Sediment geochemistry and facies analysis as tools to interpret the paleolandscape evolution and pre-hispanic settlement dynamics on the eastern shore of Lake Texcoco (Mexico)

Previous studies have shown that prehistoric hunter-gatherer groups and Mesoamerican societies settled on the eastern shore of the former Lake Texcoco. The lake shore was a fluvial-lacustrine landscape shaped by seasonal and long-term transgressions and regressions. However, the basis for linking sedimentary environments to paleolandscapes and pre-Hispanic settlements dynamics is lacking. Thus, we focus in this study on reconstructing sedimentary environments using geochemical and sedimentary facies analyses to study the paleolandscape inhabited by agricultural societies in the Lake Texcoco region. To test this approach, we studied the interface between the San Bernardino and Chapingo Rivers with the lacustrine realm on the eastern shore of Lake Texcoco. We defined sedimentary facies by analyzing their macro and microscopic attributes, as well as using XRD, p-ED-XRF, TOC, C/N, and texture analyses to assess their chemical, mineralogical, and sedimentological characteristics. The combined results allow eleven facies to be assigned to three distinct environments, i.e., lacustrine, transitional fluvial-lacustrine, and fluvial settings. The stratigraphic sections showed a lake transgression with a minimum age of 1293–1242 cal yr BP (657–708 CE) and 1363-1294 cal yr BP (587–656 CE). The absence of archaeological sites in the lower plains during the Late Classic period supports the interpretations of the lake phase. At least two regression phases are interpreted. The first event occurred during the Epiclassic period with a minimum age of 1154–1051 cal yr BP (796–899 CE). The second event has a minimum age of 560–518 cal yr BP (1390–1432 CE), which is consistent with the rise of multiple settlements during the Late Postclassic period. This interpretation is further supported by the increase in settlements during the Postclassic period, probably related to an increase in the variety of natural resources available.