CLIMATIC CONSTRAINS ON ANGIOSPERM POLLEN DISTRIBUTION PATTERNS DURING ALBIAN TIMES: EVIDENCE FROM THE LUSITANIAN BASIN, PORTUGAL

The mid-Cretaceous is characterized by significant evolutionary changes in terrestrial ecosystems. During this period, the typical vegetation of the so-called Mesophytic consisting of ferns, conifers and other gymnosperms is replaced by the Cenophytic flora dominated by angiosperms. The Albian (113-100.5 Ma) represents a key interval in early angiosperm evolution as documented by extensive compilations of macro- and microfossil angiosperm remains. Likewise, a wealth of new multi-proxy data has substantially increased the knowledge on long- and shorter-term variations in mid-Cretaceous climate. At the moment, the lack of high-resolution terrestrial plant fossil records covering mid-Cretaceous strata hampers our understanding to link changes in continental climate evolution and the subsequent impact on angiosperm and other vegetation types.

The angiosperm radiation during the Albian is paralleled by a gradual rise in global sea surface temperatures and atmospheric pCO_2. In order to link changes in humidity and temperature to angiosperm evolution, a stratigraphically well-constrained high-resolution angiosperm pollen record covering the Albian stage is presented The pollen record is derived from shallow-marine deposits in the Lusitanian Basin of Portugal. The pollen record shows a distinct increase in abundance (from 5% to 15%) and diversity (from ~15 to ~25 taxa per sample) among angiosperms from the Early to Late Albian followed by declining values in abundance (10%) and diversity (~17 taxa per sample) in the latest Albian to Early Cenomanian. This apparent decline in both abundance and diversity of angiosperm pollen contrasts with the established view of continuously increasing angiosperm dominance during the Albian to Cenomanian.