REGIONAL CONTROLS ON THE DEVELOPMENT OF CARBONATES IN EAST NATUNA BASIN AND LUCONIA AREA

摘要

The East Natuna - Luconia area consists of a basin and stable platforms in the offshore SW Borneo. It is located in an intermediate position between areas of subsidence and faulting in the north and zones of pronounced compressional tectonic in the south. The area is characterized by extensive development of carbonates that started in the Early Miocene through Late Miocene.Regional seismic study indicates that Luconia and nearby areas had undergone an extensional phase during the Late Oligocene to Early Miocene and subsequently followed by episodic compressional phase during the Middle Miocene. During the extensional and the subsequent isostatic readjustments, the area was a part of a depression zone bounded by the uplifted regions that formed the basin edges in the southwest, south and southeast. Areas in the proximity to the main uplifted region in the east and southwest were dominated by clastics, whereas, carbonates thrived on the rifted margin in the west associated with the rising of sea levels. A similar setting has also affected the development of the East Natuna area.The subsequent compressional tectonic then resulted in inversion and folding. This phase was responsible for the upliftment of parts of the East Natuna - Luconia region as marked by the widespread occurrences of anticlinal folds. These folds formed the sites for widespread carbonate growth during high sea level phases of the latest Middle Miocene to the Late Miocene period.The recurrent low sea-level phases during the Late Miocene exposed most of the carbonate buildups as indicated by multiple karstified surfaces. A large part of carbonates within the East Natuna basin and Luconia was demised during this period. A major sea level rise at the base of Pliocene had drownedmost of the carbonate in this region except a few buildups in the northwest region of the area, which still thrive up to the present day.