Scotland Chalk nomenclature (Scottish Chalk Province) - Inner Hebrides Group: Strathaird Limestone Formation: Difference between revisions
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=====Name===== | |||
Name | |||
The Strathaird Limestone Formation was formally proposed by Braley (1990). | The Strathaird Limestone Formation was formally proposed by Braley (1990). | ||
=====''Type section''===== | |||
''Type section'' | |||
Strathaird [NG 5365 1790], Skye. | Strathaird [NG 5365 1790], Skye. | ||
=====''Primary Reference Section''===== | |||
''Primary Reference Section'' | |||
Laig Gorge [NM 4735 8750] on Eigg, Camasunary [NG 5181 1775], and two sections at Allt Eoghainn, Strollamus [NG 5965 2645] on Skye, An Leac headland, Soay Sound [NG 4400 1695], and numerous localities of the Clach Alasdair Conglomerate Member on Mull. | Laig Gorge [NM 4735 8750] on Eigg, Camasunary [NG 5181 1775], and two sections at Allt Eoghainn, Strollamus [NG 5965 2645] on Skye, An Leac headland, Soay Sound [NG 4400 1695], and numerous localities of the Clach Alasdair Conglomerate Member on Mull. | ||
=====Formal subdivision===== | |||
Formal subdivision | |||
Includes the Clach Alasdair Conglomerate Member and the Laig Gorge Sandstone Member. | Includes the Clach Alasdair Conglomerate Member and the Laig Gorge Sandstone Member. | ||
=====''Lithology ''===== | |||
''Lithology '' | |||
Dark grey micritic limestone and two clastic members. A basal Laig Gorge Sandstone member and the Clach Alasdair Conglomerate Member. | Dark grey micritic limestone and two clastic members. A basal Laig Gorge Sandstone member and the Clach Alasdair Conglomerate Member. | ||
=====''Definition of upper boundary''===== | |||
''Definition of upper boundary'' | |||
Unconformable below the Beinn Iadain Mudstone Formation or at an erosion surface beneath the Palaeogene basalts. | Unconformable below the Beinn Iadain Mudstone Formation or at an erosion surface beneath the Palaeogene basalts. | ||
=====''Definition of lower boundary ''===== | |||
''Definition of lower boundary '' | |||
Unconformable upon the Gribun Chalk Formation and Feorlin Sandstone Formation. | Unconformable upon the Gribun Chalk Formation and Feorlin Sandstone Formation. | ||
=====''Thickness''===== | |||
''Thickness'' | |||
2 to 6 m on Eigg, 2.5 m on Skye and 2 m of the Clach Alasdair Conglomerate Member on Mull. | 2 to 6 m on Eigg, 2.5 m on Skye and 2 m of the Clach Alasdair Conglomerate Member on Mull. | ||
=====Distribution===== | |||
Distribution | |||
Throughout the Inner Hebrides islands but poorly represented in Morvern. | Throughout the Inner Hebrides islands but poorly represented in Morvern. | ||
=====''Previous names''===== | |||
''Previous names'' | |||
Part of the Silicified Chalk and its derivative names in earlier accounts. | Part of the Silicified Chalk and its derivative names in earlier accounts. | ||
NOTE: - Hancock (2000), confusingly, utilised the term Gribun Formation or Gribun Conglomerate Formation to describe rocks above the Chalk (silicified Chalk) of? Santonian age which is the named Gribun Chalk Formation. This unit is probably equivalent to the Strathaird Limestone Formation (in part) of Braley (1990) or the Clach Alasdair Conglomerate Member of Mortimore, Woods and Gallois (2001). Probably the same beds as Hancock's (2000) Gribun Chalk. | NOTE: - Hancock (2000), confusingly, utilised the term Gribun Formation or Gribun Conglomerate Formation to describe rocks above the Chalk (silicified Chalk) of? Santonian age which is the named Gribun Chalk Formation. This unit is probably equivalent to the Strathaird Limestone Formation (in part) of Braley (1990) or the Clach Alasdair Conglomerate Member of Mortimore, Woods and Gallois (2001). Probably the same beds as Hancock's (2000) Gribun Chalk. | ||
Probably equivalent to the Laig Gorge Limestone Member (LAGL) as mapped on Rum Sheet 60 where Braley (1990) uses the name Strathaird Limestone Formation. | Probably equivalent to the Laig Gorge Limestone Member (LAGL) as mapped on Rum Sheet 60 where Braley (1990) uses the name Strathaird Limestone Formation. | ||
=====Parent===== | |||
Parent | |||
Inner Hebrides Group. | Inner Hebrides Group. | ||
