Page 37 - Carbonate Platforms Facies, Sequences, and Evolution

32
tive
and
rates
ways
filled
form
those
posits
areas.
waters
blocks
pelagic
so
favoured
the
was
Hettangian
was
sand shoals
started
cementation
tilted
sea-level
that
dolomitization.
of
and beach-rock.
karstic
and
Platform collapse
ramp-like profile.
Plat form exposure
early
rise.
the
lime-muds
suddenly
70-140mm 10- 3 yr.
varying
up-building.
reported for the
The
to the foundering
responsible
It was
(Schlotheimia
cavities.
of the Massiccio platform
became
were
These
The
in an humid-climate regime.
for
flooded
platform
trend
cementation
at
values
non-cyclic
depositional
angulata
eastern
(Fig.
and
the
Circulation
are
12
extensive
deposited
and
sediments
of
imply differential subsidence in its
emergent with
T.
Zone)
margin
III).
and
post-Triassic Tethyan
recurrence,
beginning
had
built by non-oolitic lime­
Most of the shallow-water Massiccio Limestone plat­
contrasting facies and thickness of the platform de­
plat­
Deposition of the Massiccio Limestone was interrup­
towards the east, probably caused by a slower rela­
deeper-
rapid subsidence balanced by carbonate production
different
appears to have been controlled by a rapid relative
freshwater
the
of southern Apennines (D'Argenio, 1970; Bernoulli,
the platform deposits documents an irregular and
interior and also its margins were cut by extensional
fractures and the resulting blocks reacted in different
that have a seaward prograding trend
ted at the end of the Hettangian. Most of the platform
Some
(Ferriera
Formation) and this was rimmed by an oolitic shoal
karstification.
meteoric
with fewer crinoid-coral mounds. The shoal growth
produced shallowing upward sequences with calcrete
Rapid uplift prevented deposition
Rates of subsidence vary in the different sections
Dissolution breccias and internal vadose sediments
different
higher than
a
and are in the order of
The western margin faced a deeper basin, where
sea-level rise that prevented lateral outgrowth and
diagenetic
processes resulted. Local, more gradual emergence
but compare rather well with the Triassic platforms
forms and for the ancient deposits of recent platforms
is also recorded in the western basin where on the
local
1972; Wilson, 1975). The depositional behaviour of
Sinemurian by a neritic sea (Fig. 12 IV). This event
of
Cocozza and A.
the
the
and
form,
Rosso
The
spread
records
deposits
(Atractites
Gandin
blocks.
deep-water
the
first
Neocomian.
main stages.
derived from
with
shallow-water
leading
( Posidonomia
Climate control
locally includes
deposition
(Bernoulli et al. ,
The diachronous
to
to Pliensbachian (
deposition
and karstification.
Along
deposition
alp
stage,
basin
of
a
clasts
bucklandi
facies
the instabiiity of
irregular
ina
of
the
of
persistent
continuous drowning of
of
began
the
dated
turbidites,
marls
the
beds)
occurrence
Zone).
the
marginal
as
western
(Diaspri),
of
during
uplifted
with
the blocks
bedded in the Cherty Limestone.
the filling of the neptunian dykes.
Cherty
slumps
morphology
depth
the
of
plateau
Lower
early
shallow-water
blocks
during
pelagic
Differential
the
margin and
breccia-blocks
also the open fissures of the neptunian dykes.
and debris
Limestone
increased
and
in
different parts of
sedimentologic evidence. The drowning of the plat­
dis­
inter­
by Cherty Limestone and most of the blocks pre­
deepening of the plateau. It is marked by the wide­
Maim­
the Ammonitico Rosso on the newly formed plateau.
the
water sediments of Ferriera Formation, Ammonitico
Sinemurian
platform is attested to by both biostratigraphic and
morphology
during drowning.
During this stage the neptunian dykes were sealed
seafloor
in the deposition of the red and grey cherty facies of
nodular facies
viously emergent along the former western margin
as demonstrated by the karstic dissolution affecting
(Amaltheus margaritatus Zone), records the general
of the previously drowned ones were newly uplifted,
of the platform subsided. This is attested to by the
Conversely some
Eoderoceras assemblages) resulted
the
platform interior, some of the blocks were uplifted
(Atractites bucklandi Zone) followed the dissection
1979) was achieved through three
Sinemurian
grey cherty facies or the pink crinoidal facies of the
Ammonitico Rosso were deposited. The latter filled
The second stage, ranging from Upper Sinemurian
and subaerial processes produced early lithification
On the sunken blocks either the
et al., 1979). From the beginning of Toarcian, with
bivalves
and
The Massiccio Limestone is a pure calcareous unit in
resulted in the deposition of radiolarian cherts in a
(Bernoulli
The third stage, at the end of the Pliensbachian
of the platform and led to the differential collapse of
that
carbonates
flow