10:45 AM - 12:15 PM
[BCG07-P10] Aromatic hydrocarbon signatures reveal evidence of paleo-wildfires during the Lower Cretaceous period in the Kitadani Formation, Tetori Group, Japan
Keywords:Tetori Group, Cretaceous , Albian, Wildfire, Paleoenvironment, PAHs
The Tetori Group is mainly comprised of non-marine Lower Cretaceous deposits, and notable for its profound macrofossil records important for reconstruction of terrestrial ecosystems in East Asia. In the Cretaceous terrestrial realm, intense and frequent wildfires under high oxygen concentrations potentially played a significant role in the evolution of ecosystems and paleoclimate through disturbances of terrestrial ecosystems and alteration of the biogeochemical cycle[1]. To test this hypothesis, it is necessary to enrich the information on the fire activity globally and compare it with biota and other paleoenvironmental information. In this study, we conducted organic geochemical analysis of sedimentary rocks and plant fossils in the Kitadani Formation of the Tetori Group in the Kitadani Dinosaur Quarry, Fukui Prefecture, to evaluate the preservation (maturity) of organic matter and the characteristics of molecular composition derived from wildfires based on the composition of polycyclic aromatic hydrocarbons (PAHs).
The thermal maturity of organic matter in the Kitadani Formation was estimated to be equivalent to vitrinite reflectance value of ca. 0.8% (oil window) based on methylphenanthrene maturity indices (MPI-1 & MPR). Diversity in the compositions of PAHs was observed among sedimentary rock samples of the Kitadani Formation, which were collected from different depositional environments such as distinctive fossil-bearing horizons (bonebeds and pterosaur track layer), floodplains, and abandoned channels. However, coronene, a product of high-temperature combustion, was consistently detected in sedimentary rock samples, suggesting recurring occurrence of high-temperature biomass burning around the river during Albian. By combining the PAHs compositions obtained in this study with the data from previous study [2], we found the coronene content in the Kitadani Formation was significantly higher than those in lower stratum of the Tetori Group and Kuzuryu Group, potentially indicating an increase in fire frequency from Aptian to Albian age. The record of paleo-wildfire during the deposition of the Kitadani Formation in the Kitadani Dinosaur Quarry was likely a result of multiple factors, including the increase in atmospheric oxygen concentration [1] and the warming and aridification during the late stage of the Tetori Group’s deposition as suggested by plant fossil assemblages and paleosol analysis [3].
[1] Brown et al. (2021). Cretaceous Research, 36, 162-190.
[2] Hasegawa & Hibino. (2011). Island Arc, 20(1), 23-34.
[3] Sakai et al. (2018). Jour. Geol. Soc. Japan, 124, 171-189.
The thermal maturity of organic matter in the Kitadani Formation was estimated to be equivalent to vitrinite reflectance value of ca. 0.8% (oil window) based on methylphenanthrene maturity indices (MPI-1 & MPR). Diversity in the compositions of PAHs was observed among sedimentary rock samples of the Kitadani Formation, which were collected from different depositional environments such as distinctive fossil-bearing horizons (bonebeds and pterosaur track layer), floodplains, and abandoned channels. However, coronene, a product of high-temperature combustion, was consistently detected in sedimentary rock samples, suggesting recurring occurrence of high-temperature biomass burning around the river during Albian. By combining the PAHs compositions obtained in this study with the data from previous study [2], we found the coronene content in the Kitadani Formation was significantly higher than those in lower stratum of the Tetori Group and Kuzuryu Group, potentially indicating an increase in fire frequency from Aptian to Albian age. The record of paleo-wildfire during the deposition of the Kitadani Formation in the Kitadani Dinosaur Quarry was likely a result of multiple factors, including the increase in atmospheric oxygen concentration [1] and the warming and aridification during the late stage of the Tetori Group’s deposition as suggested by plant fossil assemblages and paleosol analysis [3].
[1] Brown et al. (2021). Cretaceous Research, 36, 162-190.
[2] Hasegawa & Hibino. (2011). Island Arc, 20(1), 23-34.
[3] Sakai et al. (2018). Jour. Geol. Soc. Japan, 124, 171-189.