=====''Age and biostratigraphy ''===== | |||
''Age and biostratigraphy '' | |||
Upper Cretaceous, Turonian. | Upper Cretaceous, Turonian. | ||
=====''References''===== | |||
''References'' | |||
Braley (1990); Lowden, Braley, Hurst and Lewis (1992). | Braley (1990); Lowden, Braley, Hurst and Lewis (1992). | ||
This Formation is not mentioned in Mortimore, Wood and Gallois (2001) although the Clach Alasdair Conglomerate Member is utilised for the beds intervening between the Gribun Chalk Formation and the Ben Iadain Mudstone Formation. | This Formation is not mentioned in Mortimore, Wood and Gallois (2001) although the Clach Alasdair Conglomerate Member is utilised for the beds intervening between the Gribun Chalk Formation and the Ben Iadain Mudstone Formation. | ||
====Clach Alasdair Conglomerate Member==== | |||
=====''Name''===== | |||
''Name'' | |||
The Clach Alasdair Conglomerate Member was formally proposed by Braley (1990). | The Clach Alasdair Conglomerate Member was formally proposed by Braley (1990). | ||
=====''Type section''===== | |||
''Type section'' | |||
Clach Alasdair [NM 4540 8831], Eigg. | Clach Alasdair [NM 4540 8831], Eigg. | ||
=====''Primary Reference Section''===== | |||
''Primary Reference Section'' | |||
Caisteal Sloc nam Ban [NM 431 312] in the Wilderness and Allt na Teangaidh [NM 453 328] on Mull. Strathaird [NG 5365 1790] on Skye. | Caisteal Sloc nam Ban [NM 431 312] in the Wilderness and Allt na Teangaidh [NM 453 328] on Mull. Strathaird [NG 5365 1790] on Skye. | ||
=====Formal subdivision===== | |||
Formal subdivision | |||
None | None | ||
=====Lithology===== | |||
Lithology | |||
Conglomerate (principally silicified chalk clasts) with a coarse sandstone matrix. | Conglomerate (principally silicified chalk clasts) with a coarse sandstone matrix. | ||
=====''Definition of upper boundary''===== | |||
''Definition of upper boundary'' | |||
Top of member not seen at the type-site at Clach Alasdair on Eigg nor at Strathaird on Skye. | Top of member not seen at the type-site at Clach Alasdair on Eigg nor at Strathaird on Skye. | ||
May be unconformable beneath the Ben Iadain Mudstone Formation at the Gribun, Allt na Teangaidh, Mull (Mortimore, Wood and Gallois, 2001). | May be unconformable beneath the Ben Iadain Mudstone Formation at the Gribun, Allt na Teangaidh, Mull (Mortimore, Wood and Gallois, 2001). | ||
=====Definition of lower boundary===== | |||
Definition of lower boundary | |||
Unconformable on beds attributed to the Morvern Greensand at the Clach Alasdair type-site on Eigg (Braley, 1990), and unconformable on the Strathaird Limestone Formation at the type-site of that unit on Skye. Considered to rest on the Gribun Chalk Formation elsewhere according to Mortimore, Wood and Gallois (2001).'' '' | Unconformable on beds attributed to the Morvern Greensand at the Clach Alasdair type-site on Eigg (Braley, 1990), and unconformable on the Strathaird Limestone Formation at the type-site of that unit on Skye. Considered to rest on the Gribun Chalk Formation elsewhere according to Mortimore, Wood and Gallois (2001).'' '' | ||
=====''Thickness''===== | |||
''Thickness'' | |||
0.5 m at Strathaird and 0.4 m at Clach Alasdair in Braley (1990) and up to 2.5 m at Caisteal Sloc nam Ban, Mull in Mortimore, Wood and Gallois (2001). | 0.5 m at Strathaird and 0.4 m at Clach Alasdair in Braley (1990) and up to 2.5 m at Caisteal Sloc nam Ban, Mull in Mortimore, Wood and Gallois (2001). | ||
=====Distribution===== | |||
Distribution | |||
Known throughout the Inner Hebrides Eigg, Skye and Mull and in Morvern. | Known throughout the Inner Hebrides Eigg, Skye and Mull and in Morvern. | ||
=====''Previous names''===== | |||
''Previous names'' | |||
None | None | ||
=====Parent===== | |||
Parent | |||
Strathaird Limestone Formation. | Strathaird Limestone Formation. | ||
=====''Age and biostratigraphy ''===== | |||
''Age and biostratigraphy '' | |||
Upper Cretaceous, Turonian, but considered to be Campanian in age by Mortimore, Wood and Gallois (2001). | Upper Cretaceous, Turonian, but considered to be Campanian in age by Mortimore, Wood and Gallois (2001). | ||
=====''References''===== | |||
''References'' | |||
Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001). | Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001). | ||
(In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined). | (In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined). | ||
====Laig Gorge Sandstone Member==== | |||
=====''Name''===== | |||
''Name'' | |||
The Laig Gorge Sandstone Member was formally proposed by Braley (1990). | The Laig Gorge Sandstone Member was formally proposed by Braley (1990). | ||
=====''Type section''===== | |||
''Type section'' | |||
Laig Gorge [NM 4735 8750] on Eigg. | Laig Gorge [NM 4735 8750] on Eigg. | ||
=====''Primary Reference Section''===== | |||
''Primary Reference Section'' | |||
Strathaird [NG 5365 1790] on Skye. | Strathaird [NG 5365 1790] on Skye. | ||
=====Formal subdivision===== | |||
Formal subdivision | |||
None | None | ||
=====''Lithology ''===== | |||
''Lithology '' | |||
Medium- to coarse-grained poorly sorted sandstones and conglomerates. | Medium- to coarse-grained poorly sorted sandstones and conglomerates. | ||
=====''Definition of upper boundary''===== | |||
''Definition of upper boundary'' | |||
Unconformable at an erosion surface above a coarse very poorly sorted conglomerate with the grey micritic limestones of the remainder of the Strathaird Limestone Formation at Strathaird on Skye but apparently conformable at a burrowed horizon with the same limestones at Laig Gorge on Eigg. | Unconformable at an erosion surface above a coarse very poorly sorted conglomerate with the grey micritic limestones of the remainder of the Strathaird Limestone Formation at Strathaird on Skye but apparently conformable at a burrowed horizon with the same limestones at Laig Gorge on Eigg. | ||
=====''Definition of lower boundary ''===== | |||
''Definition of lower boundary '' | |||
Unconformable on the Gribun Chalk Formation but considered absent in Mull and Morvern by Mortimore, Wood and Gallois (2001). This is the basal unit of the Strathaird Limestone Formation according to Braley (1990). | Unconformable on the Gribun Chalk Formation but considered absent in Mull and Morvern by Mortimore, Wood and Gallois (2001). This is the basal unit of the Strathaird Limestone Formation according to Braley (1990). | ||
=====''Thickness''===== | |||
''Thickness'' | |||
3.0 m at Laig Gorge, Eigg. | 3.0 m at Laig Gorge, Eigg. | ||
=====Distribution===== | |||
Distribution | |||
Known on the islands of Eigg and Skye. | Known on the islands of Eigg and Skye. | ||
=====''Previous names''===== | |||
''Previous names'' | |||
None | None | ||
=====Parent===== | |||
Parent | |||
Strathaird Limestone Formation. | Strathaird Limestone Formation. | ||
=====''Age and biostratigraphy ''===== | |||
''Age and biostratigraphy '' | |||
Upper Cretaceous, Turonian. | Upper Cretaceous, Turonian. | ||
=====''References''===== | |||
''References'' | |||
Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001). In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined. The member is not considered to be in the sequences on Mull or Morvern. | Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001). In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined. The member is not considered to be in the sequences on Mull or Morvern. | ||
[[category:Scotland_Chalk_nomenclature_(Scottish_Chalk_Province)_-_Inner_Hebrides_Group | 05]] | [[category:Scotland_Chalk_nomenclature_(Scottish_Chalk_Province)_-_Inner_Hebrides_Group | 05]] | ||
Revision as of 15:08, 6 February 2014
Name
The Strathaird Limestone Formation was formally proposed by Braley (1990).
Type section
Strathaird [NG 5365 1790], Skye.
Primary Reference Section
Laig Gorge [NM 4735 8750] on Eigg, Camasunary [NG 5181 1775], and two sections at Allt Eoghainn, Strollamus [NG 5965 2645] on Skye, An Leac headland, Soay Sound [NG 4400 1695], and numerous localities of the Clach Alasdair Conglomerate Member on Mull.
Formal subdivision
Includes the Clach Alasdair Conglomerate Member and the Laig Gorge Sandstone Member.
Lithology
Dark grey micritic limestone and two clastic members. A basal Laig Gorge Sandstone member and the Clach Alasdair Conglomerate Member.
Definition of upper boundary
Unconformable below the Beinn Iadain Mudstone Formation or at an erosion surface beneath the Palaeogene basalts.
