Depositional Environment Based on Palynological and Foraminiferous Analysis of The Klasaman Formation in The Salawati Basin Klayili Area Klayili District Sorong Regency West Papua Province

Abstract

The Salawati Basin, West Papua is a mature basin producing oil. One of these basins was filled by sediments from the Klasaman Formation consisting of shale, claystone, sandstone, especially in the northern part there are conglomerates, rarely coral reef limestone deposited in a deltaic to fluvial environment. An a analysis of the depositional environment in the Klasaman Formation provides knowledge on the facies development and depositional environment in the study area. The study was carried out by using the surface geological data such as measured stratigraphy section (MS) with approaches of palynology, foraminiferous and petrography analysis. The development of palynology studies in Indonesia, especially in Eastern Indonesia is still very minimal and can be improved along with the increasing number of oil and gas exploration moving to transitional environments. The results of the analysis show that the Klasaman Formation is Late Miocene-Pliocene (N18) with stratigraphy sorted from the oldest to the youngest units, namely carbonate sandstone units and conglomerate units. The geological structure that developed in the study area was controlled by a structure Klayili Normal Fault which causes a subsidence in the Northwest–North part of the study area and folding in the Southeast, namely Klayili Syncline. Overall facies development as a delta plain environment that show shallowing upward vertical succession with relatively dominant progradation process. Carbonate sandstone as the older unit was deposited in a lower delta plain environment as a tide dominated delta with mangrove vegetation to a peat swamp with freshwater vegetation. There are three facies associated with this unit which are distributed channel, marsh, and interdistributary bay. Conglomerate as the younger unit was deposited in the upper delta plain environment which is influenced by tide-fluvial dominated delta. Several facies associated with this unit are distributary channel, interdistributary bay, swamp, and crevasse splay.