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identifying 13 additional sequences as well. The base level actually fell just below One clear trend in the Triassic is the
The Triassic portion of Haq and pdmsl in the Anisian, reserving this trend overall low seastands of this period. If one
Al-Qahtani (2005) was mainly based on in the Fassanian substage of the early were to also include the lowstands on both
cycles identified from the Arabian Ladinian when a steady rise is seen that ends of the Triassic, i.e., in the latest
Platform. For the current reappraisal, those culminated in the highest sea levels of the Permian (starting ca. 260 Ma) as well as
data have been further augmented with Triassic (~50 m above pdmsl) in the the earlier Jurassic (ending ca. 180.5 Ma),
third-order cycles from published sources Tuvalian substage of the late Carnian. From it represents an interval of almost 80 m.y.,
as follows: the Triassic of Northern this peak the trend reverses again to a long- when the sea levels were universally low
Germany (Aigner and Bachmann, 1992) term decline in the Lacian substage of the and do not seem to have risen more than
and Induan through Ladinian of Black early Norian. Through the Alaunian and 50 m above pdmsl at the highest point (in
Forest (Bourquin et al., 2006); Induan much of the Sevatian substages of the late the Carnian). This 80-m.y. period was also
through Carnian of Balaton, Hungary Norian, the base level remained steady and an interval when there is no known evi-
(Budai and Haas, 1997); the Triassic of very close to pdmsl. At the Norian-Rhaetian dence of large continental glaciations any-
Transdanubian Range in Hungary, the boundary the base level dips once again where in the higher latitudes. Such a long
Calcareous Alps of Austria and of Germany, just below pdmsl, recovering for a short duration of oceanic withdrawal from the
and the Lombardi Basin in Italy (vide Haas time in the mid-Rhaetian and then declin- large landmass of Pangaea seems unique in
and Budai, 1999, and references therein; ing rapidly to almost 50 m below pdmsl in the Phanerozoic Earth history and would
also see the GSA data repository [see foot- the latest Triassic and earliest Jurassic. have had important repercussions for
note 1]); the Triassic of Sverdrup Basin The short-term sea-level curve, superim- global climates and biodiversity (see fur-
(Embry, 1997); the Triassic of Norwegian posed on the long-term eustatic curve, is ther discussion in the GSA data repository
Barents shelf, Bjørnøya and Svalbard (van based on sequence boundaries that are [see footnote 1]). These could potentially
Veen et al., 1992; Glørstad-Clark et al., consistently correlatable in several basins include the presence of large desert areas
2010; Mørk et al., 1989); the Triassic of are therefore considered widespread. Two and widespread salinas in arid regions,
Arabian Platform (Sharland et al., 2001, cycles, one each in the Norian and the extreme climates, especially in the conti-
2004; Haq and Al-Qahtani, 2005); the nental interiors, high sea-surface tempera-
Triassic of United Arab Emirates (Maurer Rhaetian (TNo2 at 222.5 Ma and TRh1 at tures, relatively flat equator-to-pole gradi-
et al., 2008); the Triassic of Spiti, northern 203.5 Ma), are included tentatively, pending ents, and sluggish surface circulation.
India (Bhargava et al., 2004; Krystyn et al., their confirmation from other areas as Deeper circulation would be characterized
2005); Induan through mid-Anisian of east- being more widespread. The amplitudes by warm saline bottom waters with inter-
ern Yangtze Platform, China (Tong and of third-order cycles (measures of sea-level mittent loss of vertical stratification leading
Yin, 1998); and the Triassic of Carnarvon falls in meters) are particularly difficult to to widespread anoxia. Tropical shallow
Basin, Australia (Gorter, 1994). It is appar- estimate. The estimates of sea-level falls marine areas during relative highs could be
ent from this list that the Triassic sea-level are always relative to the preceding high- sites of carbonate and extensive evaporite
variations as documented in the new stand, and their determination criteria can deposition. Biodiversities would decline
cycle chart remain mostly centered in include such relative measure as thickness when summer temperatures exceeded a
the Tethyan realm (its western boreal and of the system tracks, bio- and lithofacies certain threshold both on land and at sea.
its eastern low to temperate latitudes exten- depth assessments, depth of incision of A long period of lowstand and continuous
sions) (see the GSA data repository [foot- shelves (in case of type-1 sequences), and high temperatures also mean a deficit of
note 1] for the complete documentation partial back-stripping (see Haq, 2014, biologic evolutionary innovations, and evi-
of the sequence boundaries of the Tethys for further discussion). In the cycle chart dence gathered by Triassic paleoclimatic
realm). presented here (Fig. 1) they are averaged and paleoceanographic studies confirms
from stratigraphic estimates in several these paleoenvironmental consequences.
RESULTS AND DISCUSSION basins and should be considered best Biodiversity was decimated at the end-
The results of the revision of the Triassic guesstimates. They are categorized into Permian extinction event and, after the
cycle chart are shown in Figure 1. Since the three groupings of sea-level falls: major Early through Middle Triassic recovery,
revised eustatic curve is largely based on (>75 m of fall relative to previous high), declined once again during the long inter-
the sections in the low- to mid-latitudes of medium (25–75 m of relative fall), and val of the Late Triassic (these issues are
the Tethys Ocean, the biochronological minor (<25 m of relative fall). Most Triassic discussed in the GSA data repository [see
scheme that is adopted here (after Ogg et sea-level falls were apparently of medium footnote 1]). The Triassic paleoenviron-
al., 2016) is also Tethys-centric. to minor magnitudes. The six falls that mental scenarios demonstrate the close link
The long-term eustatic trend shows that exceeded the 75 m amplitude, and are between eustasy, climates, and biodiversity.
at the dawn of Triassic sea levels were near therefore considered major, include TIn3 The driving mechanism for the third-
or a few meters higher than the present-day at 250 Ma; TAn4 at 242.1 Ma; TLa3 at 238 order cyclicity in the Triassic remains
mean sea level (pdmsl) and then rose only Ma; TCa2 at 233.5 Ma; TCa3 at 229 Ma; unidentified, an interval characterized by
~10–20 m in the Induan and Olenekian. and TNo4 at 209.7 Ma. exceptionally long sedimentary eustatic

Figure 1. Triassic sequences and variations of sea level. Time scale after Ogg et al. (2016). Biozone cross-correlations are after Hardenbol et al. (1998).
Sequence boundaries (sea-level fall events) are redesignated following a numbering scheme suggested by Hardenbol et al. (1998), however, the letter
T is prefixed to each designation for convenience to make the numbers unique and not to confuse them with similar numbers in other periods.
(Two events, in the Norian and Rhaetian [TNo2 and TRh1] are included provisionally, pending documentation of more widespread occurrence.)

6 GSA Today | December 2018