Laevaptychi as reliable paleotemperature archives: high-resolution stable isotope compositions of Kimmeridgian (Jurassic) lamellar structured aspidoceratid lower mandibles from Zengővárkony (Mecsek Mountains, Hungary)

Fieldwork provided well-preserved Laevaptychus sp. ex gr. hoplisus–obliquus specimens from the lower Kimmeridgian of Zengővárkony (Mecsek Mountains, south Hungary). This study presents the stable isotope analysis of these aptychi and control samples from brachiopods (Nucleata and Pygope) derived from the Zengővárkony section bed 3. Rarely observed structures in the upper lamellar layers of the studied laevaptychi revealed 24–32 concentric lamellae that represent primary textural features and indicate excellent preservation. After careful screening for diagenetic effects, stable oxygen isotope compositions yielded seawater temperatures between 20 and 26 °C in good agreement with earlier studies on Jurassic formations, with improved precision. Our research presents for the first time that well-preserved laevaptychi may be a reliable data source for paleoclimate and paleotemperature reconstructions.