Sedimentary conditions and palaeoenvironment during the Early Cretaceous: Evidence from macerals and organic carbon isotopes of the coal from Hailar Basin, Northeast China

Abstract

The Cretaceous represented a Period of intense palaeoenvironmental change. Coal seams preserve continual records of palaeoenvironments, such as wildfire events that occur during peat accumulation. To understand wildfire events and terrestrial climate variations during the peat accumulation, maceral characteristics and organic carbon isotope compositions were examined in the Lower Cretaceous coals from Yimin and Baorixile mines, which are located in the south and north of Hailar Basin, Northeast China, respectively. The dominant macerals are inertinite and huminite and the former has an average content of 57.9 % and 51.3 % in the Yimin and Baorixile mines, respectively, indicating the coals are an inertinite-rich. The features and abundance of inertinite shows they are formed by high frequency-wildfire events. The palaeo-wildfire temperatures estimated by average inertinite reflectance of the Yimin and Baorixile coal mines are proximately 333 °C and 344 °C, respectively, indicating that the palaeo-wildfire were the type of ground fire. The difference in palaeo-wildfire temperatures between the Baorixile and Yimin coal mines indicates that different vegetation types were developed in the northern and southern regions. Wildfire, an important event of the Early Cretaceous peat-accumulating system in the Hailar Basin, might have influenced the evolution of vegetation and ecological cycle both in the land and water systems. The subtle variability of the organic carbon isotope in the coal seam profile implies a response to the palaeoclimate change of seasonally wet and dry.