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Megabeds in Istrian Flysch as markers of synsedimentary tectonics within the Dinaric foredeep (Croatia)

Istrian Flysch is deposited during Eocene in the Dinaric foredeep and is composed of hemipelagic marls and various gravity flow deposits. The later are predominantly 5-40 cm thick turbidites, developed mostly as laminated and cross-rippled sandstone beds (Tb-e, Tc-e and Td-e Bouma sequences). Besides the turbidites, there are deposits characterized by a significant thickness, occasionally more than 10 m, described as complex (bipartite) megabeds. The megabeds are composed of debrites in the lower part (Division I), and high- density turbidites in the upper part (Division II). A distinct clast composition of each megabed indicates that the lithoclasts were derived from tectonically active slopes and fault scarps along which collapses of different parts of Cretaceous to Palaeogene neritic carbonate succession, that underlays the Flysch, have occurred. The Division II deposits are well cemented, normally graded calcirudite/calcarenites composed mostly of ortophragminids, nummulitids, and red algae, originating from the outer ramp environments. Redeposited marl, found in matrix of the debrites and as intraclasts in some megabeds, implies that the collapses along the synsedimentary fault scarps and steep slopes occurred also within the foredeep itself, during the fast tectono- sedimentary evolution of the Dinaric foreland basin.

Adriaic microplate ; Dinaric foreland basin ; mass transport deposits ; Eocene ; External Dinarides

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