Environmental changes in central Mesoamerica in the Archaic and Formative periods

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-025-01039-6 ORIGINAL ARTICLE Environmental changes in central Mesoamerica in the Archaic and Formative periods Margarita Caballero1 Ana María Soler1 · Beatriz Ortega1 · Socorro Lozano-García2 · Donají Montero3 · Esperanza Torres2 · Received: 3 July 2024 / Accepted: 31 October 2024 © The Author(s) 2025 Abstract This study aims to improve the understanding of climatic fluctuations in the southern Basin of Mexico (BM) during the Archaic (11,500–4,000 cal bp) and Formative (4,000–2,000 cal bp) archaeological periods, when early sedentary settlements at the Zohapilco and Atlapulco sites developed from ∼8,000–7,500 cal bp. This study is based on the analysis of diatoms, pollen, microalgae, charcoal, magnetic susceptibility, geochemistry (organic carbon and titanium) and micromorphology in sediments from a section in a 5 m deep trench at Tulyehualco in the southern BM, close to the Zohapilco and Atlapulco archaeological sites. The chronology is based on five radiocarbon dates and on the correlation with two dated tephra layers. Abundant diatoms and microalgae attest for a period of high lake levels during the deglaciation (17,000–11,000 cal bp), followed by lowering lake levels during the Greenlandian (11,000–8,200 cal bp) when summer insolation peaked, and more oxidative subaerial conditions likely caused poor pollen preservation. Micromorphological analysis showed soil development processes and poor diatom and pollen preservation that confirmed subaerial (dry land) conditions during the 8,200 cal bp cold event. Zohapilco and Atlapulco were first occupied during this period of environmental difficulty. Better diatom and pollen preservation suggest a return to wetter conditions at ~ 7,500–6,500 cal bp, but unusually high charcoal concentrations could reflect human impact in the landscape since the mid Archaic. The diatom record showed that the late Formative (2,000 cal bp, 50 bc) abandonment of sites in the BM was associated with a new reduction in lake levels and a sedimentation hiatus. Keywords Holocene · 8.2 ka event · Palaeolimnology · Diatoms · Pollen · Charcoal · Basin of Mexico Introduction Communicated by W. Gosling. Margarita Caballero 1 Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Ciudad de México CP 4560, México 2 Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Ciudad de México CP 4560, México 3 Dirección de Salvamento Arqueológico, Instituto Nacional de Antropología e Historia, Hamburgo 135, Cuahtémoc, Ciudad de México CP 06600, México In central Mesoamerica during the late Pleistocene there was a series of lakes which provided attractive habitats for the megafauna as well as for humans. These lakes provided valuable resources along migration routes and become key areas for human settlement during times of rapid environmental changes at the end of the Pleistocene and during the Holocene, over the last ~15,000 year. Climatic variability during this time was strongly influenced by changes in summer insolation between both hemispheres (Wanner et al. 2015). The early Holocene (Greenlandian 11,500 to 8,200 bp– all ages mentioned in the following are calibrated dates and expressed as bp) was marked by a maximum in summer insolation over the Northern Hemisphere (NH), while the rest of the Holocene showed a decreasing summer insolation trend, but increasing in the Southern Hemisphere. These changes in insolation have been associated with a 13 Vegetation History and Archaeobotany southward migration of the Intertropical Convergence Zone (ITCZ) and a weakening of the NH summer monsoon systems during the Northgrippian (8,200 to 4,200 bp) and the Meghalayan (4,200 bp to present) (Haug et al. 2001; Wanner et al. 2015). On top of this long-term trend, there were short-term climatic fluctuations in the Holocene with cold events such as the one at 8,200 bp, now used as a marker for the transition between the Greenlandian and the Northgrippian (Walker et al. 2019). It is generally accepted that this cold event was caused by a similar mechanism to the Heinrich Stadials during the Late Pleistocene (Hodell et al. 2008; Wanner et al. 2011; Correa-Metrio et al. 2012; Lachniet et al. 2013; Metcalfe et al. 2015; Vieten et al. 2024). This would involve meltwater pulses over the North Atlantic with a reduction in the strength of deep water circulation, cooling sea surface temperatures at tropical latitudes, weakening NH monsoon activity and southwards displacement of the ITCZ. A southward migration of the ITCZ Fig. 1 Location maps; a, The Basin of Mexico (BM) in central Mesoamerica; b, location of the study site (Tuly-15, red star) in the BM and other sites mentioned. 1, Tepexpan (Lamb et al. 2009; Sedov et al. 2010) on the shore of Lago de Texcoco; 2, Lago de Texcoco (Chávez-Lara et al. 2022); 3, Lago de Xochimilco (Ortega-Guerrero et al. 2018); 4, Lago de Chalco (Caballero et al. 2019); 5, Agua El Marrano (Lozano-García and Vázquez-Selem 2005). Dotted line shows the extent of lake deposits, blue stars represent palaeoenvironmental records 13 and a weakening of the Mesoamerican monsoon would have brought drier conditions to Mesoamerica during the Meghalayan and Northgrippian, punctuated by more intense droughts during cold events. These climatic changes could have been of relevance for the development of complex human societies during the Archaic (11,500–4,000 bp) and Formative (4,000–2,000 bp) cultural periods in Mesoamerica (Rosenswig 2015). One of the most important lacustrine areas in central Mesoamerica was the Basin of Mexico (BM, Fig. 1a), which had a key role in the development of the nucleated, stratified societies in this region (Niederberger 1979; Rosenswig 2015; Acosta-Ochoa 2017). Particularly, the lakes in the southern portion of the BM, Chalco and Xochimilco, (Fig. 1b) have provided some of the oldest directly dated human remains in Mesoamerica, such as the “Tlapacoya I” skull, with an age of ∼12,000 bp (Gonzalez et al. 2003), and the “Tlahuac woman”, dated to ~9,400 bp (Serrano Sánchez et al. 2021). Furthermore, these lakes hold evidence of early settlements dating to the mid Archaic (~8,000–7,500 bp, Playa I phase, Figs. 2 and 3), at the well-known Zoahapilco site, on the northern shore of Lago de Chalco (Niederberger 1976, 1979), and the more recently studied San Gregorio Atlapulco, an islet in Lago de Xochimilco (McClung de Tapia and Acosta-Ochoa 2015; Acosta-Ochoa et al. 2021). Even though palaeoenvironmental records in the BM have documented important climatic changes during last 15,000 years, mainly from the lakes Texcoco, Chalco and Xochimilco, (Fig. 1b), their Holocene sediments are often incomplete. For example, some of the records analysed from Lago de Texcoco showed a sedimentary hiatus at the Pleistocene/Holocene transition (Lozano-García and Ortega-Guerrero 1998; Lamb et al (...truncated)