Characteristics of Rocks Based on Petrographic and Geochemical Analysis: A Study in the ‘Land of a Thousand Megaliths’, Indonesia

The megalithic traditions of Central Sulawesi represent one of Indonesia’s most important prehistoric cultural landscapes, widely recognized as “The Land of a Thousand Megaliths.” Despite their significance, scientific investigations into the lithological sources of the megaliths remain limited, with most previous research focusing primarily on archaeological and cultural aspects. This study aims to characterize the petrographic and geochemical properties of rocks associated with megalithic artifacts in the Bada and Behoa Valleys of Poso Regency, Central Sulawesi. A total of seven representative rock samples were collected based on lithological diversity and field resemblance to megalithic artifacts. Petrographic analysis was conducted using thin section microscopy to determine mineralogical composition, textures, and structural features, while geochemical analysis was performed through X-ray fluorescence (XRF) to quantify major oxides and support tectonomagmatic interpretations. The petrographic results revealed that five samples belong to plutonic igneous rocks—classified as quartz monzonite and monzonite—while two samples were identified as metamorphic rocks, namely amphibolite and biotite–chlorite schist. Geochemical data indicate that the plutonic rocks are predominantly ferroan, with affinities to both calc-alkaline and tholeiitic magma series, whereas the metamorphic rocks are associated with island arc tholeiite protoliths. Weathering assessments show that most samples remain fresh, except for one moderately weathered monzonite. The results demonstrate that megalithic builders utilized locally available rocks that possessed suitable durability and mechanical strength for carving and construction. The findings further suggest a strong geological–cultural connection, as the communities strategically selected rock materials that ensured long-term preservation of the monuments. This study provides new insights into the raw material sources of megalithic artifacts in Central Sulawesi and contributes to broader discussions on lithic technology, resource procurement, and heritage conservation. By integrating petrographic and geochemical approaches, the research establishes a scientific foundation for future geoarchaeological studies and supports conservation strategies for safeguarding Indonesia’s megalithic heritage.