Archeointensity in Northeast Brazil over the past five centuries

摘要: Abstract This study presents the first archeointensity results from Northeast Brazil obtained 14 groups of architectural brick fragments sampled in city Salvador, Bahia State (13°S, 38.5°W) and dated between middle XVIth century beginning XIXth century. The dating is ascertained by historical documents complemented archeological constraints, yielding all cases age uncertainties less than 50 years. Analyses were carried out using two experimental protocols: 1 — “zero field–in field” version classical Thellier method as proposed Coe (TT-ZI), including partial thermoremanent magnetization (pTRM) pTRM-tail checks, 2 Triaxe procedure involving continuous high temperature measurements. Both TRM anisotropy cooling rate effects taken into account for intensity determinations. effect was further explored TT-ZI protocol three increasing slow times (5 h, 10 h 25 h) 450 °C room temperature. Following slowest time retained our study, decreases raw values 4% to 14%. For each fragment, a mean computed only when data specimens (between 6) satisfied coherence test at ∼ 5%. A total 57 (183 specimens) considered computations site-mean values, with derived standard deviations 8% corresponding means. When separately techniques, always agree within 5%. good consistency observed similar or close ages, which strengthen their reliability. Our principally show significant decrease geomagnetic field half XVIIth XXth One result second suggests that reached maximum around 1600 AD. evolution agreement expected Salvador available global models. However, accuracy these models appears well constrained ∼ 1550 AD ∼ 1650 AD.