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Triassic palaeogeography and fluvial dispersal across the northwest European Basins

Triassic dryland fluvial systems occur infilling extensional and post‐rift basins across northwest Europe. These systems were deposited by streams draining off the major basin margin catchments of Greenland, Fennoscandia, the Scottish Highlands and the remnant Variscan mountains. Fluvial drainage was dominantly endorheic in character, and terminated in playa, aeolian dune, sabkha or marsh settings. Whilst the ambient basin climate fluctuated through varying levels of aridity and humidity, the dispersal of sand into these basins was critically dependant on catchment run‐off from the major, basin flanking regions. In the Early Triassic the Tethyan monsoon drove seasonal precipitation over the Variscan mountains which transported sediment northward into arid dune fields and playa. In addition, far‐travelled fluvial systems supplied sediment from distant, wetter catchments. Through the Middle and Late Triassic the effects of the Tethyan monsoon apparently weakened, and sand‐prone fluvial systems draining off the Variscan mountains were more limited in areal extent, but expanded during pluvial episodes. However, Greenland and Fennoscandia maintained sediment supply from the north, with perennial run‐off from Fennoscandia able to maintain marshes and levels of vegetation cover not encountered elsewhere in the region and to episodically drive major exorheic drainage systems into the Tethys Sea. Published climatic simulations are consistent with these observations, which indicate that Greenland, and particularly Fennoscandia, had precipitation levels higher than the regions to the south with a positive precipitation: evaporation balance. Copyright © 2009 John Wiley & Sons, Ltd.