CHEMOSTRATIGRAPHY OF THE BARREMIAN-APTIAN EL PUI SECTION, ORGANYA BASIN, SOUTH CENTRAL PYRENEES, SPAIN: ENVIRONMENTAL CONDITIONS ASSOCIATED WITH CARBON ISOTOPE SEGMENTS C2 - C6, ACROSS OAE1A

The expanded latest Barremian-Early Aptian hemi-pelagic sedimentary record of the El Pui section (237 m) includes a distinct carbon isotopic signature correlative with the Tethyan record (Menegatti et al., 1998). The high-resolution data allow us to more accurately define carbon isotope segments C2 to C-6, as well as temporal redox changes specific to the semi-enclosed Organyà Basin associated with these episodes.

Characteristically, segment C2 corresponds to a positive shift with values around -24‰ (23.5‰ max) interrupted by a well defined short-lived ~ 1.52‰ inflection in the lower half of that interval. Segment C3 shows the lowest negative values at -27.95‰, harbinger of the onset of OAE1, which is correlated with the sharp positive shift (> 4‰) indicative of segment C4 (-23.72 ‰ max). The subsequent positive values (~ -24‰) distinguish segment C5, until a further positive shift (- 22.76‰) distinctive of segment C6.

Concomitant time-series of redox sensitive trace element concentrations (Ni, V, Cr, U, Th, and Co) indicate that conditions in the Organyà Basin remained under varying degrees (dysoxic to suboxic) of oxygen-deficient conditions (Sanchez-Hernandez and Maurrasse, 2014) throughout the latest Barremian- early Aptian time interval studied. These recurrent conditions were apparently more prolonged and frequent in the restricted basin than observed in coeval sections elsewhere in the Tethyan domain; however, the geochemical records concur with the microfacies analysis and demonstrate an absence of complete anoxia, even during the interval C4 to C6 correlative with OAE1a.

Menegatti, A.P., Weissert, H., Brown, R.S., Tyson, R.V., Farrimond, P., Strasser, A., Caron, M., 1998. High-resolution δ13C stratigraphy through the Early Aptian ‘Livello Selli’ of the Alpine Tethys. Paleoceanography 13, 530–545.

Sanchez-Hernandez, Y., Maurrasse, F.J-M.R., 2014. Geochemical characterization and redox signals from the latest Barremian to the earliest Aptian in a restricted marine basin: El Pui section, Organyà Basin, south-central Pyrenees. Chemical Geology 372, 12–31.