Page 196 - Carbonate Platforms Facies, Sequences, and Evolution

On
the
182
OTA
Age
units
rests
ever,
places
in Fig.
middle
Table 1.
the
Barreiro
breccias.
the
w
prehensive
(Fig.
in Barreiro
Bioclasts
wackestone
Barreiro #4
unit
The buildup
#4
directly
ln� t
Caba'<os
foraminifera,
basis
are
is
in
13).
alu :t
its upper
of
much
than
out crop!
on
may
facies,
II
this
margin
that
by -pass
Upper Kimmeridgian.
Ramalho
formation
thicker
Middle
common
reef
well
for
an d
extend
(U.KIMMERIDGIANl
composed
The lower
stromatoporoid framestones
boun d
including
thin-section
and
®
Bacinella
(1971)
into
unit
bindstones
algal ly
age limit in the
Jurassic
consists
debris
sequence
back
P.M.
and is
the
outcrops,
apparently
of
studies
varied
shoals
reef
dominantly
anomaly (#4) and its flanks (#1 and 2).
fragments
of
in
but
concluded
of
three
of
early part
the
tidal
missing.
limestones,
algae
cores
that
encountered
consists largely
Ellis, R.C.L.
(E. Matos, pers. comm.). Ramalho's (1971) identifi­
#1-3 is Upper Oxfordian in age. How­
coral­
12. Clearly, the data base is much less com­
are
Kimmeridgian
of the
carbonate sequence beneath the Abadia formation
lower
with
low-energy oncolitic wackestones (association 4) and
The
in
the
stylinid
upper unit of deeper-water limestones and limestone
cation of the Amaral formation overlying the buildup
and
available from both the central part of the seismic
of
distinct
overlain by an
hi gh and
system
flat/c han nel
loferitic cycles
of
and
sists
®
and
with
occur
clastic
low-energy
The
corals,
the
a
of
core 2.
present.
clay-rich
at
may
a
? Solenopora
brachiopods,
main
Tubiphytes-
the
variety
have
nerineid
transition
ridges
of
microsolenid
base
microsolenid
Wilson and R.R. Leinfelder
Tubiphytes -
been
framework
buildup.
stones and packstones
of
inozoans,
A
lagoon exhibiting mud
interbedded
in tra
shallow, mostly restricte d
between
shallower-water conditions.
corals,
the
corals,
expos ure
organisms,
the
wackestones,
with
of
oysters
than the wackestones
black pebble
deposited
0 4
containing
0
number
core,
sol
of
in
t�
and
in
of
nerineid
of the middle
chiefly
horizon
the
platform
E
situ
which,
large
Upper Ki mmeridgian
containing
unit
due
large
to
lower
shallow-water
light-coloured
stromatoporoids
like
heads
Fig. 10. Interpretative cross-section across the Ota buildup showing distribution of the facies associations described in
The second unit, between 2358 and 2363 m, con­
bio­
brachi­
though has greatly increased its porosity. The wacke­
sedi­
ments of the buildup and the deeper-water carbon­
lower parts of this core has destroyed its structure,
corals, some of which are oyster-encrusted, are also
gastropods,
cyclinid
foraminifera. Small in situ heads of chaetetids and
of
higher-energy,
limestone lithoclasts (largely consisting of association
unit,
the main frame builder, are platey and are encrusted
may have been deposited on slopes just basinwatd
angular
wackestones and packstones
wackestones occurring at Montejunto,
opods, nerineids and foraminifera and small in situ
microsolenids. The microsolenid corals, which form
ates of the upper unit that cap it is represented in
and
crusts, with lesser numbers of inozoans, bryozoans
are less
and skeletal algae. Pervasive dolomitization of the
thrombolitic
the
�m�e�re�s�------ �,
5 0 0