The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions

Thomas Clements,Mark Purnell,Sarah Gabbott

doi:10.1144/jgs2018-088

Thomas Clements, Mark Purnell + Show 1 more

Open Access

https://doi.org/10.1144/jgs2018-088

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Abstract

One of the best records of late Paleozoic ecosystems, the Mazon Creek Lagerstätte is world famous for its striking flora and fauna preserved within siderite concretions. Distinct from other late Carboniferous concretionary Lagerstätten because of the remarkable fidelity of soft tissues and pigments that are frequently preserved, the Mazon Creek has seen a revival in investigations during the last 10 years using modern palaeontological techniques. However, many of these modern investigations build upon a literature that incorrectly interprets the palaeoenvironment of the Mazon Creek and the separate biotas: there is a lack of evidence to support a distinct freshwater fauna. Here, we present a detailed overview of the Mazon Creek Lagerstätte, including the palaeoenvironmental conditions, organisms present and the complex taphonomic processes involved in fossil formation. Investigation into the formation of siderite concretions and the complex taphonomic processes controlling soft-bodied preservation are still continuing but are reviewed in detail.

Highlights

The late Carboniferous (Pennsylvanian) Mazon Creek Lagerstätte, Illinois, USA, is exceptional for the diversity and abundance of preserved fauna and flora found within siderite concretions
Preserved fossils from the Mazon river area have been known since the mid-19th century, but it was only after intensive strip mining for coal began in the 1940s that the importance of the Mazon Creek Lagerstätte (Mazon Creek) was truly realized
Several companies, including the ‘Peabody Coal Company’ extracted coal for over 50 years, resulting in the accumulation of immense spoil heaps that were picked over for fossil-bearing siderite concretions by collectors and researchers for decades. This resulted in huge collections of fossil material being amassed; it is not uncommon for collectors to own tens of thousands of fossiliferous concretions, with many hundreds of thousands of Mazon Creek fossils being donated to museums worldwide or sold privately

Summary

Site location and age

The Mazon Creek is named after a tributary of the Illinois River SW of Chicago (Illinois, USA), that flows close to the town of Morris, Grundy County, Illinois, USA (Fig. 1). The fossiliferous concretions are found across an area of c. 150 km spanning several counties; when found in situ, the concretions occur within the lower 3–8 m of the Francis Creek Shale Member. Baird (1979) stated that the Francis Creek Shale Member was deposited at 290 Ma based on Eysinga (1975), whereas later work and reviews Baird et al 1985a; Shabica & Hay 1997; Schellenberg 2002) used an age of 296 Ma based on Harland et al (1982). The latter age is based on studies utilizing palynological and palaeobotanical data (Pfefferkorn 1979; Wagner 1984; Peppers 1996), which indicate an age that equates to the upper part of the Moscovian stage, the top of which has been dated at 307.0 ± 0.1 Ma (Cohen et al 2013)

Cuboza Scyphozoa Hydrozoa Anthozoa Unknown

Common name

Forming a sideritic tomb for Mazon Creek organisms

Findings

Summary and future work