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Mudrock deposition in an ancient dryland system: Moor Cliffs Formation, Lower Old Red Sandstone, southwest Wales, UK

Marriott, Susan B.; Wright, V. Paul


Susan B. Marriott

V. Paul Wright


Studies of the lowermost Old Red Sandstone of South Wales (Pridolian-Lochkovian) have revealed that the mudstones that constitute up to 80% of some of the formations have been deposited in a variety of environments. In addition there is a variety of lithofacies associations present in some mud-dominated units that suggests diverse mechanisms of deposition. This paper considers the Moor Cliffs Formation and examines four distinct mudrock facies. The overall depositional environment is considered to have been a multi-stage, multi-channel system, similar to a modern dryland river system, with mud-dominated, moderately sinuous ephemeral rivers that reworked muddy floodplain sediment over a proximal braidplain during seasonal flooding. The alluvial deposits were pedified to varying degrees as calcic Vertisols, which, due to seasonal wetting and drying, provided soil aggregates for reworking by wind and water as sand- or silt-sized pellets. Very infrequent flooding events (superfloods) resulted in extensive stripping of the floodplain surface and the introduction of allochthonous sand sheet deposits over wide areas in this normally sediment-starved system. Depressions (pans or waterholes) on the floodplain formed ephemeral lakes following floods, and acted as sediment traps for dust from the frequent dust storms occurring in the system. © 2004 John Wiley and Sons, Ltd.


Marriott, S. B., & Wright, V. P. (2004). Mudrock deposition in an ancient dryland system: Moor Cliffs Formation, Lower Old Red Sandstone, southwest Wales, UK. Geological Journal, 39(3-4), 277-298.

Journal Article Type Article
Publication Date Jul 1, 2004
Journal Geological Journal
Print ISSN 0072-1050
Publisher Wiley
Peer Reviewed Not Peer Reviewed
Volume 39
Issue 3-4
Pages 277-298
Keywords Old Red Sandstone, ephemeral streams, soil aggregates, inclined heterolithic stratification, calcrete, palaeosols, superfloods
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Publisher URL
Additional Information Additional Information : Lead author. This article was the culmination of several field seasons classifying and analysing mud rocks in the Old Red Sandstone and developing a new model for their deposition. It was the first paper to consider a modern dryland environment as an analogy for the ORS.

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