Palynology and the triassic/jurassic boundary

Abstract

Characteristic latest Triassic palynofloras are first developed in the Norian with the association of Camarozonosporites laevigatus, Chasmatosporites apertus, C. magnolioides, Cingulizonates rhaeticus, Densosporites fissus, Granuloperculatipollis rudis, Kyrtomisporis laevigatus, K. speciosus, Limbosporites lundbladii, Ovalipollis ovalis, Perinosporites thuringiacus, Rhaetipollis germanicus, Ricciisporites tuberculatus, Selagosporis mesozoicus, Semiretisporis gothae, Triancoraesporites ancorae, Zebrasporites interscriptus and Z. laevigatus. These forms persist into the Rhaetian and, in some instances, into the basal part of the overlying Jurassic. Palynofloral resolution of the Triassic/Jurassic boundary is largely based on the disappearance of typically late Triassic morphotypes; undoubtedly post-Triassic species, e.g. Cerebropollenites mesozoicus and C. thiergartii, however, are rarely conspicuous elements of the basal Jurassic palynofloras and may not become dominant elements until the late Hettangian or Sinemurian. A palynological definition of the Triassic/Jurassic boundary is further complicated by the lack of agreement on the legitimacy of the Rhaetian Stage, the location of the type section of the basal zone of the Hettangian Stage, and the uncertainty over the precise definition of the top Triassic/basal Jurassic within the stratotype sections proposed. In this context, the unsatisfactory nature of a palynologically defined Triassic/Jurassic boundary in northwest Europe is discussed.