A Complementary Section for the Proposed Toarcian (Lower Jurassic) Global Stratotype: the Almonacid De La Cuba Section (Spain)

Abstract

We present the biostratigraphy (ammonites, brachiopods, foraminifers, and ostracodes), lithostratigraphy, sedimentology, sequence stratigraphy, magnetostratigraphy, and isotope stratigraphy of the Almonacid de la Cuba section located in the Iberian Range, central eastern Spain. This section, which contains a continuous and expanded record of the Pliensbachian–Toarcian boundary (Early Jurassic), has been proposed as a complementary section for the Toarcian GSSP. An excellent ammonite based biozonation has been obtained. Four ammonite assemblages characterized by the presence of Pleuroceras, Canavaria, Dactylio ceras (Eodactylites), and Dactylioceras (Orthodactylites) have been distinguished. The base of the Toarcian is located at level CU35.2, based on the first occurrence of Dactylioceras. The occurrence of taxa from the NW European and the Mediterranean provinces is useful to improve the correlation between both provinces. For aminiferal and ostracode assemblages are rich and diversified and no significant biostratigraphic events take place at the Pliensbachian–Toarcian boundary. The magnetostratigraphic data presented here are the most complete record of reversals of the earth magnetic field for the Pliensbachian–Toarcian boundary. A good record of the onset of the positive δ13C excursion reported in the Lower Toarcian of many European sections has been obtained. Average paleotemperatures measured at the latest Pliensbachian Spinatum Biochron of about 12.5°C, recorded a marked increase of the seawater temperature which started during the Toarcian, reaching average temperatures of 16.7°C at the Tenuicostatum Biochron. The obtained 87Sr/86Sr values fully agree with the LOWESS calibration curve.