Depositional environmental evolution of Kalibiuk formation based on paleontological molluscan Study, Cisaat River section, Bumiayu, Central Java, Indonesia

Abstract

This paper presents new finding from the sedimentary sequences, overlooked by previous researchers, which provide insights to the sea level changes during the deposition of the Middle to Late Pliocene Kalibiuk Formation. Data were acquired from fieldwork via detailed measured section of each sedimentary sequence from the bottom to the upper part of the formation followed by molluscan fossil association analyses. Lithologically, the Cisaat River stratigraphic section is dominated by greenish grey claystone with some light grey fine-grained sandstone intercalation. Based on about 50 m stratigraphic section, 10 molluscan fossils associations were successfully determined. The sequence from bottom to top are: Corbula – Natica association, Nassa sp. association, Olividae – Turricula association, Pecten – Telina association, Telina – Placuna association, Corbula – Marginella association, Placuna – Natica association, Turritella association, Turritella – Marginella association and Dentalina – Architectonica association. Changes in vertical succession of the molluscan association indicates a development from shallow marine to terrestrial depositional environment before gradually overlain by terrestrial sediments of the Kaliglagah Formation. At least there are 2 deepening - shallowing sea level cycles during the deposition of Kalibiuk Formation observed from this section.