Naranjo, John C.1,
J. A. (Toni) Simo1, Eduard Dragan1,
Alan R. Carroll2 (1) University of Wisconsin-Madison,
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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California