Page 160 - Carbonate Platforms Facies, Sequences, and Evolution

in
in
in
this
tors
and
highs
forms
Hurst
1981).
Belize
setting
record
in
turn
&
platform
(Heckel,
localized
ductivity
is
and
paper,
isolated
sediment
have
Numerous
development
and
limits
also
1974;
the
the
Surlyk
of
have been
of these
the
controlling
been
carbonate
basin
modern
the formation
term
Great
platforms
Wilson,
the
(1984)
rate
production
of
thesized geophysical data
important
gins in the southern Alps.
determining whether a
and
a
from evolutionary changes,
carbonate
and
organisms
systems.
referred
buildups,
rates
Barrier
(Bice &
seamount
can
total
to
group
ancient
because
sudden
is
Reef
development
much
1975; James,
it
of
Mullins
as
also
platforms
of
platform will
initiated along crustal
necessary
that argue for
Stewart,
local or regional environment that affect
like
used
amount
to
dominantly upward or outward (Bice, 1986).
1983).
small,
carbonate
(1983)
grow
of
controls
1985).
pre­
plat­
have played a major role in determining the charac­
Castellarin (1972) and Bosellini et al. (1981) demon­
strated the structural origin of several platform mar­
syn­
bonate sediment that can accumulate. Tectonically­
car­
produce carbonate sediment are also important fac­
the pro­
bounded structural highs (seamounts) and their sub­
fault­
Australia.
create
controlled subsidence rates are also important factors
structural
most of the sediment is biogenic, the organisms that
structures
control on the locations of platforms in the Bahamas,
control of platform margins in northern Greenland.
that provided the starting topography and variations
The evolution of carbonate platforms is strongly
documented the structural
(Schlager,
Aside
rate and total amount of crustal subsidence, which
do not emphasize the small sizes of these features,
environmental requirements of these organisms, and
In
platforms. Evolutionary changes in these organisms
the
(Centamore et al., 1971; Bernoulli & Jenkyns, 1974),
be a direct result of the tectonic setting. The tectonic
sequent drowning, which represents a critical stage
in the evolution of the entire basin. The structural
the nature and quantity of carbonate they produce
The Jurassic carbonates of the northern Apennines
because
ter of carbonate platform sediments by altering the
pinnacle
these features. The terms using carbonate platform
to some, we feel it properly conveys the small sizes of
seamounts
control the
of carbonate
and they may imply that these features are extremely
changes in the
tied to the rate of sediment production, and because
although it may evoke a submarine volcanic edifice
ing
the
rise
that
high
is
depths
mounts
changes
of these
formerly
platform
drowning
Lowering
Isolated carbonate seamounts,
in
can
(see Fig. 1).
used,
is
outpace
resulted
the
sediment
Italy
Apennines (Fig.
also
the
effects of crustal
also
1)
from
as an
drowning occurred.
relative
much more
or reef top
can therefore
Umbria-Marches
used
sediment
event
halt
drops in relative sea-level.
seamounts was a
as
Importance of the drowning
production,
be thought
in
extension
sea-level.
has been
accumulation
portion
of
surface
even
of
and
of
defined
The
which
the rapid
to
by
rate of carbonate sediment production.
indicate that these features are horsts.
response to
with
lowered
the
the
term
thinning
carbonate
as remnants
of
below
production
Kendall
of
In this paper, Schlager's (1981) definition of drown­
played by tectonic and ecologic factors in the forma­
sedi­
These sea­
extensive carbonate platform
sunlight that is present only at shallow-water depths.
combined
subsidence and eustatic sea-level
demonstrate that the drowning
tion and drowning of these seamounts. These studies
northern
of the excellent exposures of Jurassic carbonates in
reefs, when in fact the field data discussed below
The purpose of this paper is to assess the roles
subsidence
a
147
the
zone of maximum carbonate production (1-15 m),
&
Schlager (1981) to describe the condition where the
but is still within the euphotic zone so that a slight
A comparison of the stratigraphy of the Sibillini
Apennines) and the nearby Abruzzi platform (Fig.
relative sea-level drop or stillstand could enable the
that the decreased sedimentation rates cannot bring
crust, and ecologic factors that greatly reduced the
top below the euphotic zone. Many of the organisms
ment, resulting in the drop of the platform or reef
the
that produce carbonate sediment require abundant
carbonate sediment that is needed to keep pace with
incipient
greater-water
of
northern Apennines. Before the Jurassic drowning
drowning event was followed by the deposition of up
history, but they evolved quite differently after the
event, these two areas shared a very similar geologic
Mountains (which is representative of the northern
occurs when the platform top drops to depths such
sediment production. Complete or terminal drowning
platform or reef to return to the zone of maximum
reasonable
the platform top back to the shallow-water zone of
In the Sibillini Mountains, the
2) illustrates the importance of the drowning in the