Archaeomagnetic results from Cambodia in Southeast Asia: Evidence for possible low-latitude flux expulsion.

Extensive spatial and temporal distribution of high-quality data are essential for understanding regional and global behaviors of the geomagnetic field. We carried out chronological and archaeomagnetic studies at the Angkor-era iron-smelting site of Tonle Bak in Cambodia in Southeast Asia, an area with no data available to date. We recovered high-fidelity full-vector geomagnetic information from the 11th to 14th century for this region, which fill gaps in the global distribution of data and will significantly improve the global models. These results reveal a sharp directional change of the geomagnetic field between 1200 and 1300 CE, accompanied by an intensity dip between 1100 and 1300 CE. The fast geomagnetic variation recorded by our data provides evidence for the possible existence of low-latitude flux expulsion. Related discussions in this paper will inspire a new focus on detailed geomagnetic research in low-latitude areas around the equator, and exploration of related dynamic processes.

First Direct Dating for the Construction and Modification of the Baphuon Temple Mountain in Angkor, Cambodia.

Architecture represents key evidence of dynastic practice and change in the archaeological world. Chronologies for many important buildings and sequences, including the iconic temples of medieval Angkor in Cambodia, are based solely on indirect associations from inscriptions and architectural styles. The Baphuon temple, one of the last major buildings in Angkor without textual or scientifically-derived chronological evidence, is crucial both for the context and date of its construction and the period when its western façade was modified into a unique, gigantic Reclining Buddha. Its construction was part of a major dynastic change and florescence of the Hindu-Mahayana Buddhist state and the modification is the key evidence of Theravada Buddhist power after Angkor's decline in the 15th century. Using a newly-developed approach based on AMS radiocarbon dating to directly date four iron crampons integrated into the structure we present the first direct evidence for the history of the Baphuon. Comprehensive study of ferrous elements shows that both construction and modification were critically earlier than expected. The Baphuon can now be considered as the major temple associated with the imperial reformations and territorial consolidation of Suryavarman I (1010-1050 AD) for whom no previous building to legitimize his reign could be identified. The Theravada Buddhist modification is a hundred years prior to the conventional 16th century estimation and is not associated with renewed use of Angkor. Instead it relates to the enigmatic Ayutthayan occupation of Angkor in the 1430s and 40s during a major period of climatic instability. Accurately dating iron with relatively low carbon content is a decisive step to test long-standing assumptions about architectural histories and political processes for states that incorporated iron into buildings (e.g., Ancient Greece, medieval India). Furthermore, this new approach has the potential to revise chronologies related to iron consumption practices since the origins of ferrous metallurgy three millennia ago.