The Hunsrück Slate (Hunsrückschiefer) is a Devonian Lagerstätte famous for exceptional preservation of a highly diverse fossil fauna assemblage. The various fossil localities are quarries located mostly south of the River Mosel and west of the Rhine in western Germany. The biota of the Hunsrück Slate are commonly called "Bundenbach fossils" after the nearby German community of Bundenbach. More formally, the Hunsruck Slate is properly designated as a Konservat Lagerstatte due to the many fossils that exhibit preservation of soft tissues.

Preservation and Taphonomy

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The sediments were deposited during the Late Pragian to Early Esmian Ages of the Devonian, making them some 396-390 Mya. Hunsrück is the only marine Devonian Lagerstätte having soft tissue preservation, and in many cases fossils are coated by a pyritic surface layer. Preservation of soft tissues as fossils normally requires rapid burial in an anoxic (i.e., with little or no oxygen) sedimentary layer where the decomposition of the organic matter is significantly slowed. The pyritization found in Bundenbach fossils facilitated preservation and enhanced the inherent beauty of the fossils.

Pyritization is rare in the fossil record, and is believed to require not only rapid burial, but burial in sediments low in organic matter, but high in concentrations of sulfur and iron. Such pyritization is also prevalent in the lower Cambrian fossils from the Maotianshan shales of Chengjiang, China, the oldest Konservat Lagerstatte of Cambrian time.

The best localities for exceptionally preserved fossils are in the communities of Bundenbach and Gemünden. The slates were widely quarried in the past, mainly for roofing tiles from small pits, of which over 600 are known. Today, only a single quarry remains open in the main fossiliferous region of Bundenbach. There are also areas of the Hunsrück Slates where fossils are neither well preserved, nor pyritized, indicating that there also existed environments with shallow and fully oxygenated water.

Diversity of Fauna

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More than 260 animal species have been described from the Hunsrück Slate. The deposites in a strip some 15 Km wide and 150 Km long running from northwest to southeast. In the main depositional basins of Kaub, Bundenbach, and Gemünden, echinoderms are concentrated in the southwestern area around Bundenbach, with brachiopods predominating in the northeast. The presence of corals and trilobites with well-developed eyes and the rarity of plant fossils from the central basin areas suggest a shallow-water environment. Other animal fossils include sponges, corals, brachiopods, cephalopods, cnidarians, gastropods, and worm trace fossils. Trilobites and echinoderms are relatively abundant in some horizons. Crinoids and starfish are the predominant representatives of the echinoderms, although holothurians (sea cucumbers) are also represented. More than 60 species of crinoids are described from the found in the Hunsrück Slate. Both placoderm armoured fish and agnatha jawless fish have been discovered.

References

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• The fossils of the Hunsrück Slate. Marine Life in the Devonian by Bartels, C, Briggs, D, AND Brassel, G., Cambridge Univeristy Press. 1998
• Bundenbach - Lower Devonian Hunsrück Slate of Germany Hunsrück slates site description and many Bundenbach fossil pictures

Fossils