SYNTHESIS OF THE PALYNOLOGICAL CONTENT OF THE LOWER CRETACEOUS CONTINENTAL DEPOSITS IN FRANCE: STRATIGRAPHIC IMPLICATIONS
Abstract
A first attempt at a biostratigraphic and palaeoenvironmental synthesis
of the palynological content of French Lower Cretaceous
continental deposits is the subject of this paper. Palynomorphs
listed in previous studies on Berriasian–Albian non-marine palynology
have been taken into account, gathering 360 species
of pollen grains and spores altogether. In addition, 70 samples
have been recovered from outcrops of argillaceous rocks, mostly
corresponding to the Purbeck and Wealden facies of southern
England. The samples concerned are from the departments of
Charente-Maritime, Charente, Savoie (Berriasian, Valanginian,
Albian), Oise, Seine-Maritime, Pas-de-Calais (Hauterivian–Barremian),
and Isère (Aptian). Early Cretaceous miospores are commonly
long-ranging; hence, it is necessary to consider fluctuations
in their abundance within palynological assemblages if they are
to have any biostratigraphic value. Lower Berriasian assemblages
are often dominated by gymnosperm pollen grains, associated
with anemiaceous spores such as Cicatricosisporites australiensis
and C. hughesii. These taxa are also found in younger strata, but
upper Berriasian–Valanginian assemblages are characterized by
containing more abundant lygodiaceous verrucate spores associated
with the appearance of gleicheniaceous Clavifera triplex from
the Valanginian onwards. Many genera have been erected to accommodate
Mesozoic verrucate spores. The considerable overlap
between diagnoses diminishes the stratigraphic significance of
the constituent species. Only the genera Concavissimisporites and
Trilobosporites are considered useful here. Hauterivian–Barremian
assemblages are similar to those of the Valanginian, but differ in
the reduction in numbers of verrucate spores and a commensurate
increase in abundance of Cicatricosisporites and Appendicisporites
associated with the first occurrences of monoaperturate angiosperm
pollen grains, such as Clavatipollenites hughesii, within
Barremian deposits of northern France. Considered to be more
typical of Albian assemblages, Clavatipollenites rotundus has been
recovered from lower Aptian deposits in south-eastern France. Aptian
palynofloras are also characterized by the appearance of other
monoaperturate pollen forms, such as Retimonocolpites. Very little
information is available on French Albian assemblages. They are
defined by the diversification of dicotyledonous tri– and polyaperturate
pollen grains associated with the virtual disappearance of
lygodiaceous verrucate spores.