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Earth Science Conservation Review
| Soldierstown Quarry, Moira – Clay-with-Flints |
| Site number: | 1311 | ||
| Locality Type: | Status: | ESCR | |
| Grid Reference: | J156633 | ||
| Google maps: | 54.50537,-6.21541 | ||
| County: | Council area: | Lisburn & Castlereagh City Council | |
| Period: | Cretaceous, Tertiary | ||
| Site Description | |
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| Highlights: | |
Because of the unique array of geological features that were formerly exposed here, Soldierstown Quarry is included in this report as a Site of Special Scientific Interest. The only evidence of the majority of those features is now recorded only in the photographic record due to a combination of persistent flooding and efforts to landscape the site for redevelopment. | |
| Introduction: | |
Although chalk production had been already been abandoned, by the time of the mapping by the Geological Survey of Ireland in 1868, a very large quarry, or set of quarries, had been opened in Ballynanaghten Townland. In 1954, during the remapping of this area by the Geological Survey of Northern Ireland, chalk production had still not re-started at the quarries, but it was noted that there was an intention by a local entrepreneur to develop a new quarry face in the NW corner of the site in 1955. Production of chalk at Soldierstown Quarry may therefore have recommenced in the latter half of the 20th century but ceased in the 1990’s due to continuous flooding and an increasing amount of overburden consisting both of basalt lava and Clay-with-Flints. More recently the site was drained and an effort made to landscape the rock walls and develop buildings on the floor of the quarry. However, this project was subsequently abandoned and the quarry is once again flooded. | |
| Description: | |
Site Geology: When the quarry is drained, exposed in the west wall is the unconformable contact between chalk of the Late Cretaceous Ulster White Limestone Formation and the overlying basalt lava flows of the Lower Basalt Formation of the Early Palaeogene Antrim Lava Group, the Clay-with-Flints and the channel occurrence between basalt lava flows. However, in a flooded condition only the top metre of the chalk and the Clay-with-Flints is exposed in the southwest corner of the site. Located above the water level two flows of basalt lava are exposed in the west face. The north face of the quarry was formerly occupied by the full thickness of the main channel feature that is filled with Clay-with-Flint lithologies, but this was subsequently concealed during restoration of the site and is no longer exposed. Ulster White Limestone Formation: No formal record of the lithostratigraphy of the chalk exposed in Soldierstown Quarry is available. However, an appraisal by Fletcher (1977) of the succession exposed in Richardson’s Quarry [J167 630], 1km ESE of Soldierstown Quarry, recognised about 27m of Late Campanian to Early Maastrichtian chalk of the Ulster White Limestone Formation, divided into 4 members. At the base of the section, the Garron Chalk Member rests unconformably on the Late Triassic Mercia Mudstone Group and is succeeded by the Portrush Chalk, Ballymagarry Chalk and Tandragee Chalk members. In this part of south Co. Antrim and adjacent areas in north Co. Down, the Ballymagarry Chalk Member is renowned for possessing fine examples of paramoudra, the largest examples of flint nodules present in the Irish chalk (Figures 2 and 3). Clay-with-Flints: The Clay-with-Flints, which occurs stratigraphically between the Cretaceous chalk and the Early Palaeogene basalt lava flows, is exposed only in the southwest corner of the site, just above the water level in the quarry. It is less than 1m thick and occurs only intermittently so that some 30m to the north along the face, the chalk and lowest basalt lava flow are in direct contact. Antrim Lava Group: Overlying the top of the Cretaceous chalk and the Clay-with-Flints are two flows of basalt lava of the Early Palaeogene Lower Basalt Formation. In the quarry it is evident that the higher of the two lava flows overstepped the first flow southwards onto the Clay-with-Flints deposit covering the chalk land surface. It may be inferred that both basalt lava flows emanated from an eruptive centre located to the north of the quarry. In hand specimen, the basalt of both flows is hard and appears to be fresh and thus suitable for Ar-Ar dating. However, in thin section the lowest (first) flow of primitive olivine basalt with ~10% olivine phenocrysts, shows a significant degree of alteration that would have been sufficient to reset the Ar40/Ar39 ratio which could otherwise have been used for dating purposes. Clay-with-Flints lithologies in the Antrim Lava Group: The unique status of Soldierstown Quarry is based on the occurrence of a channel feature located between the first and second flows of basalt lava, but which is still filled with lithologies typical of the Clay-with-Flints. The proximal end of this channel is located in the west wall of the quarry but is only exposed when the quarry is dry (Photograph 3A). In contrast, the greater part of the thickness and width of the distal end of the channel was exposed in the north face of the quarry but has recently been concealed as a result of landscaping the site for development (Photograph 3B). Subsequently the site restoration process was discontinued and the quarry re-flooded, so that all trace of the channel feature is now concealed. Quaternary Deposits: Drift deposits overlying rock head consist of brown glacial till (boulder clay) varying from 1m to 3m thick. The Clay-with-Flints detail: There are two separate occurrences of lithologies typical of the Clay-with-Flints. 