Category:Scotland Chalk nomenclature (Scottish Chalk Province) - Inner Hebrides Group: Difference between revisions

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[[Category:Scotland_Chalk_nomenclature_(Scottish_Chalk_Province)]]
Name
 
 
 
The Inner Hebrides Group was formally proposed by Braley (1990). See also Lowden, Braley, Hurst, and Lewis, (1992) and Mortimore, Wood, and Gallois, (2001) in which volume a number of the correlations in the earlier work are adjusted and the dating of the sequence refined.
 
 
 
 
 
 
 
''Type section''
 
 
 
At various localities for the constituent formations in the Inner Hebrides and Morvern. Principal exposures are at Beinn Iadain and Loch Aline Mine in Morvern, at Gribun, Carsaig and Auchnacraig on Mull, at Clach Alasdair and Laig Gorge on Eigg and Strathaird on Skye.
 
 
 
 
 
 
 
''Primary Reference Section''
 
 
 
At the type-sites of the constituent formations and members.
 
 
 
 
 
 
 
Formal subdivisions
 
 
 
Divided into seven formations and a number of constituent members. These are from the oldest the Morvern Greensand Formation, Lochaline White Sandstone Formation, Coire Riabhach Phosphatic Formation, Gribun Chalk Formation, Feorlin Sandstone Formation, Strathaird Limestone Formation (including the Clach Alasdair Conglomerate Member and Laig Gorge Sandstone Member) and the Beinn Iadain Mudstone Formation. This latter probably principally of basal Palaeogene in age a description is included herein for completeness.
 
 
 
''' '''
 
 
 
''Lithology ''
 
 
 
Glauconitic sandstones, pure silica sands, silicified chalks, flints and conglomerates.
 
 
 
 
 
 
 
''Definition of upper boundary''
 
 
 
Unconformable beneath the Paleocene lavas or conformable (?) beneath the Beinn Iadain Mudstone Formation of presumed Paleocene age.
 
 
 
 
 
 
 
''Definition of lower boundary ''
 
 
 
Unconformable at the erosion surface below the Morvern Greensand Formation.
 
 
 
 
 
 
 
''Thickness''
 
 
 
The group comprises a highly condensed sequence and is variable in thickness depending on the relative development of its constituent parts. The group may be as little as a few metres thick but is between 10 to 15 m on Mull and between 11 to 22 m in Morvern.
 
 
 
 
 
 
 
Distribution
 
 
 
Known from the Inner Hebrides islands of Mull, Eigg, Skye, Scalpay, Soay and Raasay and also from the Morvern district of the Scottish mainland.
 
 
 
 
 
 
 
''Previous names''
 
 
 
Generally the Cretaceous rocks of the Inner Hebrides have been described using that title or, because of their limited outcrop, as individual constituent units attached to a locality i.e. Morvern Greensand. Some of these gained greater acceptance and were applied more widely.
 
 
 
 
 
 
 
Parent
 
 
 
None
 
 
 
 
 
 
 
Age and biostratigraphy
 
 
 
Upper Cretaceous, Cenomanian to early Campanian.
 
 
 
 
 
 
 
''References''
 
 
 
Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001).
 
[[Category:Scotland_Chalk_nomenclature_(Scottish_Chalk_Province) | ]]

Revision as of 10:59, 28 January 2014


Name


The Inner Hebrides Group was formally proposed by Braley (1990). See also Lowden, Braley, Hurst, and Lewis, (1992) and Mortimore, Wood, and Gallois, (2001) in which volume a number of the correlations in the earlier work are adjusted and the dating of the sequence refined.




Type section


At various localities for the constituent formations in the Inner Hebrides and Morvern. Principal exposures are at Beinn Iadain and Loch Aline Mine in Morvern, at Gribun, Carsaig and Auchnacraig on Mull, at Clach Alasdair and Laig Gorge on Eigg and Strathaird on Skye.




Primary Reference Section


At the type-sites of the constituent formations and members.




Formal subdivisions


Divided into seven formations and a number of constituent members. These are from the oldest the Morvern Greensand Formation, Lochaline White Sandstone Formation, Coire Riabhach Phosphatic Formation, Gribun Chalk Formation, Feorlin Sandstone Formation, Strathaird Limestone Formation (including the Clach Alasdair Conglomerate Member and Laig Gorge Sandstone Member) and the Beinn Iadain Mudstone Formation. This latter probably principally of basal Palaeogene in age a description is included herein for completeness.



Lithology


Glauconitic sandstones, pure silica sands, silicified chalks, flints and conglomerates.




Definition of upper boundary


Unconformable beneath the Paleocene lavas or conformable (?) beneath the Beinn Iadain Mudstone Formation of presumed Paleocene age.




Definition of lower boundary


Unconformable at the erosion surface below the Morvern Greensand Formation.




Thickness


The group comprises a highly condensed sequence and is variable in thickness depending on the relative development of its constituent parts. The group may be as little as a few metres thick but is between 10 to 15 m on Mull and between 11 to 22 m in Morvern.




Distribution


Known from the Inner Hebrides islands of Mull, Eigg, Skye, Scalpay, Soay and Raasay and also from the Morvern district of the Scottish mainland.




Previous names


Generally the Cretaceous rocks of the Inner Hebrides have been described using that title or, because of their limited outcrop, as individual constituent units attached to a locality i.e. Morvern Greensand. Some of these gained greater acceptance and were applied more widely.




Parent


None




Age and biostratigraphy


Upper Cretaceous, Cenomanian to early Campanian.




References


Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001).