Late Quaternary tropical lowland environments on Halmahera, Indonesia

Results of a case study of landform development and sedimentation in humid tropical lowland environments on Halmahera island, eastern Indonesia, are p resented with the aim to better characterise tropical lowland environments in the context of Late Quaternary environmental change studies. First, the geologic, morphologic and environmental settings of the two areas, the inte rior Kao River plain and the Kao coastal zone (N. Halmahera), are presented . Subsequently, data concerning Late Pleistocene and Holocene landform deve lopment, sedimentation and coastal processes are discussed. Pleistocene lan dform development involved volcaniclastic, sedimentation, base levelling of coastal lowlands, prolonged weathering and crust formation, coastal uplift and eustatic sea level change. A conspicuous ferricrete crust in the subso il of the coastal plain is tentatively dated with C-14 AMS analysis and iso topes of organic matter encapsulated in the soil ferricrete have been deter mined. Due to interacting sea level change, neotectonic uplift, climatic, h ydrologic and vegetational change, unequivocal evidence for anomalous Late Pleistocene or Holocene environmental conditions is difficult to obtain. Du rin- the Nhd-Late Holocene, a low-energy fluvial systems and swamps existed in the interior Kao River plain; a dense open swamp/swamp forest vegetatio n contributed to extremely high sedimentation rates in this depositional ba sin. Palynological analysis of the organic swamp deposits indicates little or no change in sedimentary environmental settings and swamp vegetations, a nd indications for early human presence in the area. In the coastal area ac cretion and delta progradation occurred after the Early-Mid Holocene format ion of a marine erosion cliff. Tentative evidence for early human presence in the Kao area is derived from charcoal particle frequencies in sediments and the existence of natural grasslands in the coastal zone. As most of the geologic and environmental characteristics of the tropical lowlands in the Kao area are common in eastern Indonesia, the study provides useful inform ation for ongoing research in the region. (C) 2001 Elsevier Science B.V. Al l rights reserved.