sufficient data are accrued to warrant further refine- facies, and provides a valuable insight into the ment. The use of such a common standard will succession of the central North Sea. It is there- greatly facilitate comparison of stratigraphic data of fore possible to apply techniques such as all types and from all parts of the world. magnetostratigraphy to a basinal North Sea succes- sion, and thereby assess the relationship between Biostratigraphy the zonally based biostratigraphic schemes established for onshore sections and the FDO-based Calcareous nannofossils. A more or less com- schemes established for the offshore hydrocarbons plete record of the early Paleogene standard cal- boreholes. Additionally, the Paleocene sections of careous nannofossil zones is present in the Goban Downloaded from http://sp.lyellcollection.org/ by guest on October 2, 2021 CORRELATION OF THE EARLY PALEOGENE IN NORTHWEST EUROPE" AN OVERVIEW 3 Spur DSDP Sites 549 and 550, which together may the onshore and offshore basins of NW Europe (see be regarded as providing a composite oceanic Powell 1992; Heilmann-Clausen 1994). reference section