The combination of geological mapping and correlation of platform-to-basin
successions on seismic-scale outcrops in the Western Dolomites (Schfern/ Ro
sengarten area) allows a detailed reconstruction of the growth of a Middle
Triassic carbonate platform over a time interval of five ammonoid zones (Re
itzi, Secedensis, Curionii, Gredleri and Archelaus zone).
Tuff layers (the so-called "pietra verde"), which can be traced throughout
the basinal succession (Buchenstein Fm.) and also in parts of the slope sed
iments (Schlern Dolomite Fm.) were used as main correlation tool. In additi
on they indicate a duration of < 5 Ma for the whole platform evolution (Mun
dil et al. 1996).
The platform shows a strong aggradation of 600-700 m in the Reitzi and Sece
densis zone, a transition to progradation in the Curionii zone and a rapid
progradation of more than 3 km in the Gredleri and Archelaus zone. When it
stopped growing, due to Late Ladinian igneous activity; the platform reache
d a thickness of 850 m and a total progradation of approximately 5.5 km.
Sedimentation rates on platform top during aggradation reach values of 200
Bubnoffs (m/Ma); progradation during the Gredleri and Archelaus zone took p
lace with an average rate of 2700 m/Ma. Volume-based calculations on platfo
rm sedimentation suggest a continuous increase in carbonate production duri
ng platform evolution. During the progradation the production within one am
monoid zone was six times higher than during the whole aggradation phase.
The impact of relative sea-level changes and episodic fallouts of acidic vo
lcaniclastics (pietra verde) on the platform development is discussed.