Carbon isotopes and sequence stratigraphy

Abstract

The carbon isotope (613C) stratigraphy of the late Lower Cenomanian to early Lower Turonian is presented for three sections (Folkestone in the Anglo-Paris Basin, Wfinstorf in the Lower Saxony Basin and Speeton in the Cleveland Basin). The similarity between these isotope curves suggests that they were controlled by synchronous, global processes and can be used for high resolution correlation. Furthermore, sequence stratigraphic analysis of this interval reveals that each isotope excursion is associated with a sequence boundary and/or onlap surface. This is also demonstrated for the whole of the Cenomanian for the section at Speeton. We show that most (if not all) 6~3C excursions are synchronous within the limits of current stratigraphic resolution.We interpret the increase in background 613C values as representing an increase in the area of ocean floor (specifically continental shelf) available for burial of marine organic carbon caused by the mid-Cretaceous rise in eustatic sea-level. Thus background 613C values may provide an independent method for estimating past eustatic sea-levels. We interpret the sharp 613C excursions as reflecting more rapid changes in the carbon cycle particularly the rate of burial of organic carbon within sediments, and/or of storage in deep and intermediate water masses, at times of rapidly changing sea-level. Carbon excursions may be useful in locating sequence boundaries when other criteria are obscure or lacking.

Secular variation in Late Cretaceous carbon isotopes: a new δ13C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)

“…They rise again by + 0.8 ‰ δ 13 C from the base of the Acanthoceras (Table 1) indicated by circled numbers and arrows. Additional biostratigraphic sources: Culver Cliff -Jarvis, Murphy & Gale (2001); Dover -Jenkyns, Gale & Corfield (1994), Gale (1995Gale ( , 1996; Trunch -Wood, Morter & Gallois (1994); Speeton -Mitchell (1996), Mitchell, Paul & Gale (1996). Isotope data sources: Culver Cliff - Paul et al (1994b), Jarvis, Murphy & Gale (2001); Dover -Jenkyns, Gale & Corfield (1994) ;Lamolda, Gorostidi & Paul (1994), Mitchell (1996); Trunch -(this study); Speeton -Mitchell, Paul & Gale (1996).…”

“…Jarvis et al (1988a) documented carbon-and oxygen-isotope curves across the Cenomanian/Turonian boundary. The isotope data reported here are those of Jenkyns, Gale & Corfield (1994), replotted against our revised logs, with additional higher resolution sample data for the Middle Cenomanian from Paul et al (1994b) and Mitchell, Paul & Gale (1996), and for the Cenomanian/Turonian boundary interval from Lamolda, Gorostidi & Paul (1994).…”

“…Section details have been provided by Hill (1888), Jeans (1973Jeans ( , 1980, Paul et al (1994b), Gale (1995), Mitchell (1995Mitchell ( , 1996, Mitchell, Paul & Gale (1996) and Mortimore, Wood & Gallois (2001). A highresolution carbon-isotope stratigraphy of the Upper Albian-basal Turonian has been documented by Mitchell and co-workers (references above); the stratigraphic and δ 13 C data presented here are those of Mitchell, Paul & Gale (1996, fig.…”

“…In this study, the cyclostratigraphic units of Gale (1990Gale ( , 1995 have been identified in our sections, and are used to constrain our carbonisotope correlations at a couplet scale. Calibration of the couplet scheme in individual sections was achieved by identifying key faunal and lithological marker beds, many of which were first defined in northern Germany (Ernst, Schmid & Siebertz, 1983), but which have been subsequently recognized in England and France (Mitchell, Paul & Gale, 1996;Robaszynski et al 1998).…”

“…Based on the succession at Speeton, Mitchell, Paul & Gale (1996) described seven isotope events in the Cenomanian: the Albian/Cenomanian Boundary Event (ACBE); three Lower Cenomanian events (LCE I-III); two Middle Cenomanian events (MCE I-II); and the Cenomanian/Turonian Boundary Event (CTBE). The uppermost three of these were correlated with southern England and Germany.…”