LATE CRETACEOUS AND CENOZOIC TECTONOSTRATIGRAPHIC DEVELOPMENT OF THE EAST JAVA SEA BASIN, INDONESIA

The East Java Sea Basin is underlain by a metamorphic basement complex . Subsidence of this basement during the Late Cretaceous resulted in a ccumulation of up to 3 km of marine Upper Cretaceous sediments (megase quence 1). Contraction and near peneplanation of the Upper Cretaceous sediments and underlying basement occurred before the middle Early Eoc ene, producing a regional unconformity which defines the base of megas equence 2. The Cenozoic East Java Sea Basin started to form during the Early Eocene by crustal extension on both planar normal faults and ex tensionally reactivated Cretaceous thrusts. Normal faulting was pulsed from the Early Eocene to Early Oligocene and affected a progressively larger area with time. Complex structural geometries evolved in respo nse to local extensional reactivation of obliquely orientated pre-exis ting structures. The resultant Palaeogene fault-controlled sub-basins were filled with fluvial, coastal plain and shelf elastic and carbonat e sediments recording an overall transgressive evolution. Regional sub sidence became dominant over fault-controlled subsidence during the Ea rly Oligocene. Basin-fill during this time was dominated by deep marin e, fine-grained elastic sediments. A regional unconformity of intra-Ol igocene age is recognized and is overlain by Oligocene to lowermost Mi ocene deep water calcareous mudrocks and limestones which locally onla p erosionally truncated Eocene rocks. The Lower Eocene to lowermost Mi ocene sediment package comprises megasequence 2. Regional inversion of Palaeogene sub-basins commenced in the Early Miocene and continues to the present day. The syn-inversion Lower Miocene to Recent sediments comprise megasequence 3. Inversion has resulted from regional contract ion and resultant reverse reactivation of Palaeogene normal faults and Cretaceous thrusts. Regional subsidence has been continuous during th e inversion history, resulting in a gradual reversal of depocentre loc ation; Palaeogene depocentres became Neogene highs, whereas Palaeogene platforms became Neogene depocentres. Miocene deposition during inver sion was dominated by the alternation of fine-grained carbonate-domina ted and elastic-dominated cycles. Subsequent Pliocene sandstone deposi tion followed fluvial incision during an Early Pliocene lowstand. The depositional history, during the Pleistocene to Recent, records rapid relative sea-level changes; progradation of elastic and carbonate sedi ments, erosional truncation, channelling and slumping. The Tertiary st ructural geometrical evolution and preserved sediment distribution can be explained by dominantly dip-slip fault movement during the extensi onal and contractional phases of basin development and deformation. Ba sin-scale cross-sectional geometries similar to classical positive flo wer structures have evolved by the reverse reactivation of a geometric ally complex extensional fault system.