Wildfire records in Late Permian lacustrine deposits (Gohan Formation, Korea): Implications for paleoenvironmental reconstruction

Abstract

Soot-black carbon (S-BC) produced by biomass combustion typically accounts for less than 10 % of the sedimentary organic carbon in modern lacustrine deposits, but how much in ancient lacustrine deposits is not well known. Considering that records of wildfires are common in Late Permian sediments worldwide, this study focuses on the S-BC of the Late Permian Gohan Formation, a lacustrine sediment distributed in central Korea. S-BC occurs throughout the Gohan Formation sequence, and although its concentrations are low at 0.01 to 0.90 wt% (average 0.17 wt%), it accounts for 23 to 91 % (average 54 %) of TOC. The carbon isotopic composition of S-BC ranges from −25.6 to −17.1 ‰ with an average of −21.8 ‰. Variations in S-BC carbon isotopic composition throughout the sequence suggest that the paleohumidity conditions of the S-BC sources for the Gohan Formation varied considerably, some of which differed significantly from the watershed paleohumidity conditions. Excluding S-BC, more than two thirds of the sedimentary organic carbon in Gohan paleolake sediments were derived from phytoplankton, with the remainder originating from terrestrial plants. The large variations in the δ¹³C of algae (−33.0 to −16.8 ‰) suggest that the dissolved inorganic carbon pool of the Gohan paleolake was alternately affected by episodes of increased primary production and increased organic matter respiration.