[B-CG06] Decoding the history of Earth: From Hadean to the present

[BCG06-16] Early Cretaceous Tricolpate pollen from the deep-sea chert of Shimanto Belt, Shikoku, Japan

*Yuki Nakagawa¹, Julien Legrand², Masayuki Ikeda¹ (1.The University of Tokyo, 2.Department of Geosciences, Faculty of Science, Shizuoka University)

Keywords:Cretaceous, Eudicots, OAE, Bedded chert

The early evolution of angiosperms is a hotly debated topic in plant evolution as an “abominable mystery” since the age of Charles Darwin. Recently, the possibility that the rapid diversification of angiosperms may have prompted an explosive diversification of pollinators, herbivores, and predators (the Cretaceous Terrestrial Revolution; KTR), has been raised. In particular, the eudicots, which account for about three-quarters of all living angiosperms, are thought to have dispersed around the Barremian-Aptian (ca. 125-115 Ma), more than 10 Ma later than the onset of dispersal of monocotyledons and magnoliids. However, age constraints are mostly based on biostratigraphy, such as pollen assemblages, and although calibration by radiometric ages in North China, their phylogenetic position remains controversial.
In this study, we report palynomorph assemblage from the Barremian-Aptian deep-sea bedded chert of the Goshikinohama section of the Shimanto Belt, deposited in the pelagic Pacific Ocean. We could obtain an assemblage of about 80 palynomorphs dominated by spores, with few gymnosperm pollen and one tricolpate angiosperm pollen fossil, Tricolpites sp., derived from eudicots. The first occurrence of Tricolpites sp. is within a δ¹³C negative excursion interval at the beginning of the OAE 1a based on radiolarian-δ¹³C stratigraphy. During the OAE 1a, the abundant occurrence of terrestrial plant fragments in the same section implies an enhanced hydrological cycle (Nakagawa et al., 2022), possibly related to the angiosperm early diversification and KTR.

Reference
Nakagawa et al., 2022, Global and Planetary Change, 215, 103886.