ABSTRACT: Chemostratigraphic signals are becoming common tools in chronostratigraphic correlations. Specifically total organic and carbonate carbon percentages (TOCorg/carb) and carbon isotope curves are diagnostic in Cretaceous Aptian-Albian-Cenomanian strata. Cretaceous carbon isotope signals define oceanic anoxic events (OAEs) and have been subdivided into successive segments. These segments are used as correlation markers because they represent oceanographic and depositional conditions, and hence, incur time significance. Although the segments have been integrated with biovents in key sections, numerical ages of the segments have yet to be calibrated. Because direct correlation of these segments of carbon isotope curves with interbedded radiometrically dated beds is not possible currently, other methods must be applied to interpolate numerical ages. Graphic plots of five sections successfully integrate carbon isotope segments with established numerically dated chronostratigraphicmarkers. Carbon isotope segments were first defined in European Tethys Cismon and Rotter Sattel Barremian-Albian sections. The Aptian segments were subsequently identified in the Mexican Santa Rosa Canyon sectionwhere the lower Albian segments were defined. Each section haswell documented microfossils andmagnetochrons that relate the segments to biozones. These bioevents and chronozones enable the carbon segments to be integrated with a comprehensive Cretaceous time scale, the CRECSDB42. Ages assigned to the segments enable them to be used in sections where local fossil zones are recorded such as in the Chihuahua basin in northernMexico. The age calibration of carbon isotope segments measures the durations of the oceanic isotopic excursions. The durations fluctuate up to and after OAE 1a at irregular frequencies different from climatic cycles. Changing durations of carbon isotope segments may be clues to changes in processes or the effects of the process that altered the ocean carbon reservoir in addition to climatic changes.


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