Early Cretaceous wildfires and their palaeoenvironmental significance in the Jiuxi Basin, Gansu Province, Northwestern China

The occurrence of palaeowildfires in terrestrial ecosystems coincides with the colonization of plants, rendering it one of the most significant geological events and holding paramount importance for comprehending paleoclimate and paleoenvironmental changes. This study provides strong evidence of persistent palaeowildfire occurrences in the Jiuxi Basin, Northwestern China, during the Aptian to Albian period, considering the abundant, continuous, sedimentary charcoal fossils from the uppermost Chijinbao, Xiagou, and Zhonggou Formations of the Hanxia Section. Micromorphological studies based on the scanning electron microscopy indicate that substantial portion of the charcoal fossils originated from conifers. The fusinite reflectance values of the charcoal fossils range from 1.32% to 4.32%, indicating that the palaeowildfire temperatures may have been 330 degrees C to 700 degrees C, and can be divided into three stages, evolving from ground fires to surface fires and crown fires, and finally developing to ground fires. Furthermore, high atmospheric oxygen and seasonally dry climate promoted the frequent palaeowildfire environment in the Jiuxi Basin during the late Early Cretaceous. However, the persistent and repeated wildfires may have effected the palaeoecosystem of the Jiuxi Basin during the late Early Cretaceous, which is evidenced by the decline of coniferous trees and the increase of the early herbaceous angiosperms.