Isotope studies of carbonate rocks of La Luna Formation (Venezuela) to constrain the oceanic anoxic event 3 (OAE3)

Sr-87/Sr-86 ratios, delta C-13, and delta O-18 determinations performed on 30 bulk carbonate rocks are presented to constrain the isotope characteristics regarding Oceanic Anoxic Event 3 in the La Luna Formation, Maracaibo Basin. The samples were collected along a 22 m profile in San Miguel region (Merida State, Venezuela). The exhibited Sr-87/Sr-86 ratios are between 0.707659, at the base, and 0.707733 at the top of studied section, corresponding estimated younger numerical ages than the inferred ages dated as Santonian (85.8-83.5 Ma) based on occurrence of Dicarinella asymetrica. The obtained Sr-87/Sr-86 ratios are certainly higher than expected for Santonian sea Sr and they are attributed to regular riverine strontium fluxes in the restricted (gulf-like) Maracaibo Basin. The values of delta O-18 data between -3.76 parts per thousand and -11.76 parts per thousand are distributed in two distinct clusters in a same way and coherent as for 8.13C data which are in a range between -1.75 parts per thousand and -13.87 parts per thousand. One of the clusters delta C-13 = -2.5 +/- 1.0 parts per thousand and delta O-18 = -10.0 +/- 1.5 parts per thousand), illustrate the homogeneous marine deposition under tropical conditions, while the other, more variable, probably could reflect the cyclicity of temporally changes in Pacific versus Atlantic Ocean circulation with cooling water or cooling trend climate. These delta C-13 values around -2.5 +/- 1.0 parts per thousand do not fit with the significant carbon isotope excursion as expected for the oceanic anoxic event (OAE) and support the work hypothesis that Coniacian Santonian anoxic event (denominate as OAE3) is not a global one. (C) 2016 Elsevier Ltd. All rights reserved.