Geology of the Rochdale district : a brief explanation of the geological map Sheet 76 Rochdale
Crofts, R.G.; Hough, E.; Northmore, K.J.. 2010 Geology of the Rochdale district : a brief explanation of the geological map Sheet 76 Rochdale. Nottingham, UK, British Geological Survey, 30pp.Full text not available from this repository. (Request a copy)
This Sheet Explanation provides a summary of the geology and applied geology of the district covered by the geological 1:50 000 Series Sheet 76 Rochdale, published in 2009. Detailed information can be found in individual Technical Reports. The Rochdale district lies predominantly within the county of Lancashire while the area around Todmorden lies within West Yorkshire. The main population centres are the mill towns of Rochdale, Todmorden, Bacup, Rawtenstall, Haslingden, Blackburn, Accrington, Burnley, Darwen and Ramsbottom. These main population centres are separated by areas of agricultural land, with scattered villages and large expanses of moorland. The bedrock is composed entirely of rocks deposited during the Carboniferous, about 359–299 million years ago (Figures 1; 2). The oldest rocks proved at surface in the district are Namurian (upper Carboniferous), which are known from boreholes to lie conformably on Tournasian to Visean (lower Carboniferous) mudstones and limestones. The Namurian rocks are represented by the Millstone Grit Group, a thick succession of interbedded sandstone, siltstone and mudstone and subordinate thin coals and seatearths. The Millstone Grit Group occurs at outcrop over most of the south central and eastern areas, and in the north-western corner of the district. Commonly it forms upland scenery with extensive moorland associated with poor acid soils. The thick sandstones form a series of dissected escarpments with thin peat cover. Much of this area provides a catchment for water supplied to the main urban centres of the district as well as Bury and Bolton in neighbouring districts; the sandstones have also been extensively exploited for building stone. The Millstone Grit Group is overlain by the Pennine Coal Measures Group of Langsettian (Westphalian A) age, a succession of mudstone, siltstone and sandstone with subordinate coal, seatearth and ironstone. The Coal Measures crop out extensively in the district. Most of the larger urban areas, including Blackburn, Accrington, Burnley and Rochdale, are sited on the Coal Measures. The abundant water helped to stimulate early urban development and the rapid expansion in the 19th century owes much to the mineral resources, including coal, brick clay and sandstone. Today, mineral extraction is much reduced and coal mining has virtually ceased with coal extracted only from opencast sites. Unconsolidated Quaternary deposits are present over much of the district and date from the last Devensian glaciation. The deposits either occur as a thin veneer on the higher ground or as thicker deposits on the lower ground, particularly within narrow channels carved into the bedrock. During the subsequent Flandrian, there was a significant development of landslips, which was caused by glacial overdeepening, stream rejuvenation in drift-filled valleys or faulting. Some of the glacial material has also been reworked to form river terraces and alluvium, and extensive peat development has occurred on the moorland.
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|Date made live:||29 Mar 2010 14:06|
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