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Boletín de la Sociedad Geológica Mexicana

versão impressa ISSN 1405-3322

Bol. Soc. Geol. Mex vol.71 no.2 México Ago. 2019  Epub 30-Out-2019

http://dx.doi.org/10.18268/bsgm2019v71n2a16 

Artículos

An updated catalog of pre-hispanic archaeomagnetic data for north and central Mesoamerica: Implications for the regional paleosecular variation reference curve

Catálogo actualizado de datos arqueomagnéticos Prehispánicos para el norte y centro de Mesoamérica: Implicaciones para la curva de referencia de variación paleosecular regional

Ana Ma. Soler-Arechalde1 

Cecilia Caballero-Miranda1 

Jaime Urrutia-Fucugauchi1 

María Luisa Osete-López2 

Verónica López-Delgado3 

Avto Goguitchaichvili4 

Alan Barrera-Huerta5 

1Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, Coyoacan, CDMX, Mexico. * anesoler@igeofisica.unam.mx

2Facultad de Ciencias Físicas, Departamento de Física de la Tierra, Astronomía y Astrofísica. Universidad Complutense. Plaza de Ciencias,1. Ciudad Universitaria. 28040, Madrid, Spain.

3Posgrado en Ciencias de la Tierra. Instituto de Geofísica. Universidad Nacional Autónoma de México. Campus Morelia. Antigua Carretera a Pátzcuaro 8701, Ex Hacienda de San José de la Huerta, 58190 Morelia, Michoacán, Mexico.

4Instituto de Geofísica. Universidad Nacional Autónoma de México. Campus Morelia. Antigua Carretera a Pátzcuaro 8701, Ex Hacienda de San José de la Huerta, 58190, Morelia, Michoacán, Mexico.

5Posgrado en Estudios Mesoamericanos. Universidad Nacional Autónoma de México. Ciudad Universitaria, 04510, Coyoacan, CDMX, Mexico.

Abstract

Despite the immense cultural heritage of Mesoamerica, there is still no reference archaeomagnetic curve available for Central Mexico and adjacent areas. The present research has two simultaneous objectives: to obtain finer characteristics of the geomagnetic field elements over archaeological past, and to build up a reliable regional archaeomagnetic dating tool for the time span of 350 BC. to 1500 AD. For these purposes, 72 previous were compiled and analyzed with 40 new data selected from unpublished reports and theses performed in the paleomagnetic laboratories of the Geophysics Institute of UNAM (CDMX and Morelia). Most of the samples carry thermo-remanent magnetization, 31 cases were unburned stuccos, and 3 mural paintings carrying detrital or pictorial remanent magnetization. A total of 112 archaeomagnetic directions constitute the core of the updated catalogue. Special effort should be paid for to the time intervals of 500 BC.-AD. 200 and AD. 1200-325 where there is a major lack of reliable archaeomagnetic results. The present paleosecular variation curve agrees reasonably well with the fluctuation observed in the SW United States area. The differences in the intervals between AD. 600-720, AD. 850 and 1000 and AD. 1200-1325 may be rather attributed to the lack of reliable data than to local non-dipole field. It is urgent to gather a greater number of high-quality data supported by radiome tric ages to improve the reference curve in both regions.

Keywords: Archaeomagnetic dating; geomagnetic field; paleosecular variation; central Mexico

Resumen

Aunque el patrimonio cultural de Mesoamérica es cuantioso, aún no se cuenta con una curva de variación secular del campo geomagnético mediante datos arqueomagnéticos para el centro de México y áreas adyacentes. La presente investigación persiguió dos objetivos: obtener características más precisas de los elementos del campo geomagnético en el pasado arqueológico para el lapso 350 aC. a 1500 dC., además de construir una herramienta de datación arqueomagnética confiable para el centro y Sur de México, región que corresponde con la porción central y norte de Mesoamérica. Para ello se compilaron y seleccionaron 72 resultados previamente publicados en revistas arbitradas junto con 40 datos provenientes de informes de proyectos o tesis. La mayoría de las muestras portan magnetización termo-remanente, únicamente 31 son estucos no quemados con magnetización remanente detrítica y 3 pinturas murales con magnetización remanente pictórica. Un total de 112 direcciones arqueomagnéticas constituyen el núcleo del catálogo actualizado. Es necesario un mayor número de datos respaldados por edades radiométricas y de mayor calidad para mejorar la curva de referencia en México, en particular para los lapsos entre 500 aC. y 200 dC. y entre 1200 dC y 1325 dC. La curva de variación paleosecular que se presenta muestra buena correlación con la fluctuación observada en el área SO de Estados Unidos. Las grandes diferencias entre ambas áreas para los lapsos 600-650 dC., 850-1000 dC. y 1200-1325 dC. pueden ser mayormente atribuidas a la falta de datos confiables más que al campo no dipolar local.

Palabras clave: Datación arqueomagnética; campo geomagnético; variación paleosecular; centro de México

1. Introduction

The variation of the geomagnetic field in the archaeological past can be obtained from the well dated burned archaeological artifacts, bearing some spinels like titanomagnetites, as principal carriers. Archaeomagnetic data retrieved from thermoremanent magnetization are considered the most accurate and reliable compared to the data from lakes and sediments which may be smoothed and/or offset due to their magnetization acquisition process. These data are used to draw up regional PSV reference-curves or global prediction models building upon the knowledge of the geomagnetic field variations for the periods covering the last few millennia. Reference PSV curves can also be used for dating purposes by comparing the archaeomagnetic field information (direction and/or intensity) of archaeological material within a region with the known PSV curve of the Earth’s magnetic field for the corresponding region (Lanos and Dufresne, 2008; Pavón-Carrasco et al., 2011).Well-defined PSV curves in southwest USA are scarce (Sternberg and McGuire, 1990; Eighmy et al.,1990; Wolfman, 1990a) in contrast to Europe, where several well-defined PSV curves are available for different regions (Gómez-Paccard et al., 2006; Schnepp and Lanos, 2005; Gallet et al., 2002).

Mesoamerican culture in Mexico had great development, since the Olmec civilization, which left strong evidence of numerous big cities with trade networks that covered all of Mexico and Central America. Many investigations headed by the INAH (Instituto Nacional de Antropología e Historia) were carried out in the XX century elaborating regional sequences with ceramics and architectonic styles as chronological controls. The chronology was divided into three broad periods: The Formative or Preclassic from 2000 BC. to AD. 300, the Classic from AD. 300 to 950 and the Postclassic from AD. 950 to the contact with the Spaniard in AD. 1521. A period denominated Epiclassic between AD. 800-1200 corresponds to a brief flowering of secondary-states that grew with the collapse of great cities such as Teotihuacan and Monte Albán (López-Austin & López-Luján, 2014). By 1960 the radiocarbon method began to be employed, but due to the relatively high cost, the poorly constrained laboratory techniques or the lack of a rigorous sampling methodology, some aberrant dates were obtained and consequently unreliable sequences were developed. Wolfman (1990b) visualized the archaeomagnetic dating as a great tool to provide an unattainable precision for the chronometric results solving cultural-historical problems. He then published the first directional secular variation for Mesoamerica with samples of twelve sites in Mexico, two in Guatemala, one of Honduras and six in El Salvador. A total of 81 burned samples were measured in the Wolfman research and only one directly related to a radiocarbon date.

