Clarification of stratigraphic correlation and dating of Late Cainozoic alluvial units in Peninsular Malaysia

Numerous mine exposures, drillholes and marine seismic profiles have facilitated detailed study of the Late Cainozoic alluvium in Peninsular Malaysia. In 1979, Daud Batchelor, building on the work of D. Walker and others proposed a regional Late Cainozoic stratigraphic scheme incorporating the traditional division of “Old Alluvium” and “Young Alluvium”, and correlated Indonesian offshore units of Aleva and others. The important distinction between Old Alluvium (OA) and Young Alluvium (YA) in presently emergent areas of the Sundaland continent shows that the OA comprises less well sorted generally aggrading alluvial fan/plain deposits of broad palaeochannel systems while the YA infills V-shaped valleys incising the palaeo-landscape. These units reflect a major intervening palaeogeomorphological change. The Transitional Unit erected by Batchelor in 1979 was deposited during transition between the two dominant regimes. In 1988 Batchelor published evidence for dating these units using eustatic sea level and climatic changes, palaeomagnetism, vertebrate palaeontology and radiocarbon dating. Suntharalingam in 1983 formally erected Late Cainozoic stratigraphic units including the continental Simpang Formation and Beruas Formation. He correlated the Simpang Formation with the Old Alluvium of Walker and believed it to be Pleistocene, and the Beruas Formation with Walker’s the Young Alluvium. A difference in views exists on dating of the Simpang Formation/OA. Batchelor in 1988 demonstrated that its age extends from Late Pliocene to Early Pleistocene time, prior to the Brunhes normal magnetic period (>0.775 Ma Before Present; BP), while the YA/Beruas Formation was determined as Late Pleistocene to Holocene. In 1993, Kamaludin and others suggested however, that the Simpang Formation dates until the Late Pleistocene based on “young” radiocarbon dates (28 ka BP to 67 ka BP). The present study argues strongly against such young OA/Simpang Formation ages and believes instead that young dates attributed to the OA have either (1) been wrongly attributed and actually derive from younger units, or (2) the original carbon has been contaminated with young carbon near the dating limit of the C-14 method. The former case is apparent where the upper sequence in the Pantai Remis area, Perak, attributed to the Simpang Formation/ OA by Kamaludin and others, is from my own studies believed to be mainly YA/Beruas Formation, as prefigured in the Teluk Mengkudu sequence published by Batchelor in 1988 (Table 2). As the prime YA equivalent, it is recommended that the Beruas Formation/YA be extended to include alluvium deposited from the beginning of the Wurm glacial period (Marine Isotope Stage 4) at around 75,000 years BP.