ALI, JASON R. and ERNEST A. HAILWOOD, Department of Oceanography, Southampton University, Southampton SO9 5NH, UK.

ABSTRACT: Magnetostratigraphy of the Palaeocene/Eocene boundary beds of the southern UK: Implications for Thanetian Sequence Stratigraphy.

Preliminary magneto- biostratigraphic studies of the Palaeogene of southern England established the base of the Thanetian type-section within Chron C26N. The upper part of the Thanet Formation was positioned within Chron C25R and the overlying Woolwich/Reading Formations were placed within Chron C24BR; Chron C25N is missing from the sedimentary record of Kent. The start of Chron C24BN was located at the base of Division B of both the London Clay Formation, UK, and the Ieper Clay Formation, Belgium.

Our latest efforts have focused on the Upper Paleocene preserved in East Anglia and London. The oldest Palaeocene sediments in southern England (C26R) occur at subcrop in Norfolk, in the Ormesby and Hales boreholes. The upper Paleocene there is very different to that in the London area and north Kent; there is no lateral equivalent of the Woolwich/Reading Formations (probably removed by erosion), and the London Clay Formation includes at its base an additional unit, the Hales Clay, which is overlain by the Harwich Member (Knox et al., 1990).

Integrated stratigraphic investigations have been carried out by the British Geological Survey (R. Knox, N. Hine and R. Ellison) and the Southampton Paleomagnetic Group on a number of borehole sections drilled along a traverse between London and Norfolk. These latest investigations allow a much clearer understanding of the time taken for the `Thanetian Sea' to transgress across the southern UK, and the complexities of the sequence stratigraphy of the middle (approx. NP7) part of the Thanetian type-section.

These studies permit a more precise determination of the northern limit of the preserved Woolwich/Reading Formations in East Anglia. Palaeomagnetic investigations of the Oldhaven Formation and lower part of the London Clay Formation (Harwich and Walton Members) have led to the dismissal of the `Oldhaven' normal polarity magnetozone; these units are reverse polarity magnetised, and were deposited during the middle part of Chron C24BR.

Recently acquired data suggest that a record of Chron C25N may be preserved in the Central London area. A normal polarity magnetzone (c. 2m thick), which has been positively assigned to the NP9 nanoplankton zone has been found within an expanded Woolwich Bottom Bed unit. The limited areal extent (several square km) of this package, known from numerous civil engineering project boreholes, and the nature of the depositional contacts bounding this unit suggest that it may be an isolated remnant, pre Chron C24BR. This unit is overlain by the Woolwich Bottom Bed proper.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.