Palynostratigraphy, plant palaeoecology and palaeoenvironments of the Albian–Cenomanian (mid-Cretaceous) amber-bearing successions from Asturias, Northern Spain

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This paper presents two localities in the Asturias region (northern Spain) where the Albian–Cenomanian (mid-Cretaceous) succession comprising four lithostratigraphic units deposited in coastal sedimentary environments is exposed. These successions are characterised by siliciclastic and carbonate rocks containing diverse fossils, lignite fragments, and amber. The studied materials yield well-preserved palynological assemblages from the Albian–Cenomanian transition, an understudied interval in the Iberian Peninsula. The palynofloras are dominated by conifer pollen from Cheirolepidiaceae, Cupressaceae and, to a lesser extent, Araucariaceae, Pinaceae, and Podocarpaceae. While not as numerous, spores of ferns and allied plants and angiosperm pollen are very diverse, accounting for 148 and 99 identified taxa, respectively. Multivariate analyses of the full set of 19 assemblages highlighted four palaeoecological associations representing distinct environments: drylands, Araucariacean woodlands, wetlands, and hinterlands (uplands). Stratigraphic trends show a transition from Cupressaceae-dominated assemblages in the lower part of the succession to Cheirolepidiaceae-dominated ones upwards, interrupted by a phase characterised by increased abundances of fern spores, taxodioid pollen, and bisaccates in the Ullaga Formation. This interval is interpreted as reflecting relatively more humid conditions, possibly linked to the terrestrial expression of Oceanic Anoxic Event 1d. Comparison with coeval palynological successions from other amber-bearing sites in western Europe indicates closer affinities with Iberian palynofloras than with those from eastern France.