Upper Toarcian-Lower Bajocian (Jurassic) Hammatoceratoidea (Ammonitina) of the Betic Cordillera (southern Spain): biostratigraphy and zonal correlations

Abstract

Abstract Betic hammatoceratoids from several sections of the Subbetic domain (Middle and External Subbetic) are here analysed from a biostratigraphic standpoint. Fifty-five hammatoceratoids “species” belonging to 17 genera occur throughout the Upper Toarcian-lowermost Bajocian interval. The best fossiliferous sections containing hammatoceratoids are located in the central and eastern sector of the Median Subbetic. In these areas grey marls and marly-limestone rhythmites are the predominant lithofacies from the Upper Toarcian to Lower Bajocian interval. Hammatoceratidae are the dominant hammatoceratoids during the Upper Toarcian, the Erycitidae are more common in the Lower Aalenian, and Zurcheriinae are especially abundant in the uppermost Aalenian-lowermost Bajocian. Six ammonite biozones, which can be easily correlated with the standard ammonite zones, have been defined based on the stratigraphic ranges of these species. These biozones are : a) Geczyceras meneghinii Biozone, which is equivalent to the Meneghinii Zone (Levesquei Subzone p.p. and Pseudoradiosa Subzone) and Aalensis Zone (Mactra Subzone p.p.); b) Erycites barodiscus Biozone, which ranges throughout the Aalensis Zone (Mactra p.p., Aalensis and Buckmani Subzones) and the Opalinum Zone (Opalinum Subzone); c) Erycites fallifax Biozone, which can be correlated with the Comptum Subzone of the Opalinum Zone; d) Spinammatoceras tenax Biozone, which coincides with Murchisonae Zone-Bradfordensis Zone (Bradfordensis Subzone); e) Malladaites pertinax Biozone, which coincides roughly with Bradfordensis Zone (Gigantea Subzone)-Concavum Zone (lower part of the Concavum Subzone); f) Haplopleuroceras mundum Biozone, extending to the upper part of the Concavum Subzone to the lowermost Bajocian (Discites, p. p., Zone). Although some of the recorded hammatoceratoids are typical of the western Tethys, others (especially the genera Eudmetoceras and Euaptetoceras) are globally widespread. Consequently, the use of these taxa enables stratigraphic correlations, not only with the western Tethys, but also with other palaeogeographic areas such as the central Tethys, eastern Pacific and even the eastern Tethys.