Holzmaden Ammonite
Dactylioceras sp.
Posidonienschiefer (Posidonia Shale)
Early Jurassic
Holzmaden, Germany
This is a very good representative specimen of the most common ammonite found in the famous lagerstatten near Holzmaden, Germany. The ammonites are partially replaced by pyrite and are found on the bedding plans of early Jurassic Poidonia Shale. See scale for size.
The Holzmaden Shale is the name given to the Posidonienschiefer outcropping within the region of Holzmaden, Germany. The shale up to 15% organic matter and is bituminous. The Posidonschiefer where it outcrops in the Holzmaden area consists of 6-8 meters of black, bituminous marls with intercalated limestone layers of the lower Jurassic (Lower Toarcian) period, dating to an age of approximately 180 million years as dated by zones of the ammonites Harpoceras falcifer, Dactylioceras tenuicosttum and Hildoceras bifrons. The combination of diffused pyrite admixed with a high percentage (of up to 15%) of solid organic matter accounts for the dark color of the fine-grained marls of the Holzmaden shale, suggesting a depositional environment that was starved of oxygen and rich in hydrogen sulfide, as in a stagnant basin. A very diverse marine fauna is characteristic of the formation and includes fish, plesiosaurs, ichthyosaurs crocodiles, squids, crinoids, and plants