A major zone ofintense deformation trending WNW has been discovered in the neighbourhood of Sg. Balingian between Sibu and Bintulu. The zone probably continues offshore where a gravity lineament follows the same direction. The West Balingian and West Baram Lines mark the boundaries of the offshore hydrocarbon provinces and together with the newly discovered shear zone, appear to form a fundamental tectonic framework for this part of NW Borneo. The distribution of heat flow, igneous rocks,

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... ene deltas and Oligocene-Miocene carbonates across N Sarawak and N Kalimantan appear to be related to the framework which extends across central Borneo. The nature of the lineaments is discussed in terms of the regional tectonic evolution of northern Sarawak as well as providing clues to indicate what lies beneath this part of Borneo.