Leaf fossils of Sabalites (Arecaceae) from the Oligocene of northern Vietnam and their paleoclimatic implications

The Hoanh Bo Trough‐a landward keyhole to the syn‐rift Late Eocene–Early Oligocene terrestrial succession of the northern Song Hong Basin (onshore north‐east Vietnam)

“…The taxonomical composition of this assemblage resembles more those dated to Latest Eocene/Early Oligocene and described, for instance, in the Cao Bang, Rinh Chua, and Na Duong formations in Vietnam (Wysocka et al, 2018, 2020), and by Tang et al (2020) from China. Furthermore, such findings correspond closely to studies of strata from the Yen Me region by Trung et al (1999, 2000) and Song et al (2021). The observed differences may suggest this pollen assemblage is younger than the other three and existed under slightly cooler climatic conditions.…”

“…Similar climatic signals can be observed when considering fossil leaves found by Trung et al (1999), Song et al (2021), and Nhan and Danh (1975) in sediments belonging to studied formations. Taxa representing warm‐temperate climate: Quercus , Liquidambar , Fagus , Phoebe , and Magnolia occur together with thermophilus ones– Laurus and Sabalites .…”

“…The studied deposits from the Hoanh Bo and Dong Ho areas (Figures 1-2) outcrop in a more or less east-west oriented depression referred to as the Hoanh Bo Trough, which in turn is sometimes subdivided into the Dong Ho and Cua Luc troughs (Figure 1c) (e.g., Fyhn et al, 2018;Petersen, Tru, Nielsen, Duc, & Nytoft, 2005;Tru, Diep, Quan, Hung, & Hien, 2002). Moreover, in some papers, the names Hoanh Bo and Dong Ho basins have also been employed (e.g., Song et al, 2021;Tha et al, 2015Tha et al, , 2017Trung, Bat, An, Khoi, & Hieu, 1999;Viet, 2003).…”

“…According to the initial description by Nhan and Danh (1975) Magnolia janschinii, Laurus nobilis (Trung et al, 1999), and Sabalites colaniae (Song et al, 2021). The total thickness of the Dong Ho Formation reaches 140-418 m, and its age has been designated as Oligocene (Petersen et al, 2001(Petersen et al, , 2005Song et al, 2021;Thanh & Khuc, 2006;Trung et al, 1999).…”

“…According to the initial description by Nhan and Danh (1975), the Dong Ho Formation is composed of thick‐bedded grey conglomerates, sandstones, siltstones, oil‐bearing shales, thin coal seams, and thick‐bedded claystones. The siltstones, claystones, and oil‐bearing shales usually contain spores and pollen assemblage of Gleichenia sp., Quercus sp., and Liquidambar sp., and leaf imprints of Pecopteris totangensis , Magnolia janschinii , Laurus nobilis (Trung et al, 1999), and Sabalites colaniae (Song et al, 2021). The total thickness of the Dong Ho Formation reaches 140–418 m, and its age has been designated as Oligocene (Petersen et al, 2001, 2005; Song et al, 2021; Thanh & Khuc, 2006; Trung et al, 1999).…”