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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. [ABSTRACT FROM AUTHOR]

The Early Permian (Asselian) Mengkarang Formation of the western Jambi Province, Sumatra, is well exposed in the valley of the Merangin River. No consensus regarding the depositional environment of this section had been reached hitherto. This section preserves abundant evidence of a Permian forest, named the Merangin Fossil Forest herein, which grew at the foot of an active volcano, where pyroclastic flows often made way and destroyed the vegetation and where epiclastic reworked pyroclastics rapidly entombed the vegetation. The present assessment is based on a detailed study of three localities using multiple lines of evidence, including petrography, silica typing including hot cathodoluminescence microscopy and spectroscopy, and palynofacies analysis. In situ Agathoxylon was near enough to the volcanic slope to be buried rapidly, shallow enough to avoid extreme crystallization in the lumina, and far enough from the metamorphic centre not to get recrystallized. All these combined contingencies make this a most unique find that provides significant insights into a rarely studied palaeoecological setting from the Early Permian. [ABSTRACT FROM AUTHOR]