Sedimentary basins evolution and olistoliths formation: the cases of Carpathian and Sicilian regions

The early stage of basin formation in carbonate platform settings, from rifting to further crustal thinning, is generally characterised by mass movements from the faulted margins towards the stretching and drowning sectors. Avalanches, debris flows deposits with extrabasinal blocks, olistoliths, olistoplaque and olistostromes mark the sedimentary record. Block tilting, related to the normal activity of faults, determines the uplift of basin margins, shedding material for the formation of oliststromes. The onset of basin dynamics could be also marked by magmatic upwelling. During the late rifting stage, mass movements decrease, sediments supply with huge olistoliths and olistostromes is less common and coarse-grained deposits prevail, alternating with periods of pelitic sedimentations. Such sedimentary evolution may be observed in several basin successions, independent of their age and geodynamic setting. Good examples are the Northern Carpathian Basin and the Sicilian carbonate platforms-basins system, compared here because of their similarities.
   During the Late Jurassic-Early Cretaceous, the Southern European Platforms system topped by carbonate sedimentation experienced rifting and that resulted in opening of the proto-Silesian Basin. Crustal stretching was accompanied by andesitic-teschenitic intrusions. The Late Jurassic-Early Cretaceous sequences of the proto-Silesian Basin were later split into different tectonic units. Neritic grey, black or brownish marly mudstones deposited during the Kimmeridgian-Tithonian were locally associated with debris flows containing olistoliths derived from the adjacent carbonate platform. The mudstones evolve during Tithonian-Berriasian into pelagic limestones and shales with a complex of turbiditic limestones, suggesting a relatively quiet tectonics. Starting from the Valanginian, turbiditic and conglomeratic sandstones with exotic blocks appear within the calcareous shales. Locally, huge olistostrome appears, containing both extrabasinal olistoliths as well as olistoliths derived from the faulted flanks of the proto-Silesian Basin. These coarse sediments evolve upwards to Hauterivian-Aptian black shales. At the end of early Cretaceous (Barremian- Albian), compressional movements started, increased tectonic activity begun and uplift initiated denudation of the margins and ridges and resulting in very thick-bedded sandstones, conglomerates and occasionally olistoliths deposited during Late Cretaceous and Early Paleogene. An oblique collision of the Inner Carpathian terranes with the North European Plate during the Late Eocene-Early Miocene led to the development of accretionary prisms of the Outer Carpathians; numerous olistostromes were formed during this time.
   In Sicily, the onset of basin opening (Imerese-Sicanian) occurred during the Triassic. It was interposed between carbonate platforms (Panormide-Hyblean-Pelagian). In the basal deep-water sediments, lenses of olistostromes with olisholiths and basaltic extrusions related to crustal stretching were deposited at the basin margins. These olistoliths were derived from mass-wasting of the Late Permian-Lower Triassic carbonate platform. Late Triassic sedimentation (pelagic marls and limestones) suggests relatively quiet tectonic activity, followed by increased crustal stretching, as suggested by olistoliths of Lower Triassic clastic limestones embedded upwards. Jurassic-Early Cretaceous sedimentation is represented by deep-water siliceous marls and radiolarites, containing several horizons of carbonate turbidites and breccias derived from erosion of the fault-controlled basin flanks. From the beginning of Late Cretaceous, deposition of basin-plain marls and limestones indicates the mature stage of basin dynamics. Upward in the succesion, thick horizons of resedimented carbonate breccias are very common, indicating the onset of tectonic inversion, from preorogenic extension to the chain building.
   Acknowledgment: This research has been partly financed by the Ministry of Science and Higher Eeducation in Poland, grant no NN307 249733.