PETROGRAPHIC AND GEOCHEMICAL CHARACTERIZATION OF THE UPPERMOST BARREMIAN - LOWEST APTIAN OF THE EASTERN PRADA QUARRY SECTION OF THE RESTRICTED ORGANYÀ BASIN, SOUTH-CENTRAL PYRENEES

Here we present preliminary results of a high-resolution, multiproxy study (petrographic, and geochemical), including major elements, n-alkanes, δ¹³C_org, δ¹⁵N, and EDS) of a 30 m section of Barremian-Aptian limestone and marlstones of the Eastern Prada Mountain Quarry section, Organyà Basin, Catalunya, Spain. Intermittent nodular dark limestone and marlstone layers show low bioturbation index (2-3) and high TOC (up to 1.45 wt. %) with characteristic microfacies of dark micrite, and isotropic allochems distribution consisting of minute fragments of echinoderms and heteromorph ammonites, rare ostracods, gastropod fragments, benthic and planktic foraminifera. Globigerinelloides blowi indicates a chronological position within the late Barremian–early Aptian. Pronounced porosity consists of cavities or vugs filled with apparent bitumen.

 Qualitative EDS analyses indicate that CaCO₃ predominates in the rock matrix, and smear slides revealed high abundance of calcareous nannofossils as the source of carbonate, predominately disaggregated nannoconid fragments. δ¹³C_org values vary from a low of -26.13‰ at 0.7 m to a high of -23.77‰, (~ 2.36‰ change) at 18 m with higher amplitude fluctuations to the top of the section at 27 m. δ¹⁵N values are high, ranging from 1.82‰ to 5.95‰ positively correlated with the δ¹³C_org profile especially between 18 m and 27 m. Biomarker results from 16 samples revealed predominance of short chain n-alkanes (<nC₂₀), which suggest in situ origin of the OM from phytoplankton, with possible contribution from microbial communities. Pr/Phy ratios in the section remain persistently below 2 (~ 0.37 - 1.63), implying that OM did not reach an overmature state, consistent with previous n-alkane results in the Organyà Basin [1]. Biolimiting elements (P, Fe) show exceptional linear correlation with Al, Si and Ti indicative of terrigenous fluxes that sustained the nutrient supply, and enhanced primary productivity in the basin throughout that time interval.

 [1] Sanchez-Hernandez & Maurrasse (2014) Chem Geo 372: 12–31.