Brunei Darussalam is located on the northwest coast of Borneo, near the equator, between approximately 114o 4’ - 115o 22’ eastern longitude and 4o2’-5o 3’ northern latitude. The country is bounded along the southern and eastern sides by the Malaysian state of Sarawak.
The Late Neogene to Quaternary lithostratigraphic units that outcrop in onshore Brunei Darussalam form an integral part of the progradational delta systems, known from the subsurface in the offshore areas. The Belait, Miri, Seria and Lambir Formations are relatively sandy units, overlying and in basinward direction transitional into the argillaceous Setap (shale) Formation. In Sarawak, time-equivalent formations include the Tukau and Sibuti Formations.
The type area of the Lambir Formation (Middle-Late Miocene) is located in the Lambir hills, to the southwest of Miri (Sarawak).The formation is also present in the Belait anticline, near Kampong Labi and in the Bukit Teraja area. The formation consists predominantly of sandstone and shale with minor limestone and marl intercalations. In the Bukit Teraja area, an overturned sequence of thick bedded, cross-bedded sandstones and intercalated rippled sandstones and clays are present in a series of outcrops along the extension of the Labi road. In the Kampong Labi area heterolithic facies, with occasional thick, cross-bedded sandstones, and occasional thin conglomerate horizons are the distinctive lithologies. In the Belait anticline the Lambir Formation is overlain by the relatively argillaceous facies of the Miri Formation.