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STUDI MIKROFASIES DAN IMPLIKASINYA TERHADAP LINGKUNGAN PENGENDAPAN BATUGAMPING PASIRAN FORMASI WONOCOLO DAERAH BAMBAN DAN SEKITARNYA, KABUPATEN REMBANG, JAWA TENGAH
The abundance of foraminifera in the study area is great potential in sedimentology, so it is interesting to do research. Research on microfacies and depositional environments is fascinating in this area because of the rich biodiversity. Determining facies zones and depositional environments can enrich the sedimentological knowledge of the research area. The research area is in Rembang Regency, Central Java, specifically in the Bamban area, Pamotan District. The research aims to identify the microfacies and depositional environment in the research area. The methods used were field observation, which resulted in a megascopic description of the outcrops, petrographic analysis, which resulted in a microscopic description of each rock thin section sample; and palaeontological analysis using large forams, which resulted in the identification of microfossils and their abundance in each rock thin-section sample. The results of the analyses are then further analysed to provide microfacie standards and facies zones in each sample, and analyses of the depositional environment are then interpreted to determine their implications. The studio analysis was carried out to produce thematic maps in the form of track maps, montage maps, facies zone maps and depositional environment maps, which represent the results of the field observations and analyses carried out and model the morphological appearance of the study area. This study was carried out on nine thin-section samples of sandy limestone of the Wonocolo Formation and obtained the standard microfacies types of the study area, including SMF- 10 (bioclastic packstone or wackestone with worn skeletal grains) and SMF-18 (grainstone or packstone with abundant foraminifera or algae). The facies zones obtained include Open Circulation Shelf Lagoon (FZ-7) and Restricted Circulation Shelf and Tidal Flats (FZ-8). Analysis of the depositional environment revealed depositional zones of Shelf Sands (SF 6) and Open Platform (SF 7). The implication of microfacies and the depositional environment of the Wonocolo Formation sandstone in the study area shows similarities but misalignment. This is due to the different parameters used to determine each facies. Previous studies have obtained similar results to this latest study due to the similarity of the significant foram fossil content that developed during the depositional process of the Northeast Java Basin. The abundant and similar group of Rotaliida fossils in each formation is one of the essential factors in the implication between microfacies and the depositional environment in the Northeast Java Basin. This research is expected to add insight and interpretation on the implication of microfacies and depositional environment of Wonocolo Formation passive limestone in the study area influenced by similar and abundant significant foram fossil associations.
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