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Abstract

Gutâi Mts. had started to be built up in Middle Miocene, ca. 15.4 Ma ago. A series of explosive events developed starting with a major magmatic explosion and caldera collapse responsible for large volumes of ignimbrites. Successive explosions followed caldera collapse triggering a series of pyroclastic currents that underwent subsequent reworking. Mass flow has been the main transport mechanism recorded by the sedimentary structures of either ignimbrites or post-ignimbrites volcaniclastics. Multiple ignimbrite units resulted from subaerial mass flows, successively emplaced by progressive aggradation from the basal layer of a density-stratified pyroclastic current. The overlying sequence is composed of different volcaniclastics of pyroclastic origin interlayered with mudstones. They preserve the original composition of ignimbrites, but lack the evidence of hot-state deposition, recording the emplacement from more or less dilute mass flows. A syn-eruptive stage of resedimentation is suggested prior to emplacement in submarine conditions, determined by the transformation of gas-supported pyroclastic currents into water-supported mass flows after transition from subaerial to submarine conditions. The syn-eruptive resedimented volcaniclastics may be correlated with the ignimbrite-type subaerial pyroclastic flows, but they show different degrees of fluidization due to the impact of submarine environment.

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