Abstract

GARCIA-PIMENTEL, Alejandra et al. Integrated archaeomagnetic and radiometric study of pre-Hispanic fireplace at El Ocote archaeological site (Aguascalientes, Mexico). Bol. Soc. Geol. Mex [online]. 2023, vol.75, n.1, e231122.  Epub May 25, 2024. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2023v75n1a231122.

El Ocote is a pre-Hispanic settlement distributed on the top and slopes of Los Tecuanes hill, to the south-west of the capital of the State of Aguascalientes, Mexico. Early archaeological survey pointed out that the site was developed during the Epiclassic period, between 650 and 900 AD. Still, the site lacks reliable absolute chronological data. An archaeomagnetic sampling involved two fire pits located on the site. 98 cubic specimens were prepared and the natural remanent magnetization of all of them was measured. Subsequently, a demagnetization process was carried out by alternating fields up to 90 mT to eliminate secondary magnetizations and obtain their primary, characteristic mean archaeodirections. Additionally, rock-magnetic experiments were carried out that included: thermomagnetic curves, hysteresis cycles and isothermal remanent magnetization curves, obtained using a Curie Balance, in order to define the nature of the magnetic carriers responsible for thermoremanent magnetization. The mean directions were calculated for both fire pits and compared to the global geomagnetic model SHA.DIF.14K, yielding time intervals 914 AD - 1079 AD and 924 AD - 1102 AD for the first and second fire pits respectively, which represent the most probable age of their last use. In addition, the directions obtained were also compared with the SHAWQ2k global geo-magnetic model and the local paleosecular variation curve of Mahgoub et al., 2019. Six radiometric ages are also reported for first time. The radiometric ages belong to carbon remains located in different fire pits located on the site and also correspond to the Mesoamerican Epiclassic period. The ages obtained for both fire pits show rather good agreement with the chronology proposed for the time of abandonment of the site and of the entire region, supporting the proposal of an almost simultaneous collapse in the northern section of the western Mesoamerican border between 900 AD. and 1100 AD.

Keywords : sample; archaeomagnetism; El Ocote; absolute Cchronology; Mesoamerica.

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