DOLOMITES - Annexes 2-8 - Provincia di Udine

NOMINATION OF THE DOLOMITES FOR INSCRIPTION ON THE WORLD NATURAL HERITAGE LIST UNESCO
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fetid dolomites consisting of alternating levels of dark siliceous laminites which are sometimes bituminous.
The laminites are often affected by slump processes and load deformations phenomena
(e.g. in the Catinaccio/Rosengarten area). The non-oxidized organic component is very important
and causes hydrocarbon impregnation that is sometimes significant. Metric intervals of bioclastic calcarenites
interspersed with platform grains are also present (calcareous algae, benthic foraminifers,
benthic macrofossils, crinoids, etc.) and document in part a contemporary depositional stage with
phases of normal exportation from active carbonate platforms. The intervals made up of prevalent
carbonate breccias are often strongly dolomitized and therefore the original clastic texture is obliterated,
making its recognition difficult. The upper part of the formation is characterized by a decrease
of granulometry, a larger mechanical elaboration of the clasts and by the presence of bioclastic calcarenites
and encrinites forming wedge-shaped bodies with limited extension. This topmost interval
tends to saturate the previous topography and most likely documents attenuation in the extensional
tectonic phenomena that appear to control the placement of the breccias. The deposition environment
is that of anoxic intraplatform basins those are rapidly deepening and are limited by active escarpments
tied to synsedimentary faults.
The contemporary open basin sediments are, on the other hand, represented by lithotypes of the
Ambata Formation, a terrigenous-carbonate unit when the sea was relatively deep, with outcropps
in the northern and eastern Dolomites and the Comelico area. The Ambata Formation can be subdivided
into two overlapping lithofacies. The first is made up of well-stratified dark biomicrites with
alternating gray silty marls that are associated with subordinate silty limestones containing rare pelagic
lamellibranchs and radiolarians. In the second lithofacies consists of millimeter- or centimeter
thick beds, mostly marly siltites and slightly bituminous calc-siltites, with plane-parallel boundaries
and rare levels of nodular limestones. The depositional environment deepens towards the top. The
first lithofacies is characterized by thin turbiditic supply coming both from the coeval carbonate platforms
(Contrin Formation) and from a terrigenous shoreline. The second, marked by an increase
in the terrigenous component and by a drastic reduction in the carbonate components, indicates a
more restricted environment with little oxygen, characterized by the deposition of distal turbidities,
testifying the crisis and the drowning of the Contrin carbonate platform. This formation is important
from the fossiliferous point of view due to the presence of light Daonella imprints (D. fascicostata,
D. pseudomoussoni), in addition to ammonoids of the genera Flexoptychites (F. flexuosus, F. indistinctus,
F. angustiumbelicatus, F. acutus), Ptychites, Aplococeras (A. avisianum), Hungarites, Proarcestes,
Parakellnerites and Norites (Reitzi and Avisianum Subzones).
ladinian platforms and basins (Sciliar Dolomite, Esino and Buchenstein formations)
The subsidence of the seafloor continued inexorably and intensified, causing the tectonic collapse
and tilting of large blocks. In some cases the tilting component favored the emersion of small parts
of these blocks, while the rest remained as a pelagic plateau. These higher areas permitted the colonization
by flourishing colonies of marine organisms, in some ways similar to those that form coral
reefs in today’s tropical oceans. They were calcareous algae, sponges and corals that possessed the peculiarity
to extract the calcium from the seawater fixing it into calcium carbonate.
Even the plateaus portions that were initially uplifted, however, later suffered the effects of the rapid
subsidence, equivalent to around a thousand meters in the arc of a few million years, and started inexorably
to move away from the light, warm and oxygenated water surface. However, the speed with
which the reefs produced calcium carbonate was enough to compensate for the subsidence of the
platform, inducing a constant upwards growth of the reef (reef aggradation) that reached one thousand
meters in some millions of years. Moreover, the production of calcium carbonate was so high allowing
lateral growth of the reef (reef progradation) that grew therefore not only in height but also in
diameter. The organisms that colonized the reef localized themselves only in the apical area and situated
a short distance from the sea surface, while the remaining largest portion, the enormous con-