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

Brlek, Mihovil ; Gaynor, Sean P. ; Mongelli, Giovanni ; Bauluz, Blanca (Universidad de Zaragoza) ; Sinisi, Rosa ; Brcic, Vlatko ; Peytcheva, Irena ; Mišur, Ivan ; Tapster, Simon ; Trinajstic, Nina ; Laita, Elisa ; Yuste, Alfonso (Universidad de Zaragoza) ; Šuica, Sanja ; Grizelj, Anita ; Kukoc, Duje ; Schaltegger, Urs ; Laita, Elisa (Universidad de Zaragoza)

Resumen: The Miocene Climatic Optimum (MCO) represents a global warm period (approximately 17‚Äì14.7¬†Ma) interrupting a long-term period of Cenozoic cooling. To elucidate if bauxitization took place in southeastern European mid-latitude areas during the MCO, we studied a section of undated massive karst bauxite (Crveni Klanac, CK) in central Dalmatia, Croatia, hosted in Upper Cretaceous limestones and overlain by Miocene Sinj Basin lacustrine deposits. Integrated mineralogical, morphological and geochemical analyses indicate the predominant mineral phases of the homogenous bauxite matrix are authigenic, subhedral to euhedral kaolinite and gibbsite. The in-situ mineralization was a consequence of pedogenic processes, indicating the CK bauxites formed autochthonously. In situ U‚ÄìPb zircon ages of the lower, middle and upper parts of the CK bauxite are very similar, dominated by Miocene and Oligocene ages, indicating that they all share similar protolith(s). Subsequent high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) analyses indicate a maximum depositional age (MDA) for the pre-bauxitic material of 16.9576 ¬± 0.021¬†Ma (2œÉ uncertainty, incorporating decay constant uncertainty). This MDA, a maximum age of autochthonous bauxitization, coincides with the onset of the MCO. Based on currently available geochronological constraints, the maximum timeframe for CK bauxitization was less than ~ 700¬†ka, which matches the records of the MCO in paleo-mid-latitude Europe. The potential imprint of pre-17¬†Ma bauxitization and contribution of older (i.e., Upper Paleogene) bauxite deposits resedimented to the CK profile, as well as degree of potential parautochthonous origin of the CK bauxites, is yet to be investigated. More than simply aligning with regional and local reconstructions of continental climatic conditions during the onset and the early stages of the MCO, the high degree of autochthony of the CK bauxites provide a precise climatic constraint. For in-situ bauxitization to occur in the southeastern parts of mid-latitude continental Europe, paleoclimatic and paleoenvironmental conditions must have had mean annual temperature greater than 17‚Äì22¬†¬8C and mean annual precipitation of more than 1100‚Äì1200¬†mm.

Idioma: Inglés

DOI: 10.1007/s00531-021-02091-z

Año: 2021

Publicado en: International Journal of Earth Sciences 110, 8 (2021), 2899-2922
ISSN: 1437-3254

Factor impacto JCR: 2.698 (2021)

Categ. JCR: GEOSCIENCES, MULTIDISCIPLINARY rank: 114 / 202 = 0.564 (2021) - Q3 - T2

Factor impacto CITESCORE: 4.6 - Earth and Planetary Sciences (Q2)

Factor impacto SCIMAGO: 0.859 - Earth and Planetary Sciences (miscellaneous) (Q1)

Tipo y forma: Article (Published version)

Área (Departamento): Área Cristalografía Mineralog. (Dpto. Ciencias de la Tierra)