A compilation of previously available results for Mexico is here reported, 35 of Wolfman, 39 published in refereed journals, 12 of them unburned samples that includes 4 of pictorial origin. 38 samples complete the catalog of 112 archaeomagnetic directions to build upon a reliable PSV curve for central and southem Mexico. For each individual study, the main information has been detailed, including the field sampling procedures, laboratory treatment and archaeological and chronological information. Rock magnetic studies have been carried out to identify the main magnetic minerals and their thermal stability. In addition, these data may largely contribute to better constraining the variation of the Earth’s magnetic field in the North and Central Mesoamerica during the last two millennia.

2. Archaeomagnetic studies in Mexico

The directional component of the geomagnetic field from Preclassic to Postclassic (AD. 1-1200) recorded in burned materials of 12 sites of Mexico were reported by Wolfman (1990b). The site locations are mentioned in Table 1 and Figure 1. The measurements were carried out in the paleomagnetic laboratories of Oklahoma, Pittsburgh and California. In Oklahoma the samples were measured in a Princeton Applied Research (PAR) spinner magnetometer. In Pittsburgh, most of the samples were measured in a Superconducting Technology (SCT) cryogenic magnetometer, and some in a PAR spinner magnetometer. A SCT cryogenic magnetometer and a Schoendsted spinner magnetometer (SSM-1A) were used in almost all cases.

Table 1 Magnetic parameters of each sample. 1st State of sampling, 2nd archaeological site, 3rd name of sample and location, 4th and 5th geographic coordinates of site (Latitude, longitude). 6th if it is burned or unburned (b/ub), 7th the number of specimens employed to the calculus of media n and the total number of the specimens of the sample N. 8th Demag: NRM if the samples were not demagnetized or the AF field in mT until the sample were demagnetized. 9th ,10th and 11th Parameters of the media direction of the sample Dec, Inc and α95 of the Fisher statistic. 12th and 13th PLat (North Latitude) and PLong (East Longitude) of the VGP. 14th Estimated date 15th method of date estimation st - stylistic of ceramics or stratigraphy and rc - related to a radiocarbon date. 16th Archaeomagnetic date obtained by Rendate software (--see Tula text). 17th Reference: thesis or paper that reported the data and a key to identify if the data was Published in Referee Journals (PRJr) or in a thesis or internals reports (uPRr unPublised in Referree Journals) (continued in next page). 

