Stratigraphy of Jaten Formation based on palynology and sedimentology analysis in Dongko Area, Trenggalek, East Java

Jaten Formation is located in the Southern Mountains of the eastern part of Java island. East Java is known as one of the largest provinces in Indonesia for oil and gas production. However, the exploited areas have primarily been in the northern part of East Java. The Southern Mountains region shows several indications of potential oil systems, such as shale outcrops in the Jaten Formation. This research aims to understand the stratigraphic characteristics of the Jaten formation using a palynological and sedimentological analysis approach. The palynological analysis result determined that the age of the Jaten Formation in the study area is estimated to be the upper part of Early Miocene to Middle Miocene, deposited in a back mangrove to mangrove environment. This determination is based on the first appearance datum of the Stenochlaena areolaris in the bottom sample (1) and the first appearance datum of the Florschuetzia meridionalis in sample 4. An increased proportion of taxa Acrostichum aureum , Calophyllum type and Spinizonocolpites echinatus characterizes the back mangrove environment. The mangrove environment is characterized by an increased proportion of taxa such as Florscuetzhia trilobata, Florscuetzhia meridionalis, Florscuetzhia levipoli Rhizophora sp, Exoecaria agallocha and Avicennia type . The increased proportion of Rhizophora sp pollen primarily influences the high proportion of mangrove taxa. Mangroves with Rhizophora sp as their main component are usually found around river estuaries and in areas with periodic influence from the sea, such as lagoons or bays. Based on the sedimentology and palynological analysis, the formation was deposited in mangrove-backmangrove environment.