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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 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')
There is not a single definition of mudstone that has gained general acceptance, [5] though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than 0.063 millimetres (0.0025 in). [6]
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,
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 ...
Mudstones, shales, lutites, and argillites are common qualifiers, or umbrella terms; however, the term mudrock has increasingly become the terminology of choice by sedimentary geologists and authors. The term "mudrock" allows for further subdivisions of siltstone, claystone, mudstone, argilite and shale. For example, a siltstone would be made ...
Rocks originating in the Carboniferous Period underlie the uplands of eastern and north Lancashire. Listed in order of succession i.e. lowermost/oldest first, they comprise the various limestones, mudstones, siltstones and sandstones of the Bowland High Group and Trawden Limestone Group, Craven Group, Millstone Grit Group, Pennine Coal Measures Group and Warwickshire Group.
Is dominated by mudstones with varying compositions and colors, divided into three main stratigraphic units: the lower beds, dark purple, marbled mudstones rich in carbonates. They contain calcitic replacements of small roots and show signs of pedogenic processes, including mud cracks and pseudobreccias.