The carbonate mass-transport deposits of the Paleocene Julian Basin (Eastern Friuli, Italy)

The Paleogene carbonate megabreccias of the Eastern Friuli, South-Eastern Alps of Italy, are thick, up to 260 m, and laterally extensive, up to 100 km, bodies attributed to catastrophic submarine landslides, which occurred in a deep-water, turbidite-filled foredeep basin (Julian Basin or Slovenian Basin of the Slovene geologists). The Grivo Flysch succession (late Paleocene-early Eocene) contains several of these mass-transport deposits (MTD) intercalated within carbonate, siliciclastic and mixed turbidites. Megabreccias are mainly composed by shallow-marine detritus from the Friuli Carbonate Platform. The latter, placed at the southern boundary of the basin, was a passive, distal margin at the time of deposition of these units, far from the deformational front of the Southern Alps. The type and the scale of the processes interred for the largest MTDs, as well as the size of the individual component slide blocks (olistoliths), are comparable with the well-studied Eocene carbonate megabreccias of the Southern Pyrenean Foreland Basin. Notwithstanding such impressive characteristics, the MTDs of the Julian Basin have attracted the attention of a limited number of researchers with only few local scientific productions, not easily available to the international community. Therefore, these bodies are still relatively poorly understood especially in terms of sedimentary processes and emplacement mechanism. Previous studies mainly addressed the litostratigraphy of the Julian Basin succession and the sedimentological characteristics of the internal organization of the MTDs. Other aspects such as the number and the ages of these bodies, thicknesses and variation of internal divisions, the provenance of the material and the triggering mechanisms have been also considered. On the other hand, many crucial issues concerning the Julian Basin MTDs have not been discussed or remain unsolved, especially in light of a modern approach that takes into account the recent progressions in marine geology regarding large-scale mass transport deposits. In particular, detailed studies on the internal kinematics and the down-slope evolution of the mass-transport have not been performed systematically, although the excellent and continuous exposures and the high basin-wide correlation potential of each bed, due to the lack of intense tectonic deformation. This favorable context allows studies on the relationships between the transport-emplacement of the MTDs and the deformation of the substratum, which have not been investigated so far. Our communication addresses these aspects, as well as the overall distribution, architecture and physiographic setting of these deposits in the framework of the Julian Basin. A general synthesis of the emplacement mechanism of the largest of these beds (ie. Vernasso unit or MB 11) will be advanced, in comparison with other fossil examples known in the literature.