CARBON-ISOTOPE AND OXYGEN-ISOTOPE STRATIGRAPHY OF THE ENGLISH CHALK AND ITALIAN SCAGLIA AND ITS PALEOCLIMATIC SIGNIFICANCE

A detailed carbon- and oxygen-isotope stratigraphy has been generated from Upper Cretaceous coastal Chalk sections in southern England (East Kent; Culver Cliff, Isle of Wight; Eastbourne and Seaford Head, Susse x; Norfolk Coast) and the British Geological Survey (BGS) Trunch boreh ole, Norfolk. Data are also presented from a section through the Scagl ia facies exposed near Gubbio, Italian Apennines. Wherever possible th e sampling interval has been one metre or less. Both the Chalk and Sca glia carbon-isotopic curves show minor positive excursions in the mid- Cenomanian, mid- and high Turonian, basal Coniacian and highest Santon ian-lowest Campanian; there is a negative excursion high in the Campan ian in Chalk sections that span that interval. The well-documented Cen omanian-Turonian boundary 'spike' is also well displayed, as is a broa d positive excursion centred on the upper Coniacian. A number of these positive excursions correlate with records of organic-carbon-rich dep osition in the Atlantic Ocean and elsewhere. The remarkable similarity in the carbon-isotope curves from England and Italy enables cross-ref erencing of macrofossil and microfossil zones and pinpoints considerab le discrepancy in the relative positions of the Turonian, Coniacian an d Santonian stages. The oxygen-isotope values of the various Chalk sec tions, although showing different absolute values that are presumably diagenesis-dependent, show nonetheless a consistent trend. The East Ke nt section, which is very poorly lithified, indicates a warming up to the Cenomanian-Turonian boundary interval, then cooling thereafter. Re gional organic-carbon burial, documented for this period, is credited with causing drawdown of CO2 and initiating climatic deterioration (in verse greenhouse effect). Data from other parts of the world are consi stent with the hypothesis that the Cenomanian-Turonian temperature opt imum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth.