Maar lakes as well as other deep volcanogenic lakes represent important Konservat Lagerstätten, which can be regarded as unique windows into past ecosystems. Pre-Quaternary maar structures or other volcanogenic lakes are frequently covered by younger sedimentary or volcanic deposits, and often only known from geophysical surveys and /or cores. The accessibility of such deposits for palaeontological excavations is clearly depending on the individual outcrop situation and several of the, at least from a palaeontological point of view, better known maar deposits are related to former or ongoing mining activities, examples are Menat (Palaeocene, France), Messel (Eocene, Germany), Enspel (Oligocene, Germany) and the Foulden Maar (Miocene, New Zealand). In some of these cases non-fossiliferous volcanic deposits are the target of mining activities, but in other cases the fossiliferous deposits themselves have been mined, leading to the destruction of important palaeontological information. The Eocene Messel Pit is an example that had a development from mine to potential waste dump to UNESCO world heritage. Several other maar deposits are still under the threat of being destroyed by mining activities, an example is the Foulden maar, representing a unique windows into past biota and ecosystems on the southern hemisphere.
This special issue and series provides info about the state of the art of the palaeontological research on selected pre-Quaternary maar and volcanogenic lakes, as well as to present new results from a wide variety of different pre-Quaternary maar lakes, with the aim to raise the awareness for such deposits as excellent Fossil-Lagerstätten.