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Earth Science Conservation Review
| Helen’s Bay – Grey Point – Lower Palaeozoic | Down |
| Site number: | 1351 | ||
| Locality Type: | Coastal Section, Foreshore | Status: | ASSI |
| Grid Reference: | J458832 | ||
| Google maps: | 54.67622,-5.73969 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Ordovician | ||
| Stages: | Ashgill | ||
| Site Description | |
|---|---|
| Highlights: | |
The Northern Belt of the Southern Uplands of Scotland has many outcrops of pillow lava, volcanic agglomerate and olistostromes. These unusual lithologies are critical to identifying and reconstructing the depositional environment and tectonic setting of the whole Southern Uplands Terrane. In the Irish continuation of the Southern Uplands such rocks are less common and/or less well exposed. The short coastal section from Helen’s Bay to Grey Point provides easy access to the best Irish outcrops. Additionally, in the outcrop at Grey Point, there are unusually clear examples of the sedimentary structures associated with high energy, proximal, turbidite sedimentation. The whole well exposed lithological succession is typical of that in the fault bounded tracts which compose the Northern Belt of the Southern Uplands-Down-Longford Terrane. | |
| Introduction: | |
The Southern Uplands - Down - Longford Terrane consists of a series of ‘blocks’ or ‘tracts’ each bounded to the north and south by important faults tracing ENE-WSW, parallel to the regional strike of bedding and formation boundaries. Craig (1982, 1984) recognised five such blocks composing the Northern Belt in Down, of which the Ballygrot Block is the oldest, most northerly and most lithologically varied. It consists of three formations: the Helen’s Bay Formation, with the spilitic pillow lavas of the Horse Rock Member near its base, the Grey Point Formation and the Rockport Formation. The rocky coast from Helen’s Bay to Grey Point, trending perpendicular to the regional strike, is the natural type locality for the first two formations, providing an excellent stratigraphic section Lapworth (1877) and Swanston (1877) identified graptolites collected from black shales in the Helen’s Bay Formation and assigned them to a late Glenkiln (? early Caradoc) age. Further collecting by Sharpe (1970) and Craig (1982) from approximately the same locality, the latter collection identified by R.B. Rickards, clearly indicates that deposition of the Helen’s Bay Formation was, at least in part, during the Nemagraptus gracilis Biozone (Lower Glenkiln). Toghill, in the Geological Survey Memoir for Northern Ireland Sheet 29 (Griffith and Wilson 1982, p.8)), “concludes that although the fauna (collected by the Survey) contains elements suggestive of the gracilis Zone much of it indicates peltifer Zone, i.e. Upper Glenkiln. There is a suggestion that other zones of the Lower and Upper Hartfell are present in the succession toward Grey Point to the north but these have not been unequivocally identified”. The Grey Point and Rockport Formations have yet to yield identifiable fossils but rest on and so can be reasonably assumed to be slightly younger than the Helen’s Bay Formation. The distinctive character of the rocks at the western end of Helen’s Bay was noted by du Noyer (in Hull et al.1871), who speculated that they might be Cambrian in age. Sharpe (1970), during his undergraduate project mapping at Queen’s University, was the first to recognise that the Horse Rock promontory is largely composed of spilitic pillow lavas erupted on the Ordovician sea floor. Craig (1982) provided detailed major and trace element analyses of the igneous rocks in the Helen’s Bay Formation, amply confirming Sharpe’s conclusion and identifying them as tholeiitic, ocean floor basalts, in their chemical composition “most similar to those of the Carlsberg and Palmer Ridges” and essentially comparable to other occurrences of sea-floor spilites of the same age in various parts of the Southern Uplands Northern Belt and in its south-westerly continuation to County Longford. | |
| Description: | |
