Awang Harun Satyana1, Margaretha E.M. Purwaningsih2
1BPMIGAS, Jakarta 2ConocoPhillips Indonesia, Jakarta
Sumba Island is a terrane, a transported geologic entity which is exotic to its surrounding areas. It is situated presently in the forearc setting of eastern Lesser Sunda volcanic arc. The origin of Sumba has been a matter of debate. There are two main competing hypotheses, origins from: (1) NW Australia or (2) eastern Sundaland. We conclude that Sumba terrane came from eastern/southeastern margin of Sundaland based on data and interpretation including: stratigraphic succession, geochronology-geochemistry of magmatic rocks, paleomagnetism, and isotope geology. We then evaluated geologic controls on fauna distribution and peopling of Sumba Island as expressed on its historical biogeography, linguistic-genetic coevolution, and megalithic archaeology. Paleogene stratigraphic succession of Sumba is similar to that of Southern Sulawesi. Erupted magmas display the characteristics of typical island arc environment at the margin of Sundaland. Paleomagnetic data of Sumba show the location of Eastern/Southeastern Sundaland in the Late Cretaceous and has occupied its present position since the Early Miocene. Potential Pb-Nd isotope characteristics of rocks from Sumba and its expected provenances showing correspondent isotopic signatures and affinities of Sundaland provenance. Based on historical biostratigraphy, Sumba contains typical Eocene low-latitude Sundaland fauna of Assilina, Pellatispira, and Biplanispira and no Eocene high-latitude Australian fauna of Lacazinella. Marine shore fish family of Phallostethidae, typical of Sundaland waters, are discovered in Sumba terrane. This suggests that Sumba shared a closer biotic relationship with Sundaland before dispersal. There is linguistic-genetic coevolution on Sumba Island. Phylogenetic reconstruction indicates that Sumbanese languages derive from a single ancestral Austronesian language. Interestingly, a positive correlation was found on the percentage of Y chromosome lineages that derive from Austronesian ancestors. It can be reconstructed that the peopling of Sumba took place from north/northwestern corner of the island and migrated to the rest of the island. Sumba is one of the few places in the world where megalithic tradition is still living. We compared exterior motifs of the Sumba megaliths compared to those of other areas in Indonesia where megalithic tradition is still living (Timor, Flores, South Sulawesi, North Sulawesi, East Java, West Java, Nias). Our study shows that megalithic tombs constructed in Sumba is similar to most western Indonesia megaliths.
* Proceedings JCM Makassar 2011 The 36th HAGI and 40th IAGI Annual Convention and Exhibition