Palynology of the central Myanmar basin corroborates Eocene-Oligocene monsoonal conditions in south-east Asia

Huasheng Huang , Alexis Licht (1) , Robert Morley , Guillaume Dupont-Nivet (2) , Zaw Win , Jan Westerweel (2)

1 University of Washington [Seattle]
2 GR - Géosciences Rennes

The Cenozoic vegetation history of Central Myanmar is only sparsely documented and yet of great interest in the context of regional paleogeographic and climatic changes. The Kalewa section, situated in the Central Myanmar Basin and recently dated by our group (Myanmar Paleoclimate and Geodynamics research group), presents an excellent opportunity to study the vegetation development from the Cretaceous to the Miocene. Here, we focus on the late middle Eocene to Oligocene time interval and document the palynoflora using 138 samples that were collected from the Pondaung, Yaw, and Letkat formations. The sediments exposed along a 1436.1 m section were formed in a predominantly fluvio-deltaic environment. Our study shows that the late middle Eocene to Oligocene Kalewa palynoflora includes at least 126 sporomorphs, belonging to 53 families and 91 genera. The dominant sporomorphs of this palynoflora are Dicolpopollis (e.g. Dicolpopollis kalewensis, derived from the rattan group Calamoideae within Arecaceae), Sapotaceoidaepollenites (from trees within Sapotaceae, such as Palaquium), and fern spores. Other typical palynofloral elements are also derived from mountain ranges (Podocarpidites, Taxodiaceaepollenites, and ?Piceaepollenites), and taxa from fluvial and deltaic floodplains such as Liliacidites (from Liliaceae), Myriophyllum type (Haloragaceae), Corsinipollenites oculus (from Jussieua within Onagraceae), cf. Florschuetzia (possibly sonneratioid), Zonocostites ramonae (from Rhizophoraceae), dinoflagellate cysts, and foraminiferal chitinous linings. In addition, the megathermal elements constitute the most significant fraction of all sporomorphs, such as Discoidites (from Brownlowia within Malvaceae), Margocolporites (from Caesalpinia within Leguminosae), Striatricolporites catatumbus (from Crudia within Leguminosae), Lanagiopollis (e.g. Lanagiopollis emarginatus, from Alangium sect. Conostigma, which has significant biogeographic significance), Palmaepollenites kutchensis (from Iguanurinae within Arecaceae), Meyeripollis naharkotensis (possibly from Myrtaceae, indicating the age from late Eocene to basal Miocene), while the temperate elements are very rare. Generally, the late middle Eocene to Oligocene Kalewa palynoflora is a seasonally dry flora characterised by moist deciduous and semi-evergreen forest that is consistent with monsoonal conditions in south-east Asia.

Domaines: Paléontologie; Climatologie

Huasheng Huang, Alexis Licht, Robert Morley, Guillaume Dupont-Nivet, Zaw Win, et al.. Palynology of the central Myanmar basin corroborates Eocene-Oligocene monsoonal conditions in south-east Asia. 10 th EUROPEAN PALAEOBOTANY & PALYNOLOGY CONFERENCE, Aug 2018, Dublin, Ireland. pp.206. ⟨insu-01878565⟩