FACIES ANALYSIS AND SEDIMENTATION MECHANISM OF VOLCANICLASTICS OF CIKARANG MEMBER OF JAMPANG FORMATION IN WEST JAVA

The Cikarang Member of Jampang Formation is one of basin fills of the Bogor Basin that is characterized by gravity flow deposits. The variations of lithologies with an abundance of volcaniclastics are found in the Tonjong River in Bojongkalong Village and indicate differences in facies and sedimentation mechanisms. We measured stratigraphy of the rock units supported by petrographic analysis and paleontological analysis. The rock units consist of 11 lithofacies: graded gravel (g1G), massive gravel (m1G), massive gravelly sand (mGyS), plane-stratified laminated sand-mud couplets (slSM), massive gravel-sand couplets (mGS), plane-stratified laminated to graded mud-sand couplets (slgMS), massive sand (mS), plane-stratified gravel-sand couplets (sGS), plane-stratified laminated muddy interval sand-mud couplets (sleSM), plane-stratified laminated muddy interval mud-sand couplets (sleMS), and slump and slide deposits gravel (sdG). The depositional environment of the Cikarang Member is inner-middle fan with changes in depositional sub-environment variations in the form of channels, sandy lobes, silty-sandy distal lobes, and proximal levees with constant paleobathymetry in the lower-middle bathymetry. The volcaniclastics of the Cikarang Member of Jampang Formation is deposited in a turbid mechanism due to a turbulent current with various cohesive debris flows (mudflows) and turbidity currents scattered in each facies association.