Complex star dunes and associated aeolian bedforms, Hopeman Sandstone (Permo-Triassic), Moray Firth Basin, Scotland

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Abstract
Summary: The Hopeman Sandstone, which is exposed at the southern edge of the Moray Firth Basin, is composed of a number of aeolian sandstone units. These units, which have been mapped continuously for 4.5 km, represent part of an ancient sand sea in which complex star dunes alternated with sand-filled star-dune corridors. The palaeowind regime was complex with prevailing winds from the NNE, secondary winds from the SSE and subordinate winds from the NW. The complex star dunes are represented by two types of deposits: Type I—large-scale or giant-scale mainly trough-formed high- to medium-angle cross-bedding, which constitute the slip-face deposits of actively migrating star dunes; and Type II—bimodally dipping more wedge-shaped large-scale or giant-scale sets, which apparently formed on the opposed flanks of relatively stationary star arm segments. The exposed star arms trend in three main directions being roughly parallel with the palaeowind directions. The dune-dune corridors contain small- and medium-sized crescentic or reversing dunes which frequently overlap the star-dune flanks, interdune flats, and rare ephemeral streams. The palaeowind pattern inferred from the Hopeman Sandstone is very similar to that inferred from early Triassic reversing dune deposits in E Greenland, suggesting the existence of a regional Trade Wind system in the period near the Permo-Triassic boundary.