Abstract. ROMAN B, Alvaro and JACKSON S, Donald. DATACIONES POR TERMOLUMINISCENCIA DE ROCAS DE FOGONES DE ASENTAMIENTOS. Datación por termoluminiscencia. Principios de la TL. by. Eduardo LH. on 9 August Comments (0). Please log in to add your comment. Report abuse. *Datacion Radiometrica Paleomagnetismo Datacion por termoluminiscencia. Estratigrafia METODOS DE DATACION Juan Camilo Polaco Valentina Ceballos.
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The field is a massif composed of four large volcanic structures and hundreds of scoria cones, lava domes and maars. This area was in the past covered by a dense forest in whose margins flourished several of the ancient cities of importance in central and southern Veracruz.
Within the forest no enduring archeological ruins have been found; but the present inhabitants of the area frequently find fragments of ceramics and stone that attest to the presence of what could have been small settlements with a seminomadic regime.
Unfortunately the objects found have been removed from their emplacement and are difficult to date. However in the course of our study of the volcanic deposits in the area we found four mudflow deposits containing pre- Columbian pottery objects and shards, as well as charcoal in some of them.
Sections of the deposits were observed in detail and sampled for granulometric analysis. The charcoal samples were dated using standard radiocarbon methods C ; where charcoal was absent the pottery shards were dated with thermoluminescence TL techniques. Since in the area there is no clayey and silty material suitable for production of pottery; the closest and largest prehispanic cities, Tres Zapotes or Matacapaare located to the west of the LTVF. Composed of four large volcanoes and more than cones and maars, it spans approximatelykm2 an area known as La region de los Tuxtlas Los Tuxtlas Region.
Nelson and Gonzalez-Caver dated the rocks of the LTVF, and found that they can be grouped in termoluminiscehcia age groups separated by a hiatus of about 1. Nevertheless researchers such as Verma consider that the origin of the LTVF is not related to the subduction of the Cocos plate thereby the problem of its origin is still unsolved. Due to the fertility of the soils formed from the basaltic rocks and heavy rainfalls, the area covered by rocks of the younger series, is nowadays the center of a daatcion In the past, however, the rainforest covered the entire volcanic field and beyond.
Some 30 km to the east, the city of Matacapan had also a long occupational history.
Smaller archeological constructions have been found to the southeast of the volcanic field and on the western side of Catemaco lake, but none in the area surrounding San Martin Tuxtla Figure 2. However, in that area the villagers have found numerous artifacts in stone and ceramics, which being removed from its original place are difficult to date or conjecture about their emplacement. Looking for evidence about possible pre-Columbian settlements in those areas we were able to find pottery shards and charcoal fragments in four mudflow deposits.
The pottery fragments correspond to the domestic type of pottery, which does not allow its cultural identification, but their age can be determined through thermo-luminescence methods. In this paper we present the general characteristics of the deposits were the objects were found, of the fragments and their ages whenever possible.
We believe this findings are relevant to the historical and environmental studies on the area. The LTVF has a tropical climate influenced by the trade winds of the northern hemisphere, which bring a significant precipitation during the summer season.
Most of the original forest was converted into farmland either to grow sugar cane or pasture for livestock. As mentioned before nowadays an area of The area constitutes a conjunction of the northernmost tropical forest, the temperate forest of central Mexico and the endemic environment. The drainage for the area is provided by numerous streams in a radial pattern with center in San Martin Tuxtla volcano most of them intermittent but also a few perennials fed by the numerous springs in the area.
The soils of the Region, mostly andisols and alfisols, were derived from the basaltic products of the many eruptions in the Field; its formation is very rapid due to the large precipitations and tropical climate Flores-Delgadillo, The landforms of the Region are predominantly lava and scoria domes and cones, maars and four large composite volcanos. In the region of study, San Martin Volcano, the tallest of all, has been classified as shield volcano Simkin and Siebert, and is composed of lava flows, and ash and lahar deposits.
This volcano presented the latest stage of volcanism with an eruptive event inwhich lasted more than 6 months in its explosive stage and about 2 years in an effusive phase Espindola et al. The cones of the study area YVS show height to base diameter ratios between 0.
These values correspond to heights between 20 and m with an average value of 80 m. These data suggests that the cones of this area are less than 50, years old Reinhardt, Figure 1 shows the locations were mudflows with pottery shards were found, these were named: Deposits at those locations exhibit the following characteristics:.
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A few hundred meters to the east of this site Site 2: This deposit contains more abundant potshards and charcoal Figure 3c. The pottery shards are centimeter-sized fragments of very coarse pottery. The proximity to the previous site and the similarity in age suggests that both sites belonged to the same settlement.
Both sites are located close to the margin of an intermittent stream. The grain size distribution of this deposit is shown in Figure 3d. The insert shows some of the fragments collected at this site.
It is located in the outskirts of the village of La Mojarra note that this is not the same town where the famous Stella 1 of early Mesoamerican origin was found, which in Figure 1 appears farther west. The deposit covers the margins of a perennial stream crossed by a road in whose lateral cuts it is exposed Figures 4a, b. It is reddish brown, massive with dispersed fragments of whitish, angular cobbles, and abundant pottery shards, some of which could be reassembled into a complete bowl-like piece of pottery Figure 4c.
