Borneo and the evolution of the Makassar Straits

Duncan WittsThe Barito Basin, located along the northwest margin of the Meratus Mountains, SE Kalimantan, contains a thick sequence of Cenozoic sediments that record several distinct phases of tectonics and sedimentation.  The Middle Eocene to Pleistocene succession records a general, progressive evolution of the basin from terrestrial to marine conditions and subsequent regression to fully terrestrial environments.  However, a lack of detailed information concerning depositional environments for these units, and their temporal and spatial variation, precludes more precise basin modelling.  This thick Cenozoic sequence also records post-depositional folding and thrusting observable at both outcrop scale, and regionally via seismic and SRTM (satellite) imaging.

 

 

 

 

 

 

 

 

 

 

 

 

As dominantly terrestrial deposits, the precise stratigraphic ages of the Tanjung, Warukin and Dahor Formations is difficult to determine and remain poorly resolved.  As such, the timing of the basin’s development and subsequent deformation remain uncertain.  Running along the southeast side of the Meratus Mountains, the Asem-Asem Basin contains a comparable sedimentary sequence.  Both basins are wonderfully exposed, with abundant outcrops within both the active and recently abandoned coalmines that can be found throughout SE Kalimantan.

The Barito and Asem-Asem Basins are one of few places in SE Asia to contain sedimentary rocks of Eocene age.  As such, these basins afford a rare opportunity to study both stratigraphic and along-strike variations in sedimentological character.  The interfingering of terrestrial and marine deposits and the presence of palynomorphs allow for accurate dating of formations and comparison of their flora and faunas with other, rare, basins of comparable age in the region.  The Barito and Asem-Asem basin are some of the few basins in SE Asia where the earliest stages of basin development can be studied.