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Depositional settings and changing composition of the Jambi palaeoflora within the Permian Mengkarang Formation (Sumatra, Indonesia)

The Merangin River section in Sumatra exposes the Permian Mengkarang Formation. This is composed of eight intervals showing upwards fining and thinning of volcanic tuffs and volcaniclastic sedimentary rocks, overlain by their reworked alluvial products. Isotopic age evaluation of the top and the base of the Merangin section indicates an average duration of 630,000 years (from 296.77 ± 0.04 to 296.14 ± 0.09 Ma). Extrapolation of the eight intervals onto neighbouring tributaries by using earlier geological studies and the strike of the beds allows for the integration of the data assembled in recent expeditions, and those from 1925, leading to the lithostratigraphic assignment of more than 2,000 palaeobotanical specimens. The compilation of all assembled palaeobotanical data indicates there is a change in composition from a palaeoflora dominated by Cordaites, ferns, or club mosses to one in which seed ferns were dominant. These changes, coupled to eustatic sea‐level fluctuations, indicate a climatic origin for this transition and extend palaeofloral trends perceived earlier in Far Western low latitudes to the Far Eastern Palaeotethys.