The Cainozoic structural history of west, central and east Kalimantan may have begun with formation of melange in the early Eocene, and a surrounding disturbed zone in which part of a mainly Cretaceous flysch trough and associated shelf deposits have been thrown into a confusion of dips and strikes. Uplift of the disturbed zone and adjacent southem outer shelf deposits of the trough was followed by sub-aerial extrusion of mid Eocene volcanics. Between early late Eocene and mid Oligocene times bursts of compression produced structural highs and a shifting pattern of complementary flanking basin depocentres. Uplifted flysch-trough sediments became a northern provenance for the basins (and perhaps a southern provenance for more flysch deposition to the north) and may have been folded further in the process. In the south the Schwaner Batholith provided a bulwark to compression, although its northern margin was upwarped as a consequence. In the east deposits prograded southeastwards away from the northern provenance. As compression tailed off and basin down warping and northern flysch provenance uplift consequently diminished, a peneplane may have begun to form on the flysch. This would have gradually decreased the amount of detritus available for filling the gradually shallowing basins. In the west downwarping and deposition probably ceased in the early Oligocene as a result of regional uplift. In the east renewed compression in the mid Oligocene caused uplift and folding, and interrupted prograding deposition. Penecontemporaneous intrusion of acid to intermediate stocks, plugs, dykes and sills occurred in both east and west. Prograding deposition recommenced in the east in the late Oligocene and has continued intermittently since; the northwestern provenance for the deposits has been uplifted from time to time, on occasion in conjunction with volcanism. The flysch fold belt that is central to the island of Borneo, on the evidence from the region analysed, was bent to its present shape in mid to late Tertiary times.