Page 184 - Carbonate Platforms Facies, Sequences, and Evolution

ting
170
The
four
. . · · ·
were
basins.
L_____j
500km
mation)
(Wilson,
summary
evolution
Lusitanian
thin,
ocean
Stratigraph y
are
of
Wilson et at.,
Mesozoic
the
1979,
significant
chart
described below.
the
of
ridge­
Basin.
Triassic-Callovian
GEOLOGICAL
1989).
OF
for
faults
transform system
the
capped
The
This sequence is typical
North
tectonic
the
by
Triassic red fluvial
unconformity-bounded
three
of the
SETTING
Lusitanian
BUILDUP
Atlantic
controls
1988; Wilson et al.,
southern
early
siliciclastics
Hettangian
on
AND
buildup development during this period.
Basin
propagated through
part
1989),
(Wilson,
of
megasequences,
rift-sag
megasequences
(Silves
P.M. Ellis, R.C. L.
TYPES
sugges­
the manner in which reactivation of Hercynian base­
Where the evaporites were thick, halokinetic struc­
The first two of these mega­
for­
suc­
from North America began in early Oxfordian times
evaporites
are
carbonate
as a simplified, and as yet, informal lithostratigraphic
the
1988;
development of which was related to events in the
sequences, and part of the third are shown in Fig. 2
ment faults affected the cover of younger sediments.
the
comprises
(Dagorda formation) which subsequently influenced
formations. The Triassic and Hettangian sediments
younger
tures formed above basement faults, but where they
cessions encountered in most North Atlantic margin
the
and
wide
most
Basin
Basin.
is
Fully
Wright,
of
marginal
of
later
Wilson and R.R.
(Coimbra,
hiatus,
the
1985)
unconformable
marine
basins,
Lower
Lusitanian Basin.
considered
Morocco
poraneous faulting.
Brenha
development in the
Leinfelder
to
and
such
spanning
southern
and
and
as
comprising
in
carbonate
the
and
Lusitanian Basin in the late
Middle Oxfordian-Berriasian
the
the
Middle
Lusitanian
and accompanied
Tucholke (1986).
whole
central
the Nova
Candeiros
deposition
of
western
Caba9os
Jurassic
Basin is
accumulated in grabens and half grabens,
parts
be the major source
the
High
Scotian
of
for
Fig. 1. Palaeogeographic sketch
returned
location of the Lusitanian Basin.
Adapted from plate 9C of Vogt &
map for the North Atlantic region
during the late Oxfordian. Box on
The base of the Upper Jurassic is marked by a basin­
metries with relatively minor indications of contem­
blanketed the basin and exhibit simple facies geo­
ments consist predominantly of lacustrine ostracod­
Throughout the basin, the earliest Oxfordian sedi­
western margin of Iberia shows the
developed on the underlying Middle Jurassic lime­
later than those in other southern North Atlantic­
formations)
by karst surfaces
though
formation.
stones (Ruget-Perrot, 1961; Wright & Wilson, 1987).
sediments
(Mouterde et al., 1971). In places, this boundary is
Oxfordian and the early part of the Middle Oxfordian
charophyte lime mudstones (Wright & Wilson, 1985;
the
This formation contains highly bituminous horizons
the
carbonate buildup phase of the basin's history, when
Lower
many hydrocarbon shows in the southern part of the
the limestones of the Montejunto formation and its
to
Shelf
equivalents were deposited. The initiation of buildup
somewhat
with a relative rise in sea-level. This was the main
Oxfordian, associated
Atlas