First archaeointensity results from Ecuador with rock magnetic analyses and 14C dates to constrain the geomagnetic field evolution in South America: Enhancing the knowledge of geomagnetic field intensity

Emilio Herrero-Bervera (1) , Stephen Athens , Evdokia Tema (2) , Luis Manuel Alva Valdivia (3) , Pierre Camps (4) , Alejandro Rodriguez Trejo (5)

1 HIGP - Hawaii Institute of Geophysics and Planetology
2 UNITO - Università degli studi di Torino = University of Turin
3 Instituto de Geofisica [Mexico]
4 Géosciences Montpellier
5 Centro de Geociencias [Queretaro]

Archaeomagnetic records from low-latitude sites are very scarce. Thus, the information about the geomagnetic field evolution in South America or Ecuador is sparse and more data are needed to constrain the field evolution in South America. In this study we present new absolute archaeointensity results from a set of 14 C well-dated (i.e. calibrated ages) prehistoric archaeological sites in northern Ecuador (South America). Potsherd fragments were sampled during archaeological excavations of 2 earthen mounds in the vicinity of Atuntaqui and Otavalo cities, and pits at La Chimba site. The pottery covers 2 distinct archaeological periods defined as 1) Ecuadorian Formative period (700 BC-1AD) and 2) the prehistoric Late period (1250-1505/1525 AD). Successful archaeointensity determinations were obtained from 56 sherds using the Thellier-Coe protocol and their rock magnetic properties. The absolute palaeointensity determinations have yielded AI values of 43.6 ± 1.3 μT for Atuntaqui, 34.2 ± 1.4 μT for the Otavalo Mound 3 (lower charcoal lens), 39.5 ± 1.4 μT for Otavalo Mound 3 (upper charcoal lens) and a range of absolute archaeointensities from 7.0 ± 0.97 μT up to 42.2 ± 2.06 μT, with a mean average of 21.20 ± 1.15 μT for La Chimba. Archaeointensity (AI) determinations of the successful mean abolute archaeointensity for the early phase (700-440BC) excavation levels 27.8 ± 1.315 μT, middle levels phase (440-40BC), 15.07 ± 0.78 μT and the late levels phase (44BC-250AD) 25.52 ± 1.575 μT. These results are in good correlation with the data from Palpa in South Peru as well as a few data results from Colombia, South America.

Domaines: Géophysique [physics.geo-ph]

Emilio Herrero-Bervera, Stephen Athens, Evdokia Tema, Luis Manuel Alva Valdivia, Pierre Camps, et al.. First archaeointensity results from Ecuador with rock magnetic analyses and 14C dates to constrain the geomagnetic field evolution in South America: Enhancing the knowledge of geomagnetic field intensity. Journal of South American Earth Sciences, 2020, 103, pp.102733. ⟨10.1016/j.jsames.2020.102733⟩. ⟨hal-02972989⟩