The Fossil Sandstone — a shallow marine sand wave complex in the Namurian of Cumbria and North Yorkshire, England

Abstract

SUMMARY The Fossil Sandstone represents marine sand deposition during the Namurian E2 a(ii) marine cycle on the Askrigg Block in northern England. Sand was shaped into sand waves in an offshore setting at least 10 km from the synchronous shoreline. These sands and associated muds are preserved in five lithofacies: 1) shale, 2) interstratified sandstone and shale, 3) wavy-laminated sandstone, 4) tabular cross-bedded sandstone, and 5) mottled sandstone. Delta progradation followed by transgressive submergence was the most likely primary basinward sand-moving mechanism. Wavy-laminated sandstone and interstratified sandstone and shale represent a sand buildup that formed as a result of marine reworking of deltaic sands. Periodic increases in current intensity caused the formation and eastward migration of sand waves on the higher portions of the sand buildup. Sand waves are represented by cross-bedded sandstone with easterly-dipping tabular foresets separated by gently dipping to nearly horizontal erosional surfaces. These foreset beds contain crinoid and brachiopod fragments and the lowermost erosional surface at each locality is overlain by a thin shale-chip and fossil hash lag. Bioturbated surfaces represent upper portions of sand bodies subject to biogenic activity between high-energy storm events or as the bodies became moribund. The Fossil Sandstone is an example of sand deposition in a mud-dominated marine shelf setting. In some, but not all aspects, it is similar to some of the Upper Jurassic and Upper Cretaceous sandstones in the Western Interior of North America.