1) In Soldierstown Quarry, as is typical of the remainder of the outcrop of the Clay-with-Flints around the Antrim Plateau, its expected occurrence consists of a single bed resting unconformably on the top surface of the Late Cretaceous Ulster White Limestone Formation, and in turn is overlain unconformably by basalt lava flows of the Lower Basalt Formation of the Palaeogene Antrim Lava Group. At its only exposure, in the southwest corner of the quarry, the bed is 60cm thick although a few metres to the north in that face it disappears altogether and the lowest basalt lava flow rests directly on the Cretaceous chalk. The bed comprises a matrix of white to cream coloured clay, medium grey in the lowest 10cm overlying the chalk surface, which is full of shards and fragments of broken flint with small to large intact flints that often show a reddish purple internal concentric staining. No further detailed analyses were carried out on samples from this section of the Clay-with-Flints. 2) In Soldierstown Quarry, a second, and unexpected, higher occurrence of lithologies typical of the Clay-with-Flints was exposed in the north face, just above the level of the local water table. From the profile of bedding surfaces in that exposure it is evident that the feature has a channel bedform but its base is only exposed at its western end and its upper level is concealed (Photograph 3B). Nevertheless, sufficient evidence is available to indicate that the base of the channel was excavated not into the top surface of chalk, but into the top of a basalt lava flow (Photograph 3A). The proximal portion of the channel is only visible in the west wall when the quarry is drained. However, its stratigraphical position between the lowest and second basalt lava flows is confirmed in that wall where the channel is 2m thick and about 40m wide. At its margins the channel tapers to a point so that the two basalt lava flows are in contact. At its distal end the channel is at least 10m deep and over 100m wide with a fill comprising several layers of bluish grey clay with whole and fragmented flints. The occurrence of carbonised wood fragments in the channel fill indicates that the land surface south of the extent of the basalt lava flows was vegetated, but was scoured periodically by lahars that transported the pre-existing Clay-with-Flints material into the channel. Towards the western margin of the main channel, about 1.5m above its base, is a discontinuous layer about 20cm thick and just over 2m long, of deep reddish brown, finely laminated, lapilli-rich clay with almost no flints (Photograph 47). This layer of ash flow tuff was one component of the original depositional sequence in the channel, which was subsequently largely eroded by the next lahar flow. Petrogenesis: The channel occurrence of lithologies typical of the Clay-with-Flints in Soldierstown Quarry has been studied in detail in order to obtain as much information as possible on its origins, the nature of the parental volcanicity and to assess any petrographical and geochemical differences that may be apparent between the various levels of the deposit. No detailed stratigraphy of the channel fill deposits has been prepared but samples were taken from the lenticular bed of banded clay and from the bluish grey flint-rich clays below and above that horizon. Geochemistry Samples of the clay matrix from the Clay-with-Flints deposit that fills the channel in Soldierstown Quarry were selected for major and selected trace element analysis. Immobile element ratios, when plotted on a Zr/TiO2 – Nb/Y discrimination diagram, show that all three samples plot in the andesite field. Petrography Three clay samples, from locations within the channel fill as described above, were investigated petrographically. Sample 1: This sample of the clay matrix is from the lowest part of the channel deposit, just above the contact with basalt of the lowest lava flow. In most of the channel complex the matrix clay in the lower levels is predominantly bluish grey with a faint but pervasive lilac tinge. However, in the deposit at the western end of the channel, below the lenticular lapilli-rich clay, the matrix clay is stained a deep orangebrown. Flint nodules in the lower part of the channel fill deposit are clast to matrix supported. Many of them are intact and relatively uncoloured and show a pattern of surface cracks that reflect a minute internal fragmentation. Other nodules show an internal red colouration either as pervasive staining or as concentric banding (Photograph 48). In