Definition of lower boundary
Unconformable upon the Gribun Chalk Formation and Feorlin Sandstone Formation.
Thickness
2 to 6 m on Eigg, 2.5 m on Skye and 2 m of the Clach Alasdair Conglomerate Member on Mull.
Distribution
Throughout the Inner Hebrides islands but poorly represented in Morvern.
Previous names
Part of the Silicified Chalk and its derivative names in earlier accounts.
NOTE: - Hancock (2000), confusingly, utilised the term Gribun Formation or Gribun Conglomerate Formation to describe rocks above the Chalk (silicified Chalk) of? Santonian age which is the named Gribun Chalk Formation. This unit is probably equivalent to the Strathaird Limestone Formation (in part) of Braley (1990) or the Clach Alasdair Conglomerate Member of Mortimore, Woods and Gallois (2001). Probably the same beds as Hancock's (2000) Gribun Chalk.
Probably equivalent to the Laig Gorge Limestone Member (LAGL) as mapped on Rum Sheet 60 where Braley (1990) uses the name Strathaird Limestone Formation.
Parent
Inner Hebrides Group.
Age and biostratigraphy
Upper Cretaceous, Turonian.
References
Braley (1990); Lowden, Braley, Hurst and Lewis (1992).
This Formation is not mentioned in Mortimore, Wood and Gallois (2001) although the Clach Alasdair Conglomerate Member is utilised for the beds intervening between the Gribun Chalk Formation and the Ben Iadain Mudstone Formation.
Clach Alasdair Conglomerate Member
Name
The Clach Alasdair Conglomerate Member was formally proposed by Braley (1990).
Type section
Clach Alasdair [NM 4540 8831], Eigg.
Primary Reference Section
Caisteal Sloc nam Ban [NM 431 312] in the Wilderness and Allt na Teangaidh [NM 453 328] on Mull. Strathaird [NG 5365 1790] on Skye.
Formal subdivision
None
Lithology
Conglomerate (principally silicified chalk clasts) with a coarse sandstone matrix.
Definition of upper boundary
Top of member not seen at the type-site at Clach Alasdair on Eigg nor at Strathaird on Skye.
May be unconformable beneath the Ben Iadain Mudstone Formation at the Gribun, Allt na Teangaidh, Mull (Mortimore, Wood and Gallois, 2001).
Definition of lower boundary
Unconformable on beds attributed to the Morvern Greensand at the Clach Alasdair type-site on Eigg (Braley, 1990), and unconformable on the Strathaird Limestone Formation at the type-site of that unit on Skye. Considered to rest on the Gribun Chalk Formation elsewhere according to Mortimore, Wood and Gallois (2001).
Thickness
0.5 m at Strathaird and 0.4 m at Clach Alasdair in Braley (1990) and up to 2.5 m at Caisteal Sloc nam Ban, Mull in Mortimore, Wood and Gallois (2001).
Distribution
Known throughout the Inner Hebrides Eigg, Skye and Mull and in Morvern.
Previous names
None
Parent
Strathaird Limestone Formation.
Age and biostratigraphy
Upper Cretaceous, Turonian, but considered to be Campanian in age by Mortimore, Wood and Gallois (2001).
References
Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001).
(In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined).
Laig Gorge Sandstone Member
Name
The Laig Gorge Sandstone Member was formally proposed by Braley (1990).
Type section
Laig Gorge [NM 4735 8750] on Eigg.
Primary Reference Section
Strathaird [NG 5365 1790] on Skye.
Formal subdivision
None
Lithology
Medium- to coarse-grained poorly sorted sandstones and conglomerates.
Definition of upper boundary
Unconformable at an erosion surface above a coarse very poorly sorted conglomerate with the grey micritic limestones of the remainder of the Strathaird Limestone Formation at Strathaird on Skye but apparently conformable at a burrowed horizon with the same limestones at Laig Gorge on Eigg.
Definition of lower boundary
Unconformable on the Gribun Chalk Formation but considered absent in Mull and Morvern by Mortimore, Wood and Gallois (2001). This is the basal unit of the Strathaird Limestone Formation according to Braley (1990).
Thickness
3.0 m at Laig Gorge, Eigg.
Distribution
Known on the islands of Eigg and Skye.
Previous names
None
Parent
Strathaird Limestone Formation.
Age and biostratigraphy
Upper Cretaceous, Turonian.
References
Braley (1990); Lowden, Braley, Hurst and Lewis (1992); Mortimore, Wood and Gallois (2001). In this volume a number of the correlations in the earlier works are adjusted and the dating of the sequence refined. The member is not considered to be in the sequences on Mull or Morvern.