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The Mercia Mudstone Group is now divided into five formations recognised and mappable across its entire outcrop and subcrop. The formations are a mix of mudstones, siltstones, sandstones and halites. Historically this sequence of rocks has been subdivided in different ways with different names in each of the basinal areas in which it is found.
A further presumed unconformity separates the breccia from the mudstones of the overlying Mercia Mudstone Group which underlie the larger part of the low ground between Exmoor and North Hill. At the top of the group is a 25m thickness of mudstones with gypsum referred to as the Blue Anchor Formation. Above this are around 12m thickness of ...
A pile up to several hundred metres thick of Triassic sandstones, mudstones and siltstones underlies Wirral, Liverpool and the coastal plains to the north. The following sequence is encountered within Merseyside: Mercia Mudstone Group. Sidmouth Mudstone Formation (formerly 'Keuper Marl') Tarporley Siltstone Formation (formerly 'Keuper Waterstones')
More recently, however, [4] there has been the recognition that it is the Mercia Mudstone Group which is seen to thicken markedly into faults imaged on seismic data rather than the Sherwood Sandstone Group. This work demonstrates the Mercia Mudstone Group to be a syn-rift phase of deposition, with the fine grained nature of the sedimentary ...
On top of the Nether Alderley Sandstone lie the Mercia Mudstones which attain a thickness of 300 m, but these are only seen on the lower plains, it is in these beds that the halite lies. Mottling in the red blocky mudstone is of two main types,
Downstream of Armitage the solid geology is primarily Mercia Mudstones, the course of the river following the arc of these mudstones as they pass through the Midlands all the way to the Humber. The mudstones are not exposed by the bed of the river, as there is a layer of gravels and then alluvium above the bedrock.
This was succeeded by mudstones with evaporites (including locally thick deposits of halite) deposited in a desert environment, forming the Mercia Mudstone Group. A major change to marine conditions is shown by the mudstones with limestones and sandstones of the overlying Rhaetian age Penarth Group. [11]
The oldest rocks exposed at or near the surface of Lincolnshire are the sandstones and mudstones of the early Triassic Sherwood Sandstone Group.Rocks from this and the overlying Mercia Mudstone and Penarth groups occur in the northwest of the county and along its western border but are generally concealed beneath a thick cover of recent deposits.