DOLOMITES - Annexes 2-8 - Provincia di Udine

NOMINATION OF THE DOLOMITES FOR INSCRIPTION ON THE WORLD NATURAL HERITAGE LIST UNESCO
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As previously mentioned, it appears obvious that the Wengen Formation presents a strong heterogeneity
of lithofacies, both in terms of lateral variation and of vertical evolution. The typical lithofacies
associations of the Wengen lithofacies are dominated by alternating black pelites and fine to coarse
sandstones that is also dark due its richness of grains of basic volcanic origin (lithic of basaltic composition,
femic minerals). The sandstones form strata from centimeters to many centimeters thick,
with a tabular to lenticular geometry, frequently with erosive bases and depositional structures such
as direct gradation, plane-parallel lamination and current-ripples. Pelitic intraclasts can be present
in the lower-middle part of the strata. The whole of these elements indicates a deposition by gravity
in a basin context, through turbiditic re-sedimentation. Deposits deformed by slumps and debrites
with a breccia texture are also visible. A pattern characterized by a cyclic organization of coarseningup/thickening–up
facies, some meters thick, is also often present, which reflects the progradation of
turbiditic cones. Locally, the lower part of the Formation comprises conglomerates and/or paraconglomerates
of quite rounded volcanic clasts of variable diameter from 1 cm to 20-30 cm (exceptionally
they can reach greater dimensions): these are the already mentioned Marmolada Conglomerate
sometimes thicker than 600 meters. Towards the top there is a general decrease in average grain size,
however the passage to the overlying San Cassiano Formation, usually is not transitional, and is evidenced
by a progressive reduction of terrigenous input and by an increase of the carbonate one. More
frequently, the upper levels of the Formation show an increase in rubble, both volcanic-detritic and
extra-basin terrigenous rubbles. Therefore the top of the unit can be marked by one or more bodies
several meters thick comprising mainly coarse sandstones/microconglomerates, which in their turn
are covered by gray marls and pelites with minor calcareous intercalations, micritic in type, referable
to the base of the S. Cassiano Formation. With regard to fossiliferous content the Wengen Formation
is famous for its invertebrate fauna and plant fossils and has returned abundant ammonoid
fauna from the Regoledanus Subzone (Protrachyceras archelaus, P. neumayri, Frankites regoledanus,
Celtites epolensis).
the recovery of carbonate sedimentation: the Cassian Dolomite and the S. Cassiano formation
Once the volcanic activity ended in the Dolomites area the calm stretch of tropical sea resumed, and
organisms proliferated in a new generation of reefs and carbonate platforms, depositing upper Ladinian/Carnian
age sediments (Cassian Dolomite). Unlike reefs formation in preceding ages Cassian
reefs tended to develop horizontally (= progradation) rather than vertically (= aggradation), the result
of decreased seafloor subsidence rates, although in northern areas the subsidence forces may have
been equal to aggradation of the Anisian – Ladinian time (Picco di Vallandro/Dürrenstein).
Geologic cross-section at the Ladinian-Carnian boundary. After the dismantling of the Marmolada/Monzoni volcanic edifice
and the partial levelling down of the submarine morphology done by the Marmolada Conglomerate and by the Wengen Fm,
on the highest points coral communities started up again. New carbonate platforms developed (Cassian Dolomite),
this time prograding on shallower basins. WEN – Wengen Fm and Marmolada Conglomerate; SCS – S. Cassian Fm;
DCS – Cassian Dolomite. (Modified from Bosellini, 1996).