The intra-Mesozoic bauxite-bearing truncations of the peri-Neotethyan realm (Dinarides/Vardar Zone): A multidisciplinary approach shedding new light on the Neocimmerian event

Once coupled with global eustatic levels, bauxites, breccias, unconformities, and hiatuses are significant markers of compressional geodynamics. Most Balkan intra-Mesozoic bauxites, embedded within widespread Triassic carbonate parental sequences, are dominantly distributed in the tectonically exhumed broader Neotethyan realm (Dinarides s.l.). The same mid-Mesozoic stratigraphic interval within the Vardar Zone contains fewer bauxites (East Vardar Zone), exposing abundant corresponding depositional truncations, with occasional nappe stacking configuration and metamorphism. This study, which initially acquired data from a large number of mid-Mesozoic unconformities, carbonate breccias, and similar age bauxites spreading across Dinarides s.l., Serbia, Bosnia and Herzegovina, Montenegro, Croatia (Inner and External Dinarides, Western and East Vardar Zone), including Hellenides in Greece, has provided valuable paleogeographic and geodynamic insights. The findings of this study, combined with the available mineralogical and geochemical data, deformation, including the resulting provenances of intra-Mesozoic bauxite deposits, have led to a complex and intriguing discussion on the tectonic origin of similar age unconformities across Dinaride-Hellenide and Vardar Zone Neotethyan regions. These Dinaride-Hellenide intra-Mesozoic unconformities, carbonate breccias, and widespread bauxites are a fascinating puzzle as no study deals with the complex and controversial processes of repeated regional-scale uplifts, erosion, and bauxite formation. The ambiguity revolves around the geodynamic origin of the Jurassic ophiolites in the first place and its connection with mid-Mesozoic Cimmerian orogenic events (Neocimmerian stage). Thus, the Triassic – Jurassic(Lower Cretaceous) Inner Dinaride Ophiolite belt is particularly interesting accounting for the absence of the latest Jurassic – earliest Cretacous stratigraphic interval. Many of the bauxite ores are produced on Middle Triassic to Jurassic parental limestones, whereby the hiatus can last until the beginning of the Upper Cretaceous.

The Triassic rifting and opening of “Dinaric Tethys”, which likely caused the pre-Neocimmerian Late Triassic shoulder uplift of early passive margins, continued into the Jurassic mid-oceanic spreading. The Triassic and Jurassic-aged zircon grains in bauxites, including new data extracted from the bauxite geochemical database, corroborate a volcanic parental affinity originating from exposed Jurassic volcanic rocks. The new geochemical analysis allowed the separation of ultramafic from mafic bauxite sources, whereby acidic sources are absent or well hidden within Inner Dinarides. Bauxite deposits at the southern edge of the Inner Dinaride area show an abundance of incompatible Mn, demonstrating a significant transgressional Oxfordian eustatic high-stand episode (precipitation of Mn on top of submerged paleokarst/bauxites). This, a Red Sea-type small ocean basin with a NE-vergent suprasubduction (“Dinaric Tethys”), lasted until the end of the Jurassic (also dated by metamorphic imprints). The tectonic exhumation processes of Inner Dinaride ophiolites involving the Neocimmerian compressive event caused the widespread uplift episode in the latest Jurassic – earliest Cretaceous, occasionally lasting until the Albian (Austrian unconformity). As a result, mid-Mesozoic long-lasting hiatuses allowed intense weathering of numerous uplifted parental limestone sites, frequently producing at least two cycles of laterites and bauxite ores. The Neocimmerian episode includes the limited length (shorter cross-lithospheric across-strike width) of the latest Jurassic ophiolite obduction on top of abutting continental crust, inclusive of the onset of Lower Cretaceous Vranduk turbidites (another marker of the closing “Dinaric Tethys”).