Geochronological advances in human first arrival date in the Philippines Archipelago (Cagayan valley, Luzon island).

The Paleolithic site of Kalinga, in the Cagayan River basin (Luzon Island), preserves the oldest known traces of human occupation of the Philippines archipelago (709 ± 68 ka1). Luzon island is also known for the fossil's discovery of Homo luzonensis (Callao cave) recently dated at 66.7 ± 1.0 ka2, that constitute the oldest human remains in the Philippines. This contribution presents the results of a geomorphological and geochronological study of the Kalinga site: the Cagayan valley, in order to precise the geochronological framework of this first human settlement. In this area, the sedimentary deposits are mainly fluvial sands terraces partly formed from volcanic minerals. Following the discovery of abundant paleontological remains and lithic tools on surface, the region was the subject of numerous excavations on several sites from the 1970s until now. Since 2014 a new project led by our research team unearthed hundreds of archeological remains (lithic tools and butchery traces) discovered undisturbed in several sequences. Apart from the early middle Pleistocene ages obtained for the Kalinga site, the geomorphology and geochronology of the area are still little known. Through the use of ESR on bleached quartz and 40Ar/39Ar on plagioclase dating methods in association with palaeomagnetism analyses, the chronology of four sequences has been constrained. Our results assert a human occupation between 709 ± 68 ka and 528 ± 40 ka reducing the chronological and archaeological gap between Kalinga and Callao hominins and placing this basin as a central piece of the human arrival in insular Asia. [ABSTRACT FROM AUTHOR]