FAULT ASSOCIATED SUB-ABSAROKA PALEOKARST AND ASSOCIATED MIDDLE PENNSYLVANIAN FILL AND PLANTS

A new sub-Absaroka paleokarst and cave fill has been discovered in north-central Illinois. The paleokarst is associated with a recently recognized fault system parallel to and assumed contemporaneous with the Sandwich Fault System just to north. The paleokarst preserves many original solution features, such as oriented grooves, pendants and half-tubes. Many of the ancient cave passages have rounded bottoms and flat roofs. Together, these suggest that the original elliptical phreatic cave passages grew upwards by paragenesis, in which the floor of the cave is protected from dissolution by the presence of sediment while the ceiling grows upward by dissolution.The fill is late Bashkirian to early Moscovian (Westphalian B-C) in age, based on palynological data and can be correlated with the Tradewater Formation. It is comprised of relatively unindurated sediments that contain well-preserved plant fossils, and most notably voltzialean conifer remains, as well as cordaite remains. Many of the macrofossils are fragmentary but charcoalified, and along with the megaspores, are uncompressed and preserve exceptional morphological and anatomical data. The presence of charcoal and polycyclic aromatic hydrocarbons (PAH's) in the fills indicate wildfire activity in this part of the Illinois Basin during this part of the Pennsylvanian.