A late Paleocene-early Eocene NW European and North Sea magnetobiochronological correlation network

Abstract

Abstract Published and unpublished data on bio-, chemo- and magnetostratigraphic events spanning the late Paleocene-early Eocene are reviewed and calibrated to a revised Geomagnetic Polarity Time Scale (GPTS), itself already in need of revision. This timescale serves as a template for placing the upper Paleocene-lower Eocene stratigraphic succession of NW Europe (Anglo-Paris-Belgian Basins) in a sequence stratigraphic framework. It is clear that an approach that integrates sequence- and magnetobioisotope stratigraphy provides a unifying correlation framework within which to delineate the disjunct depositional histories of marginal and deep marine basinal stratigraphies and allows the stratigrapher to move from rock to time. Significant conclusions of this integration include the following: 1. The major climatic warming, weakening of atmospheric circulation and faunal extinction events, which are seen in the deep sea stratigraphic record, are seen to be closely associated with the mid-part of the (redefined) planktonic foraminiferal Zone P5 and calcareous nannoplankton Zone NP9. 2. A relatively rapid ( c. 1000 years) decrease of c. 3 to 4 per mil in the δ 13 C of marine carbonates has now been recognized in high southern and northern latitude sites and at several scattered, intermediate locations. A similar excursion has been observed in mammalian teeth and soil carbonates near the base of the Wasatchian North American Land Mammal Age in the Big Horn Basin a few metres above the Argile plastique bariolée (‘type’ Sparnacian) in the Paris Basin. This δ 13 C excursion is seen to be a truly global event which occurs in both marine ( c. mid-Zone NP9) and terrestrial stratigraphies at a level estimated at c. 55.5 Ma. 3. An evaluation of the calcareous plankton biostratigraphy and stable isotope records at several deep sea sites suggests the presence of multiple unconformities in the Paleocene/Eocene boundary interval. There would appear to be no unequivocally demonstrated continuous stratigraphic section through the c. 2.55 million year interval of Chron C24r in the deep sea record or from outcrops on land, and a composite record is required to construct the sequence of events that occurred during this interval. 4. The Paleocene/Eocene boundary (which awaits the determination of a Global Stratigraphic Section and Point [GSSP]) is bracketed by the base of the Ieper Clay Formation (= Ypresian Stage), estimated here at > 54.6 Ma, and the P5/P6a zonal boundary (LAD Morozovella velascoensis ) at c. 54.7 Ma (above), and by the δ 13 C spike (and associated events) in mid-Zone NP9 at c. 55.5 Ma (below). The ‘boundary interval’ encompasses the NP9/10 zonal boundary at 55 Ma and the base of the Harwich Formation (base of the London Clay Formation Oldhaven Beds of previous authors) at c. 54.8 Ma. 5. Calcareous nannoplankton studies of recently recollected Thanetian localities in the eastern part of the Paris Basin have revealed that the Thanetian Sables de Châlons-sur-Vesles are older (Zones NP6 and NP7) than the Sables de Bracheux s.l. (= Sables du Tillet; Zone NP8). This leads to a revised framework of correlation between the upper Paleocene formations of northwest Europe. 6. The base of the Sparnacian base, taken as the Paleocene/Eocene boundary by most vertebrate palaeontologists, is correlative with a level within Zone NP9, c. 0.5 million year older than the NP9/10 zonal boundary (used by some marine micropalaeontologists to delineate the Paleocene/Eocene boundary) and > one million years older than the base of the Ieper Clay (base Ypresian) in Belgium.