Biome responses to a hydroclimatic crisis in an Early Cretaceous (Barremian–Aptian) subtropical inland lake ecosystem, Northwest China

Abstract

The Early Cretaceous palaeoclimate was characterized by arid–humid alternation and accompanied by a series of short-term extreme environmental events, resulting in significant disturbances to the terrestrial ecosystem. However, the discontinuity of terrestrial geological records leads to a lack of detailed research on the coevolution mechanism of organisms and the environment. This study aims to investigate the response of the late Barremian–early Aptian subtropical lake biome structure to the hydroclimate crisis in the Yin'e Basin based on palynology, macropalaeontology, and geochemistry (i.e., major and trace elements, organic carbon isotopes, and biomarkers). The warm and semihumid climate promoted an increase in the abundance and degree of divergence in the vegetation, and the brackish–oxic conditions of the water column were conducive to the prosperity of aquatic organisms. The early aridification of the climate led to a decline in the lake level and a salinity crisis. The saline–suboxic conditions of the water column triggered the first aquatic crisis, while bacterial populations increased gradually. Cooling and continuous aridification led to a significant reduction in the types and amount of vegetation. The insufficient supply of nutrients and the continuous shrinking of the lake caused a second aquatic crisis, and several macroscopic organisms disappeared. The multivariate correlation analysis based on geochemical parameters showed that the palaeoclimate was the key driving factor for the evolution of palaeolakes and their conditions in the water column, and there was a close relationship among the ecological environmental indicators. The petrological and geochemical parameters suggest the existence of lacustrine hydrothermal activity, which could also have a direct impact on the ecological environment of the lake. This study of the Bayingebi Formation palaeolake in the Yin'e Basin provides a strong example of the close coupling changes in the palaeoclimate and lake ecosystem to understand the continental sedimentary response to Early Cretaceous palaeoclimate warming events.