The key Cambrian succession at Andrarum, southern Sweden – Alum Shales, trilobites and insights from Euan Clarkson’s investigations

The organic-rich shales and mudstones composing the Miaolingian (‘middle’ Cambrian) through Tremadocian (Lower Ordovician) Alum Shale Formation have been extensively mined for production of alum at Andrarum in southeastern Scania (Skåne), southern Sweden. Here, the formation was exploited between 1637 and 1912, and a brief account is given of the history of the exploitation. The alum industry had its heyday in the mid-1700s when it was owned by Christina Piper (1673–1752). During this time some 900 people lived within the working area, and it had its own craftsmen, school, hospital and courthouse with a jail annex. The undeformed and virtually continuous succession at Andrarum is generally richly fossiliferous and, albeit largely covered by scree and vegetation, best exposed in the old quarries. The fossil faunas are dominated by trilobites and agnostoids, which form the basis for a detailed biostratigraphical framework. The history of geological and palaeontological research at Andrarum, since the pioneering works in the mid- to late 1800s, is reviewed. The sequence of strata was first elucidated by Alfred Gabriel Nathorst in 1869. Since then, the succession and its fossil content have been studied by a considerable number of influential researchers, such as Gustaf Linnarsson (1841–1881), Sven Axel Tullberg (1852–1886) and Anton H. Westergård (1880–1968). In the decades around the turn of the 21st century, Euan Clarkson initiated a number of projects focusing on the ontogeny, evolution and functional morphology of olenid trilobites from the Furongian at Andrarum, along with two important studies dealing with faunal dynamics and biotic turnovers. His research resulted in a series of pivotal papers on the geology and palaeontology of the Alum Shales.