Following Craig (1982, 1984), with some amendments, the distribution of the formations and members exposed in the coastal outcrop between Helen’s Bay and Grey Point is shown on the accompanying geological map and their lithostratigraphy given on the separate table. The oldest rocks occur at the southern end of the section and appear to young or face continuously northward to Grey Point. Numerous strike-parallel faults may effect some repetition or excision in the stratigraphic succession but there are no reasons to infer that any of these faults effect a large displacement. At the north-western end of Helen’s Bay beach a rock outcrop, some 20m wide and 33m across strike, is of much brecciated and altered basic igneous rock, some weakly layered volcaniclastic sediment and some brecciated pillows of about 0.3m diameter. Sharpe (1970) identified the bulk of the rock as metadolerite, ophitic textured and composed of plagioclase “almost entirely altered to calcite, chlorite and sphene” and “one pyroxene, partly altered to a colourless fibrous material which is probably uralite. The mesostasis is pale green chlorite and calcite”. The outcrop is veined and shattered throughout, typically on a centimetre scale. Sharpe noted veins of fine grained material, similar to the spilite of the pillow lava to the north, within the metadolerite and chilled against it. There is also some roughly layered or bedded sedimentary material and a few brecciated pillows. Craig (1982, p.18) noted “two highly altered black shale and mudstone xenoliths (2.5 by 1 metre) enclosed in the metadolerite and inferred from this observation that the metadolerite had been intruded into the black shales of the Helen’s Bay Formation and hence that the intrusion was of syn- or post-gracilis Zone age. A few thin (c.5cm) anastamosing veins of fresh fine-grained black basalt occur some 11m south of the wall at the north end of the outcrop. These veins are, by their fresh texture under the microscope, almost certainly Tertiary intrusions. A recently constructed sea wall and a slipway have much reduced the former exposure of metadolerite, separating it from the rest of the outcrop of the Helen’s Bay Formation. Sharpe (1970) estimated the exposed thickness of the metadolerite at 200 feet (c. 61m). At present there is an exposed stratigraphic thickness of no more than 30m of rock, measured perpendicular to the rough layering which strikes at about 110o and inclines between 5o and 75o SSE. For some 25m to the north of the metadolerite outcrop is completely covered by the concrete slipway. According to the Survey Memoir of 1871 the outcrop once included a band of graptolitic shale between two faults. Sharpe (1970) estimated the width of that shale at 70 feet (c. 21m). Immediately north of the concrete some 3m of fine grained, brecciated and veined, red and green-grey volcanoclastics crop out, terminating against a steep E-W fault face on the south side of Horse Rock. The Horse Rock promontory, which projects some 25m eastward into the bay, is largely composed of fine grained, greenish grey, pillows of soda-rich basalt (spilite) set in a matrix of pale green, fine grained, feldspathic silt and sand, siliceous mudstone and chert. Pillows range from about 8 to 60cm in diameter and are commonly flattened in layers striking at about 70 o and inclining between 50 o and 65 o to the SSE (Plate 1). Many of the pillows are broken and veined but several pillows have shapes clearly demonstrating that the local stratigraphy is inverted, facing or younging down to the north-west. A text-book example of a downward-facing pillow, 45cm by 22cm and flat in the bedding, occurs 2m south of a rusty iron mooring peg at the NE tip of Horse Rock (Plate 2). 5m westward, along the bathers’ path to the point, many pillows have the polished, green, “snakeskin” appearance characteristic of the weathered fine-grained basic rocks in many ophiolite sequences. The pillow lavas, with a stratigraphic thickness of 18m, form the Horse Rock Member of the Helen’s Bay Formation (Craig 1982). Craig (1982, pp 134 -150) provided a detailed account of the petrography and geochemistry of the lavas and of the associated metadolerite. The chemical compositions of the analysed samples, plot clearly and consistently as tholeiitic, ocean-floor basalts on a variety of discrimination diagrams. North-westward the pillow lavas are succeeded by a conglomerate of angular and sub-rounded clasts of spilite, 1 to 10cm in diameter, set in a soft green or reddish green feldspathic and siliceous sand and mud matrix (Plate 3). Craig (1982) described the contact between pillow lavas and conglomerate as sharp and sinuous. It is in part clearly faulted and in part