Page 177 - Carbonate Platforms Facies, Sequences, and Evolution

a
is
of
The
a
that
clearly
complex
these
the
existence
at
Peninsula.
conclusion
Apennines.
of
opening
interconnected
combination
seamount tops
that
of
network
noted that in the
of
shallow
Studies
the
the
cooler,
seamounts
seamounts
of
The lack of fringing
basins
ing of these seamounts.
of
did
up
less
enough
tectonic
show
reefs
the
normal
to
Liguride
not
drowning
and
SUMMARY
that
saline
is consistent with
reasonable actualistic model
1 km
faults.
was
the
Ocean
the
for
water
produce
in
deep.
the
ecological
the
These
and small sizes
depths for most
the
The
sedimentological
faulting
above
result
which made them more susceptible to drowning.
Jurassic resulted in crustal thinning through exten­
are particularly well exposed in the Sibillini Moun­
sub­
that illustrate a model for the formation and drown­
faults fragmented the interior of the regionally exten­
factors.
isolated seamounts tops would allow mixing of the
water above the seamounts with the basinal water,
suppressed the production of carbonate (a condition
sive Calcare Massiccio platform, producing a group
referred to as 'hypothermia' by Bosellini, 1987). The
Bahamas, warm, saline water is
the
observations
necessary for the effective production of ooids, which
early
of the
a decrease in the growth potential of the seamounts,
Jurassic time. The result of this change in the water,
are important ingredients in the Calcare Massiccio.
present day northern Apennines, was affected by a
of the
normal
that
sional faulting and long-tem1 subsidence of the Italian
One portion of this passive margin, the
and perhaps more saline than normal oceanic water,
and
Calcare
as observed in the Bahamas (Bathurst, 1975), which
Several of these seamounts and intervening basins
stratigraphical record of this drowning lead to the
sequent drowning of these seamounts had a profound
Figure 11 shows a series of schematic cross-sections
Massiccio depositional environment. Bathurst (1975)
of small isolated carbonate seamounts separated by
the northern Appennines and the adjacent central
created these seamounts and basins occurred during
effect on the later history of this basin, and accounts
for the important stratigraphic differences between
significant
of
quantities of ooids even though many of them were
tains. Studies of the original marginal escarpments
leading to cooler, less saline water that could have
brought on by the formation of the deep basins, was
ing.
any
ing,
cates
The
depth,
on the
change
greater
duction
appears
but
The
Tithonian
drowning.
in
that
to
the
seamounts,
relationship.
and
water
the
euphotic zone
be
these
which requires
Isolated carbonate seamounts, Italy
rate
such
seamount
Upper Tithonian
crustal
the euphotic zone
ent drowning (Fig.
of
little
that
as
seamount
rates
depths
after their formation.
coincidence
ecology
dramatic sea-level
However,
(<20 m)
the
top
of
at
sedimentary record
The
Monte
accumulation.
before
sediment
subsidence
this
remained
subsidence
there do
After the faulting and
the
at
of
apparent
drowned at the end of the Jurassic.
seamounts
During
indicates
sediments,
time.
not
Rotondo,
or environment
the
two
this
tops
associated
rapid
production
which
Some
could
stantial depths, well below the euphotic zone.
Tithonian.
abnormally
on
with
were
stages
dropped
changes that correspond
stage,
and was quite rapid with respect to sediment accumu­
first post-faulting sedi­
the seamount tops were probably deposited at sub­
al. (1981) and Cecca et al. (1981) attributed to sub­
seamount tops (which is the critical factor in deter­
al. (1979) and Cecca et al. (1981) found small com­
and low rates of sediment pro­
seamounts (Fig. llb), they entered a stage of incipi­
normal faulting was not the sole cause of the drown­
oscillations with the transition from incipient drown­
The prolonged stage of incipient drowning indi­
returned the rates of carbonate production and ac­
cumulation to high enough levels to prevent drown­
detritus found in the basins. The sedimentary record
be expected in response to this rapid faulting, there
ments produced on the seamount tops contain ooids,
lation rates. Although rapid crustal subsidence would
seamounts
tops is incomplete in the middle
more than a few meters deep. Despite this shallow
the
some of the seamount tops in the upper part of the
the late Sinemurian -early Pliensbachian (Fig. 11b)
to
places
mining a platform's survivability) was relatively low,
munities of healthy (large) hermatypic corals in the
no
the beginning of the stage of incipient drowning, so
appear to be
based on the rather small volume of shallow-water
sea-level
low
levels, allowing the seamounts to become completely
ing to complete drowning suggests a cause-and-effect
of
formation of the
Jurassic, which Colacicchi et al. (1970), Farinacci et
The
Maiolica limestones found above
aerial exposure. Nicosia & Pallini (1977), Mariotti et
of the
drowning was characterized by water depths within
a
have
to
the Jurassic, at which time they became completely,
terminally drowned (Fig. lld). The stage of incipient
163
llc) that lasted until the end of
the