Insight into the development of a carbonate platform through a multi-disciplinary approach: a case study from the Upper Devonian slope deposits of Mount Freikofel (Carnic Alps, Austria/Italy).

The development and behavior of million year-
scaled depositional sequences recorded within Palaeozoic
carbonate platform has remained poorly examined. There-
fore, the understanding of palaeoenvironmental changes
that occur in geological past is still limited. We herein
undertake a multi-disciplinary approach (sedimentology,
conodont biostratigraphy, magnetic susceptibility (MS),
and geochemistry) of a long-term succession in the Carnic
Alps, which offers new insights into the peculiar evolution
of one of the best example of Palaeozoic carbonate platform
in Europe. The Freikofel section, located in the central part
of the Carnic Alps, represents an outstanding succession in
a fore-reef setting, extending from the Latest Givetian (in-
det.falsiovalis conodont zones) to the Early Famennian
(Lower crepida conodont zone). Sedimentological analysis
allowed to propose a sedimentary model dominated by
distal slope and fore-reef-slope deposits. The most distal
setting is characterized by an autochthonous pelagic sedi-
mentation showing local occurrence of thin-bedded turbi-
ditic deposits. In the fore-reef slope, in a more proximal
setting, there is an accumulation of various autochthonous
and allochthonous fine- to coarse-grained sediments origi-
nated from the interplay of gravity-flow currents derived
from the shallow-water and deepwater area. The temporal
evolution of microfacies in the Freikofel section evolves in
two main steps corresponding to the Freikofel (Unit 1) and
the Pal (Unit 2) limestones. Distal slope to fore-reef
lithologies and associate changes are from base to top of the
section: (U1) thick bedded litho- and bioclastic breccia beds
with local fining upward sequence and fine-grained mud-
stone intercalations corresponding, in the fore-reef setting,
to the dismantlement of the Eifelian-Frasnian carbonate
platform during the Early to Late Frasnian time (falsiovalis
to rhenana superzones) with one of the causes being the
Late Givetian major rift pulse; (U2) occurrence of thin-
bedded red nodular and cephalopod-bearing limestones
with local lithoclastic grainstone intercalations corre-
sponding to a significant deepening of the area and the
progressive withdrawal of sedimentary influxes toward the
basin, in relation with Late Frasnian sea-level rise. MS and
geochemical analyses were also performed along the Fre-
ikofel section and demonstrate the inherent parallel link
existing between variation in MS values and proxy for
terrestrial input. Interpretation of MS in terms of palaeo-
environmental processes reflects that even though distality
remains the major parameter influencing MS values, car-
bonate production and water agitation also play an impor-
tant role.

Publication year:2014

Keywords:Carbonate platform, Magnetic susceptibility, Stable carbon isotope