Awang Harun Satyana1, Margaretha E.M. Purwaningsih2
1 Badan Pelaksana Migas, 2 Anadarko Indonesia Company
In Java, the Oligo-Miocene (Late Oligocene-Early Miocene) platform and reefal carbonates distribute widely. Some of these carbonates are the important producing reservoirs, such as Kujung in East Java and Middle Cibulakan/ Baturaja in West Java. The period is also noted for its volcanism known as the “Old Andesite” which distribute along the southern part of Java Island. This contemporaneity is interesting to evaluate revealing the tectono-volcanic influences on the carbonate sedimentation.
In tectono-volcanic setting, two trends of the Oligo-Miocene carbonates can be recognized : (1) Northern Trend, including the Cepu-Surabaya-Madura, North Central Java, and Ciputat-Jatibarang areas consists of the carbonates of Kujung, Prupuh, Tuban, Poleng, Middle Cibulakan, and Baturaja and (2) Southern Trend, including the Gunung Kidul-Banyumas-Jampang-Bayah-Sukabumi-Rajamandala areas. The Northern Trend has developed in the back-arc setting, 75-150 kms away from the Oligo-Miocene volcanic arc in southern Java. There is no volcanic material found within the carbonates of this trend. The distal location from the volcanic arc is considered as the reason. The Southern Trend was within the intraarc setting. No reefal carbonates are found to develop contemporaneously with the volcanism in Gunung Kidul-Banyumas-Jampang areas. Significant reefs grew during the Oligo-Miocene in the ridges at the front of the Southern Mountains including Bayah-Sukabumi-Rajamandala areas. The volcanism in Bayah area took place as earlier as Early Eocene and had diminished when Oligo-Miocene transgression resulted in reefal carbonates. In Sukabumi-Rajamandala areas, Rajamandala reefs developed prior to Jampang volcanism which took place in the Early Miocene. When this volcanism intensified, the Rajamandala reefs terminated to grow.
The window of volcanic quiescence in Java from 18 – 12 Ma (Middle Miocene) which occurred contemporaneously with the maximum global sea transgression had resulted in significant reefal carbonates development along the Southern Mountains of Java such as Wonosari/Punung in Gunung Kidul, Jonggrangan in Kulon Progo, Karangbolong/Kalipucang in Banyumas, and Bojonglopang in Jampang areas. The study has provided the regional framework on the relationship among carbonate sedimentation and tectonics and volcanism. What occurs in the Java Island on this relationship also occurs in other areas with active carbonate sedimentation and volcanism such as in Sumatra, South Sulawesi, and Philippine Arc.
* Proceedings of Joint Convention Jakarta 2003, The 32nd IAGI and 28th HAGI Annual Convention and Exhibition