Hangenberg event
The Hangenberg event, also known as the Hangenberg crisis or end-Devonian extinction, is a mass extinction that occurred at the end of the Famennian stage, the last stage in the Devonian Period (roughly 358.9 ± 0.4 million years ago). It is usually considered the second-largest extinction in the Devonian Period, having occurred approximately 13 million years after the Late Devonian mass extinction (Kellwasser event) at the Frasnian-Famennian boundary. The event is named after the Hangenberg Shale, which is part of a sequence that straddles the Devonian-Carboniferous boundary in the Rhenish Massif of Germany. The Hangenberg Event can be recognized by its unique multi-phase sequence of sedimentary layers, representing a relatively short interval of time with extreme fluctuations in the climate, sea level, and diversity of life. The entire event had an estimated duration of 100,000 to several hundred thousand years, occupying the upper third of the ‘Strunian’ (latest Famennian), and a small portion of the early Tournaisian. It is named after the Hangenberg Black Shale, a distinctive layer of anoxic sediment originally found along the northern edge of the Rhenish Massif in Germany. This layer and its surrounding geological units define the "classic" Rhenish succession, one of the most well-studied geological examples of the extinction. Sequences equivalent to the Rhenish succession have been found at over 30 other sites on every continent except Antarctica, confirming the global nature of the Hangenberg Event. Below the Hangenberg Event strata is the Wocklum Limestone, a pelagic unit rich in fossils (especially ammonoids). In some places the Wocklum Limestone grades into the Drewer Sandstone, a thin turbidite deposit which initiates the lower crisis interval. Increased erosion and siliciclastic input indicates that the Drewer Sandstone was deposited during a minor marine regression (sea level fall). This may have been caused by a small glacial phase, but other evidence suggests a warm and wet climate at the time.
