Tepexpan Palaeoindian site, Basin of Mexico: multi-proxy evidence for environmental change during the late Pleistocene–late Holocene (original) (raw)
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Geomorphology, 2010
Building up a scenario of Late Pleistocene-Holocene environmental change and human-landscape interactions in Central Mexicoone of the key areas for the natural and cultural history of Americarequires development of local paleoenvironmental reconstructions. We studied the Tepexpan section at the edge of Texcoco a paleolake, near the mouth of Teotihuacan Valley as a multiproxy record of the environmental dynamics at the shore in the Basin of Mexico throughout the period of human occupation. The section is located in an ecotone affected by intensive and variable geomorphic processes and includes lacustrine, fluvial and volcanic sediments as well as paleosols. Our chronological scale is based on 6 AMS 14 C dates from pollen concentrates and paleosol organic matter. The lower segment of the section dominated by the lacustrine sediments yielded pollen spectra; in the upper segment the record is based on the pedogenetic characteristics of paleosols. Different proxies agree in demonstrating the general trend (although some reversals are apparent) of decreasing effective moisture since MIS3: it is reflected first in the increase of herbaceous pollen after 27 ka BP, the decrease of lake level, the cessation of lacustrine sedimentation and beginning of marsh soil development at 10 ka BP and finally, the shift from hydromorphic to dryland semiarid pedogenesis in the Late Holocene. We assume that this trend was climatically controlled, whereas the deposition of sedimentary layers enriched with tephra are related to the pulses of volcanic activity; the pedosedimentary features associated with the upper soil are human-induced. Comparing the proposed scheme of environmental change with the archaeological record we propose that the initial settlers, Late Paleolithic hunters, could have utilized the wet swampy meadows which expanded on the Basin bottom as the lake level lowered and provided the niche for large herbivores during the Pleistocene-Holocene transition. Development of agriculture and the network of permanent settlements are believed to be linked to the formation of well drained soils. In the methodological perspective the study shows the potential of ecotones as highly dynamic and sensitive systems that may archive valuable paleoecological records.
Paleoindian sites from the Basin of Mexico: Evidence from stratigraphy, tephrochronology and dating
Quaternary International, 2014
We present new data on the stratigraphy, dating and tephrochonology at the most important Paleoindian sites in the Basin of Mexico. These include: a) Peñon Woman III, with the oldest directly radiocarbon dated human remains (10,755± 75 yr BP); b) Tlapacoya, with two human crania dated to just over 10 ka BP; c) Tocuila, an important mammoth site with incorporation of fossils and suggested bone tools within the Upper Toluca Pumice (UTP) lahar (volcanic mudflow). The Tocuila site also
Paleosols in the Teotihuacan valley, Mexico: evidence for paleoenvironment and human impact
Revista Mexicana de …, 2003
The Teotihuacan valley, located in the northeastern sector of the basin of Mexico, was settled by approximately 1,100 BC. The first and largest prehistoric city in the Americas developed here in AD 350-550, reaching a population of around 125,000. The demise of the Teotihuacan state is now generally believed to have culminated between AD 600-650. Causes are attributed to global climate change, environmental degradation, economic and/or political upheaval, but no direct evidence has ever been presented to support these hypotheses. The study of paleosols contributes to the understanding of the environmental conditions that prevailed in the Teotihuacan region in order to better comprehend their potential relationship to cultural and economic events in the prehistoric past. The distribution of soils in the region is directly associated with relief. Profiles at Cerro Gordo 3,050 m a.s.l.) and Cerro Patlachique (2,700 m a.s.l.) are associated with forest conditions, where paleosols are characterized by polygenetic profiles with varying degrees of development. The older soils are represented by Luvisols. Soils in lower positions (Cerro Colorado, 2,390 m a.s.l.) are stratified and poorly developed, with evidence of colluvial deposition and erosion. Soils with fluvic properties in the alluvial plain (2,250-2,350 m a.s.l.) are also poorly developed and greatly influenced by erosive processes and intensive accumulation. Those corresponding to the Teotihuacan periods (2,000-1,350 yr BP) show multiple indicators of human impact. Micromorphological evidence indicates intensive agricultural activities (deforestation, burning, compaction, and erosion). The presence of carbonates in underlying strata is related to changes in humidity. Phytoliths identified from the same strata indicate alterations in vegetation through time that reflect variable conditions of temperature and humidity. The results clearly reflect environmental modification by human populations from the initial period of prehistoric settlement up to present. Furthermore, the evidence suggests that a major impact of the prehistoric city on the landscape resulted from unmanaged exploitation of forest resources that provoked intensive erosion and significant changes in the hydric conditions of the region.
Holocene-aged human footprints from the Cuatrocienegas Basin, NE Mexico
Two sets of well-preserved human footprints have been found in tufa sediments in the Cuatrociénegas Basin, NE Mexico, and here we present their U-series dates of 10.55 ± 0.03 ka and 7.24 ± 0.13 ka. The former are the oldest known footprints in Mexico, although their exact location is unknown, the latter form part of a trackway with eleven in situ human footprints. Oxygen (and to a lesser extent) carbon isotope data from the sediments suggest that the tufa with in situ footprints formed during a transition to a wetter (less arid) period, while pollen evidence indicates the basin floor presence of Pecan (Carya) and Willow (Salix sp.) before the onset of regional Chihuahuan Desert aridity. These footprints confirm the presence of humans, possibly nomadic hunter-gatherer groups, which persisted until the 18 th Century AD.
