A CONSISTENT CARBON ISOTOPE TREND AS A POTENTIAL TOOL TO REDUCE BIOSTRATIGRAPHIC UNCERTAINTIES AT THE BARREMIAN – APTIAN BOUNDARY

Considerable chemostratigraphic data gathered over two decades on Lower Cretaceous sediments support the notion of C- isotope segments [1] that reveal major changes in the carbon reservoir. These segments have been calibrated with magnetostratigraphy and dependable microfossils at different Tethyan sections, thus providing excellent means for global correlation based on carbon isotope (δ¹³C_org and δ¹³C_carb) chemostratigraphy. Consistent patterns in the δ¹³C trend have been successfully used to identify coeval Lower Cretaceous sections lacking significant sedimentary evidence for low oxygen (e.g. absence of OM-rich shales), and reliable index macro- and microfossils.

Here we review published C-isotope curves that show a consistent negative shift (up to -1.5 ‰) associated with the Barremian-Aptian boundary at different localities worldwide: e.g., Cau section, NE Spain [2]; Provencal platform, SE France [3 - 4]; Organyà Basin, Catalunya, Spain [5]; Apulia carbonate platform of the Borgo Celano section, Italy [5]; Adriatic platform, Croatia [6]; IODP Site 765 in the Argo Abyssal Plain, located north of the Exmouth Plateau NW of Australia [7]; Comanche carbonate platform, northern Gulf of Mexico [8].

Based upon the constancy of the negative trend in the δ¹³C record, regardless of environment of these studied sections, and its correspondence with the Barremian-Aptian transition when calibrated with available index taxa, we propose that the negative excursion reflects global change in the ocean carbon reservoir. It may serve as a potential chronostratigraphic marker in the absence of reliable paleontological data. Since the application of biostratigraphy to determine the position of the Barremian –Aptian boundary has proven problematic; carbon isotope chronostratigraphy could provide a more accurate tool independent of the biostratigraphic uncertainties.

Ref: [1] Menegatti et al. (1998) Paleoceano 13: 530-545; [2] De Gea et al. (2003) Palaeo³ 200: 207–219; [3] Godet et al. (2006) EPSL 242, 254 – 271; [4] Föllmi et al. (2006) Paleoceano 21; [5] Sanchez-Hernandez & Maurrasse (2014) Chem Geo 372: 12–31; [6] Graziano et al. [2013] Boll Soc Geol It 132: 477-496; [7] DeBond et al. (2012) Isotopes Env Health Stud 48: 180-194; [8] Husinec, et al. (2012) AAPG Bull 96: 2215 – 2244; [9] Phelps et al. (2014) Sed 61: 461 – 496.