STATE Site Sample Site lat N Site long W b/ ub n/N Demag Dec Inc a95 PLat PLon Estimated Date Radiocarbon date( rc) Stylistic datw ( st) Archeomagnetic date Reference
HIDALGO HUAPALCALCO 539 Feat. 30 Rm.2 20.1 261.6 b 8/8 NRM 358.8 24.2 1.9 82.5 90.4 AD. 750–950 st AD. 850–880 Wolfman, 1990b
PRJr
563 Feat. 30 Wall 1 20.1 261.6 b 9/9 NRM 1.7 25.9 2.5 83.4 67.1 AD. 750–950 st AD. 745–785 Wolfman, 1990b
PRJr
TULA 488 Tula70, Test Pit 1 20 260.7 b 8/8 NRM 346.4 40.8 1.9 76.9 188 AD. 950–1200 st AD. 1095–1140 Wolfman, 1990b
PRJr
598 Tula70, Unit3 Feat3 20 260.7 b 9/9 NRM 344.1 34.6 2.4 74.9 170.2 AD. 950–1200 st AD. 1140–1190 Wolfman, 1990b
PRJr
415 Palacio Quemado, E Wall s415 20 260.7 b 8/8 NRM 322.4 50.5 3.9 54.5 194.8 AD. 1150–1200 st -- AD. 1169–1171 Wolfman, 1990b/revised Martínez- Miranda, 2013
440 Palacio Quemado, E Wall s440 20 260.7 b 8/8 NRM 345.5 30.4 1.5 75.8 158.2 AD. 1150–1200 st -- AD. 1160–1190 Wolfman, 1990b/ revised Martínez- Miranda, 2013
611 Palacio Quemado, E Wall s611 20 260.7 b 8/8 NRM 345 34.4 1.2 75.8 169.4 AD. 1150–1200 st -- AD. 1160–1190 Wolfman, 1990b / revised Martínez- Miranda, 2013
613 Palacio Quemado, E Wall s612 20 260.7 b 8/8 NRM 347.3 36.1 1.1 78 173.5 AD. 1150–1200 st -- AD. 1160–1190 Wolfman, 1990b / revised Martínez- Miranda, 2013
612 Palacio Quemado, E Wall s613 20 260.7 b 7/9 NRM 346.4 35.7 2.5 77.2 172.5 AD. 1150–1200 st -- AD. 1160–1190 Wolfman, 1990b / revised Martínez- Miranda, 2013
TULA 785 Palacio Quemado, E Wall s613 20 260.7 b 9/9 NRM 342.2 42.4 3.4 72.9 189.4 AD. 1150–1200 st -- AD. 1068–1098 Wolfman, 1990b / revised Martínez- Miranda, 2013
TU06 Shire Hall 2 20 260.7 b 5/10 100 351.1 28.1 2.2 80.3 143.5 AD. 1160–1190 st AD. 1100–1200 Martínez- Miranda, 2013
uPRJ
TU17 Floor W lobby Unit 5 20 260.7 b 10/12 100 339.8 32.6 8.6 70.8 168.7 AD. 1160–1185 st AD. 1100–1200 Martínez- Miranda, 2013
uPRJ
TU22 W floor of R3 20 260.7 ub 7/12 100 346.6 34.4 9.4 77.3 169.8 AD. 1160–1190 st AD. 900–1150 Martínez- Miranda,2013
uPRJ
TU23 Floor W lobby 20 260.7 ub 8/15 100 5.1 20.5 14.7 79.7 52.2 AD. 1160–1190 st AD. 1150–1350 Martínez- Miranda, 2013
uPRJ
TU27 Floor and Wall S lobby 20 260.7 ub 8/12 100 358.4 51.6 13.45 77.3 254.9 AD. 1450–1480 st AD. 1100–1350 Martínez- Miranda, 2013
uPRJ
SIERRA DE LAS NAVAJAS SNE1 Tamped soil 20.08 261.4 b 5/9 100 353.3 27 9.6 81.4 130.3 AD. 460–545 st AD. 469–540 Terán-Guerrero, 2016
PRJr
Terán-Guerrero, 2013
SNE2 Tamped soil 20.08 261.4 b 6/8 100 9.6 34.4 8.7 80.9 357.2 AD. 325–550 st AD. 330–342 Terán-Guerrero, 2016
AD. 391–550 PRJr
Terán-Guerrero, 2013
CHIAPAS CHACHI 570 Wall in small md 16.4 267.3 b 8/8 NRM 356.3 10.9 1.9 78.5 105.9 AD. 800–1000 st AD. 885–930 Wolfman, 1990b
PRJr
PANTEÓN 569 45cm below top of md 16.4 267.3 b 8/8 NRM 356.3 17.9 1.5 81.9 114.3 125 BC.–AD. 1 st 25 BC.–AD. 1 Wolfman, 1990b
400–125 BC. PRJr
LOS GRIFOS LG01 16.8 265.6 b 6/17 100 345.8 21.3 9.38 75.1 154.7 AD. 900–1521 st AD. 1385–1445 Fregoso,2010
uPRJr
LG02 16.8 265.6 b 6/14 100 352 55.5 5 69.5 246.8 AD. 900–1521 st AD. 1460–1500 Fregoso,2010
uPRJr
CDMX TEMPLO MAYOR Etapa III 19.44 260.9 ub 8/ 100 339.6 36.2 9.6 70.8 176.2 AD. 1427– 1440 st AD. 1426–1441 Hueda-Tanabe et al. , 2004
PRJr
TLATELOLCO Cui 13 Tlecuil Etapa II 19.45 260.9 b 4 100 339.6 24.6 4.8 69.4 155.4 AD. 1396–1417 st AD. 1391–1401 Guerrero, 2003
uPRJr
Cui 4a9 Tlecuil Etapa IVB 19.45 260.9 b 4 100 352.2 48 6.2 78.1 252.9 AD. 1469–1481 st AD. 1468–1474 Guerrero, 2003
uPRJr
CHAPULTEPEC Cha 1a22 kiln 19.37 260.7 b 11/22 100 353.4 32.8 10.4 83.6 158.2 AD. 350–550 st AD. 512–634 López-Delgado et al. ,2011
PRJr
COYOACÁN CHQ1y2 floor 19.35 260.8 b 7/7 100 10.5 30 9.85 79.5 7.2 AD. 600–900 st AD. 599–681 Soler- Arechalde et al. , 2013a
uPRJr
TEMPLO MAYOR TM2601 Cuauhxicalco 19.44 260.9 ub 4/8 100 2 60.2 8.6 68.3 265 AD. 1440–1469 st AD. 1459–1496 Soler-Arechalde et al. , 2012
TM2604 4 th Floor 19.44 260.9 ub 7/8 100 354.3 42.7 9.6 82.5 217.2 AD. 1469–1481 st AD. 1462–1474 Soler-Arechalde et al ., 2012
TM2605 E wall 19.44 260.9 ub 6/8 100 0.5 25.6 9.15 84 76.2 AD. 1440–1469 st AD. 1444–1464 Soler-Arechalde et al. , 2012
TM2606 Arriate 19.44 260.9 ub 7/8 100 4.5 46.1 12.5 81 287.3 AD. 1440–1469 st AD. 1461–1473 Soler-Arechalde et al. , 2012
TMOQ 19.44 260.9 b 7/8 100 0.6 36.8 7.4 88.8 288.6 AD. 1440–1469 st AD. 1461–1473 Soler- Arechalde et al ., 2013b
JALISCO TEUCHITLÁN, GUACHIMONTONES Gu1 y 2 St3 La Joyita B 20.68 256.13 ub 9/16 100 347.7 29.9 3.4 79 31 300 BC .– AD. 200 st 117–112 BC. López-Delgado et al. , 2017
PRJr
Gu3 Stove La Joyita A 20.68 256.13 b 4/10 100 354.9 46.5 8.13 83.1 40 2250+/-50 BP rc 248–77 BC. López-Delgado et al. , 2017
PRJr
Gu4 Floor St8 Circle 2 20.68 256.13 b 4/4 100 358.7 36.6 3.85 74.8 109.6 300 BC.–AD. 200 st 113–100 BC. López-Delgado et al. , 2017
PRJr
Gu5 2nd wall St7 Circle 1 20.68 256.13 ub 7/7 100 8 24.3 8.2 58.9 203.1 AD. 700–900 st AD. 683–771 López-Delgado et al ., 2017
PRJr
Gu6 3rd Wall St7 Circle 1 20.68 256.13 ub 7/7 100 4.2 28.3 8.8 84.4 162.6 AD. 700–900 st AD. 682–758 López-Delgado et al. , 2017
PRJr
Gu7 1st Wall St7 Circle 1 20.68 256.13 ub 3/7 100 351.6 15.4 7.3 75.4 310.8 AD. 700–900 st AD. 751–820 López-Delgado et al. , 2017
PRJr
Gu8 PLatform2 Circle 1 20.68 256.13 ub 5/5 100 329.2 55.8 5.17 75.1 306.6 1870+/-40 rc AD. 116–175 López-Delgado et al. , 2017
PRJr
Gu9 PLatform A Circle 7 20.68 256.13 ub 12/48 100 354 36.4 5.39 82.9 27.6 300 BC.–AD. 200 st 100 BC .– AD. 224 López-Delgado et al. , 2017
PRJr
Gu10 y 16 Intern Central tamped Circle B 20.68 256.13 ub 6/11 100 13.5 47.4 10.8 82.4 207.8 AD. 400–700 st AD. 556–625 López-Delgado et al. , 2017
PRJr
Gu11 Central Oven NW Ball Game 20.68 256.13 b 8/27 100 13.2 48.7 8.73 83.2 138 AD. 400–700 st AD. 427–523 López-Delgado et al. , 2017
PRJr
Gu13y14 Big oven 20.68 256.13 b 6/11 100 353.7 43.8 4.36 83.1 40 AD. 400–700 st AD. 556–625 López-Delgado et al ., 2017
PRJr
Gu15 Big oven 20.68 256.13 b 9/9 100 353.7 32 4.4 74.8 109.6 AD. 400–700 st AD. 530–575 López-Delgado et al ., 2017
PRJr
MEXICO TEOTIHUACAN 317 Teopancazco 19.7 261.2 b 9/9 NRM 7 50 3 79.4 296.9 AD. 425–600 st AD. 360–455 Wolfman, 1990b
PRJr
540 Viking Group 19.7 261.2 b 8/8 NRM 3.9 40.2 3.3 85.2 309.1 AD. 425–725 st AD. 455–510 Wolfman, 1990b
AD. 270–350 PRJr
786 Viking Group 19.7 261.2 b 8/8 NRM 2.1 41.1 3.1 85.7 287.4 AD. 425–725 st AD. 450–520 Wolfman, 1990b
AD. 260–340 PRJr
564 Palace 3 Rm.7 s564 19.7 261.2 b 8/8 NRM 2.4 42.7 3 84.5 284.1 AD. 425–725 st AD. 435–495 Wolfman, 1990b
AD. 250–345 PRJr
TE170 Ciudadela, Conjunto 1D 19.7 261.2 b 8/8 5 2.4 40.8 1.6 85.7 291.9 AD. 425–475 st AD. 465–505 Wolfman, 1990b
