Consequences of Lower Miocene CO2 degassing on geological and paleoenvironmental settings of the Ahníkov/Merkur Mine paleontological locality (Most Basin, Czech Republic)
Abstract
The Ahníkov/Merkur Mine paleontological locality (mammal biozone MN3a, Lower Miocene) located in the westernmost part of the freshwater, graben-related Most Basin yielded more than 150 species of fossil fauna. The finds include mammals, birds, reptiles, amphibians, trace fossils (gnawing and biting traces on reptilian and mammalian bones) and numerous invertebrate species.
Individual sites, where the fossils have been collected since 1964, are distributed along slopes of a paleovalley, whose formation was related to Oligocene movements on faults and volcanism. The axial part of this valley hosts a limestone body about 2 km long and locally more than 200 m wide with complex internal structure formed by several markedly contrasting limestone types.
The performed field mapping, evaluation of borehole data, and petrological and geochemical studies confirmed that these limestones (travertines) were formed near discharges of thermal, CO2-charged mineralized water, probably at temperatures between ca. 50 and 20 °C. Discharge of this thermal water affected the whole area also during the subsequent formation of peat, which filled the paleovalley and was later converted to lignite/brown coal.
Paleoenvironmental aspects of the locality were also characterized by a paleobotanical analysis of plant fossils recovered in the freshwater limestone.