Burmese forest ecosystems during the Cenozoic: new insights based on fossil wood

International audienceRecent data demonstrate that the Burma Terrane (corresponding to present-day western Myanmar) underwent a northward motion alongside the Indian Plate during the Cenozoic, from a nearly south-equatorial latitude in the late Cretaceous to its present location. This scenario, different from previous geological models, has implications for understanding Burmese paleoclimatic and paleobotanical archives that have been used to document the South Asian monsoon regime and the floristic exchanges between the Indian subcontinent and Asia. We provide here a synthesis of paleobotanical data from Myanmar that are re-evaluated in the light of this paleogeographic scenario. Eocene dicotyledonous fossil wood specimens and pollen (dicotyledons and palm trees) reveal the presence of a dry seasonal climate at a time when the Burma Terrane was at latitude ca. 5°N, indicating well-marked seasonal migrations of the intertropical convergence zone. Early to middle Miocene fossil wood specimens indicate a seasonally wetter climate than during the Eocene. This change can be explained by an increase of monsoonal intensity and/or changes of the regional drainage system following the collision between the Burma Terrane and Asia. We also present the first occurrence of fossil wood and palm specimens from the Paleocene of Myanmar. We identify at least five dicotyledonous morphotypes in addition to two palm stems, anatomy of which is consistent with a possible equatorial climate with limited seasonality (?)