Geological controls on the preservation of fossils and archaeology in the islands of the Riau–Lingga Archipelago, Indonesia

Abstract

The Riau–Lingga Archipelago, situated south of Singapore and east of Sumatra, holds promise from a modeling perspective for the preservation of Homo erectus and other early archaeological material, as hominins traveled south to Island Southeast Asia. The islands in the archipelago are some of the only emergent lands of the now submerged Sunda Shelf, a region ecologically and geographically conducive for early hominin and faunal movements and occupation. On the ground surveys, however, revealed very little potential for the preservation of archaeology or body fossils. This very limited preservation potential can be attributed to geological and anthropogenic controls. The dominant lithology of the archipelago is granite, which provides neither a reliable source for production of lithics nor weathers in a fashion likely to allow for long-term preservation. Chemical weathering of granites produces acidic soils, and clays and sediments produced are prone to sheet erosion which prevents the formation of soil horizons. A geologically long period of peneplanation, especially in the islands in the northern part of the archipelago, exacerbated these processes, as did large-scale deforestation in the eighteenth and nineteenth centuries for gambier cultivation. Nevertheless, this first large-scale field survey of the archipelago identified novel archaeology and fossil remains. The former includes a lithic scatter on Singkep, possibly associated with pottery sherds, as well as potential standing stones on Singkep and Kundur. Karimunbesar preserved recent rock art in addition to a well-known Sanskrit inscription, and a stone adze owned by a local villager in Lingga is of unknown and unlikely local provenance. A single fossil enamel fragment, provisionally identified as bovid, was recovered from Lingga though its age could not be determined. Our study highlights the difficulties in locating archaeological and paleontological material on stable, tectonically inactive continental islands, with implications for efforts to understand the Pleistocene dispersal of H. erectus.