Pustaka Ilmiah Universitas Padjadjaran

Abstrak

Sandstone composition of the turbidite series of the middle to late Miocene of Majalengka sub-basin, West Java, Indonesia.

The sandstone of turbidite series of Majalengka sub-basin varies in geochemical composition. This series, based on biostratigraphy evidence, can be divided into two portions; lower and upper parts. This study was conducted to determine the relationships between sandstone composition and tectonic setting. The SiO2 and Na2O contents are enriched in compare to another major element (e.g TiO2, Al2O3, FeO, MnO, MgO, CaO, K2O and P2O5). Low content of Na2O value is related with relatively small amount of Na-rich plagioclase, whereas the SiO2 value shows correlation with the increasing of immaturity of grains. The SiO2 content in this study related with the quantity of quartz in the rock samples. Results of analysis indicates that most of samples are belongs to quartz-poor greywacke that quartz contents between 11-17% and K2O/Na2O ratio below 1. The AFM diagram indicates the sandstone from lower part series were distributed in calc-alkaline to tholeiitic type, whereas in the upper part series were concentrated in calc-alkaline basalt to tholeiitic type. The CaO-Na2O-K2O ternary diagram confirms that both the lower and upper part series lie upon andesite to dacite fields. Based on TiO2-Ni diagram the provenance is originated from magmatic arc and sedimentary sources. Those rocks are belongs to greywacke to lithic arenite type. The lower part sandstone populations fall upon ARC/ ACM, while the upper part is fit in to ARC and ACM. These indicated that sedimentation process in Majalengka sub-basin during Middle to Late Miocene is affected by active tectonic which is related with subduction in the southern of West Java.