Geochemistry of last glacial lacustrine sediments in core region of the North American Monsoon, northwest Mexico: Source of biomass, hydrological balance and chemical weathering

Carbon isotopes (δ¹³C_org) in biomass, carbon (δ¹³C_carb) and oxygen (δ¹⁸O_carb) isotopes in authigenic calcite and estimations of chemical weathering of siliciclastic minerals (chemical index of alteration [CIA] and plagioclase index of alteration [PIA]) in lacustrine sediments of the ephemeral Babicora Basin, located within the core region of the North American Monsoon at northwest Mexico, helped to evaluate the source of biomass, variations in hydrological balance and sediment–water interactions during three different marine isotope stages (late MIS 4: ≥65.4–59.5 cal ka BP, MIS 3: ~59.5–28 cal ka BP and MIS 2: ~28–15 cal ka BP) of the last glacial. Comparisons of δ¹³C_org with previously published records of C/N, diatom abundance and fossil pollen indicate that biomass of the late MIS 4 was sourced from C₃ aquatic and land plants. During the MIS 3, the C₃ plants continued to contribute biomass and the influence of lacustrine algae, however, increased during its later part. The water column experienced more evaporation compared to two other MIS stages and sediment–water interactions varied between minimal to moderate (CIA: 49–68). Sediments were transported for longer distances during the wetter intervals and eroded from nearby lithologies during the drier intervals. Interactions between sediments and inflowing water (CIA: 59–65) remained homogeneous during the MIS 2. Source of the biomass, however, was variable. Lacustrine algae and C₃ land plants contributed biomass during the early MIS 2 (~28–19 cal ka BP) and contributions from the C₄ and CAM vegetation slightly increased towards the deglaciation (~19–15 cal ka BP).