New aspects of the Middle Late Triassic terrestrial impact cratering record : 40Ar 39Ar dating of the Rochechouart (France) Manicouagan (Canada) and Paasselkä (Finland) impact structures paleoenvironmental considerations and a critical look at the Late Triassic multiple impact theory This thesis critically addresses the question whether Earth experienced a giant multiple cosmic strike in the Late Triassic ~214 million years (Ma) ago as postulated by Spray et al. in 1998. According to this theory the large ~100 km Manicouagan impact structure (Québec Canada) the ~40 km Lake St. Martin impact structure (Manitoba Canada) the ~25 km Rochechouart impact structure (France) the ~20 km Obolon impact structure (Ukraine) and the ~9 km Red Wing Creek impact structure (North Dakota USA) are potential members of a ~4 500 km long impact crater chain compatible with coeval impact ages available in 1998. However no geologic evidence for the multiple Late Triassic impact scenario has been presented since that time. In this study I present new 40Ar 39Ar data for the Rochechouart and Manicouagan impact structures along with new constraints for the timing of the Obolon impact structure based on paleoenvironmental considerations...