Page 195 - Carbonate Platforms Facies, Sequences, and Evolution

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the
zone
early
The
Setting
Four
of
sections,
drilled at
reflections
block
Upper Jurassic carbonate buildups,
(Leinfelder,
the
Bahamian-like
bindstone; BfS =
location
was
Tithonian
of
1985).
Barreiro
petroleum
to
beneath
Portugal
The Barreiro buildup
penetrated the main
at
the
Barreiro
discontinuous
the
to
subjected
least
cores
to
buildup
carbonate bank,
bafflestone; FrS =
the
small anomaly to the southwest.
exploration
part of the
across widths ranging from 1 to lOrn.
anomaly
(Figs llc and
chaotic
are
12).
early
short lateral extent at its margins (Fig.
wells
occurs
which,
subaerial
seismic
just
titled-block dipping gently to the southeast.
volume are: packstones (including algal stabilized
have
taken from the
(a) Lithological log. Key: WS = wackestone; PS =
the south of and parallel to the major NNW
reflectors,
packstone; GS = grainstone; RS = rudstone; BiS =
to
during
Barreiro
framestone. The
obscured,
diagram illustrating the interfingering of facies types. A
Kimmeridgian, had no direct connection with simi­
ing moderate amplitude, moderately continuous fiat­
reflection character of the Upper Jurassic, compris­
later Upper Kimmeridgian, the Ota block stopped
relative abundances of lithologies within this sequence by
subsiding, and intraclast and ooid grainstones spread
Fig. 9. Facies variation in the reefal zone in the Ota area.
and south (Leinfelder & Wilson, 1989). During the
exposure
the
sediment)= 46%; bindstone + bafflestone + framestone =
lar, though older buildups to the north (Montejunto)
Cretaceous,
over the structure and filled karst features. From the
First recognized as a stratigraphic anomaly on seismic
the
with
of it respectively, but #3 was drilled close to another
scale bar is not shown, as the variations shown may occur
-SSE
three
relatively high-amplitude dipping reflectors with a
11). Seismic
that a clear picture of its structural setting cannot be
so
trending lineament identified on Landsat images, it
south of the Tagus estuary (Fig. 3). In it the normal
anomaly,
seems reasonable to suggest a crestal location on a
and #2 and #1 were situated to the north and west
several seismic anomalies aligned along a line just to
gained. However, as the Barreiro anomaly is one of
been
25%; grainstone = 22%; wackestone = 7%. (b) Summary
lying reflectors is replaced by a lensoid anomalous
181
wells that penetrated the Barreiro buildup is shown
#4