Calibration of early–middle Toarcian nannofossil events based on high-resolution ammonite biostratigraphy in two expanded sections from the Iberian Range (East Spain)

Abstract

This work deals with refined nannofossil biostratigraphy in two well-documented lower–middle Toarcian sections, in the Iberian Range. The sampled shallow carbonate ramp deposits belong to the Turmiel Fm. and consist of an alternation of marls and limestones. Both lithologies yield common and well-preserved ammonite assemblages, which provide a refined ammonite biostratigraphic framework. A significant calcareous nannofossil composition change has been recognized within the Serpentinus Zone, and a useful succession of nannofossil events has been calibrated to the ammonite biostratigraphy. This succession includes: FO of Lotharingius sigillatus (Mirabile Subzone); LO of Mitrolithus jansae (Semicelatum Subzone); FO of Carinolithus cantaluppii (Strangewaysi Subzone); LOs of Biscutum grande and Biscutum finchii (lower part of the Serpentinus Zone); FO of Carinolithus superbus (Strangewaysi–Falciferum boundary); FO of Lotharingius velatus (Falciferum Subzone); FOs of Discorhabdus striatus and Discorhabdus ignotus (Serpentinus–Bifrons boundary) and “acme end” of Lotharingius hauffii (Variabilis–Illustris boundary). In the studied sections, the composition changes, the biohorizons recognized and their succession are closely comparable with other early–middle Toarcian Boreal sections.