Section 4 Rio Gaido Upper Permian Italy (Permian of Italy)

Where: Italy (44.8° N, 9.8° E: paleocoordinates 7.9° N, 25.4° E)

• coordinate based on nearby landmark

• small collection-level geographic resolution

When: Zechstein (259.0 - 252.3 Ma)

Environment/lithology:

• 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.

•The coarser varieties may represent viscous subaerial debris flows, locally reworked in the late flood stage by dilute tractional flows. The finer-grained varieties , consisting of very poorly sorted mixtures of sand, silt and clay, may have been generated by rapid deposition from mud-laden sheet-flows of short duration, or graphy with little erosion, or spilled out of channels and spread over relatively flat surfaces. The finely conglomeratic top was probably deposited from waning aqueous “tail” following the debris flow slurry.

•More disorganized ungraded beds with poorly developed fabric may have been emplaced by high-concentration flood-related flows demonstrated that traction shear stresses, buoyancy, and dispersive pressure may all combine to keep clasts moving in the hyperconcentrated flows. If present, normal grading suggests that the actual clast support is mainly due to buoyancy and turbulance, and that the gravel dispersion is a more concentrated, more viscous, and slower moving lower part of the flowing turbulent suspension; the presence of inversely grading near the base suggests inertial flow and possible traction carpet deposition. In the rare cases of inverse to normally graded beds, the inversely graded part may have been emplaced by current-driven-high-density traction carpet, and the normally graded part from an overlying faster moving turbulent suspension. The capping units probably formed during the late flood stage, with tractional deposition following the main surge of the flow; they may either represent reworking of mass-flow deposits by shallow braided flows, or deposits linked to the accretion of longitudinal bars or infill of minor topbar channels in the outer braided part of the fans.

•This facies may have been deposited by more or less concentrated sheet flows, lenticular geometries may reflect shallow scouring due to local turbulence.

• 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 ).

•Very poorly sorted and structureless sandy-gravelly red brown mudstone. Shows diamitic like textures, in which a variable amounts of granules and small pebbles, and rarely sparse sub angular to sub rounded pebbles or cobbles, float in a matrix of very poorly sorted mixture of sand, silt and clay. Bed thickness averages 100 cm and ranges 25-210 cm. Internal bedding and clast imbrication are lacking. Normal grading sometimes occurs in the coarser-grained varieties. Individual beds usually have flat, non-erosional basal contacts. Beds are locally capped by fine clast-supported conglomerates, either one clast thick or displaying a crude planar lamination in the finer grained varieties.

•Framework-supported, structureless to graded, pebble to pebble-cobble conglomerates with sub-angular to rounded clasts. Structureless beds: 73%; normally graded 23%; inversely graded near the base 2%; inverse to normally graded 2%. Bed thickness averages 80 cm and ranges 12-280 cm. Sorting usually poor, occasionally moderate, and clast fabric from chaotic to moderately prevered. Clay chips locally present. Bed geometry predominantly sheet like, locally lenticular with erosional base. Normal grading may affect only the upper part of the bed, whilst the lower part is structureless. In some normally graded beds the conglomerates merges upwards into sandstone. Matrix is usually sandy, rarely sandy-pelitic or pelitic. Beds may be capped by a trough- or planar cross-bedded or planar laminated sand/gravel unit displaying a preferred fabric, rarely a silty drape. Units of this type may show an erosional base and lenticular or wedge-shaped geometry.

•Structureless or normally graded coarse to medium sandstone. Thickness averages 50 cm and ranges 6-160 cm. Normally graded varieties may grade upwards into finely sandy siltstone. The matrix of coarser varieties may contain a certain amount of silt. Clay chips locally present. Beds may be distinguished on the basis of geometry into sheet-like or lenticular, the latter with erosional base and planar top.

Size classes: macrofossils, mesofossils, microfossils

Preservation: cast, mold/impression, adpression, original carbon, original cellulose

Collection methods: core, chemical, mechanical,

Primary reference: F. Massari, C. Neri, P. Pittau, D. Fontana, and C. Stefani. 1994. Sedimentology, palynostratigraphy and sequence stratigraphy of a continental to shallow-marine rift-related succession: Upper Permian of the eastern Southern Alps (Italy). Mem. Sci. Geol. 46:119-234 [C. Looy/W. Puijk/C. Looy]more details

Purpose of describing collection: paleoecologic analysis

PaleoDB collection 31834: authorized by Cindy Looy, entered by Wilma Puijk on 27.05.2003

Creative Commons license: CC BY (attribution)

Taxonomic list

unclassified
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Endosporites
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Lunatisporites
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Circumstriatites
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Protohaploxypinus
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Lueckisporites
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Falcisporites
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Nuskoisporites
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Strotersporites
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Limitisporites
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Klausipollenites
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Sulcatisporites
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Sulcatisporites sp. Leschik 1955