apparently gradational. The conglomerate was originally described by Sharpe (1970, p. 300) as a tuffaceous agglomerate. Though the latter term is not unreasonable, given the igneous composition of the clasts, careful examination shows that all are of rounded, reworked material rather than primary volcanic ejecta (Craig 1982, p.20) and the rock is thus more properly described as an organised conglomerate, albeit entirely of reworked, resedimented, igneous rock. The fine grained matrix carries a well developed tectonic cleavage, dipping 55 o to 145 o, which appears to “flow” round the spilite clasts. These clasts are somewhat flattened in the cleavage plane and locally have a weak tectonic extension obliquely down dip (c. 40 o to 115 o). The conglomerate has a stratigraphic thickness of about 6m. In the south-eastern corner of the small bay to the north of Horse Rock (at J45898308) the conglomerate is faulted against some 3m of black shales in which, even at their exposed base, there are blocks and lenses of light grey, fine grained sandstone up to 20cm in diameter. This separating fault appears to be colinear, on a trace at 072o with the scarp forming the northern edge of Horse Rock. Nine metres of sand and shingle separate this first outcrop of black shale from more continuous black shale with numerous clasts of sandstone, spilite and chert occupying the coastal strip to the north. Elsewhere in County Down there are many outcrops of pelagic black shales within the turbidite succession, most notably at Coalpit Bay and Tieveshilly, but the black shales of the Helen’s Bay Formation are quite distinctive in the persistent presence of blocks and lenses of medium to light grey sandstone, spilite and chert. These occur as clasts and rafts, ranging from a few centimetres to at least 7m in maximum diameter, within the shales (Plate 4). The shale matrix is tectonically cleaved and the cleavage is commonly bent and wrapped around the larger sandstone clasts. Though essentially planar the cleavage is also locally scaly and anastamosing, in the style of the scaly cleavage seen in many fine grained mélanges and olistostromes. Many small (metre-scale) irregular folds contort both bedding and cleavage. Despite sedimentary and tectonic deformation graptolites and graptolite fragments are readily obtained from the black shale, particularly where bedding and cleavage are strictly parallel. Craig (1982, pp. 20 - 22) considered the alternative tectonic and sedimentary processes which might have produced this striking mixture of sedimentary lithologies at Helen’s Bay and concluded that sedimentary mixing is the more likely. The pervasive shearing and the admixture of exotic lithologies characteristic of tectonic mélanges are simply not present. The deposit of black shales with its enclosed sandstone, chert and spilite is thus identified as an olistostrome, defined essentially as a chaotic mixture of sediments where the mixing is entirely due to sedimentary processes. The larger blocks of sandstone, i.e. those greater than 4m in maximum diameter, are technically “olistoliths” the smaller blocks properly described as “clasts”. Many of the olistoliths and clasts are so sharply angular as to suggest lithification at the original site of deposition, prior to resedimentation in the Helen’s Bay Formation (Plate 5). The interpretation is that they have been transported by gravitational sliding or slumping from higher platforms or slopes in the submarine topography down into the deeper pelagic environment in which the black shales were being deposited. While the spilite and chert clasts could presumably have been derived by instability and reworking of the older parts of the Helen’s Bay Formation itself, the sandstone of the olistoliths is petrographically distinct from the local Grey Point and Rockport Formations in that it lacks the fresh ferromagnesian minerals characteristic of the latter. The sandstone olistoliths and clasts are clearly reworked from an older formation not seen at Helen’s Bay. Examples are well exposed at the base of the concrete supports for the pipe line on the north side of the small bay immediately north of Horse Rock (J45898309) and the same clast-rich olistostrome lithology persists for 100m to the north. Throughout this coastal section the bedding dips steeply, between 50 o and 80o, SSE but is overturned so that all beds young or face NNW. The