Page 16 - Carbonate Platforms Facies, Sequences, and Evolution

in
14
the
ber
The
only
This
ation
is
areas:
The
Punta
The
zoppii,
France
marine ·
defined.
sections
trilobite
tidal-fiat
(Rasetti,
of
siltstonY,·s,
(Matoppa
(i)
early
still
interpreted
thickn.ess
fauna
the
they
deeper-water
in
it
Botomian age
the
Manna
mixed
limestones
Coscinocyathus
fauna,
1972)
is
formation,
oolitic-,oncolitic
and
formation
are
as
·complex
(Montagne
a
and
is
up
'piordanella
Member)
and
dolomite
setting
a
Nevertheless
to
ar�haeocyathids
progress,
in
mainly
to
Member)
sequence
number
absent.
dianthus,
depositional
algae and archaeocyathids,
Manna Member) (Gandin,
dominated
(Rozanov &
flanking
limestone
Noire),
to
the
Nebida Formation (Botomian)
800 m
some
trilobites
delta
and
The
by
an
found
eastern and southeastern areas,
siliciclastic,
meneghinii
Sardinian
in
with
evolving
in
1990a).
Spain
intercalations
the
sabkha
thick,
eastern
the
archaeocyathan
in the
and
fold belt (Debrenne & Gandin, 1985).
Debrenne,
evidence
eastern
environment
rare inte r calations of quartz-sandstone.
The
and
small
Porocoscinus,
( Taylorcyathus
and
T.
from
shallowing-upward
shales and lenticular carbonate
Punta
occur.
trilobite
plain-coast
intercalated
(upper
consists
1974).
In
along
archaeocyathids
of
suggests
to part of the Nevadella Zone of North America.
archaeo­
Annulo­
silicic­
deltaic­
assem­
facies dis­
However, although the detailed analysis of this mem­
exposed' area (Bechstadt et al., 1985). The interpret­
cyathid buildups. In the upper part of the sequence
the early-dolomite intercalations gradually decrease
siliciclastics.
the
rectus,
(Punta .Manna Member) has alternating sandstones,
fungia and Anthomorpha) are indicative of a general
mixed carbonate siliciclastic sequence (Figs 2 & 3).
and sandstones include mounds built by Epiphyton
Enantiaspis
Morocco
blages have been correlated with those of southern
enantio[>''a and has been correlated by Rasetti (1972)
the
Member · , includes Hebediscina sardoa, Dolerolenus
an oolitic, margin in the western edge of the presently
lastics are mostly fine-grained silts and shales with
in
assemblages
tribution of lower Punta Manna Member documents
a
with those of the Siberian platform and Altai-Sayan
The
limestone and
southern
mainland.
units of
easternmost
Manna
whereas the upper part
In the lower part (Matoppa Member) green siltstones
a
siliciclastic fraction is dominated by
backshoal-lagoon/
eastern edge is controversial. Bechstadt et al. (1985)
Punta
(lower
prodelta
Cocozza and A.
and
and
rare
and
In
In
mite
clastic
search
sabkha
ocyathid
dolomite
in
south
sequences,
Gandin
gives
skeletal
facies
trilobite
by
fauna
Iglesiente
material
(sensu Esteban,
way
at
(Gandin, 1990a).
ripple
is
northwestern
algae
to
anhydrite (Fig. 6b ).
mudstone
of oolitic grainstone
and
progress);
the
from
lenses
Farther east both the
well developed in the
of
fragments
marks,
top
and
facies
west;
1976) (Fig.
(Debrenne & Gandin, 1985).
of
lglesiente
composed
chert nodules which are
limestone
(4)
and
northern
Laminated Dolomite (Botomian)
fiaser
entrapping archaeocyathids are
(Epiphyton)
of
the
the
and
and
dolomite, 200-250 m thick (Figs 2 &
and
alternates
Sulcis,
north-northwest.
pseudomorphs
typical
(Buggerru
only
3).
A
of
sequence
with
the
in
area)
archaeocyathids
which decreases from north to south and east (re­
the western area, indicate a provenance of the silici­
In north­
western area is characterized in lglesiente by ihter­
calations of goethite-rich layers, interpreted as fresh­
homo­
are made up of: (1) banded dolomicrosparitic mud­
shallowing­
planar stromatolites. The poorly diversified archae­
the barite lenses disappear. All these features suggest
genera such as Aldanocyathus and Coscinocyathus
a deeper-water rather than a tidal-fiat environment
tidal-fiat early-dolomite and
the
In eastern Sulcis this unit thins out; the early dolo­
even-
water, bog-lake deposits (Carannante et al., 1975).
barite.
These intercalations are replaced towards the east
stone; (2) planar or wavy stromatolites (Fig. 6a); (3)
are lacking in the east whereas they are common and
stromatolites with fenestrae; and (4) vadose pisolite
shales and silts, with rare fine sandstones; (2) channel
upper part of the unit (Debrenne & Gandin, 1985).
cross-bedding
4c) and/or desiccation
the
This unit consists of evenly bedded and laminated
western Iglesiente (Buggerru area), archaeocyathids
and Epiphyton crinitum are enclosed in oncoids and
for the eastern outcrops of Punta Manna Member
source is suggested by the grain size of the sandstones
early-dolomitic
similar
(3) palaeocurrents for
in
upward (intertidal to supratidal) cycles prevail; they
Botornian
stromatolites
intercalated in the
breccias. Thin, discontinuous, locally silicified layers
occur as well as barite lenses
pseudomorphic after
are lacking. Oncolitic facies contain archaeocyathids
planar stromatolites prevail and the supratidal facies
geneous black limestone (Bechstadt et al., 1985); the