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Earth Science Conservation Review
| Gibson’s Quarry, Portadown – Clay-with-Flints |
| Site number: | 1302 | ||
| Locality Type: | Status: | ESCR | |
| Grid Reference: | H981546 | ||
| Google maps: | 54.43093,-6.48834 | ||
| County: | Council area: | Armagh City, Banbridge & Craigavon Borough Council | |
| Period: | Cretaceous, Tertiary | ||
| Site Description | |
|---|---|
| Introduction: | |
Since the production of basalt at Gibson’s Quarry ceased early in 2009, the quarry and associated machinery have been moth-balled on a care and maintenance basis. It is believed that the owners are considering an alternative use for the quarry that may involve a waste disposal facility. In terms of its condition, the quarry environment is still largely dry, with only small areas of standing water on the floor and limited vegetation growth which is restricted to older stock piles of waste material. Throughout its production history this quarry was commissioned to produce basalt aggregate. In the early 1970’s, the quarry was extended southwards and in the process uncovered the base of the basalt lava sequence resting on white chalk of the Ulster White Limestone Formation, with the Clay-with-Flints intervening between the basalt lavas and the chalk. The chalk surface and Clay-with-Flints were initially exposed in the southeast corner of the site (Photographs 2A and 2B). Unfortunately, that section was covered later with quarry spoil, but a new exposure of the chalk surface and Clay-with-Flints was revealed in the southwest corner of the site. This report was compiled using data from the two sections described above. | |
| Description: | |
Site Geology: Ulster White Limestone Formation: Along the south side of the quarry the top surface of the Late Cretaceous Ulster White Limestone Formation is inclined northwards at 15o-20o. Although only about 2m of chalk is exposed beneath the Clay-with-Flints, a borehole in the quarry encountered a total thickness of 15m of chalk-with flints underlain by purplish red and pale green mudstone of the Late Triassic Mercia Mudstone Group. The precise age of the chalk in Gibson’s Quarry is not known. Nevertheless, the association of common Inoceramus shell fragments with a diverse brachiopod fauna including Carneithyris, Cretirhynchia aff. arcuata and a possible Kingenella strongly suggest a correlation with the Late Campanian Portrush Chalk Member. In addition, scattered around the south end of the quarry are many examples of very large, barrel shaped flints identical to paramoudra. Their occurrence here would suggest that either, the chalk in the quarry correlates with the Ballymagarry Chalk Member, the only known source of paramoudra in the Ulster White Limestone Formation, or that this member was eroded in post-Cretaceous times and these distinctive flints were subsequently incorporated into the Clay-with-Flints, from which they have been released by quarrying (Figures 2 and 3). Clay-with-Flints: At the time of the resurvey of the Portadown area by the Geological Survey of Northern Ireland in 1975, the Clay-with-Flints horizon was exposed in the SE corner of the quarry and measured just over 2m thick. The lowest 2m were described as consisting of, “Pale buff yellow cobble conglomerate of flints (2-20cm) set in matrix of pale tea green clays occasionally streaked red.” At the top of the section was a 3cm continuous bed of woody black lignite which in turn was overlain by 3cm of pale greenish blue clay representing either an ash deposit or the thoroughly decomposed base to Flow 1 of the basalt lava sequence. Antrim Lava Group: In the quarry there are at least 5 separate basalt lava flows, representing the Lower Basalt Formation of the Early Palaeogene Antrim Lava Group. The lowest three flows are each in the order of 10-20m thick. Flows 1 and 2 at the base of the quarry consist of massive, variably vesicular and rubbly, fine-grained basalt while the overlying Flow 3 exhibits a well developed colonnade in coarse-grained olivine basalt. Flows 4 and 5 are only exposed in the NW corner of the quarry at the top of the working face. While Flow 4 is 3m thick, only about 1m of Flow 5 is exposed at the top of the quarry face. Minor normal faults, with N-S and W-E orientation, affect the basalt flows in the quarry and have small downthrows of about 3m to the south and west respectively. Quaternary Deposits: At the north end of the quarry the basalt flows are overlain by at least 10m of glacial till which represents a section through the drumlin that occurs in the northern part of Cornamucklagh Townland. The Clay-with-Flints detail: The lithostratigraphy of the Clay-with-Flints in Gibson’s Quarry is illustrated in the vertical section (Figure 11). A thickness of 1.4m to just over 2.5m was measured in the section formerly exposed in the southeast corner of the quarry which is now concealed by spoil (Photograph 2A). Petrographical descriptions and geochemical analyses were obtained from samples taken from that first section of the Clay-with Flints. Photographs of the Clay-with-Flints in this quarry illustrate