olistostrome thus has a stratigraphic thickness of at least 70m. A few thin (less than 10cm) beds and discontinuous lenses of light green bentonite occur in the succession. Bentonites, representing submarine falls of fine grained volcanic ejecta, clay and glass, are common in the Southern Uplands - Down - Longford Terrane (Cameron and Anderson, 1979). A dyke of lamprophyre, of a type common further south in the Ards Peninsula (Reynolds 1931) but not previously reported at Helen’s Bay, occurs at J45908321 in the floor of a deep gully beneath the supports for a pipeline. Several discontinuous lenses of lamprophyre, up to 45cm thick, crop out on a line trending 140 o. The weathered surface of the dyke is dark grey and characteristically pitted. The freshly broken surface shows pale blue phenocrysts, pseudomorphs after amphibole, in a fine grained grey matrix. North of the olistostrome, between J45898317 and J45908320, the coastal outcrop is of black shales of the same lithology as the olistostrome matrix. These shales are graptolitic, contain lenses of chert and thin beds of bentonite but lack the sandstone clasts of the olistostrome below. Northward again the olistostrome facies repeats: shale with sandstone clasts is the dominating lithology as far north as J45888332. The olistostrome repetition might be tectonic, effected by faulting, as suggested by Craig (1982, p.22), but there is no exact repetition of individual beds or of olistostrome thicknesses above and below the black shale member. More simply the upper olistostrome may represent a stratigraphic return of the slumping which had occurred earlier. Toward the top of the upper olistostrome, from J45908325 northward, sandstone beds 0.2 to 0.5m thick appear within the olistostrome, without obvious disruption or discontinuity, increasing northward in number and in individual bed thickness. A 10m wide shingle beach at J45898331 has strongly sheared grey and black shales and thin sandstones with many small faults, both parallel to and cross-cutting the stratification, cropping out on both sides of the break in outcrop. The beach probably conceals a shear zone. Some 5m north of the beach the laminated shales are succeeded by turbidites. These are coarse-grained grey sandstones with thin shale interbeds. Many of the sandstone beds display well developed sole markings on their southern surfaces. These turbidites are the base of the Grey Point Formation. The formational boundary is taken as the bedding plane bounding the most northerly outcrop of dark grey shale, striking 053o and dipping 86o south. This surface traces across the outcrop immediately north of the more southerly of two water or sewage tanks, buried in the rock at high water mark at J45888332. The remainder of the coastal outcrop north-westward to Grey Point (J45768340) and westward to the shingle cove at J45698333 forms the type locality of he Grey Point Formation, whose stratigraphic thickness is thus at least 150m. Over this entire outcrop the beds dip steeply south-south-eastward but consistently, on the evidence of abundant sedimentary structures, particularly well developed sole markings and graded bedding, face or young north-north-westward. Individual sandstone beds are typically 0.4 to 1.5m thick but there are several massive beds of ungraded sandstone ranging up to 5m thick. Some of these beds of ungraded sandstone channel down spectacularly into the underlying strata. Channels range up to 2.5m deep and at least 10m wide. A particularly impressive example occurs at J45848337 (Plate 6). The groove casts and other sole markings which decorate the upturned bases of many sandstone beds are sometimes multiple, implying erosional or scouring action by turbidity currents travelling in different directions across the sea floor (Plate 7). These are quite the best examples of channels in the turbidites of County Down and the best examples of sole-markings in the Ordovician Northern Belt. The whole outcrop provides a text-book demonstration of the sedimentary facies and structures associated with proximal turbidites. Many of the sandstone beds also contain ovoid carbonate concretions, typically 30 to 200mm in maximum diameter and evident as depressions weathered out on joint surfaces in the sandstone beds. Full descriptions of the sedimentary structures and turbidite sedimentology are given by Craig (1982, 1984). Between the massive