Karst bauxite formation during Miocene Climatic Optimum (central Dalmatia, Croatia): mineralogical, compositional and geochronological perspectives

The Miocene Climatic Optimum (MCO) represents a global warm period (approximately 17–14.7 Ma) interrupting long-term of Cenozoic cooling. To elucidate if bauxitization took place in southeastern European mid-latitude areas during the MCO, we studied section undated massive karst bauxite (Crveni Klanac, CK) central Dalmatia, Croatia, hosted Upper Cretaceous limestones and overlain by Sinj Basin lacustrine deposits. Integrated mineralogical, morphological geochemical analyses indicate predominant mineral phases homogenous matrix are authigenic, subhedral to euhedral kaolinite gibbsite. in-situ mineralization was consequence pedogenic processes, indicating CK bauxites formed autochthonously. In situ U–Pb zircon ages lower, middle upper parts very similar, dominated Oligocene ages, that they all share similar protolith(s). Subsequent high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) maximum depositional age (MDA) for pre-bauxitic material 16.9576 ± 0.021 Ma (2? uncertainty, incorporating decay constant uncertainty). This MDA, autochthonous bauxitization, coincides with onset MCO. Based on currently available geochronological constraints, timeframe less than ~ 700 ka, which matches records MCO paleo-mid-latitude Europe. potential imprint pre-17 contribution older (i.e., Paleogene) deposits resedimented profile, as well degree parautochthonous origin bauxites, is yet be investigated. More simply aligning regional local reconstructions continental climatic conditions early stages high autochthony provide precise constraint. For occur Europe, paleoclimatic paleoenvironmental must have had mean annual temperature greater 17–22 °C precipitation more 1100–1200 mm.