thin section the sample has been completely devitrified and now consists of secondary clay minerals, opaque oxides and hematite. Clasts include detrital flints (up to 2mm), rounded opaque, oxidised volcanic lithic fragments such as lapilli (up to 2.4mm) and angular quartz crystals/crystal fragments (average 0.2mm). The flint clasts vary from colourless, and apparently unaffected by their incorporation into the flow, to heavily stained with slightly lobate margins suggesting reaction and partial assimilation as a result of early incorporation whilst the flow was still at high temperatures. The matrix is composed of brown clay minerals, patches of red hematite, fine-grained quartz and disseminated opaque oxides presumably replacing primary volcanic glass. Although devitrified, the primary fabric of deformed glass shards and fiammé is well preserved and is picked out by concentrations of opaque oxides and the differing optical density of the individual primary fragments. Clasts appear wrapped by the fabric suggesting that the deposit was subject to compaction and flow. This sample is a devitrified ash-flow tuff that had been originally welded to some degree. Sample 2: This sample, from the lenticular bed of laminated, lapilli-rich clay that occurs at the western side of the channel, consists of abundant small, dark red lapilli in a paler reddish brown clay matrix (Photograph 49). In thin section the matrix is composed of a fine-grained intergrowth of quartz, clay minerals and hematite and shows some suggestion of a primary fragmental structure. The differing optical densities pick out fragments within the matrix, while trails of hematite and opaque oxides define a banded structure suggesting flow, wrapping around the clasts. Clasts include abundant, largely opaque fragments (up to 5mm), rounded, stained and altered flints and small angular quartz crystals/crystal fragments. This sample is of a devitrified ash-flow tuff. Sample 3: This sample, from the layered fill of the channel above the lenticular bed of laminated lapilli-rich clay, consists of bluish grey clay with conspicuous white flint nodules in a matrix- to clast-supported framework. The matrix is composed of an anastomising network of brown to green clay minerals picking out some primary fabric and a dark brown cryptocrystalline intergrowth of quartz, opaque oxides and clay minerals. Clasts consist mainly of rounded flint (up to 4.5mm) with a dirty appearance and saccharoidal texture, rarer rounded and almost completely opaque, oxidised clasts and angular quartz crystals/crystal fragments (0.15mm) within a finer matrix. It is suggested that this sample is of a fragmental deposit that has been substantially altered subsequent to deposition. In conclusion, it is evident that the lower two samples originated as volcanogenic deposits, probably welded ash-flow tuffs which were subjected to flow and during that process entrained the flint clasts. The upper part of the channel fill, above the lenticular bed of lapilli-rich clay may also have started as a volcanogenic deposit but was subsequently remobilised and re-deposited as a volcaniclastic deposit. The sequence of processes that led, firstly, to the formation of the channel in the top surface of the lowest flow of basalt lava and, secondly, to its infill by lithologies typical of the older Clay-with-Flints deposit was contemporaneous with the onset of basaltic volcanism in Northern Ireland. However, immobile element ratios in clay samples from all levels in the deposit show that the sequential events which produced the various layers in the channel were the product of andesitic volcanism. Palaeo-environmental reconstruction: Both basalt lava flows show a variable degree of columnar jointing, with the upper flow having a more regular colonnade (Photograph 3A). The presence of columnar jointing is assumed to indicate that the basalt lava flowed into, and was ponded in, a topographic depression where the presence of standing water aided the formation of the columnar jointing during cooling of the lava. Thus, it is evident that surface water was present before, during and after the extrusion of both basalt lava flows and that water in the form of lahars flowed periodically, but regularly, into the topographic depression carrying the volcanic mud-flint mix in channels. Based on the southwards overstep of the second lava flow over the first flow, and presumably onto the land surface of the Clay-with-Flints and chalk, it is also apparent that both flows were derived from a volcanic source located north of the quarry. The corollary of this is that the vegetated land surface located south of the quarry site, and south of the toe of the first lava flow, was basalt free and was developed on top of the Clay-with-Flints. Periodic rainfall on higher ground in the area created fluvial systems that flowed northwards towards the depression within which the quarry is now located and, in the process, reworked and remobilised the volcaniclastic clay and flint nodules that constituted the earlier Clay-with-Flints. In the lowest level of the channel fill, although the flint nodules still retain their