Early-Mid Pleistocene environments in the Valsequillo Basin, Central Mexico: a reassessment
Journal of Quaternary Science, 2016
The Valsequillo Basin in Central Mexico has been of interest due to the presence of megafaunal remains and evidence for early human occupation, but research has been controversial. It has been suggested that extensive and deep lakes characterized the Early Pleistocene environment but sediment exposure is highly fragmentary and reliable dating has been difficult. Here we report, for the first time, Early Pleistocene palaeoenvironmental reconstructions using stable isotopes, diatoms, tephra and pollen. We studied several stratigraphic sections of mainly non-volcanic rocks, containing the 1.3-Ma Xalnene Ash as a stratigraphic marker. The isotope and other proxy data show that topographically low points in the basin were occupied by spring-fed, shallow water lakes during the Early-Mid Pleistocene, with a trend to drier conditions. The basin was a dynamic volcaniclastic environment during this period, with the production of the Toluquilla volcanic sequence and other rhyolitic-dacitic volcanic ashes interbedded with the lake sediments at the sections studied. There is no evidence from the sections for extensive and deep lakes before or after deposition of the Xalnene Ash. Wetter conditions in the basin during the Early Pleistocene would have made it attractive for megafauna.
GEOCHEMICAL JOURNAL, 2009
This paper presents stratigraphy, mineralogy, multi-element geochemistry, organic and inorganic carbon contents in the sediments along a 255 cm long depth profile from Lake Tecocomulco in the north-eastern part of the Basin of Mexico. Mineralogical abundance, elemental ratios, chemical index of alteration (CIA), abundance of CO 3 and C org divide the depth profile into geochemical zones and provide insight to the volcanic eruptions and phases of different paleohydrological events during the last 31,000 14 C yr BP. The dacite to rhyolite air fall tephra pre-date the LGM (ca. 31,000 14 C yr BP) and might be from a Plinian eruption event at the Tláloc volcano located at 60 km in the south-west of the lake. The lake sediments are characterized by higher CIA values and metal contents between ca. 30,000-29,000 14 C yr BP. Between ca. 28,000-25,700 14 C yr BP, sediments have lower CIA values and contain easily weatherable amphiboles. Abundant calcite and low CIA suggest arid conditions during ca. 25,700 and ca. 16,300 14 C yr BP, respectively. Between ca. 16,300 and 3,300 14 C yr BP, the sediments show lower CIA and sediments of the last ca. 3,300 14 C yr BP show highest CIA, C org and higher metal contents. Given the regional nature of this record, we interpret the geochemical history at Lake Tecocomulco in terms of variable precipitation, inflow and aeolian activity.
AbstrAct—The Water Canyon Paleoindian site near Socorro, New Mexico, is directly associated with an extensive buried wetland deposit, or black mat. This landscape-scale feature, which was extant across the late Pleistocene–early Holocene transition, represents the remains of a wetland resource that, during the early Holocene, may have served as an ecological refugium for flora, fauna and Paleoindian groups as other regional water sources disappeared. Today the organic-rich deposit has proved to be an important proxy data archive for environmental , climatic and archaeological reconstructions. Our recent paleoenvironmental reconstruction efforts at the site have focused largely on the period from ~8300 to 11,100 radiocarbon years ago, and have generated a range of proxy data, including dated pollen profiles, stable carbon isotope values, charcoal species identifications, and both faunal and macrobotanical remains. The pollen data currently provide the most robust basis for our paleoenvironmental reconstruction and, together with our chronometric data, affirm that the black-mat forming wetland served as a persistent place of ecological diversity. These findings provide us with provocative glimpses of past environments in a heretofore largely understudied region of the American Southwest, and add to a growing body of Southwest reconstructions that will ultimately enable researchers to compare paleoenvironments and paleoclimates at both local and regional scales.
Late Pleistocene and Holocene Paleoenvironments of Chalco Lake, Central Mexico
Quaternary Research, 1993
In order to establish paleoenvironmental conditions during the late Quaternary, four cores from the Basin of Mexico (central Mexico) were drilled in Chalco Lake, located in the southeastern part of the basin. The upper 8 m of two parallel cores were studied, using paleomagnetic, loss-on-ignition, pollen, and diatom analyses. Based on 11 14C ages, the analyzed record spans the last 19,000 14C yr B.P. Volcanic activity has affected microfossil abundances, both directly and indirectly, resulting in absence or reduction of pollen and diatom assemblages. Important volcanic activity took place between 19,000 and 15,000 yr B.P. when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry, cold climate. During this interval, abrupt environmental changes with increasing moisture occurred. From 15,000 until 12,500 yr B.P. the lake level increased and the pollen indicates wetter conditions. The highest lake level is registered from 12,500 to ca. 9000 yr B.P. Th...
The Water Canyon Paleoindian site near Socorro, New Mexico is directly associated with an extensive buried wet meadow deposit. While extant across the Pleistocene – Holocene transition and into the middle Holocene, this landscape-scale deposit arguably represented a persistent, regional wetland resource, not only for plants and animals, but Paleoindian groups as well. Today, as a black mat, it represents an important proxy data archive for environmental, climatic and archaeological reconstruction. Our recent research efforts at the site have focused largely on the period from 8300 to 9900 radiocarbon years ago, and have generated a range of proxy data, including dated pollen profiles, stable carbon isotope data sets, charcoal species identifications and both faunal and macrobotanical remains. These findings provide us with provocative glimpses of past climates in a heretofore understudied region of the American Southwest.