Provenance of Mesozoic sandstones in the Banda Arc, Indonesia

• Main Author: Zimmermann, Sebastian
• Format: Dissertation
• Language: English
• Published: Royal Holloway, University of London 2016

Quartz-rich sandstones in the Banda Arc Islands (Indonesia) are thought to be the equivalent of Mesozoic sandstones on the Australian margin and are important potential hydrocarbon reservoirs. They have been exposed by on-going collision resulting in the opportunity to study their provenance. Previous studies suggest that rivers draining Australia will have provided most sedimentary input. There have been suggestions of a northern provenance for some Timor sediments. This study combined several methodologies to investigate provenance characteristics of these rocks in order to reconstruct the palaeogeography, possible sediment pathways and most likely sources. The project included extensive fieldwork in various islands of the Banda Arc (Sumba, Timor, Babar and Tanimbar) and sampling of relevant material. Subsequently, conventional light and heavy mineral point-counting with textural classification was performed. Additional detrital zircon laser ablation geochronology (LA-ICP MS) U-Pb dating was executed to gain a comprehensive dataset. Results show a number of new and surprising features for the geological units analysed. Some formations are consistent with an Australian source. However, many of the sandstones are texturally immature and contain volcanic quartz and volcanic lithic fragments. Commonly mixed sources of contemporaneous acidic igneous, recycled sedimentary and metamorphic origin are suggested. In the Tanimbar Islands and Babar, sediment came from both Australia and acidic igneous rocks from the Bird's Head west of New Guinea. Sandstones in Timor show differences from east to west. The east contains a greater acidic igneous signature, whereas the west is more dominated by metamorphic sources. The analyses suggest better connectivity to continental Australia in the Triassic than in the Jurassic and Cretaceous. Zircon populations in the Cretaceous, heavy minerals and immature textures (especially in rocks from Sumba, Timor and Tanimbar) suggest that they were derived from metamorphic and recycled sedimentary sources. Mesozoic to Archean zircons suggest derivation from Australian crust that had collided in Sundaland during the Cretaceous. A new model is proposed to explain the dynamic evolution and allochthonous history of some of these island fragments.