Deciphering the very early phase of angiosperm evolution using palynology

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The timing of the first appearance of angiosperms (flowering plants) is a matter of considerable debate in palaeobotany. The fossil record clearly indicates significant diversification of crown-group angiosperms in the Early Cretaceous, with the first 10 ‒ 15 Myr being represented by fossil pollen only. However, this pre-Aptian record of angiosperm pollen is very fragmentary (based on spot samples) and often based on findings from strata lacking precise stratigraphic assignment. Given the fact that the Early Cretaceous change from gymnosperm- to angiosperm-dominated ecosystems represents one of the most dramatic turnovers in the terrestrial biotic history of the younger Phanerozoic, this scarcity of well-dated fossil evidence is startling. To fill this gap, we propose to study stratigraphic sections located in the Lusitanian Basin of Portugal, an area well known for its exceptional angiosperm mesofossils and rich pollen floras. The chosen sections cover Valanginian – Barremian strata in marine near-shore facies. Precise stratigraphic control can be achieved by the combination of existing bio- and sequence-stratigraphic information with new strontium- and carbon-isotope chemostratigraphy. Pollen assemblages will be studied with different imaging techniques including transmitted light as well as scanning electron microscopy (incl. single grain analysis). This approach will enable comparison with existing records, in particular from the Weald basin and from adjacent Portuguese mesofossil localities. Information on the broader plant community context will be obtained by studying the accompanying palynoflora. The combined chemostratigraphic and palynological approach of this proposal aims at providing new insights into the very early evolution and diversification of angiosperms and into terrestrial environmental dynamics during the Early Cretaceous.