Field analyses of stratigraphy, structure, and tectonic geomorphology of Savu Island defi ne the age and provenance of accreted Australian continental margin sequences and overlying synorogenic cover, and the structure, kinematics, and uplift history of the transition from subduction to collision in the eastern Sunda-Banda arc. The results highlight the dominant infl uence of lower plate composition and structure in shaping Savu Island and initiating intraforearc shortening. Provenance and biostratigraphic analyses of rocks accreted to the edge of the Sunda-Banda forearc indicate that they mostly consist of Triassic to Cretaceous synrift and postrift successions of the Australian continental margin. These rocks are similar in composition and provenance to Gondwana sequence units found throughout the Banda arc to the east, such as the Triassic Babulu, Jurassic Wai Luli, and Cretaceous Nakfunu Formations of Timor. Previously unrecognized units of pillow basalt are found interlayered with Jurassic beds and incorporated into mélange and mud diapirs. These basalt occurrences have major and trace element compositions similar to those of Indian Ocean mid-oceanic ridge basalt and are likely associated with Jurassic development of the Scott Plateau volcanic margin. Southdirected thrusting of these units via a duplex thrust system detached the Middle Triassic section of the underthrust Scott Plateau. The Savu thrust system consists of a series of active north-directed thrust faults found onshore and offshore the north coast of Savu. Thrust faults mapped onshore, penetrated by the Savu #1 well and imaged in vintage seismic refl ection profi les, offset the youngest deposits of Savu. The uplift history and deformation pattern associated with the Savu thrust is investigated at a variety of temporal scales. Foraminifera-rich synorogenic deposits indicate low average surface uplift rates until after 1.9 Ma ago, when pelagic chalk deposits were raised from depths of >2500 m to the surface in fewer than 1 Ma. Island emergence is well documented by uplifted coral terraces that encrust the highest ridges to 338 m elevation. U/Th analysis of uplifted coral yields ages of 122 ka near sea level, indicating slow uplift rates of 0.2 mm/a over the past 400 ka.Most synorogenic deposits are stripped from the south coast, exposing parts of the accretionary wedge. The deeply eroded nature of this part of the island, combined with its steep fi rst-order stream gradients, indicates that it underwent rapid rock uplift and exhumation in the past 1-2 Ma. However, the south coast region is now subsiding, as evidenced by drowned streams and southtilted, submerging coral terraces. Streams draining north over the Savu thrust system show convex-upward patterns with gradients commonly associated with intermediate uplift rates. Flights of coral terraces also document growth of the island to the north above thrust-related folds.These results inform us that the transition from subduction to collision involves (1) strain partitioning away from the subducti...

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The palaeogeography of the marine Upper Cretaceous sequences of the Northwest Shelf of Australia has been interpreted mainly from quantitative studies of the fossil foraminifera in the sediments. Due to the distribution of wells, the Dampier and Browse Basins are the areas mainly discussed.The Dampier Basin Upper Cretaceous sequence began with deposition of relatively deepwater carbonates, following a late Aptian-early Albian hiatus. The moderate incline of the basin floor was accentuated by westerly tilting of the basin, probably in the early Turonian. At this time a condensed carbonate facies, indicative of the deepest water interval present within the basin sequence, formed in the western part. The eastern edge of the basin rose above sea level at this time. Sedimentation of carbonates in the western basin was terminated at the end of the Santonian by a regional regression. Clastic shelf sediments covered much of the area throughout the Campanian and Lower Maestrichtian during this regression. In the Upper Maestrichtian, a transgression then resulted in renewed deposition of calcareous sediments over most of the basin.Uninterrupted sedimentation occurred in the Browse Basin from Aptian into Albian times. A gentle basin slope resulted in the development of a very wide shelf zone which received fine clastics throughout Albian and early Cenomanian time. In the early Cenomanian the western part of the basin underwent a progressive tilting into slope water depths, and the facies changed rapidly from clastics to carbonates. It is interpreted that the central and eastern sections of the basin rose above sea level, due to this basin tilting. Transgressive inundation of this exposed land surface commenced in the Lower Santonian. Owing to its shallower character, the regional Campanian regression affected the eastern Browse Basin more strongly than the remainder of the Northwest Shelf, and the area was entirely infilled before the end of the Cretaceous.Differences in the sequences between these two basins are largely due to the initial basin gradient (high in the Dampier Basin and low in the Browse Basin), which had a profound effect on the facies developed. There are, however, other differences in the timing of events, due to local tectonic movement.

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