Determining the burial age of the Ngandong palaeoanthropological site stratigraphy: an application of red thermoluminescence (RTL) dating methods

The Ngandong palaeoanthropological site in Central Java, Indonesia is located on an abandoned fluvial terrace 20 meters above the Solo River. The site is composed of sandy fluvial deposits ranging from two to four meters thick that contain two distinct stratigraphic layers rich in vertebrate fossils. Dutch Geological Survey excavations from 1931 to 1933 uncovered approximately 25,000 vertebrate fossils from these layers, including twelve crania and two tibiae that were identified as being from Homo erectus. Homo erectus fossils have been uncovered elsewhere along the Solo River at sites Sambungmacan and Trinil, but the Ngandong specimens have attracted special attention from paleoanthropologists because of their unique and seemingly modern cranial morphology. Recent (27-46 ka) ages have been measured from associated bovid tooth enamel via electron spin resonance (ESR) dating, but these ages have not been corroborated by other dating methods and the age relationship between the bovid and H. erectus fossils within the Ngandong assemblage is unknown. This study seeks to determine the minimum age of the Ngandong Homo erectus by dating the burial of the sandy fluvial deposits associated with the fossiliferous layers. Preliminary optically-stimulated luminescence (OSL) dating of sands from Ngandong indicated poor natural signal response on the blue wavelength. Because the sands are sourced from the volcanic range in southern Java, the natural luminescence signal is strongest on the red wavelength; therefore, the red thermoluminescence (RTL) dating method with the dual-aliquot protocol is most accurate for determining the burial age of these sediments. Presented here are the challenges and results of dating the volcanic quartz from Ngandong with these methods.