Page 187 - Carbonate Platforms Facies, Sequences, and Evolution

can
that
eral
lief'.
types
terms
These
facies.
These
of
quences
only
The
are
meridgian
are
are
shelf-break
This occurs
be
ramp system.
in
variations,
They are
Wilson
'platform',
occurring
facies.
age
relatively
and
inferred
recognized,
Upper
'shelf'
Of Upper
(1975)
They
within
thin
relatively thick
discussed in a later section.
Buildup types and locations
from
which
and
for
contain
(up
are
Postrift passive basin fill sequence
Salt-controlled carbonate buildups
(Montejunto
(up to
to
Fault-controlled carbonate buildups
the basin (Fig. 4, columns 2 and 3).
geographic regions within the basin.
'ramp'.
Oxfordian to
distinct
'locally
tensive enough to be termed platforms.
largely
developed
megasequence
500m)
1500m)
term carries no inference about
in
of
None
the Lusitanian Basin (Fig. 4, columns 5-8).
2.
Upper
formation
sedimentological
of
characteristics of the Upper Jurassic carbonate se­
carbonate depositional systems in Portugal are ex­
geometry (i.e., ramp, shelf, etc.) or internal compo­
carbonate sediment which possesses topographic re­
contain lime-mud dominated facies with strong lat­
Kim­
Oxfordian-Lower Kimmeridgian (Montejunto for­
origins,
the
sition. We follow Tucker's (1985) definition of the
The use of the term 'buildup' in this paper follows
data
shelf-break
dominated by grainstones and packstones with little
shelves,
shelves,
lateral facies variation and do not display a distinct
formed ...
Upper
and
distinct
Figure 4 summarizes the age and principal facies
Ota limestones) developed only on the east side of
Four
on the southwest side of the Basin in
strata exposed around the Sintra granite (Fig. 3; Fig.
mation) age and occur on the northwestern side of
deposits common in the lower half of the sequence.
Kimmeridgian-Tithonian
age (Mem Martins and Farta Pao formations), it is
4, column 2) and represents a prograding carbonate
dominated by carbonate mud facies with debris flow
1.
9).
the
The
Age
Lime
Setting
Upper
Fluvial
The
sections.
important
the basin.
Upper Jurassic carbonate buildups,
underlying
Abadia
They
mudstones
Oxfordian
sandstones
are
Portugal
Caba�os
basement
formation
of
The Serra de Montej unto
and
the
probably
is
(Mouterde
formation
buildup is bounded to the
FAULT-CONTROLLED
is
et
Montalegre #1 and Barriero #1-4.
structural trend
Lourinha
al. ,
Limestone cap on prograding siliciclastics
applicable
dominated
and
to
by
the basin at the Serra de Montejunto and at
1971).
affecting
exposed to the southwest of
BUILDUPS
exposing Middle Jurassic carbonates in its core.
equivalent carbonates in other Atlantic settings.
considered to
east by a WNW­
high­
associations are based on lithological and palaeonto­
time­
Montejunto anticline (Fig. 5) have yielded ammon­
energy ooid grainstones (Fig. 4, columns 2-4, 6 &
It caps the prograding slope deposits of
occurs over much of the central and southern part of
and were encountered to the south in the boreholes
which passes northwards into a monoclinal flexure.
These buildups are exposed on the northeast side of
Ota,
outcrop is terminated by a fault (the Pragan�a Fault)
Mesozoic development of the basin (Wilson et al.,
the
formation dip gently to the northwest (Fig. 5). The
1989), from which the limestones of the Montejunto
logical data and the stratigraphical and spatial setting
of individual sequences that are described in later
within these sequences and are summarized in Table
environmental interpretations of the facies
Nine carbonate facies associations are recognized
ites indicating the Bifurcatus to Planula Zones of the
The
ESE trending normal fault, which is parallel to an
middle Oxfordian in age (Ribeiro et al., 1979), and
the overlyingTojeira member has yielded ammonites
Torres
Vedras formations overstep the limestones on the
northern side of the buildup, whereas the southern
be
the
This very thin (<100m) unit (the Amaral formation)
part of it is deformed by a large asymmetric anticline
173