• Rivers probably underwent a definite decrease in depth downstream and a sharp fall-off in their average discharge in the lower part of their courses, due to a number of factors including:

•A) Loss of water by evapo-transpiration and lower precipitation.

•B) Infiltration into a permeable alluvium.

•The rivers were probably exotic, and reduced to a network of low-gradient, shallow, ephemeral wadi distributaries plugged during repetive flash-flooding events and subject to frequent avulsions.

•

• The Upper Permian deposits of the eastern Southern Alps display the typical features of early rift successions: onset of sedimentation after a long period of subaerial erosion, and upward fining trend from red beds, trough evaporates to marine carbonates, with backstepping pattern of component sequences. These are though to be part of second order Upper Permian-Scythian rift-related sequence.

•

•Val Gardena sandstone and the Bellerophon Formation ( Upper Permian ) in the Dolomites and Carnia show an overall transgressive trend and record the transition from continental red-bed to marine sedimentation in an extensional tectonic setting. The eastward progression of the Bellephron transgression resulted in the diachrony of the boundary between Val Gardena Sandstone and Bellephron Formation. The transgression was actually punctuated by a series of cyclical pulsations, which resulted in complex interfingering of terrigenous, evaporitic and carbonate deposits and in the subdivisions of the sedimentary succession into a number of sequences. The various vacies are essentially contempareous and follow one another along a paleoslope gently inclined towards the east, so that the red beds grade basinwards (i.e. eastwards ) through sabkha and lagoonal deposits into marine carbonates.

•

•In the area between the Adige Valley and the Karawanken Mountains the Bellephron Formation ranges in thickness from 0 ( westernmost area ) to 360 m.

•

•The Bellephron Formation consists of a very complex array of lithofacies, its depositional area may be subdivided from west to east into

•1) Coastal belt characterized by sabkha-type sediments interfingering with terminal fan deposits.

•2) Hypersaline lagoon or restricted inner shelf, characterized by evaporates and carbonate deposits.

•3) An inner carbonate shelf.

•The transition from coastal to offshore environments was extremely gradual, suggesting a very gentle depositional gradient, and resulting in sedimentation particularly sensitive to environmental changes. The Bellephron Formation is sharply or transitional overlain by a regional widespread member between different sections, in the absence of outcrop continuity.

•

• The Upper Permian succession of the Southern Alps displays the typical features of early rift successions. The overall pattern is that of transgressive, backstepping and onlapping arrangements of deposits suggesting a background of regional subsidence.

•

•Sedimentation started in graben-like depressions, and was initially fed by local sources. Later as a result of regional subsidence and morphogenetic evolution of the basin, the original depositional areas joined, ultimately resulting in an unified and increasingly expanded depression with sedimentary fill progressively onlapping the margins of the basin. Basin opening is recorded by coarse scree and alluvial fan deposits.

•

•The thickness of Val Gardena Sandstone in the study area ranges from zero ( Trento area ) to more than 500 m ( Comelico area ). In the Dolomites and Carnia, the red beds grade into the evaporitic and carbonate deposits of the Bellerophon Formation. The transgression progressively encroached on western areas. A structural high between the Adige Valley and the Giudicarie Line prevented the westward progression of the transgression, so that the Bellerophron Formation appears on a broad scale as a sedimentary wedge pinching out westwards. The Bellephron Formation is overlain by the Lombardian Unit ( continental sediment ).

•

•Terminal fan facies

•Generally single-storey ribbons and sheet like composite channelized bodies, generally of mixed load type, showing on average an upward increasing reduction in thickness and river bedload content; these are encased in an increasingly overbank of sediments, leading to low channel interconnections. This evolution is typically absent or very poorly developed in the marginal parts of the basin and in the less subsiding areas characterized by reduced thickness of sedimentary succession. Simple single-storey ribbons range from 0.9 to 4.3 m in thickness. The sediments involved range coarse sands, locally bearing granules and small pebbles, to fine sands and mudstone. Channel fills exhibit a sharp, fairly incised, irregular erosional base, sometimes with a remarkedly stepped appearance, floored by mudstone clasts and sometimes-reworked calcrete nodules. Vertically accreted ribbons commonly display a crudely developed fining-upward textural sequence, with trough cross bedding of upward decreasing scale, locally accompanied by planar lamination; small ribbons of this type may have been deposited by single flood events. Other ribbons show an inclined heterolithic stratification suggesting limited lateral migration, with muddy members of the couplets usually reaching the base of the channel.

•Thick muddy intercalations, sometimes pedogenically modified, may occur in the lateral accretionary units indicating that the fill was highly episodic in some channels. Burrow networks are relatively common in the upper part of the channel fills.

•Internal scouring surfaces, in place floored by mudstone clasts, are quite common, and several stages of scour and fill are characteristic, especially in channelized bodies of the inner more proximal zone of the system, and suggests highly fluctuating hydrodynamic conditions.

•Sheet like sandstones, mostsly resulting from lateral and to a limited extend also vertical amalgation of ribbons and small-storey internal organization can be found.

•Channel fills are interbedded with a great variety of interchannel sand and silt units deposited during flooding. Splay sandstones and commonly form a volumetrical large proportion of the total sand framework, especially near the transition into inferred sabkha sediments and may extend far into the interchannel areas, reflecting the extremely flashy and ephemeral nature of the associated streams. Splay deposits include both sheet sand layers showing virtual non-erosional basal contacts with the underlying sediments, and more discontinous and lenticular beds with broadly erosional bases. Sheet sandstone layers partly appear to be wings tapering away from channel sandstone bodies and sometimes coalescing to form extensive sheet-splays. The may be rich in vegetal debris and show small-scale flood sequences. Wave ripples draped by mud laminae are also locally observed.

•The upper surface of some play sandstone layers show evidence of a local shallow scouring. Splay sandstones and associated mudstones in places show root traces and or invertebrate burrows and are occasionally interbedded with dolomite and gypsum layers. Horizons with mud cracks in the mudstones.

•Spaly sandstones may appear organized into thickening and coarsening-upward sequences 6-10 m thick, displaying a clear upward increase in the sand/mud ratio. These consists of basal mudstone intervals with sparse, thin, sandstone interbeds passing up into thicker-bedded sheet-sandstones and eventually single channel fills.

•

•Mouth bar

•Small-scale upward thickening and coarsening sequences 3-6 m thick are generally observed at the transition from lagoonal/marine to continental facies associations. Muddy layers alternate with thin-bedded sandstones in the lower part, and progressively disseappear, to grade upwards into a amalgated package of sandstone layers generally displaying unidirectional structures such as ripple-drift cross-lamination, trough cross bedding and planar-lamination; the sequence may be capped by erosive based channel sandstones. The facies association is thought to represents small mouth-bars encroaching on a shallow-water basin.

•

•

•

•