The 'fatus' of East Timor: stratigraphy and structure

[Truncated] Timor Island, situated approximately 600 km north of northwest Australia, is the orogenic product of the collision of the northern edge of the Australian continental plate with the Banda volcanic arc. Collision has produced a complex fold and thrust belt comprising rocks of the Australian continental margin, rocks of Asiatic affinity, and more recent synorogenic deposits. East Timor occupies the eastern half of Timor Island.

Across Timor Island, a strike-parallel chain of steep-sided limestone massifs, known locally as ‘fatus’, form high peaks in both East and West Timor. Despite many early workers observing most ‘fatu’ limestones to be dominantly Triassic in age, most modern literature follows the reconnaissance mapping of Audley-Charles (1968) in interpreting the fatus of East Timor as coherent blocks of Miocene limestone. This study is based on 6 months of detailed field mapping on and around the major fatus of East Timor, including: Mount Mundo Perdido, Mount Laritame, the Builo Range, Mount Bibileu, the Paitchau Range and Lake Iralalaru region, the Matebian Range, Mount Taroman, Mount Loelako, the Saburai Range and the greater Maliana basin region.

Findings from this study differ markedly with most current stratigraphic and structural interpretations of the fatus. The central regions of all fatus studied are observed to comprise either Late Triassic or Early Jurassic shallow water limestones of Australian affinity, associated with a complex range of other lithologies including Triassic-Jurassic interior-rift basin deposits, Cretaceous to Oligocene pelagites, limestones and volcanics of Asiatic affinity, and Plio- Pleistocene synorogenic deposits.

Detailed structural mapping shows that the fatus of East Timor are dominated by recent, high angle, oblique-slip and strike-slip faults present at all scales, that have been active into the Pleistocene and control the present-day topography. The fault architecture and stratigraphic distributions in the study areas are comparable to pop-up structures and pull-apart basins developed at restraining and releasing bends or step-overs in zones of strike-slip, both in scaled sandbox models, and strike-slip systems elsewhere in the world.