Evidence of multiple late Bashkirian to early Moscovian (Pennsylvanian) fire events preserved in contemporaneous cave fills

Abstract

During a low sea level stand and wet climate phase at the end of the Mississippian, Lower Palaeozoic limestones at the northern edge of the Illinois Basin were karstified. The caves and fissures that formed were infilled subsequently with clastic sediments of Pennsylvanian age (late Bashkirian–early Moscovian (= Atokan, Duckmantian/Bolsovian, Westphalian B/C)). The earliest infills comprise organic-rich, almost coaly, sediments, while sands, silts and fine clays were deposited subsequently. The sediments are fossiliferous and contain abundant plant fragments, most notably cordaitalean and conifer remains. Many of the plants and megaspores are uncompressed and have undergone minimal thermal alteration. Charcoal occurs throughout the sedimentary infills but is most abundant in the later deposits, where conifer remains predominate. These conifers are currently amongst the oldest known from North America. The presence of cordaitalean remains in the earliest coaly infills is supported by the detection of specific fernane derivatives. The lipid extract of the cave fill sequence contains polyaromatic hydrocarbons (PAHs), such as pyrene, chrysene, benzo[ghi]perylene, and coronene, which distribution further attests to the importance of wildfire in preserving the plant remains.