Abstract/Summary

The Llanos de Moxos in the Bolivian Amazon, the second largest South American wetland, hosts many endemic species and a rich archaeological record that spans the entire Holocene. Despite its ecological and archaeological importance, very little is known about its Holocene environmental history. A growing body of evidence suggests that neotectonics played an important role in shaping its modern landscape and controlling past flooding dynamics, but the chronology and vertical displacements of past tectonic events are still largely unknown. Here, we present new data from a core taken at Lake Oceano, a large ria lake in the northern part of the Llanos de Moxos. To identify changes in the lithology and environment, we performed a battery of analyses, such as XRF scanning, mineralogy, granulometry, C/N and C and N stable isotopes, and also built an age-depth model using eighteen radiocarbon dates obtained from accelerator mass spectrometry (AMS) determinations. Based on the sedimentology and chemical analyses, we identified three major disturbances in the lake sedimentation that we interpret as positive tectonic events (i.e., tectonic uplifts). The first identified event occurred at approximately 13,400 cal yr BP and led to the formation of the lake by blocking the river course. A second uplift event took place around 10,000 cal yr BP, accompanied by a significant change in the geochemistry of the lake sediments. Furthermore, we have verified a third event at 6000 cal yr BP, previously recognized as responsible for the onset of Lake Rogaguado (aprox. 100 km NE of Lake Oceano), one of the largest lakes in South America. Overall, we show that ria lakes can provide key sedimentary archives to reconstruct the past timing and intensity of tectonic events. We discuss the interplay between tectonics and climate, highlighting the connection between tectonics and the region’s flood history, with crucial implications for the interpretation of both archaeological and palaeoecological records throughout the Holocene.