Page 35 - Carbonate Platforms Facies, Sequences, and Evolution

1).
30
red
highs,
beds
developed.
purely
The
first
(Verrucano)
carbonate
water confined basin (Monte
an
deposits,
to the east to a rapidly-subsiding,
deposition
evaporitic
T.
consisting
were produced (Boccheggiano Anhydrite).
of
wide tidal fiat­
which to the west graded into the La Spezia shallow­
fine­
deepened and radiolarian-rich limestones were de-
commenced,
(Tocchi Formation). In Norian time on the structural
During the Rhaetian the western La Spezia basin,
grained siliciclastics alternated with early dolomite
sabkha system, where sulphates and early dolomite
Directly on the basement or on Middle Triassic
platform
building an oolitic sand shoal (Grezzoni Dolomite)
and sulphates and were laid down in coastal lagoons
S. Croce Member) and
Cocozza and A.
the
relief
occurrence
Gandin
margin
subsident
of
this
built
sabkha
by
margin
system
encrusting
was
suggests
the
courtesy of M. Fazzuoli.
crudely-laminated internal
replaced
organisms.
Fig. 11. Karstic cavities in the
like configuration, to a shallow intrashelf basin.
by
sediment. (b) Fresh-water calcite
Massiccio Limestone. (a) Vadose,
beds), eastward (Monte Cetona) rimmed by a low­
to the east the platform sloped down with a ramp­
development of an eastern, probably shallow-water
negative zone during this time that at present is not
rimmed by an oolitic shoal facing a deeper basin and
the Upper Triassic Tuscan platform was to the west
The
confined, metahaline lagoon ( Rhaetavicula contorta
a
persistent oolitic margin of the Grezzoni Dolomite
filling of karstic pipes. Photographs
posited (Portovenere Member). To the east of the
individual
exposed for structural reasons. At the end of Rhaetian