Page 26 - Carbonate Platforms Facies, Sequences, and Evolution

is
fossil
black
found
1978).
morphs,
hantkeni
Rhaetian
in
lodontids,
sediments
This unit,
is missing
Anhydrite
Norian
commonly
low-density
assemblages
stromatolites.
and
The Upper
two
shoals (Fig. 12).
with
deposited under
with
and
limestone
mostly mudstones
associations
an
although
Fossils,
of
Triassic
Portovenere
facies
oolites
assemblages
lnvolutinas
superposed
probably passed
anhydrite
60-100 m thick,
Glomospirellas, the second,
in
associated
(Ciarapica & Zaninetti, 1984).
evidence
and
Agathammina
the
hantkeni) diagnostic of Rhaetian.
Member.
water of the La Spezia basin (Fig.
Worthenia
bioclastic packstone and
locally very
consists
of
with
sequences of
because of the structural
into the
Rhaetavicula contorta beds (Rhaetian)
dominated
arid climate in a
(Ciarapica
consists of
12).
of
The
lower
this
region (Ciarapica & Passeri, 1978; 1980).
assemblages,
&
by
celestite
escheri,
skeletal
setting
dasycladacean algae ( Gyroporella,
australpina
abundant,
part,
the
grainstone,
facies
Phy­
mega­
The facies, consisting of oolitic and skeletal grain­
black lime­
boundaries exist with the underlying evaporitic se­
pseudo­
wacke­
complex en-
Passeri,
Boccheggiano
stromatolites, document an arid setting in a shallow
stone, wackestone with foraminifera, mudstone and
to the west by an oolitic shoal flanked by the deeper
disappear in the upper part (Figs 2 & 9). Gradational
the tidal flats graded to an hypersaline lagoon whose
of the
form
Rhaetian with Trasina
The Grezzoni Dolomite includes poorly diversified
first
stone and packstone including low diversity bivalve
To the east
& Passeri, 1978). The Grezzoni Dolomite is bounded
and
subtidal to supratidal depositional system (Ciarapica
(Rhaetavicula contorta) and foraminifera (Triasina
soporella, Diplopora) and foraminifera. The last are
and
mudstone,
organisms and stromatolites (Ciarapica et al., 1982).
transition
and
are
quence and the overlying Massiccio Limestone. The
Triasina hantkeni and radiolarians in the upper part
In the Monte Cetona area of southeastern Tuscany
metahaline lagoon bounded to the east by low-relief
dasycladacean algae and mounds built by encrusting
characterized by skeletal banks with Megalodon and
Tuscany were
The depositional setting represents a confined, wide
stone, alternating with black shales which gradually
the upper part of the Rhaetavicula contorta beds are
bivalves
or
on
and
west
Alps,
lower
beds).
upper
The
calcite
raneus
graded
the
the
phology
resulting
detached
adjoining
Massiccio
document
to
containing
part
Liassic age.
Hettangian.
and
Ammonitico
Westward
veins
was
a
brachiopods,
basis
Spirillina
dasycladacean
from
of
recrystallization
boundary
Massiccio
of
sections
is
Rosso
the
corals,
Carbonate deposition during early rifting, Italy
the
and
algae
initially
Limestone displays a
the
neptunian
liassica
structural pattern (Fig.
Rhaetavicula
1975; Fazzuoli, 1974a,
at
and
from repeated
depressed,
Schlotheimia
normal-marine
age
are
a
12).
the
tidal-flat system developed;
minor
Limestone
dykes,
and arenaceous foraminifera.
of
emergent
northern
more
Thaumatoporella
is
top
gradational,
controlled
vertical
contorta
waters
locally
the
echinoderms,
angulata
Massiccio Limestone (Lower Liassic)
by
complex
the
b) (Figs 2 &
land,
and
greatly variable
locally
are common (Fazzuoli et
and
Apuane
beds,
the
( Palaeodasycladus
tigraphy (Boccaletti et at. , 1975; Fazzuoli,
subsident
a
sponge
whose
upper
(Boccaletti
at. ,
dolomitization.
common.
whose
internal
underlying
et
and
Alps,
karstic features
bedded marly limestone of Ammonitico Rosso.
affected
area,
In
age
one
which during Carnian and Norian, sulphate depo­
mor­
mediter­
stra­
parvovesiculifera),
1981).
The areal distribution of the facies and the
unconformable and is marked by an abrupt contact
at.,
basement
23
limestone whose thickness ranges from 50 to 1000 m.
vironmental setting. On the structural highs (Apuane
it was bounded to the
by an epicontinental basin and to the east it
Montagnola Senese) the Grezzoni Dolomite
in
Solenoporacean and
spicules
Common fossils are gastropods, bivalves, ostracods
its
and
They
Formation that is an ammonite-rich calcareous unit
1974a, b)
Limestone interfingers with the Ferriera
general
the
by
lack of terrigenous material in both the carbonate
and evaporitic sequences document a wide platform
by a wide metahaline lag o on (Rhaetavicula contorta
sition prevailed over the carbonates (Boccheggiano
Anhydrite), and during Rhaetian this was replaced
This unit consists of a massive body of pure white
is
between the white massive limestone and the pink
9). While the
At the base it is bounded by the Grezzoni Dolomite
by
overlying units (Giannini et al. , 1972). The Massiccio
thickness in
lateral facies
Elsewhere in Tuscany, the age of the
is
and
Massiccio Limestone is assumed to be Hettangian