Angiosperm radiation, diversification, and vegetation shifts through the Albian–Cenomanian of the northern Iberian Peninsula: Palynological evidence from the Las Loras UNESCO Global Geopark

Abstract

During the mid-Cretaceous (Aptian–Turonian), angiosperms diversified and expanded their range significantly, but were potentially affected by several environmental crises. The Iberian Peninsula is particularly relevant to studies of paleobotanical events through this interval owing to its intermediate position between Gondwanan and Laurasian floral provinces and its wealth of assemblages containing early angiosperms. The Las Loras UNESCO Global Geopark is a unique area for paleobotanical studies of the mid-Cretaceous in the Basque-Cantabrian Basin, which currently has a depauperate record of floral evolution through this interval. Our palynostratigraphical results have clarified the chronostratigraphic positions and improved correlation of various formations in the Las Loras region. These results assign the Escucha Formation to the lower–upper Albian, the Santa María de las Hoyas Formation to the middle Cenomanian with diachronous (upper Cenomanian) deposits towards the west, and the Abejar Formation to the lowermost upper Cenomanian. Our new paleoecological results and a review of previous palynological data reveal notable changes in plant communities in the Iberian Peninsula through the Albian–Cenomanian. A conifer-dominated flora prevailed through the early–middle Albian but a shift to more diverse communities with increased presence of angiosperms typified the late Albian–early Cenomanian. The middle Cenomanian was characterized by conifer dominance but with expanded angiosperm diversity marked by the first occurrence of the Normapolles group. Finally, the late Cenomanian featured sporadic dominance by angiosperms, particularly the Normapolles group, in deposits associated with the Oceanic Anoxic Event 2.