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component in the oxygen-isotopic signal come from Argentina (Mitchum and (though still a part of the western Tethys)
is considered negligible in the Jurassic. Uliana, 1985; Legarreta and Uliana, 1996, follow those suggested by Hardenbol et al.
Jurassic of the Neuquén Basin). A number (1998) and later by Ogg and Hinnov (2012).
An examination of the available of other studies of the Jurassic that were Calcareous nannofossil zones of the
sequence-stratigraphic reports of the undertaken at the broader (second-order) Jurassic, also included, are mostly of long
Jurassic (up to 2017) revealed that many scales were not considered relevant for a duration and of limited correlative utility
sections around the world cannot be cor- third-order scale synthesis, but they do in this period. However, sometimes they
related with precision with the European sometimes provide additional constraints do provide additional criteria for
stage stratotypes due to the provincial for the long-term trends. As our ability to correlations.
nature of ammonites, though other fossil more precisely correlate sequences
groups can be helpful for cross-correla- improves in the future (through ancillary The two columns on the right in Figures
tions. The earlier syntheses presented by fossil biozones and other multiple, overlap- 1 and 2 show sea-level events (mostly
Haq et al. (1988) and Hardenbol et al. ping, correlative criteria, such as che- third-order and some consistent fourth-
(1998) still form the basis of the current mostratigraphic methods), these deposi- order sequence boundaries) and sea-level
synthesis. Additional information on third- tional cycles may be extended to other curves (long-term and short-term) for the
order sequences that form a part of this parts of the globe where the marine Jurassic. When sequence boundaries are
reappraisal comes from Britain and France Jurassic record is well preserved, such as correlatable in several basins they are con-
(Wignall, 1991, from Kimmeridgian of New Zealand. sidered widespread (though global validity
Dorset and France; Partington et al., 1993, cannot be verified due to the Eurocentric
Kimmeridgian to Ryazanian of North Sea; RESULTS nature of most of the data). The criteria for
Herbin et al., 1995, Kimmeridgian and the long-term curves (shown in the last
Tithonian of Dorset and Yorkshire in the The cycle chart resulting from the reap- column on the right) have been discussed
UK and Boulonnais Basin in France; praisal of global stratigraphic data of the earlier in this paper, and the shorter-term
Taylor et al., 2001, Late Jurassic of Wessex- Jurassic is presented as two figures (Fig. 1 sea-level curve that is derived from the
Weald Basin; Williams et al., 2001, for the Early Jurassic and Fig. 2 for the sequence-stratigraphic data to its left. The
Kimmeridgian and Tithonian of Wessex Middle and Late Jurassic). The figures amplitudes of third-order sea-level changes
Basin; Hesselbo, 2008, from the Jurassic represent the established biochronostratig- (rise and falls in meters) shown here are
onshore sections of Britain); Poland raphy of the Jurassic, plotted against the averaged from stratigraphic estimates in
(Pienkowski, 2004, Early Jurassic of Polish results of the current synthesis of the several basins and should be considered
Basins); Greenland (Surlyk, 1990, Jurassic sequence cycles, their revised ages (and an approximate (see discussion in Haq, 2014).
of East Greenland); Russia (Sahagian et updated numbering system partly adapted They are subdivided into three magnitude
al., 1996, mid- to Late Jurassic of Russian from Hardenbol et al., 1998). A sea-level categories of sea-level falls: major (>75 m),
Platform; Pinous et al., 1999, Callovian to curve based on the onlap record is the final medium (25–75 m), and minor (<25 m).
Oxfordian of western Siberia); Portugal product of the synthesis. The biochro- Most sea-level events fall within the
(Leinfelder, 1993, Kimmeridgian of nostratigraphic parts of the figures show medium category.
Lusitanian Basin); Denmark (Johannessen the latest (GTS 2016 of Ogg et al., 2016)
et al., 1996, and Johannessen, 2003, Late age model from the Rhaetian (latest The long-term sea-level envelope (indi-
Jurassic of North Sea and Danish Central Triassic stage) through Berriasian (the cating the maximum flooding of continen-
Graben); and northern Switzerland (Gygi early Cretaceous stage). This is tied to a tal margins and interior basins) shows that
et al., 1998, Oxfordian-Kimmeridgian; composite paleomagnetic reversal scale sea level remained close to or below pres-
Colombié and Ramell, 2007, that remains tentative below the Bajocian. ent-day mean sea level (pdmsl) from the
Kimmeridgian). Other areas of the Tethys The seafloor magnetic anomaly record is latest Triassic through the Hettangian and
include the Arabian Platform (Sharland et fragmentary below this level because the early Sinemurian, rising only a few tens of
al., 2001, 2004; Haq and Al-Qahtani, 2005, older Jurassic oceanic lithosphere has been meters above pdmsl in the late
mid- to Late Jurassic; Al-Husseini and largely subducted. Even for the Bajocian Sinemurian-Pliensbachian, and by the late
Matthews, 2006, Oxfordian–early through Tithonian interval, it is dependent Pliensbachian it reverted back to levels
Kimmeridgian), and India (Krishna, 2005, on a single site from the eastern Pacific comparable to pdmsl. In the Toarcian,
mid- to Late Jurassic of Kutch Basin). For (ODP site 801). The polarity scale from the there is an apparent long-term rise that
the depositional cycles identified in Tibet, Oxfordian to Tithonian is, nevertheless, may have peaked at ~75 m above pdmsl. In
where a nearly complete Jurassic record fairly well verified in multiple sections and the latest Toarcian, the sea levels fell again
exists (Li and Grant-Mackie, 1993), direct basins. The stages, Hettangian to to a few tens of meters above pdmsl, a
correlation with the sub-boreal third-order Tithonian, currently considered standard trend that continued into the early
cycles of Europe and those from the west- subdivisions for the Jurassic, are tied to Aalenian. From the late Aalenian onward,
ern Tethys could not be established due to ammonite zones that, much like in the there is a gradual sea-level rise trend, with
differences in ammonite assemblages, but Cretaceous, are the most common fossil a few tens of meters of dip in the Bajocian
the authors show similarity in trends, and group for correlation in the Jurassic. The and another in the latest Callovian–earliest
even tie some of the major sequence cross-correlation between zones from the Oxfordian that culminated in the peak high
boundaries with those in Europe. From the relatively warm-water Tethyan regions and of the Jurassic in the late Kimmeridgian–
Southern Hemisphere the only data that cooler-water boreal/sub-boreal regions early Tithonian. Near the Kimmeridgian-
could be considered for this synthesis Tithonian boundary, the sea level may
have been as high as ~140 m above pdmsl.
6 GSA Today | January 2018