Vegetation dynamics, angiosperm radiation and climatic changes in the Lusitanian Basin (Portugal) during Albian times

The mid-Cretaceous is characterised by significant evolutionary changes in terrestrial ecosystems. During this period, the typical vegetation consisting of ferns, conifers and other gymnosperms was replaced by an angiosperm-dominated flora. Long ranging and continuous records from the continental realm are mostly lacking due to the prevalence of sedimentary gaps. Here a comprehensive palynological and clay mineralogical dataset covering early Albian to early Cenomanian strata from the shallow marine São Julião section (Lusitanian Basin, Portugal) is analysed to reconstruct the vegetation composition as well as climate and weathering conditions in the continental realm. The palynological assemblage is dominated by non-saccate Classopollis and Inaperturopollenites gymnosperm pollen with low abundances of spores and angiosperm pollen. The clay mineralogical data is mainly composed of kaolinite and mica and shows two conspicuous intervals of high kaolinite abundances in the late Albian. Based on the ecological preferences of the associated parent plants of the spore-pollen assemblage, a gradual relative temperature increase is inferred in the hinterland of the Lusitanian Basin during the early Albian to early Cenomanian interval. The clay mineralogy and palynological record show that the climate in the continental hinterland of the Lusitanian Basin was semi-arid to sub-humid and punctuated by two distinct humid phases during the late Albian. Multivariate statistical analyses and a comparison with the nearby Guincho section demonstrate the significance and reproducibility of the spore-pollen record. Furthermore, the palynological assemblage implies that angiosperms and ferns occupied similar palaeo-ecological habitats, namely as understorey in Cheirolepidaceae, Araucariaceae and Cupressaceae conifer-dominated forests.