AD. 285–330 PRJr
TE171 Ciudadela, Conjunto 1D 19.7 261.2 b 8/8 5 3 39.1 0.6 86.3 309.3 AD. 425–475 st AD. 475–495 Wolfman, 1990b
AD. 295–325 PRJr
MEXICO TEOTIHUACAN CEE2 Ciudadela Conjunto E 19.7 261.2 b 9/9 100 1 38.3 2.8 87.9 287.9 AD. 415–460 st AD. 412–427 Terán-Guerrero, 2016
AD. 550–600 AD. 520– 528 PRJr
Terán-Guerrero, 2013
TECAMAC HT2A Tlecuil Front I-A SII E1 SqJ2 19.6 260.9 b 3/4 100 322.5 41.9 4.9 55 185.3 AD. 1500–1600 st AD. 1474–1487 Saavedra- Cortés,2010
uPRJr
MORELOS XOCHICALCO XO40-52 Acropolis S8 R6 18.83 260.6 ub 6/13 100 302 10 5.6 81.4 47.5 AD. 652–675 st AD. 676–738 Soler- Arechalde and Caballero- Miranda, 2008a
uPRJr
XO60-61 Acropolis S5 south E2 wall 18.83 260.6 ub 16/16 100 1.2 28.7 5.4 85.5 66.8 AD. 652–675 st AD. 677–752 Soler- Arechalde et al., 2008b
uPRJr
XO30-32 S2 Sector G 18.83 260.6 ub 13/15 100 351 14 3.3 78.2 85.5 AD. 664–723 st AD. 716–768 Soler- Arechalde and Caballero- Miranda, 2008a
uPRJr
XO7-8 West Altar Observatory floor 18.83 260.6 b 10/10 100 341 20 9.16 69.8 148.4 AD. 980–1025 st AD. 967–1031 Hueda-Tanabe and Soler- Arechalde, 2001
uPRJr
XO11 Acropolis wall 18.83 260.6 ub 8/8 100 352 31 13.43 82.1 156.4 AD. 980–1025 st AD. 1017– 1115 Hueda-Tanabe and Soler- Arechalde, 2001
uPRJr
OAXACA BRAWBEHL 408 Feat 69-27 16.9 263.7 b 8/6 NRM 357.3 36 2.9 86 224.2 250 BC.–AD. 200 st AD. 60–120 Wolfman, 1990b
PRJr
LAMBITYECO 318 Feat 68-24 16.9 263.7 b 8/7 NRM 1 15.2 1.2 80.8 77.5 AD. 700–800 st AD. 700–730 Wolfman, 1990b
PRJr
319 Feat 69-2 Md. 190 16.9 263.7 b 8/7 NRM 348.9 27.7 2.9 79.1 163.8 AD. 900–1200 st AD. 1049–1090 Wolfman, 1990b
CA 1200? PRJr
321 Md 190 16.9 263.7 b 8/7 NRM 348.3 29.8 2.7 78.7 170.7 AD. 900–1200 st AD. 1055–1100 Wolfman, 1990b
CA 1200? PRJr
407 Md 190 Zone B 16.9 263.7 b 8/8 NRM 348 32.6 3.4 78.5 179.6 AD. 900–1200 st AD. 1070–1155 Wolfman, 1990b
CA 1200? PRJr
MONTE ALBÁN 541 Md.88 Baked area No.11 17 263.3 b 14/16 NRM 354.6 30.4 2.6 84.8 166.7 AD. 400–700 st AD. 565–600 Wolfman, 1990b
PRJr
744 Cerro Atzomba, Patio E 17 263.3 b 8/8 NRM 354.9 34.2 3 84.8 193.9 AD. 400–700 st AD. 510–575 Wolfman, 1990b
PRJr
TIERRAS LARGAS 527 Area A Feat. 11 17.1 263.2 b 8/8 NRM 355.4 16.3 2.1 79.7 109.4 AD. 700–1200 st AD. 645– 680 Wolfman, 1990b
AD. 895– 940 PRJr
529 Feat. 2 Hearth 1 17.1 263.2 b 8/8 NRM 354.8 16.9 1.9 80.2 114.9 AD. 700–1200 st AD. 635–670 Wolfman, 1990b
AD. 900–945 PRJr
TOMALTEPEC 749 Feat.3 17 263.3 b 8/8 NRM 0.2 39.2 2.5 84.8 265.8 250 BC.–AD. 200 st AD. 245–305 Wolfman, 1990b
PRJr
754 Floor A5 17 263.3 b 6/8 NRM 359.4 35.1 1.7 87.6 250.5 250 BC.–AD. 200 st AD. 55–85 Wolfman, 1990b
PRJr
PUEBLA CERRO ZAPOTECAS 596 Md.2 Excav.A, Lev.6 19 0 261.7 b 8/8 NRM 0.7 30.4 1.9 87.3 66.9 AD. 500–900 st AD. 785–820 Wolfman, 1990b
PRJr
MANZANILLO 783 N milpa, Sec.2 19 261.8 b 7/8 NRM 359.8 38.5 2.6 87.3 258.6 AD. 350–500 st AD. 470–530 Wolfman, 1990b
AD. 245–315 PRJr
784 Sq. 55AA 19 261.8 b 8/8 NRM 2.8 39 0.8 86 302.5 AD. 350–500 st AD. 475–495 Wolfman, 1990b
AD. 295–325 PRJr
QUINTANA ROO DZIBANCHÉ DZ1 S 2 18.6 271.2 ub 4/8 100 313.3 38.5 13.3 46.2 193.5 AD. 540–650 st AD. 274–316 Straulino-Mainou et al. , 2016
PRJr
DZ3 East. Building Small Acropolis 18.6 271.2 ub 5/10 100 359.4 55.6 15.4 72.5 269.6 AD. 550–600 st AD. 422–521 Straulino-Mainou et al. , 2016
PRJr
DZ4 North Building Small Acropolis 18.6 271.2 ub 6/10 100 49.5 65 9.4 40.8 314.5 AD. 550–600 st AD. 463–508 Straulino-Mainou et al. , 2016
PRJr
TLAXCALA XALASCO XA4 Floor early Xolalpan 19.41 262.2 ub 6/6 100 358.8 32 8.2 87.6 111.3 AD. 325–415 st AD. 330–393 Terán-Guerrero, 2016
AD. 399–410 Terán-Guerrero, 2013
PRJr
XA7 Floor early Xolalpan 19.41 262.2 b 8/8 100 341.3 28.5 9.6 71.7 161.8 AD. 540–720 st AD. 540–589 Terán-Guerrero, 2016
AD. 651–720 Terán-Guerrero, 2013
PRJr
VERACRUZ LA JOYA Lj26A-29B East Platform Pre Classic Oven wall 19.1 263.8 b 7/8 100 12.5 25 6.8 76.6 18.3 BC. 400–170 rc BC. 400–170 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
Lj30A-33B East Platform Pre Classic Oven floor 19.1 263.8 b 9/9 100 4.7 29 8.3 84.3 31.7 BC. 400–170 rc BC. 400–170 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
LJ11 Pyramid Pre Classic Oven wall 19.1 263.8 b 5/5 100 348.8 17.9 7.6 75.3 132.9 BC. 350–300 rc BC. 350–300 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
LJ12A-15B North Platform St II floor 19.1 263.8 ub 5/6 100 352.2 46 5.9 79 224.5 AD. 230–410 rc AD. 420–440 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
VERACRUZ LA JOYA LJ16A-19A North Platform St II floor 19.1 263.8 b 3/4 100 349.8 38 7.5 80.2 188.9 AD. 230–410 rc AD. 337– 360 Aguilar-Parra and Morales-Sánchez, 2011
AD. 406–430
uPRJr
LJ20A-25G North Platform St I & II floor 19.1 263.8 b 13/13 100 323.9 56.6 8.4 53.7 211.4 AD. 230–410 rc AD. 304–325 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO50 North Platform St I & II floor 19.1 263.8 b 16/16 100 352.1 37 2.9 82.4 187.2 AD. 230–410 rc AD. 409–427 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO37 East Platfotm St IIIA Floor 1 19.1 263.8 b 1/1 100 359.9 39.9 7.1 86.4 262.4 AD. 380–580 rc AD. 423–432 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO38 East Platform St IIIA Fl. 2 19.1 263.8 b 1/1 100 348.4 23.1 5.7 76.8 143.4 AD. 380– 580 rc AD. 365–420 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO39 East Platform St IIIA Floor 3 19.1 263.8 b 2/2 100 342.8 32 5.3 73.6 170.6 AD. 380– 580 rc AD. 327–371 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO40 East Platform St IIIA inf floor 19.1 263.8 b 10/12 100 353.7 38.2 3.3 83.6 197.1 AD. 400–570 rc AD. 412–429 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO41 East Platform St IIIA inf floor 19.1 263.8 b 8/8 100 347.7 36 4.9 78.4 180.3 AD. 400–570 rc AD. 408–425 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO42 East Platform St IIIA inf floor 19.1 263.8 b 3/3 100 349.1 28.3 6.4 78.8 154.5 AD. 400–570 rc AD. 340–422 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO43 East Platform St IIIA inf floor 19.1 263.8 b 6/6 100 348.4 34.4 6.9 79 174.8 AD. 400–570 rc AD. 402– 424 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO44 East Platform St IIIA inf floor 19.1 263.8 b 6/8 100 352.6 29.4 6 82.2 149.7 AD. 400–570 rc AD. 353–423 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
JO45 East Platform St IIIA inf floor 19.1 263.8 ub 11/12 100 355.9 42.2 7.1 83.5 229 AD. 400–570 rc AD. 415–435 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr
Jo01-Jo22 East Platform St V-VI Floor 19.1 263.8 ub 22/22 100 356.7 39.1 3.1 85.7 219 AD. 400–570 rc AD. 700–1000 Aguilar-Parra and Morales-Sánchez, 2011
uPRJr

