Abstract In this work, we present a description of the sedimentary fill of a well-exposed lacustrine succession in the Ecuadorian Andes. The Guayllabamba basin is an intermontane basin located in the Andean range of Ecuador, and part of its sedimentary history is represented by a volcanically influenced c. 100 m-thick lacustrine unit of Pleistocene age. We create a stratigraphic cross-section from the eastern to western lake margins and identify 19 facies that were used to carry out a palaeoenvironmental reconstruction. The Guayllabamba palaeolake was developed in a tectonic depression surrounded by volcanoes and it was filled with sediments derived from the erosion of the volcanic edifices, the reworking of unconsolidated pyroclastic deposits and deposition of pyroclastic currents into the lake. The lake shows a deepening trend, passing from shallow deltaic sedimentation to varved diatomites with turbidites. Abundant ash-fall beds, monolithological pumiceous deltaic sequences and pumice-dominated thick ignimbrites show the impacts of volcanism on lacustrine sedimentation within this basin. Soft-sediment deformation and gravity flow deposits are common owing to the intrabasinal tectonic activity and to the intrusion of a lava body. Aulacoseira -rich diatomites dominate the background lake sedimentation. The outcrops of the Guayllabamba basin are outstanding examples of the interaction between volcaniclastic and lacustrine sedimentation.

Abstract Volcán de Colima, one of the most active volcanoes in Mexico, experienced at least nine flank failures during the last 30 000 years, with catastrophic effects on the environment that implies the formation of temporary dams where lacustrine sediments accumulated for hundreds of years. These lacustrine sequences preserve an exceptional record from which to reconstruct the effect of subsequent volcanic eruptions and, eventually, contemporary environmental and climatic conditions. Here we analyse an Early Holocene lacustrine sequence, named ‘Gypsum King’, which accumulated in a short-lived temporary lake, likely formed by emplacement of the 10 755–11 230 cal years BP Mesa-Yerbabuena debris avalanche. Through detailed analysis of the 1.8 m thick lacustrine sequence ( 14 C ages, sulfur content, grain size), it was possible to identify the 8.2 kyr global climate event and better constrain the Early Holocene main sub-plinian to plinian eruptions of Volcán de Colima. The results presented here highlight the potential to explore sulfur content and abrupt change in grain size in lacustrine sediments as additional proxies to better constrain eruptive phases in volcanic environments. Finally, the Gypsum King sequence provides the first evidence of the 8.2 kyr global climate event along the Eastern tropical Pacific Coast.