First archaeomagnetic results from Colombia (the Bogotá Savanna Pre-Hispanic sites): Implications for the Caribbean absolute geomagnetic intensity variation curve

Abstract

Colombia is located along so-called intermediate area between two major American civilizations: Mesoamerica and Central Andes. Despite impressive archaeological sites throughout whole Colombian territory and great cultural heritage, still no regional geomagnetic secular variation curve is available. Here, we report first, systematic archaeointensity measurements on the Bogotá Savanna Pre-Hispanic pottery samples corresponding to a radiometrically well dated archaeological context. Seventy-two samples belonging to six potsherds were subjected to the full battery of rock-magnetic experiments in order to select the most suitable samples for double heating palaeointensity experiments. The selected samples exhibited magnetically and thermally stable behavior pointing to titanium-poor titanomagnetite as responsible for magnetization. Under our imposed selection and acceptance criteria, only 37 specimens coming from two pottery fragments provided high-quality technical determinations. These new data together with all up to now available similar-quality determinations from the Caribbean region were used to build a first regional reference curve using a bootstrap method. The main variation tendency observed in the Caribbean curve is rather similar to the North American (central Mexico and southern United States) patterns but show substantial difference with the South American regional variation curve, most probably influenced by non-dipole contribution due to the South Atlantic Magnetic Anomaly. This first Caribbean curve extends the knowledge of the absolute intensity variation over the three millennia and should be considered as most reliable dating tool in Colombia and surrounding regions.