APPLICATION OF OLEANANE AND STERANE INDEX FOR BIOSTRATIGRAPHIC AGE DETERMINATION: EXAMPLES FROM KANGEAN OILS, NORTHEAST JAVA BASIN

Abstract

Northeast Java Basin is known as mature Cenozoic basin, yet this understanding override possibility of
sediment older than Cenozoic. This thoughthas brought current exploration strategy of this basin concerning
within only Cenozoic sediments. Therefore, it is believed that the source rock in this basin was also derived
from Cenozoic sediments, especially the Ngimbang Formation, which was formed during Late Eocene
to Early Oligocene in the stage of Early Synrift. On the other hand, the occurrence of Alisporites sp has
pointed Cretaceous sediments is a potential source rock. However, it is still debatable due to the presence of
Alisporites similis in Serawak Basin of Malaysia, which is present until Paleocene. Three crude oils from the
Kangean oil fi eldNortheast Java Basin, namely NEJB-748, NEJB-749 and NEJB-750have been investigated
using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS).Kangean oils are
classifi ed as mixed oil with organic matter originated from marine and terrestrial deposited under oxidizing
and reducing conditions. Moreover, Kangean oils show very low oleanane and steraneindexthat may lead
us to the conclusion that the oils were originated from Cretaceous source rock.