Carbon- and oxygen-isotope stratigraphy of the English Chalk and Italian Scaglia and its palaeoclimatic significance

Abstract

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, Sussex; Norfolk Coast) and the British Geological Survey (BGS) Trunch borehole, Norfolk. Data are also presented from a section through the Scaglia facies exposed near Gubbio, Italian Apennines. Wherever possible the sampling interval has been one metre or less. Both the Chalk and Scaglia carbon-isotopic curves show minor positive excursions in the mid-Cenomanian, mid- and high Turonian, basal Coniacian and highest Santonian–lowest Campanian; there is a negative excursion high in the Campanian in Chalk sections that span that interval. The well-documented Cenomanian–Turonian boundary ‘spike’ is also well displayed, as is a broad positive excursion centred on the upper Coniacian. A number of these positive excursions correlate with records of organic-carbon-rich deposition in the Atlantic Ocean and elsewhere. The remarkable similarity in the carbon-isotope curves from England and Italy enables cross-referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the Turonian, Coniacian and Santonian stages.The oxygen-isotope values of the various Chalk sections, although showing different absolute values that are presumably diagenesis-dependent, show nonetheless a consistent trend. The East Kent section, which is very poorly lithified, indicates a warming up to the Cenomanian–Turonian boundary interval, then cooling thereafter. Regional organic-carbon burial, documented for this period, is credited with causing drawdown of CO2 and initiating climatic deterioration (inverse greenhouse effect). Data from other parts of the world are consistent with the hypothesis that the Cenomanian–Turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth.

Changes in paleo-circulation and the distribution of ammonite faunas at the Coniacian–Santonian transition in central Poland and western Ukraine

“…Isotopic data, reported here, infer paleotemperatures for the Polish Sea (Lipnik-Kije section) that are anomalously high: higher than for the area of East Kent (UK), a part of Boreal Atlantic, and perhaps higher than those inferred for Spain, which was a part of northern Tethys Ocean (Jenkyns et al 1994;Lamolda and Paul 2007). The Dubovcy section in western Ukraine has a paleoposition which predisposes it for a comparative investigation.…”

“…8. Correlation of the Coniacian-Santonian δ 13 C curves; Olazagutia (Lamolda and Paul, 2007); East Kent (Jenkyns et al 1994); Dover and Trunch (Jarvis et al 2006); Lipnik-Kije and Dubovcy (this paper). Note that vertical and horizontal scales for all curves have the same scale the offset in bulk data δ 18 O curves between particular sections in terms of paleotemperatures can be questionable, although relative trends and the magnitude of differences in bulk-rock oxygen isotopes can be interpreted as gross climate signals (Stoll and Schrag 2000;Voigt and Wiese 2000).…”

“…Its usefulness for global correlation has been proved by different authors for different intervals (e.g. Schlanger et al 1987;Arthur et al 1990;Jenkyns et al 1994;Voigt and Hilbrecht 1997;Voigt 2000;Voigt and Wiese 2000;Gale et al 2005Gale et al , 2007Lamolda and Paul 2007; for a complete review see Jarvis et al 2006). Jarvis et al (2006) provided detailed carbon stable isotope data for the Cenomanian -Campanian plotted against the lithoand biostratigraphic logs of the Chalk succession in England.…”

“…As they noted, their reference curve is remarkably similar in shape to published, supposedly eustatic, sealevel curves with increasing δ 13 C values accompanying sea-level rise and transgression, and falling δ 13 C values characterizing sea-level fall and regression. Although an increasing number of Coniacian-Santonian (mid-Upper Cretaceous) sedimentary sections around the world have been investigated by means of stable isotope geochemistry (Coplen and Schlanger 1973;Arthur et al 1985;Jenkyns et al 1994;Huber et al 1995;Gruszczyński et al 2002;Zapata et al 2003;Leckie et al 2005;Jacobs et al 2005;Li et al 2006;Jarvis et al 2006;Lamolda and Paul 2007;Gale et al 2007), detailed correlation of stable isotope curves for the Coniacian-Santonian boundary interval, is less clear-cut than for other Upper Cretaceous intervals (Jarvis et al 2006).…”

“…We therefore assume that the pattern of δ 18 O differences in the studied sections reflects, at least in part, some original paleotemperature control. On a regional scale, we compare the oxygen stable isotope records from East Kent, UK (Jenkyns et al 1994) -fig. 9).…”