PALEOCURRENT STUDY OF NYALINDUNG FORMATION THROUGH MOLLUSCS PALEONTOLOGICAL ASPECTS IN CI GALASAR TRAVERSE SECTION, SUKABUMI, WEST JAVA
Nyalindung Formation contains mollusc fossils in the Classes of Gastropoda and Bivalvia which can be used as environmental proxy for paleocurrent study, although this study has not been carried out in this rock unit. Located in Ci Galasar River, Nyalindung District, Sukabumi Regency, the research traverse section showed beds of mollusc fossils with several stratigraphic unit and locality fossils of Middle Miocene. Paleocurrent analysis was conducted in four location distributed in three different stratigraphic unit.
Based on molluscs shells’ orientation, Nyalindung Formation in research area was deposited in different current direction. Measured in four locations, the current showed changes in the ancient currents from bimodal, complex, unimodal within direction N 291 ° -300 ° E, and unimodal in N 281 ° -290 ° E direction. These changes are combined with fossils association and later interpreted as changes in depositional environment setting. The bimodal current alongside the presence of Turritella terebra talahabensis and Cypraea sp. indicates litoral environment. Meanwhile, complex shells’ orientation with the presence of Gemmula (Gemmula) granosa woodwardii, Dientomochilus javanus, and Terebra talahabensis indicates litoral to neritic environment that is strongly affected by waves. The unimodal current in N 291 ° -300 ° E showing similar fossil association with complex current indicates similar environment setting, which is litoral to neritic, but with lower influenced of waves and more on faster unidirectional current. Lastly, N 281 ° -290 ° E current direction showed large bivalves fossil association such as Chione tjikoraiensis and Cavatodens jonkeri which indicates inner neritic environment influenced by unidirectional current. Based on tectonic setting in Middle Miocene, the unidirectional current affecting the deposition of Nyalindung Formation is suspected as long shore current.