| Summary: | This research revealed the impact of climate, volcanism and humans on the late Holocene evolution of a tropical delta in southern Mexico. Palynological, tephrochronological, limnological, geomorphological and sedimentological techniques have been applied to reconstruct the evolution of the Usumacinta-Grijalva delta coast over the past 6000 years. Observed changes are correlated with climate, volcanism, and land use changes, partly reconstructed from a multiproxy study of sediments from lake Tuspan. The geomorphological and sedimentological study of the extensive beach-ridge plain was supported by LiDAR data, 14C and OSL dating, GPR measurements, grain-size analyses, and chemical fingerprinting of volcanic glass and pumice fragments. The new detailed chronology of the beach-ridge plain established in this study shows that the exceptionally long sequence of around 500 subsequent beach ridges was formed due to ample long-term riverine sediment supply, partly related to a high availability of easily weatherable Los Chocoyos ignimbrites in the catchment of the Usumacinta River. The elevation of the beach ridges appears not to be determined by sea level fluctuations or changes in storm activity as previously accepted, but relates to the variability in fluvial sediment supply, reflecting decadal-scale precipitation changes within the river catchment. A centennial-scale variability in precipitation during the Pre-Classic Period was found that significantly correlates with the North Atlantic δ14C atmospheric record, with a comparable periodicity of ~500 years, indicating an important role of North Atlantic atmospheric-oceanic forcing on precipitation in the Maya Lowlands. A dramatic change from dry to wet conditions occurred during the Middle Pre-Classic period, around the well-known 850 BCE (2.8 ka BP) event. This wet period was likely unfavourable for agricultural intensification in the Central Maya Lowlands, and may have delayed the development of Maya civilization in this area until the start of the Late Pre-Classic ...
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