Late Triassic continental vertebrates and depositional environments of the Fleming Fjord Formation, Jameson Land, East Greenland

Abstract

A diverse assemblage of fossil vertebrates has been discovered in the Fleming Fjord Formation (Malmros Klint and Ørsted Dal Members) in East Greenland between latitudes 71°15'N and 71°50'N. The fauna includes several species of mammals as well as prosauropod (Plateosaurus) and theropod dinosaurs, turtles (cf. Proganochelys), pterosaurs, aetosaurs (Aetosaurus ferratus, Paratypothorax andressi), labyrinthodont amphibians (Gerrothorax, Cyclotosaurus and possibly other taxa) and fishes (including sharks, actinopterygians, coelacanths and lungfish). The association of the genera Aetosaurus, Plateosaurus, Proganochelys, Cyclotosaurus and Gerrothorax is shared with well known European Norian faunas, and confirms the paleogeographic proximity of Greenland and Europe during Late Triassic time. On this evidence, the Ørsted Dal Member may be estimated to be at least as old as mid-Norian, but a comparable age estimate for the underlying Malmros Klint Member cannot be made on the basis of the fauna as presently known. The Malmros Klint Member is characterized by composite cyclicity with four orders of cycles involving silt-rich, ephemeral lake or playa-mudflat systems, loess beds, wave-reworked sand flats, flat pebble conglomerates and paleosols. The rhythmicity and thickness ratios of the beds are evidence that depositional conditions were controlled by Milankovitch cycles, with climatic conditions varying from humid, to dry with seasonal rainfall, to arid. Cyclical sedimentary conditions and climatic fluctuations appear to have continued during the subsequent deposition of the overlying Ørsted Dal Member.