engleski

Middle Triassic autoclastic deposits in the vicinity of Bosansko Grahovo (SW Bosnia and Herzegovina)

Middle Triassic volcaniclastic rocks have been recognized at several localities in the vicinity of Bosansko Grahovo, in the southwestern part of Bosnia and Herzegovina in the External Dinarides. Peculiar types of autoclastic rocks were investigated. These are peperites and hyaloclastites. Regarding specific structures, mineral composition and micropetrographic characteristics hyaloclastites observed at section Bosansko Grahovo I represent genetic succession. It was possible to further differentiate hyaloclastites into a) in situ hyaloclastites, b) slightly resedimented hyaloclastites and c) resedimented hyaloclastites. Genesis of peperites is related to lava emplacement in unconsolidated water saturated pelagic lime mudstones. In situ hyaloclastites and slightly resedimented hyaloclastites were formed due to quenching at the contact of basaltic lava effusions with sea water. Detritus of resedimented hyaloclastites, where volcanic rock fragments are mixed with limestone/chert clasts, imply reworking after fragmentation and redeposition possibly in the vicinity of primary volcanic basalt effusion. All rock types occurred in the deep sea troughs that formed as a consequence of Middle Triassic extensional tectonic and rift related wrench faulting. All investigated rock types represent the first findings of autoclastic deposits in the External Dinarides. Biostratigraphic constraints achieved by means of conodont species Neogondolella excentrica, Paragondolella excelsa, Paragondolella trammeri and Gladigondolella tethydis indicate Late Anisian to Early Ladinian interval of the autoclastic deposits from Bosansko Grahovo.

autoclastites ; hyaloclastites ; peperites ; Middle Triassic ; External Dinarides ; Bosnia and Herzegovina

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