The origin of the East Java Sea basins deduced from sequence stratigraphy

Abstract

A study of facies distribution through time shows there are at least six different basinal areas, which are usually described as a single entity called the “East Java Basin”. Each of these different depositional lows, plus the transgressed platforms between them, have a unique stratigraphic history, and distinct sets of petroleum systems with different exploration risks. The development of the main phases of sedimentation indicate that the east Java basinal system was formed as a continuation of extension around the Makassar Straits, and not as a back-arc basin. This interpretation is based on a tectonically pulsed east to west trend in crustal thinning, subsidence and transgression. In addition there were elongate and anastomosing faults along the southern edge of this extending crust, creating a unique stratigraphic zone south of the Rembang Line Fault. Periodic changes in strain strongly affected this faulted southern margin, including a mid-Oligocene tectonic event that also created a new depocentre, the Sibaru Trough. A poorly defined lithostratigraphic term, the Ngimbang Formation, is recommended to be abandoned. Its historical usage for a series of highly diverse lithofacies, spanning four or five major unconformity-bounded sequences, renders it meaningless. Its long-standing and inconsistent use is one of the factors that has prevented a clearer stratigraphic history from emerging. An alternative nomenclature based on facies and natural sequences of deposition is recommended instead. • Demonstrate synonymy & ambiguity of widely used formation terms. • Propose a sequence based terminology as the only workable alternative. • Clarification of the basic depocenters and their history of sediment fill. • Assert the absence of Eocene sediments in the Central Deep graben. • Demonstrate the Sibaru Trough is not a rift graben as previously thought.