Page 212 - Carbonate Platforms Facies, Sequences, and Evolution

A
al.
by
198
into
The
a
Eliuk
Grow,
played
largely
Both
drowning
geometry
suggested
American
no
prograding
thicknesses
nature
(1978,
1982),
sudden
reefal,
that
thin cap of
of
Facies variation
and
event
of the
inner part of the
sediments in this
Ramalhal buildup.
aggradational
Atlantic
1979,
the
reefal
significant
carbonate
aggradational
similar
(Stage
stituents' (Jansa, 1981).
to
short-lived
only
part
margin
and
1981)
American
taining similar facies (Ellis et
geometries
(Mattick, 1982; Erlich et al. ,
III).
deeper-water
in
in
carbonate
to
has
shelf-edge
occur within the Upper Jurassic
clinoforms
were present near the edge, and
modern
the
region to consist
of
the
sea-level
those that do not, aggrade (Stage II).
as a carbonate bank system in which
buildups.
been
shelves
described
aggradation was caused by a rapid rise.
along
which
reefs
the
than differing eustatic sea-level changes.
P.M. Ellis,
carbonates
In
fall,
skeletal,
progradational
Explanations
aggradational
the
and II) vary widely from author to author.
'oolitic
largely of
(Stage
for
development
described
(Schlee
R. C. L.
records
buildups receiving siliciclastic sedi­
aggradational and progradational buildup types de­
Meyer (1989) recorded three stages in the devel­
opment of North American Atlantic margin carbon­
platform', where 'coral-stroma­
buildups, equivalent to Meyer's Stage III and con­
non-
toporoid and sponge bioherms were only rare con­
these Portuguese buildups, though this does not rule
it out as a factor influencing either the position or
Portugal,
as
whereas
shoals
Meyer
amount of lithofacies data based on core samples.
salt-influenced
the Portuguese buildups, they developed comparable
Lusitanian
Basin as well as a number of examples of drowned
ments from the hinterland prograde (Stage I), while
a!. , 1985). Clastic input
Mattick (1982),
the
of
a
shelves
Basin are linked to local tectonic conditions, rather
phases
(1987), in contrast, postulated a eustatic control,
rise. The two buildup geometries in the Lusitanian
1987; Meyer, 1989), or
II).
two main styles of buildup growth (Meyer's Stages I
whereby rapid shelf-margin progradation was caused
however, takes exactly the opposite view! Erlich et
&
developed
ate buildups. The first of these (Stage I) consists of
peloidal
The Nova Scotian shelf has yielded the greatest
wackestones and biomicrites were deposited in the
North
veloped during the same period of relative sea-level
shelf-break
a!. ,
and
A
reef.
some
work.
vidual
is
Firstly,
buildup
bioherms
Recent
Secondly,
1987)
is
dominated
wave base.
(equivalent
( Solenopora)
heads
modern,
the
into
to
coral-chaetitid
However,
shelf-edge reefs,
a
reefal
extremely
also
similar
diagenetic breccia.
on
buildup in Portugal.
Wilson and R. R. Leinfelder
well-developed
within
to
challenged
reef-fiat
frames
rare
Meyer's
breccias
the
gave
building
by
a
in
and below by wackestones
structure,
those
tone),
up
basis
Stage
two
Shell-Amoco-Sun
within
pared them to Wilson's (1979)
of
semi-exposed
of
II
grainstones
and
'modern
the
wells
other
knoll-reef
which were considered by Jansa et a!.
analogous
and
from the
and shales.
analogy for the
Solenopora identified by Eliuk
much of the lowest core in Demascota.
electric
reef-fiat
to
buildup)
likened to red algae in modern reef fiats,
Demascota
aspect'
of the shallow-water facies in cores 2 and 3.
drilled
bounded
coral-stromatoporoid
'knoll reefs',
log
(1978)
to
in
lowing a drowning event. Eliuk (1978), Jansa et
core
show
visaged that this passed up into a persistent coral­
They com­
Eliuk en­
Deeper-water thrombolitic boundstones, contain­
(1983) and Ellis (1984) agreed that the cored inter­
upwards trend, capped by deeper water facies fol­
environ­
Portugal, this sequence shows a general shallowing­
Baltimore Canyon Trough area also indicate a grain­
Cores from an eastward pro­
was re­
such as those cored in Shell Demascota G-32 (Fig.
In Portugal, Solenopora only occurs as indi­
reefs,
a!.
lack of binding and encrusting algae within the frame­
frameworks.
ing the characteristic microfossil Thartharella, form
skeletal oncolitic grainstones and packstones, with
24). Like the Barreiro and Ramalhal buildups from
but there was less agreement about the significance
Jansa et a!. (1983) and Ellis (1984) suggested that the
data,
the
ment. He considered that the presence of red algae
reefal intervals represented by cores 2 and 3 (Fig.
modern
formed in quiet-water conditions at or just below,
observations.
deep-water
vals within this well exhibit a true reefal framework,
stone and packstone-dominated shelf edge (Erlich et
similar shallowing-upwards sequence (Fig. 24), from
deeper-water wackestones to coral-stromatoporoid
a
salt-controlled
grading clinoform interval penetrated by 0337 Civet
the
Demascota
and
which
24) were no more than 15-20m thick (consisting of
above
identified as the milleporid Milleporidium remesi by
reef-fiat debris, were interpreted by Ellis (1984) as a
(1983) to be
Ellis (1984), who also remarked at the conspicuous
packstones
2