sandstone beds of the Grey Point Formation there are interbedded grey shales and thin (less than 10cm) sandstone beds in units up to 1.5m thick. These fine grained rocks show excellent development of the regional slaty cleavage (S1). At Grey Point the cleavage invariably dips more gently to the south than the bedding in the same outcrop so that structural vergence is consistently to the south and all beds face upward in the cleavage at this locality (Plate 8). The cleavage does not penetrate the more massive sandstone beds. The entire outcrop at Grey Point is transected by many strike-slip faults. These are predominantly sinistral in sense of displacement but dextrals also occur. Where bed correlation across the fault surfaces can be established the slips are generally less than 20m and commonly less than 5m. Gullies have been eroded along many of the fault traces. Veining is also ubiquitous. Quartz veins dominate in the Helen’s Bay Formation but veins of carbonate are not uncommon, particularly in the Horse Rock spilites. Epidote, chlorite and prehnite have also been identified in the quartz veins (Craig, 1982, p.22). This is in complete accord with the relatively low grade, prehnite-pumpellyite, metamorphism affecting all Northern Belt sediments. Caledonian deformation at a depth of some 10km is implied, apparently during the thrusting which accreted these rocks from the Iapetus sea floor to the southern margin of Laurentia (Oliver et al. 1984, Kemp et al. 1985). Craig (1982) collected graptolites from five localities in the olistostromes and black shales forming the upper part of the Helen’s Bay Formation. Her map (1982, Fig. 2.5) shows that all five are in the central part of the 220m wide outcrop, between J45898318 and J45908325. The graptolites, identified by R.B. Rickards, include Climacograptus bicornis, Dicellograptus elegans, Didymograptus superstes, Glyptograptus euglyphus, Nemagraptus gracilis and Orthograptus calcaratus (Craig 1982, p.24, 1984, p.185). Dr. Rickards regarded three of the five faunae to be from the Nemagraptus gracilis Biozone with the remaining two indeterminate. In the Geological Survey Memoir for Sheet 29, Griffith and Wilson offer a contrasting view. “From the identification of graptolites collected from the mudstones overlying the agglomerate, Dr. Toghill concludes that although the fauna contains elements suggestive of the gracilis Zone much of it indicates the peltifer Zone, i.e. Upper Glenkiln. There is a suggestion that other zones of the Lower and Upper Hartfell are present in the succession towards Grey Point but these have not been unequivocally identified and precise correlation with a specific section is not attempted here” (Griffith and Wilson, 1982, pp.7-8) Neither the identifications nor the precise localities on which the Survey opinions are based are recorded in the Memoir. Further collecting and identification from the full thickness of graptolite-bearing rocks in the Helen’s Bay Formation is obviously desirable so that the stratigraphic range can be determined. No fossils have yet been obtained from the Grey Point Formation. | |
| Importance: | |
National geology: The Helen’s Bay - Grey Point coastal section includes, at Horse Rock, the best outcrop of pillow lavas in Northern Ireland. It also offers the most completely exposed succession of the lithologies which characterise the northern belt of the Southern Uplands - Down - Longford Terrane, from ocean-floor tholeiites through volcanic-clast conglomerate, pelagic black shales, olistostromes into proximal turbidites. All of these rocks show characteristic structural features of demonstration quality. International geology: The Southern Uplands - Down - Longford Terrane now figures in many internationally used textbooks as a model accretionary prism, produced by the offscraping of oceanic sediments from a subducting slab of Ordovician oceanic crust. The unresolved ‘Southern Uplands Controversy’, between proponents of this model and those favouring the interpretation of the same rocks as a rotated thrust stack of sediments and lavas accumulated in a back arc basin, is also widely quoted in the international literature of geotectonics. These outcrops probably present the best opportunity in Ireland to study the lithologies involved and to further research their interpretation. | |
| Interpretation: | |