overall shape and many appear unbroken, the intensity of internal fracturing present in them suggests that there was significant and frequent contact between nodules during flow of the lahars. Over a period of several rainfall cycles the channel (s) ultimately delivered a succession of lahars, composed not only of reconstituted Clay-with-Flints but with the addition of fresh volcanic ash from contemporaneous basaltic volcanism, into the depression after the first lava flow had cooled and before the second flow was erupted. Within the channel complex only one example of basalt clast has been found (Photograph 50). This may indicate that the pattern of tributaries feeding the flow of volcaniclastic sediment into the main channel either did not encounter the first basalt lava flow or traversed only a very limited area of land occupied by that lava flow. | |
| Conclusions: | |
In Soldierstown Quarry, the occurrence of lithologies typical of the Clay-with-Flints provides a unique insight into aspects of the volcanic evolution of northeast Ireland before and during the early stages of basaltic magmatism, related to the Iceland Plume, and to the development of Northern Ireland within the North Atlantic Igneous Province. They also convey information on features of the local landscape and climate during this formative period in the history of volcanism hereabouts. 1) After the end of chalk sedimentation in the Late Cretaceous and the withdrawal of the sea, the resulting land surface, which became vegetated, was subjected to a prolonged period of weathering during which gentle regional uplift developed the earliest intra-Palaeogene unconformity on the top surface of the chalk. 2) An early Clay-with-Flints deposit was formed on top of that land surface as a mix of residual flint nodules, derived from the prolonged weathering and solution of the chalk, and products of a cataclysmic volcanic eruption of probable andesitic or rhyodacitic composition. Biostratigraphical data suggest that the formation of the Clay-with-Flints occurred in the earliest Palaeogene. 3) The first basalt lava flow of the Early Palaeogene Antrim Lava group (Lower Basalt Formation), which flowed southwards over the Clay-with-Flints land surface gathered small flints in the lower parts of the flow (Photograph 51), encountered a waterlogged land surface and in cooling developed a crude columnar jointing. 4) As the effects of the Icelandic Plume impinged on the landscape, regional doming controlled the outpouring of basalts and marginalised fluvial systems. Subsequent subsidence led to the flow of lahars back into the area of basalt lava flows. Thus, the top surface of the first lava flow became eroded with the formation of channels. 5) The source area for the sediment that now fills the channel complex eroded into the top surface of the first lava flow was basalt-free and consisted exclusively of vegetated Clay-with-Flints. Successive pulses of sediment, which originated from the south in the form of lahars, flowed from that source area initially reworking and ultimately mixing fragments of carbonised wood and contemporaneous basaltic volcanic ash into the pre-existing Clay-with-Flints. Heavy falls of lapilli-rich volcanic ash of more basic composition were interspersed with the lahars but their deposits only survived at the margins of the channel. 6) When the channel complex was completely filled, the depression that existed in the area, once again, became the site of a lake into which flowed, from the north, the second flow of basalt lava that reached farther south than the toe of the first flow and, in the presence of water, developed an incipient colonnade. | |
| Notes: | |
The full series of Clay-with-Flints records is as follows: Record no. 1300 Introduction to Clay-with-Flints of Northern Ireland Record no. 1301 Belshaw’s Quarry – Clay-with-Flints Record no. 1302 Gibson’s Quarry, Portadown – Clay-with-Flints Record no. 1303 Devlin’ Quarry, Moneymore – Clay-with-Flints Record no. 1304 Glenshane Pass – Clay-with-Flints Record no. 1305 Donald’s Hill – Clay-with-Flints Record no. 1306 Tircrevan Burn – Clay-with-Flints Record no. 1307 Ballycastle – Clay-with-Flints Record no. 1308 Demesne Quarry, Glenarm – Clay-with-Flints Record no. 1309 Magheramorne Quarry, Larne – Clay-with-Flints Record no. 1310 Bellevue, Belfast, Co Antrim – Clay-with-Flints Record no. 1311 Soldierstown Quarry, Moira – Clay-with-Flints | |
| Keywords | |
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| Rocks: | Chalk, Clay, Flint, Basalt |
| Access | |
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| Approach: | Private land. Disused quarry (Photograph 46), Ballynanaghten Townland [Grid Ref: J156 633], north of Soldierstown Road and 1.4km north of Moira Railway Station, Co. Antrim (Figures 33 and 34). |
| Restrictions: | Private land |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 28 Mar 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Soldierstown Quarry, Moira – Clay-with-Flints, County , site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1311. Accessed on 2026-11-08. |
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