SYNTHESIS OF THE PALYNOLOGICAL CONTENT OF THE LOWER CRETACEOUS CONTINENTAL DEPOSITS IN FRANCE: STRATIGRAPHIC IMPLICATIONS

Abstract

International audienceA first attempt at a biostratigraphic and palaeoenvironmental synthesisof the palynological content of French Lower Cretaceouscontinental deposits is the subject of this paper. Palynomorphslisted in previous studies on Berriasian–Albian non-marine palynologyhave been taken into account, gathering 360 speciesof pollen grains and spores altogether. In addition, 70 sampleshave been recovered from outcrops of argillaceous rocks, mostlycorresponding to the Purbeck and Wealden facies of southernEngland. The samples concerned are from the departments ofCharente-Maritime, Charente, Savoie (Berriasian, Valanginian,Albian), Oise, Seine-Maritime, Pas-de-Calais (Hauterivian–Barremian),and Isère (Aptian). Early Cretaceous miospores are commonlylong-ranging; hence, it is necessary to consider fluctuationsin their abundance within palynological assemblages if they areto have any biostratigraphic value. Lower Berriasian assemblagesare often dominated by gymnosperm pollen grains, associatedwith anemiaceous spores such as Cicatricosisporites australiensisand C. hughesii. These taxa are also found in younger strata, butupper Berriasian–Valanginian assemblages are characterized bycontaining more abundant lygodiaceous verrucate spores associatedwith the appearance of gleicheniaceous Clavifera triplex fromthe Valanginian onwards. Many genera have been erected to accommodateMesozoic verrucate spores. The considerable overlapbetween diagnoses diminishes the stratigraphic significance ofthe constituent species. Only the genera Concavissimisporites andTrilobosporites are considered useful here. Hauterivian–Barremianassemblages are similar to those of the Valanginian, but differ inthe reduction in numbers of verrucate spores and a commensurateincrease in abundance of Cicatricosisporites and Appendicisporitesassociated with the first occurrences of monoaperturate angiospermpollen grains, such as Clavatipollenites hughesii, withinBarremian deposits of northern France. Considered to be moretypical of Albian assemblages, Clavatipollenites rotundus has beenrecovered from lower Aptian deposits in south-eastern France. Aptianpalynofloras are also characterized by the appearance of othermonoaperturate pollen forms, such as Retimonocolpites. Very littleinformation is available on French Albian assemblages. They aredefined by the diversification of dicotyledonous tri– and polyaperturatepollen grains associated with the virtual disappearance oflygodiaceous verrucate spores