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Abstract

Tridacnidae shells, a valuable archive of past environments, are common in the Balobok Rockshelter archaeological site on Sanga-Sanga Island in the south Philippines. This site was occupied during the mid-Holocene (ca. 5000-8800 14 C yr B.P.), a period of Neolithic cultural expansion in the Philippines. This paper focuses on the preservation of two shell specimens, Hippopus hippopus and Tridacna maxima, unearthed from two mid-Holocene layers within the rockshelter. The shells' mineralogy and microstructure (prismatic and crossed-lamellar) were studied using micro-Fourier transform infrared spectroscopy and scanning electron microscopy to determine if the samples were suitable as paleoenvironmental records. Both shells are still aragonitic but aragonite crystals of both microstructure types are partly dissolved. This dissolution, characteristic of meteoric water alteration, precludes their utility in paleoenvironmental geochemical studies. Nevertheless, these shells are abundant in archaeological sites in the region and may be better preserved in other depositional contexts; more studies on Philippine Tridacnidae shell diagenesis are needed.

This paper integrates the first rock art directly dated with radiocarbon (14C) in Southeast Asia with the archaeological activity in the area and with stylistically similar rock art in the region. Peñablanca is a hotspot of archaeological research that includes the oldest dates for human remains in the Philippines. The caves in Peñablanca with known rock art were revisited and only 37.6% of the original recorded figures were found; the others are likely lost to agents of deterioration. A sample was collected from an anthropomorph and accelerator mass spectrometry (AMS) dated to 3570–3460 cal BP. The date corresponds to archaeological activity in the area and provides a more holistic view of the people inhabiting the Peñablanca caves at that time. A systematic review was used to find similar black anthropomorph motifs in Southeast Asia to identify potential connections across the region and provide a possible chronological association.

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