Page 129 - Carbonate Platforms Facies, Sequences, and Evolution

of
118
the
the
such
They
from
ment
stones
narrow
side of
to
ordinate,
a
can
Spain
one
middle
cially during
metre-scale).
be
hinge
environments:
and
block
block,
the
Resedimentation
a hinge,
northernmost
The
are missing.
to
'Hinge-sequences'
lines.
lenticular,
(Seyfried,
late
high-to-medium
part
compared
sediments
of
edge of a
1981;
general
took place
another,
with
energy
were
Toarcian.
developed
at
ferruginous
or the reverse,
Ferruginous
the
one
on
Vera,
the study
tectonic controls were also involved.
tilted block. On more gradual slopes
can
swept
platform),
steep
top
the toe
crusts
Domerian-Bathonian.
oolitic
along steep slopes washed by mass-flows.
area)
1984)
depositional
However,
of
of
slope
with
environments,
or
beds
towards
A comparison between the Crussol outcrops
small temporarily sheltered areas (of decimetre-
of
marly limestones with Zoophycos were deposited.
common, as well as hardgrounds and firmgrounds.
with mudstone to packstone textures whereas grain­
ment sequences' are characterized by sliding, slump­
'Escarp­
swells, with multiple internal disconformities, espe­
escarp­
The vertical change from an escarpment environ­
sub­
always highly varied, condensed and/or discontinu­
or stratigraphic gaps are associated with high-energy
the
called umbilics). There was no flat shelf between the
a
the
ing of neritic clasts and calcareous or silty turbidites.
basin or toe of the escarpments. It is striking that, in
are usually larger than the swells which are related
Platforms
Sediments can only have been
rarely preserved lenticular beds consist of micrites
ments. Such disturbed successions have been called
to the top of tilted blocks (Elmi, 1984). Sedimentary
'escarpment sequences' (Elmi, 1984) and developed
Tlemcenian Domain of western Algeria (Elmi, 1981,
emergent zones and the bottom of the sedimentary
basins either on shallow slopes or on basin-borders.
hemipelagic
narrow
(in
to
trapped during short-lived low-energy times and in
assume that
effects. If the effects are diverse, and even opposite,
and the
(gentle-ramp
1983a; Almeras & Elmi, 1984). Sedimentation was
related to general movements of sea-level as during
can in places be
but prominent seamounts. Comparable settings are
are
ranged from peritidal to pelagic, on relatively deep
known during the differentiation stages of several
Apennines (Bernoulli, 1971), the Subbetic Ranges
Tethyan basins as, for example, the Italian Central
eustatic
the
sea-level changes have general, or at least regional,
setting
ous. These conditions are related to the steepness of
the slopes at platform borders where they cross the
S. Elmi
or
zone
At
slope
fluvial
ditions
swell
sea-level
Eynesses
During
Callovian;
thickening
Hettangian
a
existed
existed
sands
and
became
rounding swells
fault,
existed
Rosieres,
gap
changes
a
and
toward
from
network, delimiting
during
(Fig.
from
the
similar
the
(late
accumulation
formed
7).
the
the
during the late Oxfordian.
to
tectonic regime (Colongo et
of
regularly in each sub-basin.
subsidence
early
subsidiary
Rhaetian
basin
with
stratigraphic evolution (Fig. 8).
an escarpment
of
the
Triassic
middle
those
was
middle
During
of
the
Liassic
missing
-earliest
elongated, they can be called 'gutters'.
Ucel
to
the
La
(eastward)
strong
Toarcian
the Bathonian to the earliest late Oxfordian.
Oxfordian.
the
regression,
Crussol
Upper
in
formed during
to
Cal­
a/. , 1979; Elmi, 1984).
Rousse­
could deepen strongly by comparison with the sur­
Con­
and became mainly westward, occurring in the di­
following Sinemurian-Pliensbachian times; a hinge
differing tectonic behaviour caused the contrasting
early
Bathonian (gaps can span the Rhaetian-Domerian
the
At Crussol a hinge
the
basin occured from the late Bathonian to the middle
lovian and Lower Oxfordian deposits; and a gentle
middle Bathonian (with gaps); pelagic outer shelf to
Such locations are called
narrow subsiding zones which
Hinges were commonly separated by distances of
The best palaeotectonic markers are shallow-water
a few kilometers and they formed a multidirectional
1984; Elmi & Ameur, 1986). If the deep zones were
interval); then middle Bathonian sinking occurred
were slight and can be ruled out. Carnian-Norian
can only be related to sedimentary progradation and
deposits or alluvial fans; their change in thickness
Hettangian
Planzolles lineament (Fig. lA, no. 1 and Figs 4 & 9).
Rosieres well (farther south) establishes clearly that
and an escarpment and pelagic basin existed from
here 'umbilics' (Elmi, 1981, 1985a; Almeras & Elmi,
to tectonic controls because bottom-level differences
the
only
the orientation of the sediment thickening changed
rection of the margin. This evolution is well seen in
areas where profiles can be drawn across the margin,
such as along the down-dropped northern structural
Jurassic transgression). These beds thicken rapidly
across certain faults. Triassic sandstones (Formation
early
shoreline and shallow-marine deposits accumulated
along a border recording the local effects of global
Bariolee d'Ucel) thicken from 5 to 7 m across the les
happens
Rhaetian,
Formation,
The sense of such abrupt lateral thickness changes
through time, recording modifications of the overall