Figure 1 Location of the archaeological sites in Mexico sampled for archaeomagnetic research. 

Most directions of the Natural Remanent Magnetization (NRM) showed good clustering with α95 less than 4° and their temporalities consistent with other chronological contexts. Alternative-field demagnetization was done in Oklahoma and Pittsburg laboratories using over 10 samples, only 4 of Teotihuacan. With the 35 data samples from of Mexico in addition to the 29 samples from Guatemala, El Salvador and Honduras, Wolfman constructed the first secular variation curve for Mesoamerica. All the samples were dated by architectural style, ceramics or stratigraphy, which potentially decreases the accuracy of the curve.

2.1. Sites previously sampled by Wolfman

Chiapas State

Chachi y Panteón (16.4°N, 267.3°W). Site located at Maya lowlands of Chiapas, in the Central Depression occupied by Mixe-Zoque groups since 125 BC. to AD. 1000. Two samples were taken, 569 of earlier occupations and 570 of the latest.

Hidalgo State

Huapalcalco (20.1°N, 261.6°W). A site with its major development during the Epiclassic (AD. 700-900) due to the obsidian exploitation under Teotihuacan influence is considered as the precedent of Tula. Two samples were taken here from this period: samples 539 and 563.

Tula (20°N, 260.7°W). The capital city of the Toltecs, a Mesoamerican civilization that was developed between AD. 850 until AD. 1150. Wolfman sampled between 1969 and 1972, accepting that the chronology of the site ended around AD. 1000. New evidences and radiocarbon data allowed to expanding the chronology, related to samples 415, 440, 611, 613, 612 and 785, initially rejected by Wolfman. Samples accepted by Wolfman were 488 and 598.

Oaxaca State

Brawbehl (16.9°N, 263.7°W). This is the first settlement of Tlacolula Center, Valley of Oaxaca. A sample stratigraphically related to the time span 250 BC. to AD. 200 was taken, its number is 408.

Lambityeco (16.9°N,263.7°W). Site located in the Valley of Tlacolula and belonging to the Central valleys of Oaxaca. The age of this site seems to be contemporary with Monte Alban specialized in salt production. Its greatest splendor was during the Postclassic (AD. 800-1200), coinciding with the decline of Monte Alban. Four samples were obtained from Epiclassic to Postclassic: 318, 319, 321 and 407.

Monte Alban (17.0°N, 263.3°W). Zapotec site that dominated the central valleys of Oaxaca during the Classic (AD. 400-800). Two samples of this period were taken: 541 and 744.

Tierras Largas (17.1°N, 263.2°W). Formative-period site located in the Etla Valley of Oaxaca with the evidence of occupation until the Postclassic. Two samples of Postclassic (AD. 700-1200) were sampled: 527 and 529.

Tomaltepec (17.0°N, 263.3°W). Formative site of the central valleys of Oaxaca (200 BC.-AD. 250). Two samples were collected from this period: 749 and 754.

Puebla State

Cerro Zapotecas (19.0°N, 261.7°W). Epiclassic site (AD. 650-900) located west of Cholula, that grew with the latter’s decay. Sample: 596.

