The Kačák Event (Czech pronunciation: [ˈkatʃaːk]) or Kačák-otomari Event is a widely recognised bioevent or series of events that occurred close to the end of the Eifelian Age of the Middle Devonian Epoch. It involved a global eustatic rise in sea-level. It was named for the Kačák Member of the Srbsko Formation in Bohemia, where it is represented by a black shale interval within a sequence of limestone. In marine environments, this appears as an anoxic event, often forming potential hydrocarbon source rocks such as the Marcellus Shale. Within the Old Red Sandstone continent, it is represented by the Achanarras lake, the deepest and most widespread lake that developed within the Orcadian Basin. The event is associated with significant extinctions, particularly amongst the Ammonoidea.