Mélange on the Jerudong Line, Brunei Darussalam, and its regional significance

Author : Charles S. Hutchison
Publication : Bulletin of the Geological Society of Malaysia
Page : 157-161
Volume Number : 36
Year : 1994
DOI : https://doi.org/10.7186/bgsm36199414

Bulletin of the Geological Society of Malaysia, Volume 36, Dec. 1994, pp. 157-161

Mélange on the Jerudong Line, Brunei Darussalam, and its regional significance


Earth Sciences and Resources Institute (ESRI) of the Universities of South Carolina and Utah,

c/o Department of Geology, University of Malaya, 59100 Kuala Lumpur, Malaysia


Abstract: Southwards along the Jerudong Line, on the hillside east of the road between Pangkalan Batu and Kampong Masin, there is a zone of distinctive hummocky topography in contrast to the usual persistent sandstone strike ridges of the Berakas and Belait synclines. Active construction near Bukit Masin has revealed this topography to have resulted from disrupted stratigraphy. Convoluted and rolled blocks up to 3 m diameter of sandstone are embedded in Setap Shale. The outcrops are interpreted as a large olistostrome deposit. During deposition of the Belait Formation, the Jerudong Line was a submarine continental slope down which the yet unconsolidated sands slumped westwards into the deeper water part of the Baram Delta.

In a regional context, this Late Miocene continental slope extended northwards from the Jerudong Line, along the Morris Fault, curving northeastwards along the transition between the Inboard and Outboard belts of offshore Sabah. Slump scars characterize the length of this continental slope. Conventionally it is referred to as a wrench fault (Morris Fault and Jerudong Line) with 30 to 40 km of left-lateral post depositional displacement, based on offset of the interpreted palaeo-environments across the fault. These palaeo-environments have not been displaced and persist in their original relative depositional positions. The displacement is apparent because of considerably deeper water to the west of the Jerudong-Morris Fault continental slope. There are also no geological indicators along the Jerudong Line to prove wrench displacement.