The stratigraphy and correlation of the Cenomanian-Turonian boundary interval succession in Lincolnshire, eastern England
by Christopher Wood, David Batten, Rory Mortimore & David Wray, Croydon, Aberystwyth, Brighton, Pembroke
WOOD, C. J., BATTEN, D. J., MORTIMORE, R. N. & WRAY, D. S.(1997): The stratigraphy and correlation of the Cenomanian-Turonian boundary interval succession in Lincolnshire, eastern England. - Freiberger Forschungshefte C 468. - Paläontologie, Stratigraphie, Fazies, Heft 5. - S. 333-346. - Freiberg 1997.
The Cenomanian-Turonian boundary (CTB) succession at the base of the Welton Chalk Formation in eastern England is typically extremely condensed (0.5m) comprising, above the basal erosion surface, a thin group of limestone and siltstone beds overlain by argillaceous beds including a thin (100mm) black shale, the Black Band. Deep excavations at Melton Ross Quarry, Lincolnshire, have revealed an unusually expanded (>2m) CTB succession in which clay-rich beds, including three additional black shales (the top one with Inoceramus ex gr. pictus), are intercalated between the basal erosion surface and a central, continuous limestone bed, which effectively forms the base of the condensed, 'standard' CTB succession. The complex lithostratigraphy and correlations of both the condensed and expanded CTB successions are described. The clay mineralogy comprises a mixture of illite, kaolinite and smectite at the base becoming predominantly smectite upwards with the almost complete loss of kaolinite at the top. This change in mineralogy suggests either deepening or increasing transportation distance from shorelines throughout the CTB interval. Shale-normalised Rare Earth Element (REE) profiles of samples from the clay-rich beds, including the Black Band, are all sub-horizontal (no Europium anomaly), suggesting a detrital rather than a volcanogenic provenance for the CTB succession, contrary to the usual interpretation. The palynomorph content of the black shales indicates a progressively more restricted marine environment up section. The dinoflagellate cyst assemblages in the black shales below the central limestone include common Litosphaeridium siphoniphorum, a taxon absent from the Black Band ss. This pattern of occurrence matches that recorded from the coeval Black Shales facies at Wunstorf Quarry, Lower Saxony, Germany where this taxon is also absent from the black shales above the Plenus Bed limestone. The acme top of Litosphaeridium siphoniphorum in the Plenus Marls lies in JEFFERIES Bed 6 indicating that the Black Band ss is above this level. The expanded CTB succession at Melton Ross may well prove to be 'normal' in contrast to the condensed 'standard' succession.