Crustal fragments with Asian and Australian affinities that outcrop on the island of Timor were stacked together owing to the collision between the Banda volcanic arc and the Australian continent. Geochemistry of floodplain sediments (11 samples) and detrital zircon geochronology of bedload sediments (5 samples) are used to interpret the geological nature of the source units exhumed in East Timor. The geochemical data revealed source rocks with widely variable proportions of felsic and mafic material. In general, the Banda Terrane units supply higher proportions of mafic material, which tend to have lower zircon productivity, than the Australia Passive Margin or Gondwana sequences. Zircon with ages of 2150–1500 and 365–210 Ma constitute the most common populations in all stream samples. Sampling sites that are not sourced exclusively by the Gondwana Sequence and have Banda Terrane units in their watersheds are characterised by high proportions of Triassic zircon, which are common in the Sula Spur, and discordant grains. It is proposed that a significant component of the zircon found in the allochthonous units of Timor is inherited from Australian-related crustal fragments that drifted from the Sula Spur. These units were carried south as the Banda Arc progressed towards the Australian continent and emplaced in Timor with the Banda Terrane.