Tertiary Basin Initiation and Sedimentation; East Java Basin, Indonesia

Naranjo, John C.¹, J. A. (Toni) Simo¹, Eduard Dragan¹, Alan R. Carroll² (1) University of Wisconsin-Madison, Madison, WI (2) University of Wisconsin-Madison, Madsion, WI

Hypotheses for the origin of the East Java Basin (EJB) are wide ranging, and include regional extension, back-arc rifting, and regional lithospheric flexure. This problem can be addressed in part by looking at regional-scale thickness and subsidence patterns, combined with previous facies and biostratigraphy, to help constrain models for basin initiation and early evolution. To analyze changes in sediment thickness, three specific horizons that divide two major phases of the early evolution of the EJB were mapped using 2D seismic data (>10,000 line-km). Subsidence histories, including well log analyses, were compiled for key wells throughout the seismic grid and elsewhere in the basin. Based on isochron mapping, the depositional axis of the Eocene-Oligocene basin trended NE-SW. Subsidence histories and sparse lithologic reports show that dominantly clastic sedimentation was focused in areas of maximum subsidence, resulting in relatively thick basinal deposits. In contrast, the Oligocene-Miocene isochron map shows the basin had changed to a WNW-ESE orientation. Subsidence rates in general increased at this time, an observation inconsistent with a rift origin for the earlier basin history. Prolific carbonate accumulations formed in areas with ~500 m or less total subsidence through the Oligocene-Mid Miocene, whereas areas with greater total subsidence (up to 900 m) tended to become sediment-starved bathymetric deeps. A major carbonate platform formed in the northern part of the basin. Two southwest-trending projections from the platform appear to represent buildups that formed on paleohighs, corresponding to areas of lesser Eocene-Oligocene subsidence. Future work will include synthesis of Central Java Eocene-Miocene outcrop data, thermal histories based on vitrinite reflectance of coal samples, and detailed integration of subsidence histories with structural development of the basin.