Page 162 - Carbonate Platforms Facies, Sequences, and Evolution

al.,
the
the
any
the
study
After
system
is that
general
sidence
appears
between
Winterer
the
connected
of
to
area
Apennines.
Jurassic
indicate the
Vandenberg,
Liguride
that
to
evolution
to
significant
Tectonic setting
picture
(Dercourt et al.,
palaeogeographic
of
1974; Alvarez,
1979;
thin
for
DESCRIPTION
Triassic
initiation
Ocean
the
& Bosellini,
1984; Westphal et al.,
relatively
palaeomagnetic
of
persisted
OF
carbonates
rift
southeast
1976,
most
be fairly well
terrigenous
along a
of
the
of
caused
from
sudden
THE
the
valleys
the
evidence
region is complex (Dewey et al.,
seamounts
the
Europe
reconstructions)
input,
the
system
Dercourt et al.,
of
in
Liguride
established.
network of extensional faults played a
of
crust
1973;
was
Italian
the
the
early
1986)
The
reactivated as part of a fold and thrust belt.
1981; Martini et al.,
making
(Channell
(Kligfield,
Bijou-Duval et al.,
portion of the northern Apennines (see Fig.
Ocean,
under
1)
this
SEAMOUNTS
had begun to form as Italy moved away from south­
For the purposes of this paper, two points concern­
faults (D'Argenio & Alvarez, 1980), producing sub­
1977;
Liguride Ocean was preceded by the formation of a
and the
northern Apennines became part of a passive margin
appearance of pro-
1979;
15°N and 30°N latitude and isolated from
1986).
Alvarez et
Triassic
details are still not completely understood, but the
east Europe. The time of this opening is established
Jurassic, a small ocean basin, the Liguride Ocean,
1986). By the middle of the early
The history of plate motions in the Mediterranean
peninsula (often referred to as Apulia or Adria in
peninsula
Italian
(Bortolotti & Gianelli, 1976) as 160-185 Ma. Similar
probably
1986) places the study area
that persisted until the Oligocene when it became
through the Palaeogene. As will be shown later, this
the
northern
ing the tectonic setting should be stressed. The first
et al.,
key role in
favourable setting for the production of carbonate
to the opening of the northern Atlantic Ocean, the
by radiometric dates and fossil ages from ophiolites
extensional
a
Jurassic
Umbria-Marches
by
Stratigraphic characteristics of seamounts and basins
Detailed stratigraphic and sedimentologic studies of
sediments. The second point is that the formation of
the
Colacicchi et al. (1970) and Centamore et al. (1971)
the
the
the
etal
and
that
light
times
voids
The
ments,
benthic
cement
centres.
nounced
area
syntaxial
Isolated carbonate seamounts,
introduced
and ooids.
filled
brown
appear
(Centamore
that
the complete
through early
referred
fragments
to
et
Many
the
Italy
generalized
seamounts
shown
packstones
Monte Rotondo
Bugarone
with
to
(Colacicchi et al.,
of
ammonite
structural
al.,
in
a
grades
and
foraminifera
useful
with
(Fig.
of the
sequence
overgrowths,
Fig.
into
Cretaceous
1971)
highs
9a)
5.
and
terms
Formation
ooids
or
stratigraphic
refers
basins.
fragments,
(notably
abundant
echinoderms,
The
to
carbonate mudstone
the
coarser
blocky/bladed
many
fragments have micritic envelopes.
be stratigraphically
The
seamount
the
consists
of
spar
Rosa
(seamounts)
'complete
appear to
bivalves,
Pliensbachian through early Cretaceous
section
Vida/ina
benthic
differences
a
in
the
thick
facies
at
lower portions of the Bugarone Formation,
and
echinoderm
have
complete,
isopachous
primarily
sediments that appear to be stratigraphically com­
commonly with a nodular texture, containing skel­
is rep­
foramin­
some­
resented by the Bugarone and Maiolica formations.
lows
basinal
frag­
the reduced sequence refers to the greatly thinned
and
plete, the condensed sequence refers to the thinned
variations in stratigraphic thicknesses and facies in
(basins) in the northern Apennine basin at the end
Crinoidi
of the Sinemurian. These authors documented the
as the Calcare Stratificati Grigi
(Fig. 4), and Monte Cucco and Monte Nerone from
that defined these structures. Centamore et al. (1971)
sequence',
sediments
Pliensbachian
of
and wackestone,
between
sequences of sediments deposited on structural highs
sequences of sediments deposited on structural highs
that are stratigraphically incomplete. Figure 3 shows
and skeletal fragments (see Centamore et al., 1971
'condensed sequence' and 'reduced sequence', where
for a more complete description). The first sediments
In some areas,
rim
which is characteristic of the Pliensbachian), peloids
the void
martana,
skeletal
ostracods,
1970). This part of the sequence
has been examined in four locations: Monte Rotondo
to be deposited on the seamounts are found in the
ifera, bivalves and ammonites, with local packstone
and grainstone containing peloids, intraclasts, ooids
and Monte Sassotetto from the Sibillini Mountains
al. (1981), with particular reference to the Tithonian
sediments. The Rosa a Crinoidi here and at nearby
consists of wackestones
Monte
Sassotetto has been studied previously by Cecca et
been
149
the skeletal fragments have been dissolved and the
Echinoderm fragments commonly have