Depositional Pattern and Diagenesis of Neogene Resedimented Carbonates of Sunda Shelf in Banyumeneng Area, Western Kendeng Basin, Indonesia
Authors: Ridha Muhammad , Nurdiansyah Mukhammad , Zamili Jonathan Sofiawan , Triwigati Purnaning Tuwuh , Muslih Yan Bachtiar , Farida Widiastuti Nur 
Published: April 2019

This study area is located on Dolok River, Banyumeneng, Western Kendeng Basin, which has a direct relation to the Sunda Shelf as the largest sediment supply for Kendeng Basin. The study aims to determine the changes of depositional succession on Late Neogene in the Western Part of Kendeng Basin and identify the diagenesis process and the implication to the physical properties of Calciclastic Submarine Fan (CSF) Deposits.

The methods used in this study are field observation which was used to gather the stratigraphic record of deposits and rock samples analysis through petrography, microfossil, diagenesis, porosity and permeability. Measured stratigraphic section was used to determine the depositional pattern, facies and processes. Petrography analysis was used to determine the composition and diagenetic features. Moreover, the microfossil analysis was used to determine the relative age and the bathymetry of deposits, while the porosity was calculated using the mass-weighted method and permeability was calculated using the permeameter gas method to determine the quality of deposits as the hydrocarbon reservoir.

Generally, the section shows the progradation sequence characterized by the Lobe Fringe deposits which gradationally change to the Outer Shelf deposits. The lower part was characterized by thick Hemipelagic Mudstone and Thin-bedded Calciturbidite Facies, showing the part of Lobe Fringe Deposits. The second part was divided into MTD type 1 and 2, MTD type 1 consist of Conglomeratic Calciturbidite, Clast-Supported Debrites, and Graded Calciturbidite, then the MTD type 2 is slumped levee deposits, showing the high-density turbidity current channel complexes on the Gullied Upper Slope. The third part was characterized by conglomeratic calciturbidite, graded calciturbidite, clast supported debrites, and hemipelagic mudstone, included into Braided Axis Channel facies. The fourth part was characterized by the interbedded of Thin-Bedded Calciturbidite, Laminated Calciturbidite and Hemipelagic Mudstone Facies, showing the Levee facies. The upper part was characterized by thick Cross-Bedded Calciclastic deposit, showing the Outer Shelf depositional environment. Furthermore, the Flute Cast shows the NW-SE paleocurrent direction which indicates that the Sunda Shelf Paleo-Environment was considered as the major sediment supply for this area. Moreover, the Foraminifera analysis shows the Lower Bathyal - Middle Neritic bathymetry on Middle - Late Miocene (N9 N18). The porosity and permeability quality ranged from 2.13 - 6.38% and 7.54 - 86.38 mD. Combined with petrography analysis, it can be analyzed that the diagenesis processes of Banyumeneng CSF deposits are micritization or grain-coating clays, compaction, cementation, neomorphism, and dissolution. The poorly-sorted materials and highly-cementation process may restrict the pore-throat and reduce the permeability as well. As the outcrop exposed, the meteoric water acts to dissolve the cement, leaving the small porosity inside. Therefore, the pores tend to be the secondary pores which are formed by the post depositional dissolution.