Re-examining Site Formation Processes in Callao Cave, Cagayan through a Sedimentological and Geochemical Approach

Dawn Iva Satumbaga1,2* and Armand Salvador B. Mijares1

The hominin remains of Homo luzonensis in Callao Cave, Cagayan recently received older dates at 134±14 kya, increasing its range and placing its oldest record in the transition between MIS 6 and MIS 5 instead of 67 kya. This updated record provides a new context in which climatic, environmental, and archaeological interpretations are made. To understand the depositional history of Callao Cave against the background of the new chronology, a sedimentological and geochemical analysis was performed on the stratigraphic layers from the 134 kya layer up to the 14th century deposits. Bulk sediment samples were analyzed using microscope observations, carbonate content, FTIR, XRF, and XRD. Resulting data were compared against soil micromorphology, palynology, and cultural remains from existing literature. Results for the upper Neolithic and 14th century cultural layers support existing interpretations and provide additional information on bone dissolution and authigenic mineral formation. Bone dissolution and phreatic conditions are also evident in the layer containing the Homo luzonensis remains, supporting the calibration for the older dates. This paper supports the post-depositional processes inferred from soil micromorphology but recommends revisiting characterization of sediment inclusions and consequent archaeological interpretations of the lower layers. Overall, it complements existing literature on the depositional process in Callao Cave for a more complete history. This analysis is the first application of a combined sedimentological and geochemical analysis to reconstruct cave site formation processes in the Philippines, showing its potential to complement, validate, and change archaeological interpretation.