Pollen, plant macrofossils and microvertebrates from mid-Holocene alluvium in east-central Iowa, USA: Comparative taphonomy and paleoecology

Abstract

Pollen, plant macrofossils, and micromammals are commonly used in paleoecological interpretations, but rarely are found associated because of distinctly separate taphonomic pathways into the fossil record. The Lilienthal local biota, dating between 5920 ± 60 and 6300 ± 80 14C B.P., is a rare exception as the site contains all three proxies juxtaposed in alluvium, impounded upstream from a fossil log near the headwaters of Mud Creek, east-central Iowa, U.S.A. A variety of taphonomic processes can strongly influence the composition of fossil assemblages. This paper compares the taphonomic framework for each fossil group, interprets the paleoecologic signal from each, and then compares the three interpretations. Pollen and plant macrofossils are found in organic silts, indicating deposition in a quiet water environment. Microvertebrates ordinarily occur in sand-sized sediments and show evidence of fluvial transport. Despite these different pathways, all Lilienthal assemblages indicate that a largely closed mesic deciduous forest grew along Mud Creek in mid-Holocene time. Therefore, a narrow north–south ecotone must have existed between the forest and tall-grass prairie biomes in eastern Iowa. This robust data set provides a detailed picture of the paleoecology and paleogeography of this past environment.