DETERMINE A MYSTERY OF FACIES & DEPOSITIONAL ENVIRONMENT MIDDLE MIOCENE OF NGARAYONG FORMATION ACCORDING TO GEOLOGICAL FIELD MAPPING AND IMPLICATION PETROLEUM EXPLORATION IN NORTH EAST JAVA BASIN, JATIROGO, INDONESIA

The Oligocene and Miocene of the East Java Basin provide an excellent chance to identify comparative responses of clastics and carbonate depositional system to eustatic and tectonic controls (Bransden and Mathew, 1992). Depositional environment of Ngarayong Formation still has debate by numerous geoscientist in Indonesia. Some of publication says that Ngarayong is deposited in deep marine by turbidite current and another says Ngarayong is deposited in shelf or shallow marine.

The Ngarayong Formation represents a complete regressive – transgressive sedimentary cycle which ranges of properties textural grains from coarse grain sand clastic – fine grain clastic also limestones towards the top. In this stage, Ngarayong is shown a five main principle of facies characteristic. They are tidally facies of sandstone, turbidite sandstone, contourite, hemipelagic siltstone and bioclastic carbonate.

This research is proceeded with surface data & produce 5 measure section. The research method is using a field geology mapping and studio analysis. The main purpose of this study is to identify a depositional environment and facies characteristic in Ngarayong Formation as the main subject of hydrocarbon exploration in Eastern Java Indonesia.The Excelent reservoir characteristics are founded in the quartzose cross bedded shelf sandstone and sandy turbidite. The sandy turbidite facies have been the most productive and forms the primary of the exploration target.