Rhythmic sedimentary sequences in the triassic Keuper Marl (mercia mudstone group) of cheshire, northwest England

Abstract

AbstractCored boreholes in the central part of the Cheshire‐Shropshire basin form the basis of a sedimentological description of three separate parts of the Keuper Marl succession. The uppermost sequence examined is the lower part of the Middle Keuper Marl within which blocky silty mudstones and well laminated mudstones and siltstones form a rhythmically alternating pattern. Similar alternating patterns are described from the Lower Keuper Saliferous Beds and the top of the Lower Keuper Marl although, in these, the alternations are interrupted to various degrees by halite rock. The blocky and laminated facies are considered to have accumulated in emergent and flooded conditions respectively, the alternations reflecting eustatic variation.