MULTIPLE UPLIFT MECHANISMS REVEALED IN THE BANDA ARC BY MAPPING WARPED CORAL TERRACES IN TIMOR-LESTE

In order to understand how Timor-Leste is currently being uplifted, one must work backwards to understand how the island has already been uplifted. This study set out to find what the rates of uplift are across Timor and how they differ from one another in order to find the cause of this uplift. To assess this, 1 m resolution LiDAR data of Timor’s coasts were obtained from the Institute of Geosciences of Timor-Leste, which was analyzed with both ArcGIS and the TerraceM Matlab application. Using the coastal geomorphology of the coral terraces around the island, we analyzed the shape of the coral staircases, trying to match them to the pattern of uplift modelled by TerraceM. The most distinguishing feature of these profiles is the massive cliff that follows the inner edge of the 5.5 highstand, which allows us to correlate ages across a significant length of coastline. We found that the uplift rates are higher in general along the eastern part of Timor, perhaps suggesting lithospheric uplift from the low-angle of the subducting Australian continental plate. However, even within the higher uplift rates, there is much variability. The highest uplift rates were seen along promontories into the ocean, which, along with the presence of normal faults, suggests that regional folding is also driving the uplift of the terraces. The direction of regional folding is shown by the morphology of the highest coral terraces, which are all oblong. These coral platforms are trending northeast-southwest, which is the direction of the high uplift rate promontories. Therefore, the lithospheric-scale uplift model commonly accepted cannot be the only factor at play. While this is a subduction zone and there is general uplift, the uplift rates around the island are also impacted by local thrust duplexing and folding.