Diabasbrottet quarry
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The Diabasbrottet quarry (), located on Mt. Hunneberg, Västergötland, Sweden, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Floian and Tremadocian stages of the Early Ordovician. It was selected over "The Ledge" in western Newfoundland in 2000 and ratified as the GSSP by the International Union of Geological Sciences in 2002.
The first appearance of Tetragraptus approximatus, a graptolite, defines the boundary. The rock section, dominated by shale, is unusually fossiliferous, including fossilized remains of graptolites, conodonts, and trilobites. It is highly compressed, and the Ordovician section is only 12 m thick.
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