A few obsidian blades were also present. However the presence of a horizon of several tens of centimeter blocks gives the impression in some parts of being a debris flow. This deposit is located near Pizatal also spelled Pisatal crater lake, a maar of about m in diameter, and covers an extension on which sugar cane is nowadays planted Figures 5a, b.
The deposit is exposed on the sides of the road, which is leveled every year to facilitate the transportation of the sugar cane by trucks; it is brown, light brown when dry, massive, with some rounded pebbles. The deposit contains many pottery shards, some of them from more elaborate artifacts than dstacion the above deposits, for instance Figure 6c shows what seems to be a bottle stopper in the shape of an animal’s head. Findings like this are frequent, mostly after heavy rains, according to villagers of the nearby towns.
This deposit termoluminiecencia originate from overspills from the Pizatal crater lake, an event that occurred even in recent times. Unfortunately this deposit could not be dated by termoluminiscencka, since we could not find any charcoal sample, and the thermoluminescence results did not provide a reliable age due to the failure of the additive dose procedure, probably as a result of a non-favorable composition of dqtacion ceramic.
This deposit forms the banks of the intermittent Arroyo Toro Prieto stream, and is exposed by a deep trail cutting across the banks and riverbed.
The deposit is brown and massive Figures 6 a, b. It contains small fragments of charcoal and some brittle, centimeter-sized, scattered pottery fragments with very rounded edges Figure 6 c. Even from its appearance this deposit seems to be older than the other deposits. The charcoal samples were collected in aluminum sheets and sent for dating to the Laboratory of Isotope Geochemistry of the University of Arizona, Tucson, Arizona, USA where they were dated using beta counting techniques Table 1.
The samples were collected from the inside the deposits at about 30 cm from the surface exposed to the light and deposited immediately in thick black plastic bags. The U, Th and K concentrations in the matrix surrounding the samples were measured in-situ for annual dose rate determinations in with a portable gamma ray spectrometer.
The laboratory treatment of the samples is explained in Ramirez et al. In our particular case the correction for water content was made considering water saturation in the samples because of the high rainfall rates at the TVF region. The amount of water in the samples was determined from the difference in weight between dried and water saturated samples. Figure 9 shows the results of the additive dose method for calculation of the equivalent dose Q.
The results for the supralinearity correction are shown in Figure The results of the C and thermoluminescence analyses are shown in Table 1 and Table 2. The pottery shards from Arroyo Toro Prieto and Pizatal did not yield results amenable to sound estimates of the age, except to rule them out as modern. The last age corresponds to the arroyo Toro Prieto deposit and agrees very well with its characteristics, with less, small, rounded and very soft shards suggesting an older age than the age of the other ceramics.
The differences in age are significant but can be attributed to several causes, the C ages were taken from samples of charcoal of unknown origin, probably from logs of aged trees. The presence of the objects described attest to the presence of human activity in the forest. Since the objects are varied, have remained to this day and were located close to riverbeds it is reasonable to assume that the human presence occurred in small settlements in the forest, and that they carried out a seminomadic regime or else more enduring constructions could be found.
The objects themselves indicate that: The age of the deposit Arroyo Toro Prieto falls at the beginning of the classical or late pre-classic period, when the Olmec culture had been reduced to Tres Zapotes Pool, The samples from the other three sites belong to the post classic period well within the era of increasing ruralization of the population in the Matacapan area Santley et al. These data suggest that the occupation of the forest surrounding the San Andres Tuxtla volcano area by small human settlements occurred some years BP and roughly years BP as well.
Some of these settlers were probably driven out of the forest by the volcanic activity of San Martin volcano or any of the hundreds of monogenetic vents in the field.
Although there is no evidence to this claim, but old narratives picked up by this author, it would not be an uncommon episode: However, there is proof that in the last years at least 3 cone and maar forming eruptions occurred near Matacapan, leaving deposits in the site and its surroundings Reinhardt, Due to the heavy precipitation in the area those communities were also subjected to flooding and mudflow hazards. The presence of numerous mudflow deposits in the edifice of San Martin Volcano indicate that this phenomenon is recurrent and continues into our days.
The non-cohesive nature of the deposits indicates that the mass movements are due to unstable non consolidated materials. History of the Native Peoples of the Americas. Journal of Volcanology and Geothermal Research, 1. Climate and climate change in the region of Los Tuxtlas Veracruz, Mexico: Medel y Alvarado L. Constraints on the origin of alkaline and calc-alkaline magmas from the Tuxtla Volcanic Field, Veracruz. Cambridge University Press, Cambridge, U. Mexico, by Thermoluminescence Tl.
Mediterranean Archaeology and Archaeometry. Thesis, Tulane University, pp. Research Paper Series, No. Origins, behavior, and sedimentology of lahars and lahar-runout flows in the Toutle—Cowlitz river system. United States Geological Survey. Paper A, 74 pp. Smithsonian Institution, Geoscience Press Inc.
Extension related origin of magmas from a garnet-bearing source in Los Tuxtlas volcanic field. This is an open-access article distributed under the terms of the Creative Commons Attribution License. Geographical characteristics of the LTVF The LTVF has a tropical climate influenced by the trade winds of the northern hemisphere, which bring a significant precipitation during the summer season.
Characteristics of the Mudflow deposits and objects collected Figure 1 shows the locations were mudflows with pottery shards were found, these were named: Deposits at those locations exhibit the following characteristics: