Earth Science Conservation Review
| The Permian System in N. Ireland - Introduction | Antrim, Armagh, Down, Tyrone |
| Site Type: | Various |
| Site Status: | |
| Grid Reference: | |
| Google maps: | , |
| Rocks | |
|---|---|
| Rock Age: | Permian (Artinskian, Asselian, Kazanian, Kungurian, Lower Permian, Sakmarian, Tatrian, Upper Permian) |
| Rock Name: | Belfast Group, Enler Group |
| Rock Type: | Dolomitized limestone, Limestone, Mudstone, Sand, Sandstone, Siltstone |
| Interest | |
| Minerals: | Anhydrite, Gypsum, Halite |
| Other interest: | desert, sabkha |
Description:
INTRODUCTION
The Permian system was originally defined by Murchison in the Russian province of Perm and the stages of the system are shown below:
--------------------------------------------- | | | Tatarian | | | UPPER |-------------| | | | Kazanian | | |-------------|-------------| | | | Kungurian | | PERMIAN | |-------------| | | | Artinskian | | | LOWER |-------------| | | | Sakmarian | | | |-------------| | | | Asselian | ---------------------------------------------
These strata in the British Isles constitute a diverse assemblage mainly of almost barren continental sediments but varied by the presence of volcanic rocks and marine sediments. They present special difficulties in correlation, mainly because of their great lateral variability and, in many areas, their lack of usable fossils.
CORRELATION OF PERMIAN STRATA
The Permian sequences are divided into Lower and Upper Permian at the incoming of marine strata. In the British Isles sequences are divided into those present in the Bakevellia and Zechstein seas which it is assumed formed at the same time (Smith et al., 1974). The fauna of the Upper Permian carbonates is a key factor in correlation of the various marine sequences.
Pattison (1970) states that the use of faunal data in the correlation of Upper Permian strata is limited because of the close links between fauna and facies and from the poor preservation of the calcareous fossils. Fossiliferous marine strata are present in the Upper Permian sequences of the Bakevellia Sea basin with a fauna dominated by molluscs. From Grange, Belfast and Cultra collections were found to be dominated by bivalves, especially internal and external moulds of Bakevellia (B.) binneyi and gastropods. Foraminifera included Cyclogyra sp., Agathammina milioloides and Agathammina pusilla, while bryozoa from Grange included Batostomella and Thamniscus. Brachiopods collected by Hull et al. (1871) from Cultra included Productus horrida. The micro- and macrofaunas of the Magnesian Limestone were assessed by Pattison as indicating a correlation with the carbonate phases of the Zechstein 1 and 2 cycles of the Upper Permian succession in eastern England which is regarded as late Permian (Kazanian to Tatarian) in age.
Warrington (1995) described the palynology of sediments from the Larne No. 2 borehole and concluded that these were indicative of a late Permian age.
DISTRIBUTION OF PERMIAN STRATA IN NORTHERN IRELAND
There is a very limited outcrop of Permian strata in N. Ireland. Apart from Cultra (J412 809), Ballyrainey (J455 722) and Armagh City (H871 439) most data have been obtained from boreholes in East Tyrone, Armagh, Belfast, Ballyalton, Larne, Port More and on the Antrim Plateau. Exposures previously seen at Grange are no longer visible.
LITHOSTRATIGRAPHY OF THE PERMIAN
The generalised sequence of Permian sediments in N. Ireland is largely based on published works. The tripartite division of the strata was recognised by Fowler (1955) and Fowler and Robbie (1961) in East Tyrone:-
Upper Permian Marls; -Red marls, rarely green, with massive and fibrous gypsum bands Magnesian Limestone; -Yellow or cream calcareous dolomitic limestone containing quartz pebbles Basal Sands; -Dull red or purple friable sands with well-rounded quartz grains
A similar tripartite division in Belfast described the basal sequence as Basal Permian Sandstone and Brockram (Manning et al., 1979) and is similar to that at Cultra (Griffith & Wilson, 1982) (see Key Site 17 description).
The Larne No. 2 borehole proved a thick development of volcanic rocks at the base of the succession together with Upper Permian halites (Penn et al., 1983):-
Permian Upper Marls; -Reddish brown mudstones and siltstones with coarsely crystalline halite and anhydrite Magnesian Limestone; -Pale grey to white fine grained dolomite Lower Permian Sandstone; -Purple brown to red brown, very fine to very coarse grained, dolomitic and calcareous sandstones with siltstone interbeds Lower Permian Volcanics; -Tuffaceous siltstones, tuffs and lavas passing down to breccio-conglomerates and sandstones
In Armagh the tripartite division can still be recognised (GSNI, 1985).
The most recent revision of the stratigraphy of the Permian (Smith et al., 1991) was based on borehole sections in the Belfast Basin and Newtownards Trough:-
----------------------------------------------------------------- BELFAST GROUP ----------------------------------------------------------------- Belfast Basin | Newtownards Trough ---------------------------------|------------------------------- Connswater Marl Formation | Haw Hill Borehole Formation ----- | ----- Brick-red & brown silty mudstones|Reddish & brown mudstones & & siltstones, commonly calcareous|silty mudstones with inter- Towards the base anhydrite & |bedded laminated siltstone & gypsum veins occur |mudstone | Belfast Harbour Evaporite Fmn. | Newforte Breccia Formation ----- | ----- Dolomite & shelly limestone with |Breccia with a marl matrix with thin marls lying below 5m of |Lower Palaeozoic greywacke anhydrite |fragments ----------------------------------------------------------------- ENLER GROUP ----------------------------------------------------------------- Cornamuck Formation | Kennel Sandstone Formation ----- | ----- Medium-coarse grained red-brown |Medium-very coarse grained sandstones interbedded with |quartz sandstones breccias, white sandstones & | siltstones & mudstones | | Coolbeg Breccia Formation | Coolbeg Breccia Formation ----- | ----- Coarse breccia up to 8m thick |Coarse breccia up to 8m thick intercalated with red-brown |intercalated with red-brown sandstones up to 3m thick. |sandstones up to 3m thick. Breccia contain Lwr. Palaeozoic |Breccia contain Lwr. Palaeozoic greywackes, vein quartz & |greywackes, vein quartz & crystalline limestone fragments |crystalline limestone fragments -----------------------------------------------------------------
This division into the Lower Permian Enler Group and the Upper Permian Belfast Group can be applied to the other sequences in N. Ireland.
PERMIAN PALAEOGEOGRAPHY
(i) Early Permian
The first part of the early Permian in the British Isles was dominated by desert erosion and deposition; during this time the area lay deep within the Pangean supercontinent within a few degrees of the Equator. Profound geographical, structural and climatic changes resulted from Hercynian faulting, folding and uplift; these changes included the expulsion of all seas. Volcanoes and their products dominated the early Permian in N. Ireland.
The landscape was riven by downthrown graben which were limited by steep fault scarps. In the arid climate, weathering of the exposed rock surfaces produced a regolith of angular fragments in a comminuted matrix, which locally as piedmont screes reached very considerable thickness. This low lying desert with extensive thin spreads of gravel and small dune fields was widespread resulting in the accumulation of thick deposits of conglomerates and breccias.
(ii) Late Permian
The Upper Permian was ushered in by the widespread transgression of the Bakevellia Sea into the Irish Sea Basin. This inundation reduced the size of the sediment source areas. The marine carbonate Magnesian Limestone was deposited in the north while to the south thick beds of gypsum were formed in the Kingscourt area in shallow coastal lagoons or sabkhas. As time went on the shallowing seas in the whole basin were replaced by lagoonal conditions and beds of anhydrite together with mudstones and siltstones, often calcareous and with shallow water desiccation breccias and gypsum veins, were laid down. Evidence of hypersaline lakes at this time is provided by the late Permian halites in the Larne No. 2 borehole.
Throughout the Permian, the Dalradian ridge continued as a positive feature and Permian sediments north of this landmass are only known from the Port More borehole. In the west the sequences at Armagh and Grange were probably separated by another positive area, the Charlemont Block (Smith & Taylor, 1992).
The Permian system was originally defined by Murchison in the Russian province of Perm and the stages of the system are shown below:
--------------------------------------------- | | | Tatarian | | | UPPER |-------------| | | | Kazanian | | |-------------|-------------| | | | Kungurian | | PERMIAN | |-------------| | | | Artinskian | | | LOWER |-------------| | | | Sakmarian | | | |-------------| | | | Asselian | ---------------------------------------------
These strata in the British Isles constitute a diverse assemblage mainly of almost barren continental sediments but varied by the presence of volcanic rocks and marine sediments. They present special difficulties in correlation, mainly because of their great lateral variability and, in many areas, their lack of usable fossils.
CORRELATION OF PERMIAN STRATA
The Permian sequences are divided into Lower and Upper Permian at the incoming of marine strata. In the British Isles sequences are divided into those present in the Bakevellia and Zechstein seas which it is assumed formed at the same time (Smith et al., 1974). The fauna of the Upper Permian carbonates is a key factor in correlation of the various marine sequences.
Pattison (1970) states that the use of faunal data in the correlation of Upper Permian strata is limited because of the close links between fauna and facies and from the poor preservation of the calcareous fossils. Fossiliferous marine strata are present in the Upper Permian sequences of the Bakevellia Sea basin with a fauna dominated by molluscs. From Grange, Belfast and Cultra collections were found to be dominated by bivalves, especially internal and external moulds of Bakevellia (B.) binneyi and gastropods. Foraminifera included Cyclogyra sp., Agathammina milioloides and Agathammina pusilla, while bryozoa from Grange included Batostomella and Thamniscus. Brachiopods collected by Hull et al. (1871) from Cultra included Productus horrida. The micro- and macrofaunas of the Magnesian Limestone were assessed by Pattison as indicating a correlation with the carbonate phases of the Zechstein 1 and 2 cycles of the Upper Permian succession in eastern England which is regarded as late Permian (Kazanian to Tatarian) in age.
Warrington (1995) described the palynology of sediments from the Larne No. 2 borehole and concluded that these were indicative of a late Permian age.
DISTRIBUTION OF PERMIAN STRATA IN NORTHERN IRELAND
There is a very limited outcrop of Permian strata in N. Ireland. Apart from Cultra (J412 809), Ballyrainey (J455 722) and Armagh City (H871 439) most data have been obtained from boreholes in East Tyrone, Armagh, Belfast, Ballyalton, Larne, Port More and on the Antrim Plateau. Exposures previously seen at Grange are no longer visible.
LITHOSTRATIGRAPHY OF THE PERMIAN
The generalised sequence of Permian sediments in N. Ireland is largely based on published works. The tripartite division of the strata was recognised by Fowler (1955) and Fowler and Robbie (1961) in East Tyrone:-
Upper Permian Marls; -Red marls, rarely green, with massive and fibrous gypsum bands Magnesian Limestone; -Yellow or cream calcareous dolomitic limestone containing quartz pebbles Basal Sands; -Dull red or purple friable sands with well-rounded quartz grains
A similar tripartite division in Belfast described the basal sequence as Basal Permian Sandstone and Brockram (Manning et al., 1979) and is similar to that at Cultra (Griffith & Wilson, 1982) (see Key Site 17 description).
The Larne No. 2 borehole proved a thick development of volcanic rocks at the base of the succession together with Upper Permian halites (Penn et al., 1983):-
Permian Upper Marls; -Reddish brown mudstones and siltstones with coarsely crystalline halite and anhydrite Magnesian Limestone; -Pale grey to white fine grained dolomite Lower Permian Sandstone; -Purple brown to red brown, very fine to very coarse grained, dolomitic and calcareous sandstones with siltstone interbeds Lower Permian Volcanics; -Tuffaceous siltstones, tuffs and lavas passing down to breccio-conglomerates and sandstones
In Armagh the tripartite division can still be recognised (GSNI, 1985).
The most recent revision of the stratigraphy of the Permian (Smith et al., 1991) was based on borehole sections in the Belfast Basin and Newtownards Trough:-
----------------------------------------------------------------- BELFAST GROUP ----------------------------------------------------------------- Belfast Basin | Newtownards Trough ---------------------------------|------------------------------- Connswater Marl Formation | Haw Hill Borehole Formation ----- | ----- Brick-red & brown silty mudstones|Reddish & brown mudstones & & siltstones, commonly calcareous|silty mudstones with inter- Towards the base anhydrite & |bedded laminated siltstone & gypsum veins occur |mudstone | Belfast Harbour Evaporite Fmn. | Newforte Breccia Formation ----- | ----- Dolomite & shelly limestone with |Breccia with a marl matrix with thin marls lying below 5m of |Lower Palaeozoic greywacke anhydrite |fragments ----------------------------------------------------------------- ENLER GROUP ----------------------------------------------------------------- Cornamuck Formation | Kennel Sandstone Formation ----- | ----- Medium-coarse grained red-brown |Medium-very coarse grained sandstones interbedded with |quartz sandstones breccias, white sandstones & | siltstones & mudstones | | Coolbeg Breccia Formation | Coolbeg Breccia Formation ----- | ----- Coarse breccia up to 8m thick |Coarse breccia up to 8m thick intercalated with red-brown |intercalated with red-brown sandstones up to 3m thick. |sandstones up to 3m thick. Breccia contain Lwr. Palaeozoic |Breccia contain Lwr. Palaeozoic greywackes, vein quartz & |greywackes, vein quartz & crystalline limestone fragments |crystalline limestone fragments -----------------------------------------------------------------
This division into the Lower Permian Enler Group and the Upper Permian Belfast Group can be applied to the other sequences in N. Ireland.
PERMIAN PALAEOGEOGRAPHY
(i) Early Permian
The first part of the early Permian in the British Isles was dominated by desert erosion and deposition; during this time the area lay deep within the Pangean supercontinent within a few degrees of the Equator. Profound geographical, structural and climatic changes resulted from Hercynian faulting, folding and uplift; these changes included the expulsion of all seas. Volcanoes and their products dominated the early Permian in N. Ireland.
The landscape was riven by downthrown graben which were limited by steep fault scarps. In the arid climate, weathering of the exposed rock surfaces produced a regolith of angular fragments in a comminuted matrix, which locally as piedmont screes reached very considerable thickness. This low lying desert with extensive thin spreads of gravel and small dune fields was widespread resulting in the accumulation of thick deposits of conglomerates and breccias.
(ii) Late Permian
The Upper Permian was ushered in by the widespread transgression of the Bakevellia Sea into the Irish Sea Basin. This inundation reduced the size of the sediment source areas. The marine carbonate Magnesian Limestone was deposited in the north while to the south thick beds of gypsum were formed in the Kingscourt area in shallow coastal lagoons or sabkhas. As time went on the shallowing seas in the whole basin were replaced by lagoonal conditions and beds of anhydrite together with mudstones and siltstones, often calcareous and with shallow water desiccation breccias and gypsum veins, were laid down. Evidence of hypersaline lakes at this time is provided by the late Permian halites in the Larne No. 2 borehole.
Throughout the Permian, the Dalradian ridge continued as a positive feature and Permian sediments north of this landmass are only known from the Port More borehole. In the west the sequences at Armagh and Grange were probably separated by another positive area, the Charlemont Block (Smith & Taylor, 1992).
| Enlander, I., Dempster, M. & Doughty, P., 2024. The Permian System in N. Ireland - Introduction, County Antrim, Armagh, Down, Tyrone, site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=1191. Accessed on 2024-12-26 |
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