|
Jurassic-Cretaceous boundary sections in
England, the Netherlands, Germany and France have
provided evidence of a climatic shift from
semi-arid conditions in the latest Jurassic (early
Tithonian) to a more humid climate in the earliest
Cretaceous (middle Berriasian) (e.g. 1-3).
Generally, this climatic shift is marked by a
decrease in abundance of cheirolepidacean pollen,
along with an increase in typical Early Cretaceous
spores. Recent integrated terrestrial and marine
palynostratigraphic studies (2, 4) have provided a
biostratigraphic framework for Jurassic-Cretaceous
strata that improves correlations between
different areas in NW Europe, and thus also has a
bearing on the timing of this climatic
shift.
Sedimentology, clay mineralogy, as well
as terrestrial and marine palynological data
presented here provides complementary information
on how marginal deposits from the northeastern
coast of the epicontinental sea that connected the
Boreal and Tethys oceans reflect the above
addressed environmental changes at the
Jurassic-Cretaceous boundary. A latest Jurassic to
earliest Cretaceous (latest Tithonian to early
Valanginian) cored succession in southern Sweden
indicates that the predominantly terrestrial but
coast-near depositional setting during the
Tithonian to earliest Berriasian experienced a
marine flooding in the early Berriasian. During
the remaining Berriasian and the early Valaginian,
conditions shifted between near marine and marine
settings in a dynamic coastal environment, very
similar to those reported from the Danish island
of Bornholm (5-7).
Palynological data suggest
that climatic conditions changed from more
seasonally dry to more consistently humid over the
Tithonian-earliest Berriasian period, although a
conspicuous decrease of cheirolepidacean pollen as
previously reported from England, Germany and
France, is not evident in the cored succession. A
shift in clay mineralogy from a dominance of 10 Å
minerals to increasing amounts of mixed layer and
kaolinite, further indicates a change to more
humid conditions over the same time interval. 1)
P. Allen, Proc. Geol. Ass. 109, 1998; 2) O. Abbink
et al., Global and Planetary Change 30, 2001b; 3)
J. Schnyder et al. Palaeo3 229, 2005; 4) C.O.
Hunt, Geol. Soc. Spec. Publ. 2230, 2004; 5) S.
Piasecki , Bull. Geol. Soc. Denmark 32, 1984; 6)
S. Piasecki, Grana 25, 1986; 7) J. Lindgren et
al., Geobios in press, 2008.
|