Manzanillo (19.0°N, 261.8°W). Located to the SW of Cholula, its remains correspond to a Classic site (AD. 350-500). Sample: 784.

State of Mexico

Teotihuacan (19.7°N, 261.2°W). This is one of the largest centers of Mesoamerica, it has an area of 20 km², large pyramids, ceremonial, administrative and residential areas where more than 100000 people lived. The population was multiethnic and five principal stages of occupation have been determined since AD. 1 to 650. The city was divided into the ceremonial area, and several neighborhoods as Teopancazco and Xalla among others. The ceremonial area and Teopancazco were sampled in 2000. During different excavation campaigns such as 2001, 2003 and 2005 more samples of these areas were taken. Samples of Wolfman are 317, 540, 786, 564, TE170, TE171, TE172, TE173, TE176.

2.2. Sampled sites since 1999 or revisited

Chiapas State

Los Grifos (16.8°N, 265.6°W). This is a rocky shelter with occupation from the Formative to the Postclassic. Two samples of the Postclassic yielded good results. Three samples from the Formative also showed good records but due to their temporality (8800 years BP) they were not reported in this work. Samples: LG01 and LG02.

Hidalgo State

Tula (20.0°N, 260.7°W). Revisited. New explorations and radiocarbon data suggest its chronology reaches at least until AD. 1200. 23 new samples from burned and unburned stuccos were taken in the area during 2010, only 5 with good results, 2 of them unburned with α95 less than 15. The low success rate of these samples might be caused by the low content of magnetic minerals, due to the abundance of limestones or because of the intense weathering, as a result of the industrial pollution, given that even samples with clear evidence of high temperatures do not record the magnetization. The samples with good results come from the 2010 excavation: TU06, TU17, TU22, TU23.

Sierra de las Navajas (20.8°N,261.4°W). One of the principal sites that provided obsidian to Teotihuacan since Tlamimilolpa era. It is located 50 km NW of Teotihuacan, in Hidalgo State and its remains are evidence that it was a large center to exploitation, work and distribution of obsidian. Ceramics of Tlamimilolpa, Xolalpan and Metepec (AD. 200-600) were recollected. Four oriented fragments belonging to burned soils were sampled in 2006. Samples: SNE1 and SNE2.

Jalisco State

Guachimontones (20.68°N, 256.13°W). Guachimontones of Teuchitlán is an archaeological site housed in a lake basin within the valleys of the Tequila volcano, West of Mexico. The site is characterized by circular structures of monumental size surrounded by platforms that were built with masonry, a mixture of rocks and fine clays. Two exhaustive sampling of detailed stratigraphic sequences were done in 2005 and 2009. Sixteen samples from the Pre-classic to the Epiclassic (300 BC.-AD. 900) were taken showing good agreement with the stratigraphy, ceramics and radiocarbon dates. Samples: Gu1y2*, Gu3, Gu4, Gu5, Gu6, Gu7, Gu8, Gu9, Gu10y16*, Gu11, Gu13y14* and Gu15 (*two samples but processed together).

Mexico City

Templo Mayor of Tenochtitlan (19.44°N, 260.9°W). Tenochtitlan is the city founded by the Mexicas in 1325, its different stages of evolution were marked by its different governors or tlatoanis. The site was sampled in 2000, but only one sample gave a good result. In 2012 a new excavation produced four samples with better results of two different stages. Samples: etapa III, TM2601, TM2604, TM2605 and TM2606.

Tlatelolco (19.45°N, 260.9°W). City located Northwest of the Templo Mayor of Tenochtitlán. This place was built in the year of 1337 by a group of Mexicas that left Tenochtitlán, and its constructive evolution is also marked by its governors. Two samples of burnt stucco are reported: Cui13 and Cui 4a9.

Chapultepec (19.37°N, 260.7°W). Hill located at West of Mexico City center. In 2004, remains of Teotihuacan-type habitation units were are located on the south slope of the hill. Ceramics of the Metepec and Coyotltatelco periods (AD. 550-900) were also found. Burned material of the surface of a kiln was sampled and identified like Cha1a22.

Coyoacan (19.37°N, 260.7°W). Postclassic (AD. 600-900) vestiges of a residential unit very damaged due to the construction of a “tlatel”, artificial fill to gain ground to the lake. Sample: CHQ1y2.

Morelos State

Xochicalco (18.83°N, 260.6°W). The city of Xochicalco is a fortified settlement of Epiclassic (AD. 600-1100). It is one of the cities that emerged due to the fall of Teotihuacan. Its location over a 300 m hill allowed it to control the trade networks between Morelos, Oaxaca and Mexico Basin. The first sampling of the site was in 1999, and new excavations and sampling were done in 2004, 2006 and 2007. Samples: XO40-52, XO60-61, XO30-32, XO7-8 AND XO11.

State of Mexico

Teotihuacan. (19.7°N, 261.2°W). Revisited. Samples: Tp2, Tp3, Tp8, Xal1,2, 3, 4, X1, 2, 3, 4, 5, X6, 7, Tp73, Tp38, 39, 40, 41, Tp78, Tp30-31, Tp32-34, Tp75, Tp84, Tp77, CQE1, CQE2, CQE3, CEE2.

Tecama (19.6°N, 260.9°W). It was founded in AD. 1200 by the Mexicas during their pilgrimage to Tenochtitlan. Two occupation stages were sampled: Azteca III (AD. 1300-1500) and Azteca IV (AD. 1500-1600). Sample: HT2A.

Quintana Roo State

Dzibanché (18.6°N, 271.2°W). Maya site occupied since 300 BC. to AD. 1500. During the Classic (AD. 450-700) was governed by Kaan dynasty. The samples come from murals taken from the main group of buildings, where two constructions of Classic stages were identified. The principal component of the red pigment is hematite. It was the first sampling of murals for archaeomagnetic studies in the Maya area. The sampling was done in 2014. Samples: DZ1, DZ3 and DZ4.

Tlaxcala State

Xalasco (19.41°N, 262.2°W). Site occupied by teotihuacanos since AD. 100 to 700. Five unburned stucco samples were taken in 2008, two gave good results: XA4 and XA7.

Veracruz State

La Joya (19.1°N, 263.8°W). La Joya is the capital of a political entity of the so-called Central Veracruz culture descendant of the Olmecs; a major site built of stamped earth, dating from 400 BC. to AD. 1000. The samples come from oven walls, burned floors and only two from unburned floors of two periods of excavation: 2005 and 2009. Samples: Lj26A-29B, Lj30A-33B, LJ11, LJ12A-15B, LJ16A-19A, LJ20A-25G, JO50, JO37, JO38, JO39, JO40, JO41, JO42, JO43, JO44, JO45 and Jo01-Jo22.

