Albian angiosperm pollen from shallow marine strata in the Lusitanian Basin, Portugal

Abstract

The evolution of angiosperms significantly changed the composition of the terrestrial vegetation during the mid-Cretaceous. In contrast to the wealth of information available on the biology and systematic relationships of early angiosperms, the temporal patterns of their evolution and radiation are poorly constrained. Here we present a continuous angiosperm pollen record from well-dated shallow marine deposits in the Lusitanian Basin, Portugal. The São Julião section provides a solid stratigraphic framework to track angiosperm pollen distribution patterns from the early Albian to early Cenomanian at mid-latitudes. In comparison to previous angiosperm pollen records from the Lusitanian basin, the section shows an extended late Albian succession and provides new insights into the diversification of early angiosperms during this important interval. Productive palynological samples were analysed and 79 different angiosperm pollen types have been recorded. Throughout the Albian angiosperm pollen represent only a minor component of the total palynoflora. The early Albian pollen record is characterized by highly diverse assemblages of monoaperturate pollen of monocot or "magnoliid" affinity and by the first appearance of polyporate and tricolpate pollen of eudicot affinity. A distinct diversification phase among tri-and poly-aperturate pollen (e.g., Cretacaeiporites, Retitrescolpites, Rousea, Striatopollis and Tricolpites) and the presence of conspicuous pollen grains assigned to Dichastopollenites characterize the middle and late Albian palynological assemblages. Thus, the section records a striking sequence of appearances of important angiosperm pollen morphologies. Monocolpates, polyporates and tricolpates appear in the early Albian whereas tricolporates appear from the early part of the late Albian onwards. Furthermore, well-constrained biostratigraphic ranges of selected angiosperm pollen from mid-latitudes are presented. In view of these new data, the temporal framework of the palynological Subzones II-B and II-C in the Potomac Group succession from the Atlantic Coastal Plain, eastern USA is revised to a middle to late Albian age.

Early Cretaceous (Albian) spores and pollen from the Glen Rose Formation of Texas and their significance for correlation of the Potomac Group

“…The absence of such types supports the hypothesis that the Glen Rose horizons studied are older than the base of Zone II. Horikx et al (2016) reported pollen close to two of these, T. sagax and S. vermimurus, from the late early Albian of Portugal, suggesting that they may not all appear at the same time.…”

“…Similar to Retimonocolpites sp. 7 of Heimhofer et al (2007), which was assigned to R. dividuus by Horikx et al (2016).…”

“…New evidence on this problem has come from work on Aptian-Albian coastal sections in Portugal (Heimhofer et al 2005(Heimhofer et al , 2007(Heimhofer et al , 2012Hochuli et al 2006;Horikx et al 2016), which consist of near-shore marine sediments that are well dated by dinoflagellates. The mesofossil floras of Friis et al (1994Friis et al ( , 2006Friis et al ( , 2010Friis et al ( , 2011, which together with floras from Potomac Zone II contain the most intensively studied flowers of early angiosperms, are from continental deposits farther inland.…”

“…This suggests that the Glen Rose type is a distinct species and may therefore have a different range than typical T. fragosus. Horikx et al (2016) identified T. aff. fragosus from the late early Albian of Portugal, but their pollen differs more from the Glen Rose, Potomac and type material in being larger and thinner walled.…”

“…Early studies of leaves and vertebrate remains allowed some crude correlations, but present dating of the Potomac sequence is based mainly on palynological correlations with faunally dated marine sequences elsewhere, for example in England (Kemp 1968(Kemp , 1970Laing 1975;Hughes et al 1979;Hughes & McDougall 1987, 1990Hughes 1994). Both regions belonged to the same Southern Laurasian province, which is an important consideration in view of significant geographic differences among floras and diachronous appearances of angiosperm taxa at this time (Brenner 1976(Brenner , 1996 coastal sections in Portugal (Heimhofer et al 2005(Heimhofer et al , 2007(Heimhofer et al , 2012Horikx et al 2016). Studies of the Portuguese sections have challenged previous correlations of both the Potomac sequence and mesofossil floras described from continental beds in Portugal (Friis et al , 2006(Friis et al , 2010(Friis et al , 2011, notably in the part of the Albian represented in the Glen Rose Formation (Hochuli et al 2006).…”