内蒙古乌拉特后旗乌兰剖面记录的早白垩世火灾事件

Early Cretaceous Paleo-Wildfire Events Recorded on the Wulan Section in the Urat Back Banner of Inner Mongolia,China

古火灾事件研究对于重建当时的古气候及古地理具有重要的意义,白垩纪是全球火灾事件最盛行的时期之一,但在我国目前报道较少。本文通过对内蒙银根-额济纳旗盆地东部乌兰剖面早白垩世砂岩中发现的大量炭屑的显微形貌特征观察和多环芳烃(PAHs)测定,发现炭屑燃烧痕迹明显,木质细胞结构保存完好;同时在样品中检出了燃烧源的多环芳烃(PAHs)菲、芘、苯并荧蒽、苯并[e]芘等,证实炭屑是火灾产物,燃烧温度可达520℃以上。结合沉积环境分析、孢粉资料和岩石磁化率测量,认为乌兰剖面上3个炭屑密集层代表该区在早白垩世经历了3个大火频发时期,炭屑是火灾过程中松柏类和衫科类等高大乔木燃烧后的残留物,并推测大部分炭屑是由周边地区发生火灾堆积,后期通过快速搬运而来,结合前人在霍林河煤田发现的早白垩世火灾事件,推断我国华北地区在早白垩世大火频发,是早白垩世北半球中纬度火灾带的组成部分。

The Paleo-wildfire event was a common phenomenon during the Cretaceous, it is significant to research these Palaeo-wildfire events for understanding the palaeoclimate and palaeogeography. But there are little report in China. We firstly found three charcoal-bearing layers in the early Cretaceous strata on the Wulan section in the east of Yingen-Eiinaqi basin, Inner Mongolia. There are obvious burning feature and undestroyed structure of wood cells in the charcoal. Meanwhile, the measurement of the PAHs shows the oceurance of the Phe, Fla, Pyr, Chr, BaAn, Bep, etc. , which employed the combustion sources in the samples. These demonstrate that the charcoal was the remains of the wildfire, which the combustion temperature would be higher than 520~C. In conjunction with the analysis of palynologic data and sedimentary environment as well as measurement of the magnetic susceptibility, we propose these charcoal-bearing layers on the Wulan section probably indicate three stages of wildfire in early Cretaceous. The wildfire might happened in adjacent region with the flourishing tall arbors, including Coniferae and Taxodiaceae. Considering these finds and the wildfire in the Huolinhe coal by other researchers may suggest that the north of China had happened frequent wildfire events during the early Cretaceous, and it was the part of the wildfire belt in the mid-latitude area of northern hemisphere during the Cretaceous.