EXPERIMENTAL TAPHONOMY: DETERMINING POSSIBLE LEAF DEGRADATION OF FOSSIL PLANT ASSEMBLAGE ABSTRACT

An assemblage of plant fossils were collected from a road cut near the View High Drive and I-470 intersection in Kansas City, MO in 1997. These fossils, referred to as the View High Drive (VHD) assemblage, were preserved as a carbonized film within the Winterset Member of the Dennis Formation (Pennsylvanian). This stratum is part of the basic Midcontinent cyclothem which is a light gray thick-to-thin bedded marine sequence. Most of the identified taxa show signs of degradation, particularly the fern, Alethopteris. This research focuses on the potential driving mechanisms of degradation observed in fossilized leaves by using two parameters: 1) simulated experiments, and 2) comparisons of rock type and fossilized content between different assemblages. Simulated experiments used Polystichum acrostichoides leaves to gain a better understanding of taphonomic processes responsible for the physical condition of fossilized fern leaves. Physical transformations of P. acrostichoides in fluvial transportation and lagoonal post-deposition simulations were recorded. Fluvial simulations demonstrate a systematic removal of lower pinnae along the central rachis over time. Alethopteris specimens from the VHD assemblage exhibit a similar physical appearance to P. acrostichoides. Preliminary observations of leaves in the lagoonal post-depositional simulation exhibit microbial activity along the central rachis and pinna rachis where nutrient concentration is greatest. Comparisons of the VHD assemblage to a second locality near the I-435 and Holiday Drive intersection of Kansas City, referred to as the Mill Creek (MC) assemblage, demonstrate apparent differences in preservation and concentration. The MC assemblage possesses specimens with a stronger preservation (less degradation) and greater area concentration (~39%) of plant parts than the VHD assemblage (~6%). Thus, we propose the VHD specimens represent an allochthonous assemblage that experienced physical degradation from transportation. Furthermore, we propose that microbial activity may be responsible for further degradation of the VHD assemblage after deposition occurred.