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late Oxfordian of the Swiss Jura, applying the
methodology presented in Strasser et al . (1999).
Detailed analyses of thin-sections and sedimentary
structures allow identifi cation of deepening and
shallowing trends of facies evolution. Accordingly,
elementary, small-scale and medium-scale depo-
sitional sequences have been defi ned in each sec-
tion studied, which then were correlated over
the entire study area. It is seen that four small-
scale sequences regularly build up a medium-
scale sequence, and that there are two to six (in
many cases fi ve) elementary sequences comprised
in a small-scale sequence. The bifurcatus and
bimammatum zones contain 16 small-scale
sequences (Fig. 4). According to Hardenbol et al .
(1998), based on the absolute dating by Gradstein
et al . (1995), this interval lasted about 1.6 Myr.
This implies that one small-scale sequence lasted
100 kyr, which corresponds to the duration of the
short eccentricity cycle of the Earth's orbit (Berger
et al ., 1989). A medium-scale sequence would
then represent the long eccentricity cycle of
400 kyr, and an elementary sequence (where it can
be identifi ed) the precession cycle of 20 kyr. From
the observed facies trends it appears that sea level
was a major controlling factor in sequence forma-
tion. It is therefore suggested that orbital cycles
translated into climate changes (Milankovitch
cycles), which in turn controlled sea-level fl uc-
tuations. Between sequence boundaries Ox6 and
Ox7 lie eight small-scale sequences but only
660 kyr are allocated for this interval by Hardenbol
et al . (1998). On the other hand, four small-scale
sequences are contained between Ox7 and Ox8,
an interval which Hardenbol et al . (1998) estimate
to have lasted 520 kyr (Fig. 4). These discrepan-
cies are due to the error margins in absolute dating
of stage boundaries (Gradstein et al ., 1995) from
which Hardenbol et al . (1998) have interpolated
their age estimations, and/or to the possibility
that a sequence boundary dated in the basin by
Hardenbol et al . (1998) may have its strongest
expression on the platform not necessarily at the
same time (Strasser et al ., 2000). Also, some orbit-
ally induced sea-level changes may not have been
recorded in the sedimentary system (see below).
LBM
RM
BM
Paris
Basin
AM
Iberia
CM
GLH
CSH
500 km
AM
Armorican Massif
land
shallow marine
deeper marine
oceanic crust
BM
Bohemian Massif
CM
Central Massif
CSH
Corsica-Sardinia High
GLH
Gulf of Lyon High
LBM
London-Brabant Massif
RM
Rhenish Massif
Fig. 5. Late Jurassic palaeogeography of the northern mar-
gin of the Tethys Ocean, the Swiss Jura and the Paris Basin
(modifi ed from Ziegler, 1988).
The upper part of the Günsberg Member and
its lateral equivalent, the Röschenz Member, is
dominated by marls and isolated limestone beds
with shallow-lagoonal fl ora and fauna. Freshwater
algae, root traces and plant debris occur locally.
The Hauptmumienbank Member is composed of
massive limestone beds rich in oncoids. It is later-
ally replaced by the Steinebach Member, which
is characterized by oolites and coral patch reefs.
These sediments were deposited on the shallow
platform between the Paris Basin to the north and
the Tethys Ocean to the south, in the position
of today's Swiss Jura (Fig. 5). Siliciclastics were
shed from the Bohemian and the Central massifs.
Palaeolatitude was about 26-27°N (Dercourt et al .,
1993).
The interval studied has been dated by mineral-
stratigraphic correlations with ammonite-bearing
horizons (Gygi & Persoz, 1986; Gygi, 1995): it
lies in the lower part of the bimammatum zone
(semimammatum and berrense subzones) of the
late Oxfordian (Fig. 4). Gygi et al . (1998) and Hug
(2003) have established the sequence-stratigraphic
framework, which implies that the interval stud-
ied is situated between sequence boundaries
Ox6 and Ox7 of Hardenbol et al . (1998). The
sequence-stratigraphic terminology follows Vail
et al . (1991).
Pittet (1996), Pittet & Strasser (1998), Strasser
et al . (2000) and Hug (2003) have performed a
cyclostratigraphic analysis of the middle and
DEFINITION AND CORRELATION OF
DEPOSITIONAL SEQUENCES
Small- and medium-scale sequences
Within the general sequence-stratigraphic and
cyclostratigraphic framework discussed above, the
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