More Than Just Age: Geochemical signatures of radiolarites from the Internal Western Carpathians

The Internal Western Carpathians comprise a complex Alpine thin-skinned nappe system derived from the Meliata domain. In its lowermost structural position, the Meliata Unit (Meliaticum) represents a remnant of the Neo-Tethyan oceanic suture and includes the blueschist-facies Bôrka Nappe, low-grade syn-orogenic accretionary complexes of the Meliata Unit s.s., and chaotic ophiolite-bearing mélanges. In this study, we focus on deep-sea sediments from the Meliata Unit and on comparable units of similar age and structural position within the Internal Western Carpathians, particularly the Turnaicum and Silicicum. Our dataset consists mainly of radiolarites in association with shales and claystone. Although the samples can be broadly divided into Triassic and Jurassic age groups, their geochemical composition reveals information that goes beyond biostratigraphic age constraints. As pelagic sediments deposited far from major continental input, radiolarites preserve signatures of seawater chemistry, hydrothermal activity, and detrital supply. These records allow us to reconstruct depositional conditions, sediment provenance, and the tectonic evolution of the Meliata oceanic domain. All 31 samples processed by whole-rock analysis were recalculated to eliminate the carbonate component and loss on ignition. The results show pronounced variability in the processes affecting the Meliata oceanic domain through time and space. In the Al₂O₃/(Al₂O₃ + Fe₂O₃) versus Fe₂O₃/TiO₂ discrimination diagram after Murray (1994), most samples define a trend from continental margin to ocean ridge affinity. Provenance discrimination for shales after Roser and Korsch (1988) indicates mature continental sedimentary sources. PAAS-normalized REE patterns further distinguish lithological groups. Shales display higher total REE concentrations and flatter profiles, whereas radiolarites are characterized by lower REE abundances and significantly more variable patterns. Several samples show a clear negative Ce anomaly, suggesting oxidizing marine conditions or seawater influence during sedimentation. A weak positive Eu anomaly in some samples may reflect a minor terrigenous contribution. These geochemical signatures demonstrate that radiolarites and associated shales from the Internal Western Carpathians record both local depositional conditions and broader tectonic evolution of the Meliata oceanic domain. Together, they provide a geochemical framework for tracing the transition from continental-margin sedimentation to more oceanic settings. This approach highlights the value of pelagic sediments as archives of ancient basin evolution and plate-boundary processes. Additional analyses of radiolarite and siliciclastic pelagic sediment samples from other tectonic units and paleoprovenances, together with comparisons to well-characterized geological settings, are necessary to fully and reliably interpret the obtained geochemical data.

 

Acknowledgements: The research was supported by projects of the Slovak Research and Development Agency (APVV-21-0281; SK-SRB-25-0031), Grant Agency for Science, Slovakia (VEGA 1/0021/25) and National Science Centre, Poland (2021/43/B/ST10/02312).

 

Murray R.W., 1994. Chemical criteria to identify the depositional environment of chert: general principles and applications. Sedimentary Geology, 90: 213-232.

Roser B.P. and Korsch R.J., 1988. Provenance signatures of sandstone-mudstone suites determined using discrimination function analysis of major-element data. Chem Geol, 67: 119-139.