The range of lithologies cropping out on the coast between Helen’s Bay and Grey Point are all clearly of the deep marine facies which is characteristic of the whole prism of rocks forming the Southern Uplands - Down - Longford Terrane. Graptolites, the only fossils yet found, prove a Caradoc (Upper Ordovician) age for the Helen’s Bay Formation. The mafic intrusive and extrusive rocks at the base of the exposed succession have obvious ophiolitic affinities. These mafic igneous rocks are overlain by pelagic black shales and olistostromes and ultimately, in the Grey Point Formation, by high energy, proximal turbidites. Craig’s (1982) detailed geochemical study of the Horse Rock spilites identified them, by reference to various discrimination diagrams, as ocean floor tholeiites. Subsequent to deposition the entire volcanic and sedimentary succession has been tilted and overturned. All the rocks in the section described now dip steeply and all young or face to the north or north-west. Paradoxically the rocks to the south-east across the Bay and along the North Down coast all appear to be younger than those at Helen’s Bay. Further south-east, in the Ards Peninsula, graptolites prove yet younger (Lower Silurian) ages even though on sedimentary evidence the majority of beds continue to young or face north (Barnes et al. 1987). This general Southern Upland structural paradox requires the insertion of a number of major strike-parallel faults for its solution (Anderson & Cameron 1979). These major faults consistently throw down to the south and segment the prism into a series of fault-bounded blocks or tracts. Within each tract the strata young northward, as at Helen’s Bay, but the faults introduce successively younger tracts succeeding each other southward. The overall structure of the Southern Uplands - Down - Longford Terrane is thus readily interpreted as an accretionary prism of fore-arc sediments and volcanics, formed by the subduction of Iapetus oceanic crust beneath a northern continent (Laurentia). The general arrangement of strata and the southerly vergence of bedding on the accretion-related cleavage at Helen’s Bay is entirely in accord with the regional interpretation. The ongoing “Southern Uplands Controversy” (Mitchell & McKerrow, 1975, McKerrow et al., 1977, Leggett et al., 1979, Leggett 1987, McKerrow 1987, Stone et al., 1987) is essentially between proponents of the interpretation above and an alternative view that the rocks of the terrane accumulated in a back-arc basin, bounded by Laurentia to the north and a volcanic arc to the south, and were subsequently compressed into a north-facing thrust stack when the arc was shunted against Laurentia during the closure of the Iapetus Ocean. The sea-floor tholeiites, pillow lavas and deep-water sediments now exposed between Helen’s Bay and Grey Point accumulated on the floor of the Lower Palaeozoic Iapetus Ocean and were subsequently accreted to the Laurentian continental margin as that ocean was closed by northward subduction of the underlying oceanic crust. | |
| Conclusions: | |
The coastal section at Helen’s Bay to Grey Point represents a remarkable cross-section of one of the tracts in the Northern Belt of the Southern Uplands - Down - Longford accretionary prism. | |
| Notes: | |
TO BE SOURCED AND ENTERED Plate 1. Spilite pillows. Horse Rock Member, Helen’s Bay Formation. J45938308 - Horse Rock - looking NE. Weak stratification dipping 40o SE (top right to bottom left on plate). Hammer 39cm long. Plate 2. Downward facing spilite pillow which is 45cm by 22cm. (Smooth rounded top would once have been upward facing - hence subsequent inversion is indicated) Horse Rock Member, Helen’s Bay Formation. J45948309 - 2m south of rusty iron mooring peg on NE tip of Horse Rock. Scale is 7cm long. Plate 3. Organised conglomerate of reworked spilite clasts. Note apparent rounding of the clasts. Conglomerate member, Helen’s Bay Formation. J45918308 - NW side of Horse Rock looking south. Scale squares of 1cm side. Plate 4. Black shale olistostrome. Grey lenses and blocks of exotic greywacke sandstone (olistoliths) set in a dark, cleaved, shale matrix. Helen’s Bay Formation. J45908310 - Promontory 35m NW of Horse Rock. Knife is 11cm long. Plate 5. Sharply angular, rhomb-shaped clast (0.8m long) of exotic greywacke sandstone in cleaved black shale matrix. Olistostrome, Helen’s Bay Formation. J85918324 - 150m north of Horse Rock. Scale squares of 1cm side. Plate 6. 