Palaeoentomological study of the lacustrine oil-shales of the Lower Miocene San Chils locality (Ribesalbes-Alcora Basin, Castellón Province, Spain)

Abstract

For the first time, the study of the fossil record present in laminated bituminous dolostones from the San Chils locality, Lower Miocene in age (ca. 19 Ma), located at the Ribesalbes-Alcora Basin, is addressed. The identification of 11 families and three genera belonging to six insect orders (Orthoptera, Thysanoptera, Hemiptera, Coleoptera, Hymenoptera and Diptera) has been carried out. Furthermore, ephippia of cladoceran crustaceans, one bird feather, vertebrate coprolites and plant remains have been found. The San Chils palaeodiversity has been compared to that of La Rinconada, a similar outcrop in the same basin and depositional unit. Both localities correspond to lacustrine deposits and were mined during the past two centuries. This work has increased the palaeontological richness of the Ribesalbes-Alcora Basin with new findings such as specimens of the subfamily Corixinae (Hemiptera: Corixidae), some ant workers (Hymenoptera: Formicidae), a specimen assigned to the genus Exechia (Diptera: Mycetophilidae), ephippia of Daphnia (Ctenodapnia) sp. (Branchiopoda: Cladocera), the possible first report of the genus Sciocoris (Hemiptera: Pentatomidae) for the Neogene fossil record and the possible presence of the family Aeolothripidae (Thysanoptera). The current collection of fossil specimens from San Chils is small, but shows that it shared similar palaeoenvironmental conditions to that of La Rinconada, both in the lake waters and in the surroundings. The preservation of the specimens is poor due to the weathering they suffered during more than a century exposed outside the mine, but the presence of delicate structures has enabled to classify the outcrop as a Konservat-Lagerstätte, like La Rinconada.