Triassic rift sedimentation and palaeogeography of central East Greenland

Abstract

The majority of the investigated Triassic (upper(?) Scythian – Rhaetian) rocks apparently formed in continental environments comprising alluvial fans, braided rivers, aeolian deserts, flood plains, saline playa lakes and freshwater shallow lakes. In the Middle Triassic a brief but widespread marine transgression affected large parts of the basin and resulted in the deposition of barrier limestones and lagoonal mudstones. Details of sedimentary structures, bed types, facies sequences and vertical and lateral variations are discussed for each of these environments. Special emphasis is given to the remarkable variety of lacustrine facies associations. The Triassic sediments probably accumulated in a N-S trending rift valley. This fault controlled depositional basin apparently formed in connection with overall rifting of the 'Laurasian' megacontinent. Tectonic movements along N-S trending fault lines appear to have been an important control on the thickness and nature of the Triassic facies, and the basal alluvial fan sediments formed simultaneously with or slightly after tectonic uplift of the borderlands. The climate throughout the Middle-Late Triassic period was warm and subtropical with alternating dry and wet seasons. The basin was under the influence of dominant north-east trade winds (winter) and less common south-east trade winds (summer). The vertical succession of climate-sensitive rocks further suggests a gradual shift towards increased humidity during the Middle-Late Triassic times. This climate trend is explained by a northwards continental drift of the area.