3. Methods

3.1. Sampling

The locations of the 40 new structures that are reported in this paper are shown in Figure 1 (geographic coordinates are shown in Table 1). Most of the structures are stuccos exposed to fire, oven or hearths (44 samples). Between 8 and 12 specimens were collected employing a wooden cylinder and oriented with a Brunton compass. In some cases, unburned stucco was also sampled because it was proved that they have a magnetic sedimentary fabric whose magnetic signal was enhanced due to the volcanic scoria and cinder that was added to the mortars (Hueda-Tanabe et al., 2004).

3.2. Magnetic measurements

The NRM direction and intensity were measured with an AGICO JR6 magnetometer. Alternate Fields (AF) stepwise demagnetization was carried out over 8 to 12 steps until 100 mT in a Molspin demagnetizer to determine the main remanence components and stability of magnetization.

3.3. Rock magnetic properties

Hysteresis measurements and Isothermal Remanent Magnetization (IRM) cycles were performed using an AGFM Micromag magnetometer (Princeton Measurements Corp.) with maximum applied field of 1.2 T. Hysteresis parameters after paramagnetic correction were obtained: saturation magnetization (Ms), saturation remanence (Mrs) and coercitive force (Hc). IRM acquisition was measured for determination of coercitivity of remanence (Hcr). Anisotropy of Magnetic susceptibility (AMS) was measured in an AGICO´s Kappa bridge KlY2. This study was carried out to determine the magnetic fabric for unburned stuccos. In many sites of Mexico, cinder and volcanic scoria was added to the mortars and the anisotropy could reveal the preferred orientations when the stucco dries. We expected a sedimentary fabric, with the minor axes clustered and perpendicular to the plane of deposit. This fabric will allow inferring if the magnetization of unburned stuccos is of a sedimentary origin and if the measured direction is of a primary character.

4. Results

Many of the new data reported now are included in Bachelor and Master theses of students from Physics, Archaeology and Earth Sciences areas since 2003, whose paleomagnetic experiments and measurements were performed in the Paleomagnetic Laboratories of the Geophysics Institute of the National University of Mexico (CDMX and Morelia). Other data were reported in unpu blished Reports requested by and delivered to the excavation projects headed by the INAH. These reports allow access to data from which there are no digital versions.

In many cases, specimens have a linear and univectorial component of magnetization and the characteristic remanent magnetization (ChRM) may be easily determined as may be observed in examples shown on Figure 2 for well heated and unburnt structures. Principal component analysis was used to get the primary magnetization direction of each sample. Fisher statistics was applied to obtain the mean direction of the samples (Fisher, 1953).

Figure 2 Stereonet, Vectorial Diagram and Demagnetization spectra of representative samples of unburned (TM2601) and burned (CQE1 and Gu15b) stuccos. 

The resulting data are listed in Table 1 and some stereonet examples are shown in Figure 3. We only consider acceptable the samples with α95 less than 10 and until 15 in the case of the unburned stuccos. Nine samples of this type are included in the present catalog belonging to some well identified archaeological contexts and with archaeomagnetic dates that correspond with the chronology of strata.

Figure 3 Stereonet of Mean characteristic magnetization of the unburned samples: Gu1y2, Gu5, TM2604, Xal4, JO01-22, TP78 and of burned samples: Gu13y14, SNE2, TU6, TU17, HT1, LG02. 

Some hysteresis and IRM cycles that exemplify the behavior of many of the samples are reported in Figure 4. The behavior observed corresponds to poor Ti titanomagnetites. Pseudosingle domains are preponderant in the modified Day diagram (Day et al., 1977) by Dunlop (2002) (Figure 5).

Figure 4 Hysteresis and IRM cycles of the samples Gu10, TU04, Tp30. 

Figure 5 Day diagram of representative samples of Teotihuacan: Ciudadela and Xalla, Sierra de las Navajas, Xalasco, Guachimontones, Tlatelolco, Chapultepec and Xochicalco. 

Temperature-dependent magnetic susceptibility experiments carried out in a Bartington MS2 furnace indicate low-Titanium Titanomagnetites as the principal magnetic carrier. Hematites sometimes co-exist but their contribution in remanent magnetization appears to be minor.

Some examples of the AMS of unburnt and burned stuccos could be observed in the Figure 6. All of the magnetic fabrics are of sedimentary type supporting the hypothesis that the unburned stuccos can record the direction of the geomagnetic field at the time of deposition. Burned samples: CQE1, Tp30 to Tp59 of Teotihuacan and Tu05, 06y7 of Tula. Unburned samples: Tu23 of Tula, Gu10 of Teuchitlán and Jo45 of La Joya.

Figure 6 Magnetic Anisotropy Susceptibility of the burned samples: CQE1 of Teotihuacan TU05,06 & 7 of Tula, TP30 to TP59 of Teotihuacan and Gu10 of Teuchitlan. Anisotropy of Magnetic susceptibility of unburned samples: TU23 of Tula and JO45 of La Joya. (circles - minimum - k3, square - intermediated- k2, triangle -maximum - k1). 

The archaeomagnetic dates of Wolfman (1990b) were obtained from the curve that he constructed following the distribution of the VGPs and their chronological order based on stratigraphic consideration, ceramics and architecture style. Wolfman proposed two curves: one from AD. 1 to 300 and the other from AD. 300 to 1200.

The curves have a gap between AD. 100 to 300 and between AD. 915 to 1060, because there is a lack of data for these periods. The dating was performed by the intersection of the curve with the direction considering its error (α95).

The secular variation curve from 50 BC. to AD. 1600 obtained in the year 2000 for the archaeomagnetic dating, included the Wolfman data (1990b) from Mexico, Salvador and Guatemala, as well as the lava flow of Xitle volcano (100 BC.-AD. 60) data of Urrutia-Fucugauchi (1996) and the stalagmite data DAS2 (AD. 750-1975) of Latham and co-workers (1986). We employed the crossing point technique (Le Goff et al.,2002; Noel and Batt,1990) to get the intersections with the curve and achieve the dating. To better constrain the dates, stratigraphic restrictions were considered. The whole dataset was reduced to Teotihuacan (19.7°N, 261.2°E) because the greatest number of samples comes from this emblematic site.

In 2010 with the publication of the software Rendate (Lanos, 2008) a new curve was modeled with cubic splines and the previous directions were processed obtaining better age restrictions. Figure 7 shows the secular variation curves obtained. Most of the new excavation projects have been taking samples for radiocarbon dating improving the local chronologies (Beramendi et al., 2009) providing new data to complete and expand the secular variation curve of central and south Mexico.

Figure 7 Previous Secular variation curve reduced to Teotihuacan (19.7N,261.2E) with their errors ΔI and ΔD. The curve includes geological and archaeomagnetic data. 

