Page 115 - Carbonate Platforms Facies, Sequences, and Evolution

an
the
from
The
longer
nately,
Norian
sequences
repetitions
Italy
sub-littoral
third-order
tively small
than,
such
in
it
slow sea-level
to
Middle
melting is fast.
an
is
the
Muschelkalk
the
Dolomia
of red
orbital-forcing
cycles,
rises
sabkha)
and
cycles,
cycles of sea-level change.
approach
control
Muschelkalk
considered
and
geological
Principale,
has
marl-nodular
cannot
which typically
most
obtained
apparently
(Hardie
record
be
are
many
cyclicities have been recognized in the
et
to 600 000 years. This is comparable to,
laminated
from
likely
rapid
gypsum
a
used
al.,
Muschelkalk are the result of orbital forcing.
duration of Latemar cycles.
that
in
consisting
depicted
gypsum­
gin is different from that of the much thicker second­
rapid rises of relative sea-level of many fourth -fifth­
Catalan Basin where the number of cycles is rela­
that statistical techniques can be employed. Unfortu­
cycles of probable glacioeustatic/orbital forcing ori­
duration is the complete absence of cycles when sea­
thickness variations of small-scale cycles, suggesting
the
simple
rapid falls (e.g. Miall, 1986), and in many people's
shallowing-upward cycles in the Lower and Upper
pertinent to recall that in the Ladinian strata of the
(shallow
One
falls (see Fig. 21; Vail et al., 1977; Haq et al., 1987).
metre-scale
minds now (e.g. Hubbard, 1988, and this paper), the
1986;
sea-level
repeated shallowing-upward cycles). However, it is
Milankovitch-band
division of time by cycle number, ranges from 30 000
level drops below the platform margin or does not
rocks of equivalent age to the Upper Muschelkalk,
reach the inner region of a carbonate ramp. Although
major factor leading to gross over-estimates of cycle
no known mechanism. The apparent slow falls and
and much
as
as well as in the Carnian Dtirrenstein Formation and
(and this is the case with many other
nodular gypsum (lagoonal to sabkha) which could
also be responses to glacioeustatic fourth -fifth-order
It is worth pointing out that the pattern of rapid
Latemar Platform of the Dolomites in northern Italy,
to explain the fourth -fifth-order shallowing-upward
the
it cannot be proved, and persuaded by the evidence
Goldhammer et al. 1987). The maximum duration of
where the buildup of polar ice caps is slow, but their
subsidence following rifting, rather than some global
slow rises are largely the result of regional tectonic
eustatic phenomenon, for which at present there is
There has been much discussion over the apparent
Another problem is whether there
order cycles is consistent with a glacioeustatic origin,
patterns of
of
sea-level rise and slow fall or stillstand which appears
1
4
3
2
in
of
the
can
In
The
the
be
general
wedged
pattern
models.
changes
regional
of
Middle
in
barrier-type
respectively.
tectonics
Muschelkalk
Muschelkalk
Depositional
The
with buildups.
is
is
divided
that
and
aggrading
regressive
mid-Triassic
northeastern
subsidence
Middle Triassic carbonate ramp systems, Spain
into
to
model
Between
sequence
similar
similar
sedimentary
and
Muschelkalk
1
evolves
two
sedimentation
eustasy
strata
not an issue for this paper.
barrier-bank type of Read
to
to
Iberian
clastics
these
in
in
into
of
and
the
the
regressive
a
proposed
basins,
the
tectonic
and
the
(1985),
includes
CONC LUSIONS
in
for
two
the
depositional
Peninsula
Keuper,
carbonate
this
controlling
character
the
Anisian-Lower Ladinian and Carnian age.
of
and the
Catalan
homoclinal
units
evaporites
quiescence.
case
and
display
carbonate facies are mostly of a restricted nature.
Buntsandstein and Lower Muschelkalk and Depo­
basalt eruption. Deposition of the Muschelkalk car­
Al­
onlapping, retrogressive and back-stepping arrange­
crustal extension and rifting, resulting in major thick­
sequences:
homoclinal-ramp,
ramp
platforms occur above the Buntsandstein: the Lower
the result of deposition in different ramp sedimentary
Basin
the Triassic of the Catalan Basin, three carbonate
Lower
Upper
are
105
sitional sequence 2 includes the Middle Muschelkalk
were Triassic ice caps to wax and wane, but that is
are represented by the lutite-carbonate-evaporite
Muschelkalk, the Upper Muschelkalk and the Imon
Formation, of Anisian, Ladinian and Norian ages,
deposits, reef complexes and deep ramp facies in the
sea-level
facies). Deposits of the transgressive systems tracts
are composed of peritidal deposits in the lower part
of the transgressive section passing up into sand belt
Upper
The three carbonate units in the Catalan Basin are
of
ment. The Buntsandstein, Middle Muschelkalk and
unit at the top of the Buntsandstein and the Middle
homoclinal-ramp,
and Upper Muschelkalk. The lowstand systems tracts
an
On a broad scale the Triassic carbonate deposits
upper part. The two highstand systems tracts show a
the
uppermost
Muschelkalk (both continental to marine evaporitic
though it is notoriously difficult to separate the roles
the
depositional
ness changes across the Catalan Basin, and locally
bonates took place during the succeeding period of
Keuper sediments were deposited during phases of