negative values due to global changes in the oceanic carbon reservoir . Cenomanian-Turonian negative excursions are relation with the light carbon derived from the oxidation organic material during sea-level fluctuations.

Chemostratigraphy versus biostratigraphy: data from around the Cenomanian- Turonian boundary

A. S. GALE, H. C. JENKYNS, W. J. KENNEDY, & R. M. CORFIELD

Journal of the Geological Society, London, Vol. 150, 1993, pp. 29-32,

A detailed isotopic profile is presented for a stratigraphically expanded Cenomanian-Turonian boundary section in Chalk facies exposed at Eastbourne, Sussex and compared with data from Pueblo, Colorado. In both sections macro- and micropalaeontological markers (first appear- ances and disappearances) are well-constrained, and their relative pos- itions and relationship to the structure of the carbon-isotope curve are identical. This consiste relationship between two independent pheno- mena, one geochemical, the other biostratigraphical, is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon-isotope excursion in these two areas. This interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon-isotope excursion in Europe and North America.

Conclusions.

The complex and ornate carbon-isotope excursion found in expanded sections that straddle the Cenomanian- Turonian boundary occurs in a consistent position relative to biostratigraphical markers in both Europe and North America. More limited data suggest the same relationship holds true for a section in north Africa. Given the extreme unlikelihood of duplication of such a complex isotopic signal, with its consis- tent relationship to first appearances and disappearances of significant elements of the biota, on different continents at different times, it is assumed that both chemostratigraphical and biostratigraphical signatures are synchronous. Upwelling is rejected as a major influence on the carbon-isotope signal in this instance ; the principal control on 6~3C values in the ocean- atmosphere system during Cenomanian-Turonian boundary time was burial patterns of organic carbon. Carbon-isotope stratigraphy thus remains a potent means of regional correl- ation with extraordinary resolving power.

CHEMOSTRATIGRAPHY OF CENOMANIAN–TURONIAN CARBONATES OF THE SARVAK FORMATION, SOUTHERN IRAN

E. Hajikazemi I.S. Al‐Aasm M. Coniglio

Journal of Petroleum Geology, Vol. 35(2), April 2012, pp 187-206

Abstract

Stable‐isotope and trace‐element analyses from five surface and subsurface sections of the mid‐Cretaceous Sarvak Formation in southern and offshore Iran confirm the presence of the regional‐scale Turonian unconformity and of a more local Cenomanian–Turonian unconformity. The geochemical results indicate the presence of previously unrecognized and/or undifferentiated subaerial exposure surfaces. Sarvak Formation carbonates at or near palaeo‐exposure surfaces show varying degrees of diagenetic modification, and more extensive alteration is associated with longer periods of exposure. The subaerial exposure and associated diagenetic processes greatly influenced reservoir quality and amplified karstification and evolution of porosity in the Upper Sarvak Formation.

The palaeo‐exposure surfaces are identified by their negative δ13C values (as low as – 6.4%) and negative δ18O values (as low as –9.4%), together with low Sr concentrations and relatively high 87Sr/86Sr ratios. These geochemical characteristics are interpreted to be the result of the interaction of the Sarvak Formation carbonates with meteoric waters charged with atmospheric CO2. The meteoric waters also caused karstification and soil formation which in some places extends a few metres below the exposure surfaces. Depleted carbon values were not recorded in areas where palaeosols are not well developed or where the uppermost layers of the Sarvak Formation have been removed by erosion.

Thank you @ Issam Moussa

What type of d13C have been measured in the last abstract