Field Geological Characteristic of Mesozoic Paremba Sandstone, Bantimala Complex, South Sulawesi

Abstract

We conducted preliminary survey to study field geological characteristic of Mesozoic Paremba Sandstone, Bantimala Complex, South Sulawesi in order to investigate the field occurrence and the petrographic characteristic of some samples from the sandstone unit. The samples were collected from measuring section campaign in three rivers, namely Mallapie, Ceppaga and Bontorio. The field investigation shows that The Paremba sandstone occurs as a tectonic slice within mélange complex which is sandwiched by schist and melanges. The sandstones range from fine to coarse-grained sandstone forming a layer of 0.5 up to 50 cm in thickness interlayered with siltstone and shale, forming a sequence set. The sequences are intercalated with other lithologies such as limestone, mudstone, conglomerate, breccia and chert, forming a distinctive unit. In certain place, the units are intruded by basalt dike. Generally, the sandstones are grey to blackish in colour, sometimes show brown to yellowish colour if weathered. Some sandstone is calcareous as shown by strong reaction with acid and the occurrence of carbonate mineral but other samples relatively show less carbonate minerals. In all three rivers, the sandstone units have been strongly tectonized as seen by irregular fold and fault from the strike and dip of the unit layer. Petrographic analyses show that the studied sandstones consist of arkosic sandstone, siltstone and calcareous sandstone which are composed of quartz, orthoclase, plagioclase and calcite in the groundmass with opaque minerals occur as main accessory. Some samples contain muscovite, especially calcareous sample. The sandstone unit shows a typical of coarsening- and thickening updward trend with flaser, lenticular and parallel lamination sedimentary structure. It is interpreted that the sandstone were deposited in shallow marine or shelf region.