2.5m deep channel at base of massive turbidite bed which is 1 to 4m thick. Channel has poorly sorted, coarse, sandy infill and clearly erodes and cuts thin turbidites and shale units 0.03 to 0.35m thick. Bedding 052o/80o SE but younging north-westward (to left on plate). Grey Point Formation. J45848337 - 40m north of large, buried, sewage tank. Looking NE. Hammer 39cm long. Plate 7. Intersecting groove marks (casts) on the base of a Ta greywacke sandstone bed. Note that the 32 o angle between grooves indicates variability in the direction of the erosional currents. Grey Point Formation. J45858334 - 7m north of drainage tank. Looking north at base of overturned bed 052o/78o SE. Scale squares of 1cm side. Plate 8. South-vergent S1 cleavage in untypically thinly bedded greywacke sandstones and slates of the Grey Point Formation. Bedding 056o/82o SE but younging or facing north, cleavage 040o/62o SE. Bedding cleavage intersection 35 o toward 062 o. Beds thus face up to the north-west in the cleavage plane. J45868338 Looking NE along the strike of bedding. Hammer 39cm long. Two maps are appended: (1) a photographically reduced copy of a new map of the geology made at the 1:1250 scale in 1996 (2) a copy of the 10 000 Ordnance Survey Sheet showing the area requiring protection because of its interesting solid geology. The full range of ESCR site relating to the Lower Palaeozoic are as follows: Outer Ards Stratigraphic, Palaeontological and Structural sites Coalpit Bay – Lower Palaeozoic (record no. 1350) Helen’s Bay – Grey Point – Lower Palaeozoic (record no. 1351) Kearney Point – Knockinelder Bay – Lower Palaeozoic (record no. 1352) Orlock Bridge – Lower Palaeozoic (record no. 1353) Tieveshilly – Carrstown – Lower Palaeozoic (record no. 1354) Orlock Bridge - Structural (record no. 652) Whiskin Rocks - Structural (record no. 653) White House Port, Cloghy - Structural (record no. 654) Knockinelder Bay and Kearney Point - Structural (record no. 655) Millin Bay - Structural (record no. 656) Pomeroy area Craigbardahessiagh and Bardahessiagh River – Palaeontology (record no. 29) Lime Hill Farm – Palaeontology (record no. 33) Little River and Slate Quarry Bridge – Palaeontology (record no. 31) | |
| Keywords | |
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| Rocks: | Turbidite, Greywacke, Shale, Bentonite, Spilite, Pillow Lava |
| Access | |
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| Approach: | Public access via North Down coastal path. Within Crawforsburn Country Park |
| Restrictions: | Public access |
| Management: | |
Helen’s Bay - Grey Point is an area of residential property giving way northward to a wooded coastal strip, the latter functioning as recreational parkland serviced by the car park at Helen’s Bay. The much frequented North Down Coastal Path follows the coastline around the Grey Point promontory. Fishermen and women use rod and line from the rocks on the headland on most days in summer. | |
| Threats: | Preservation of these rocks for research, teaching and recreational geology faces two obvious threats. The building of further slipways and jetties for boating, similar to that which now obliterates the important succession of rocks south of and structurally beneath the Horse Rock pillow lavas, must be prohibited or at least severely restricted. Over-enthusiastic sampling and hammering of the spilite pillows by geologists and students could damage the section irreparably. Only a very few of the pillows have shapes of demonstration quality and these could easily be destroyed. It is possible, with a modicum of good sense, to obtain samples for analysis or thin section without damaging the best pillows. The black shales and olistotromes to the north of Horse Rock bear collectable graptolites but the outcrop is so extensive that it seems capable of withstanding any foreseeable amount of geological collecting without sustaining significant damage. Some of the sedimentary structures in the Grey Point Formation are again vulnerable to hammering but this would be pointless to anyone other than a deliberate geological vandal. |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 1 April 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Helen’s Bay – Grey Point – Lower Palaeozoic, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1351. Accessed on 2026-11-06. |
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