engleski

The effects of blind-thrust folding on foreland sedimentation: examples from the Eocene-Oligocene Dinaric foreland basin of Croatia

The Dinaric foreland basin of Croatia developed through the tectonic deformation and marine drowning of an emerged and denudated Cretaceous carbonate platform due to the SW-directed orogenic compression. The proximal zone of the basin was filled with a calciclastic succession of Eocene−Oligocene neritic to terrestrial deposits, ~2000m thick, traditionally referred to as the Promina Beds. The distal zone was filled with a coeval turbiditic succession of the Dinaric Flysch, which is locally overlain by the Promina Beds. The Promina Beds recorded syn-tectonic sedimentation in an evolving orogenic wedge-top (‘piggy-back’) basin. This sedimentary succession forms a SE-trending outcrop belt ~80 km long and ~20 km wide in the northern Dalmatia, where it has been studied by regional mapping and detailed logging over the last three decades. The development of the wedge-top basin is recognized to have involved formation of a series of blind-thrust growth folds, before the soling thrust system eventually extended far enough to establish the wedge-top basin’s outer limit The effects of the syn-depositional folding included: (1) formation of incipient topographic ridges that were high enough to avoid an early drowning and hosted accumulation of weathering products that gave rise to bauxites ; (2) development of ‘classical’ progressive unconformities ; (3) deposition of differing facies successions on the opposite limbs of an anticline, with both limbs synchronously recording forced regressions due to the anticline growth and transgressions due to the foreland subsidence driven by crustal loading ; and (4) deposition of contrasting facies successions on the opposite limbs of a growing syncline, with the forced regression on one limb possibly corresponding to a transgression on the other limb, or vice versa, in the case of non-synchronous thrusting. The development of blind-thrust folds in the proximal foreland basin thus resulted in rapid lateral changes in sedimentary facies successions and their thicknesses as well as a spatially differential record of relative sea-level changes. Similar syn-tectonic phenomena can be expected to have occurred in other foreland basins and should be taken into account in the stratigraphic analysis of basin-fill sedimentary successions.

blind thrusts; Promina foreland basin

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