Permian and Triassic radiolarians from chert breccia in the Nong Prue area, western Thailand: its origin and depositional setting in the Paleotethys

Abstract

Bedded chert and siliceous shale successions previously regarded as the Silurian–Devonian rock units, distributed in the Nong Prue area, northwest of Kanchanaburi, western Thailand, yielded Lopingian (upper Permian) and Lower–Middle Triassic radiolarians. We found chert breccia layers in northern Nong Prue area, mainly consisting of angular to sub-angular chert clasts with matrices of silt-sized chert grains and clay minerals. We discriminated uppermost Pennsylvanian–Lopingian (upper Carboniferous–upper Permian) and Middle Triassic radiolarian-bearing chert clasts from four different levels of the chert breccia; 28 species of 15 genera with one radiolarian gen. et sp. indet. are identified. On the basis of sedimentary characteristics of the chert breccia, we suggest that the chert breccia is of sedimentary origin. The radiolarian assemblages reported here, together with previously known lithological and paleontological evidence, further indicate that the chert breccia was deposited in the Paleotethys with chert clasts derived from fine grained siliceous rocks in the continental margin to deep ocean basin of the Sibumasu Terrane.