Publication Date:
2020-06-28
Description:
A chemostratigraphic study (13C and 18O) of the late Cenomanian and Turonian chalk succession from the “Craie 701” Poigny borehole (near Provins, Paris Basin, France) provides new high-resolution stable carbon and oxygen isotopic data. The correlations of the isotopic trends from Poigny with its English Chalk equivalent allow the development of a precise stratigraphic framework. 13C and 18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (CIE of 3‰ amplitude) without any apparent anoxia in the Late Cenomanian chalk. Comparisons with different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio section, Italy), across the Vocontian Basin, (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production modulated by a regional effect on the carbon organic burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through the Middle Turonian, including the salient CIE associated to the OAE 2 would reflect a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can be also better defined with this isotopic study. A comparison of 18O data between the Anglo-Paris Basin and Tethyan basins shows high-amplitude, long-term synchronous variations reflecting primary paleoenvironmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (-1‰ of amplitude) reflecting a warmer climate regime marks the onset of OAE 2, and two colder phases (+1‰ amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.
Print ISSN:
0037-9409
Electronic ISSN:
1777-5817
Topics:
Geosciences
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