Comments on the Structural Evolution of the Bukit Lambir Area, Sarawak, Malaysia

The Neogene sands and shales of Bukit Lambir have witnessed a surprising variety of tectonic events, including inversion, folding and thrusting. Fault measurements carried out in the field in early 2005 were combined with geologic profiles, seismic data, satellite data, and older unpublished data (such as from S.O.L, in the early part of the 20th century), and fed into one single ArcGis project. All data suggest the tectonic evolution of the Bukit Lambir area occurred in four stages: Extensional stress created grabens with faults hading around 125 degrees (Middle-to Late Miocene). The grabens quickly filled with some 12000' of interbedded sands and shales. With the onset of regional compression in the Latest Miocene, inversion of the depo-centre took place leading to moderately dipping sequences and semi-regional uplift. Further compression oblique to the Bukit Lambir trend led to shallow overthrusting, associated folding and further uplift and a steepening of strata dip. Both regional thrusts and folds hade circa 60 degrees. The compressive push originated from the South-East, as also seen in overthrusted synclines further to the south between Bakong and Lapok.