Table 1 compiles all the information concerning the location of samples, and their features: burned or unburned (b/ub), number of specimen employed to calculate the statistical means n, the total number of the specimens in the sample N. The Demag column indicates NRM if the samples were not demagnetized or, the maximum peak demagnetizing field in mT. Dec, Inc and α95 are the parameters of the mean direction of the sample resulted from the Fisher statistic; plat and plong are the paleolatitude and paleolongitude of Virtual Geomagnetic Poles (VGP). Estimated date is the date of the sample assigned by ceramic style, stratigraphy (st) or radiocarbon date (rc) related. Archaeomagnetic date is the date obtained by Rendate software. A key to identify the data Published in Referee Journals (PRJr) or the data of thesis and internals reports (uPRr unPublished in Referee Journals). As can be observed the mean α95 of unburned samples is 8.5 and usually greater than 4°. For unburned samples we accept α95 values less than 15° because of the type magnetization and potential inclination error. In all cases of unburned stuccos, the magnetic fabric has been measured confirming the sedimentary fabric (Figure 6).

5. The PSV curve for Central Mexico

The early proposed curve has been improved by including only data supported by dates obtained by other alternative methods, in our case only radiocarbon data are available. The stalagmite data (Latham et al., 1986) have been removed due to controversy in their records. The data of the Xitle (Urrutia-Fucugauchi ,1996) was also removed to include only archaeomagnetic samples.

The new curve presented includes the archaeomagnetic data of Wolfman (1990b) and those of the researches carried out in the Laboratory of Paleomagnetism of the UNAM (located in CDMX) and of Morelia Laboratory, the current National Archaeomagnetic Service since 1999, all of them compiled in Table 1.

Fisher’s statistic mean-directions and VGP poles were obtained every 50 years with a mobile window of 100 years. Table 2 shows the results and Figure 8 shows them in an equal area projection. It is important to point out that more data is still needed in the Preclassic time-span (500 BC.-AD. 200), and for the Postclassic especially after AD. 1100.

Table 2 Mean Fisher magnetic direction of geomagnetic field for Mexico every 50 years, obtained with a moving window of 100 years. Plat: North latitude of VGP, Plong: East longitude of VGP. 

DATE DEC INC a95 R K PLAT PLONG
350 BC. 0 30.2 16.3 3.908 32.65 86.5 81.2
300 BC. 357.2 31 8.4 6.887 52.94 86 123.4
250 BC. 359 35.5 5.8 8.899 79.35 89.1 167.4
200 BC. 359 35.5 5.8 8.899 79.35 89.1 167.4
150 BC. 359 33.2 5.7 8.901 81.18 88.2 112.3
100 BC. 356.1 34.7 5.8 6.945 109.8 86.3 162.6
50 BC. 356.1 34.7 5.8 6.945 109.8 86.3 162.6
AD. 1 356.9 35.3 5.2 7.939 114.3 87.1 167.7
AD. 50 354.4 39.1 7.5 7.874 55.38 84.2 196.9
AD. 100 354.4 39.1 7.5 7.874 55.38 84.2 196.9
AD. 150 354.4 39.1 7.5 7.874 55.38 84.2 196.9
AD. 200 351.7 41.1 5.4 19.5 38.11 81.4 199.3
AD. 250 348.4 43.4 7.7 12.6 30.14 77.9 201
AD. 300 352.3 40.5 5.9 16.57 37.16 82.1 198.1
AD. 350 353.8 38.6 4 20.68 63.22 83.8 191.8
AD. 400 356.6 39.4 2.4 40.55 88.48 85.9 211.4
AD. 450 356.6 39.1 2.3 42.52 87.57 86 209
AD. 500 357.1 38.6 2.6 40.46 73.46 86.6 208.9
AD. 550 357.1 39 2.7 40.41 67.64 86.4 212.5
AD. 600 357.1 39 3.1 35.41 59.59 86.4 212.5
AD. 650 356.1 37.1 5.9 24.04 24.94 86.2 187.3
AD. 700 357.5 33.2 5.6 25.05 26.32 87.2 137.8
AD. 750 359.9 30.7 4.6 19.62 50.43 86.8 82.9
AD. 800 0.1 23.3 4.4 10.91 110.4 82.5 80.5
AD. 850 0.1 23.6 4.8 9.911 101 82.6 80.4
AD. 900 351.7 30.9 4.3 27.35 41.54 81.6 151.5
AD. 950 349 31.9 4.4 22.54 47.48 79.3 160
AD. 1000 347.9 32.6 4.6 20.59 48.6 78.4 163.4
AD. 1050 347.5 33.4 4.6 19.63 51.33 78.1 166.3
AD. 1100 347.6 34.1 4.9 17.66 50.14 78.2 168.4
AD. 1150 347.6 34.1 4.9 17.66 50.14 78.2 168.4
AD. 1200 347.6 34.1 4.9 17.66 50.14 78.2 168.4
AD. 1250 352 55.5 5 5.95 109.57 72.2 239.6
AD. 1300 352 55.5 5 5.95 109.57 72.2 239.6
AD. 1350 351.1 43.2 19 3.877 24.36 80.1 206.4
AD. 1400 354.4 42.3 9.5 8.735 30.13 83 214.8
AD. 1450 354.2 43 7.6 10.73 36.97 82.5 216.9
AD. 1500 353.9 48.1 8.4 9.733 33.68 79.1 231.9

Figure 8 Stereonet of Virtual Geomagnetic Poles for Central and South of Mexico for 300 BC to AD 1500 every 100 years. 

In Figure 9 we can observe the comparison results amongst the available curves for the SW of USA. The employed data are from papers of Eighmy et al., (1990), Lengyel and Eighmy (2002) and Sternberg and McGuire (1990). The data comes from the states of Colorado, Arizona, New Mexico, Arkansas, Missouri, Louisiana and Tennessee. Lengyel and Eighmy (2002) focused on a proposal to solve the problem of damping by the use of the moving window and to the small number of samples in certain periods. Some large differences are observed between AD. 600 to 650 and AD. 925 to 1100 which can be tentatively attributed more to the lack of reliable data in the SW of USA than to the local non-dipole field, but great differences can be observed between AD. 1200 to 1325 where the lack of data is in Mexico. It is evident that more high-quality data supported by radiometric ages are strongly needed to improve the reference curves of Mesoamerica and SW of USA. Special effort should be place on put to the time intervals of 500 BC. to AD. 200 and AD. 1200 to 1325, which represent the major lack of reliable archaeomagnetic results in Mexico.

Figure 9 Polar Secular variation curves of center and south of Mexico and SW of USA from AD 600 to AD 1500. 

Acknowledgment

This work was supported by CONACYT project n° 252149 and partly by UNAM-PAPIIT IN101717.

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Recebido: 08 de Janeiro de 2018; Aceito: 02 de Agosto de 2018

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