Interactions between distal epiclastic and bio‐chemogenic sedimentation at the foothills of a mafic alkaline volcano: the case of the Oligocene Doupovské Hory Volcanic Complex (Czech Republic)

Late Oligocene (ca 25 Ma) volcano-sedimentary successions exposed on the western periphery of Doupovské Hory Volcanic Complex reveal a complex sedimentation history influenced in various ways by decay alkali basalt volcanic edifice. Weathering rocks supplied abundant reactants that promoted carbonate precipitation peripheral palaeolakes—as evidenced strongly non-radiogenic 87Sr/86Sr values (0.7038–0.7041). On other hand, sediments initial shallow lake became deformed bulldozing effect debris avalanche. The flow and avalanche deposits filled up original depression, modified basin morphology shifted lacustrine setting further away from volcano. At this stage, surface water influx surrounding granites conferred more radiogenic character (87Sr/86Sr 0.7046–0.7049) to calcrete deposits. Fossil assemblages as well limestone textures suggest significant seasonal water-level fluctuations, possibly reflecting alternating rainy dry-seasons prevalently humid Central-European climate. drying out ponds resulted 18O enrichments. Although ca 0 ‰ δ13C might mixing atmospheric CO2 during precipitation, no active conduits relevant age are known close vicinity. lower likely result mantle degassing through rift-faults, phenomenon observed magmatically extinct Ohře rift until present. This paper demonstrates limestones derived weathered alkaline basalts characterised highly Sr isotopic ratios 0.704), suggesting magmatic origin for Ca within these carbonates. Contrary notion carbonatites being present when isotopes found, results show carbonates formed alkali-basalt-sourced environments only source (and Ca) ions, not necessarily presence carbonatite.