both the former section and the current exposure in the southwest corner. At the current exposure the contacts between the Clay-with-Flints and the underlying chalk and overlying basalt lavas are clearly defined. At the previous section the upper level of the quarry in the southeast corner coincided with the top of the Clay-with-Flints and only a thin layer of basalt remained. In that section the top surface of the chalk was originally concealed by waste material but was cleared and the full thickness of the Clay-with- Flints exposed and measured. It appears that the variable thickness of the lower layer of flint-rich clay of the Clay-with-Flints in Gibson’s Quarry is a reflection of the uneven nature of the top surface of the Cretaceous chalk (Photograph 8). Evidence favouring a volcanogenic origin for the two overlying layers includes the high concentration of lapilli, indicating an air-fall ash deposit, and the virtual absence of flints in the middle layer. Based on the presence of channels excavated into the top of the flint-rich lower layer it is likely that the middle layer was also subjected to flow (Photograph 9). The contact between the lower and middle layers is sharp but irregular because of the presence, of large flint nodules, at the top of the lower layer that have a tabular shape. In areas of the lower layer that are matrix dominant, the channelised lapilli-rich clay has eroded the underlying sediment. Since the middle layer is frequently confined to channels, in places this layer may be completely absent and the lower, flint-rich layer is thus overlain by the dark reddish brown, clay-rich upper layer. However, the upper layer of the succession is also present only intermittently. In both the former and the present exposure of the Clay-with-Flints, the basal contact of the upper layer is smooth when compared to the base of the middle layer of channelled sediment. It appears likely that its intermittent presence may thus represent the infill of pre-existing depressions in the Clay-with-Flints (Photograph 10). Petrogenesis: The Clay-with-Flints in Gibson’s 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 three separate layers that make up the deposit. Geochemistry Four clay samples from the Clay-with-Flints in Gibson’s Quarry (Figure 11) were selected for major and selected trace element analysis. Using immobile element ratios it is possible to differentiate between samples 1 and 2, from the lower part of the deposit, which plot on a Zr/TiO2 – Nb/Y discrimination diagram in the andesite field, sample 3 which plots on the intersect between the andesite and basaltic andesite fields and sample 4, from the highest layer, which plots within the basaltic andesite field (Figure 4). Based on the distribution of the four samples on the discrimination diagram, it seems evident that they are representative of a magmatic system which, through time, was becoming less evolved chemically and more basic in composition. In 1999, Mitchell et al., concluded that explosive acid magmatism, induced by the melting of the crust by a rising plume of basic magma, produced the Donald’s Hill Ignimbrite Formation (DHIF) and almost certainly much of the clay fraction in the Clay-with-Flints. Whether or not that process ultimately led to the production of basaltic magma at depth, as the ultimate end member of the continuous process of evolution within the magma chamber which then gave rise to the first basalt lava flows at surface, is not known but it is certainly tempting to speculate. Petrography Two clay samples from the lower and middle layers in the Clay-with-Flints in Gibson’s Quarry were investigated petrographically (Figure 11). Sample 1: This sample was from the lower part of the deposit. In hand specimen it consisted of a pale grey clay-rich matrix with small angular fragments of grey flint and a very few dark red lapilli. In thin section clast types include subangular flints (up to 8mm), heavily haematised opaque fragments (some reaching several mm) and small (average 0.1mm) angular quartz crystals and crystal fragments. Many of the flints appear unaltered but some show reddish staining and slightly lobate margins suggesting some reaction with a hot matrix (in excess of 600ºC) during flow. In the fine-grained matrix fiammé-like structures are defined and the fabric appears to wrap around the clasts suggesting flowage of the deposit. Sample 2: This sample comes from near the top of the middle layer of the deposit. In hand specimen it shows an overall reddening with abundant small (< 1cm) dark red lapilli (Photograph 2C). The matrix is composed of a fine-grained intergrowth of quartz, clay minerals, disseminated opaque oxides and hematite. From the growth habit of the clay minerals it is possible to identify a banded structure possibly following primary flow banding. The lapilli (up to 7mm across) are heavily oxidised and reveal a concentric structure suggesting that they are accretionary lapilli (Photograph 11). They often show a ragged outline and are deformed suggesting compaction and flow after deposition. The highly oxidised nature of the lapilli, in comparison with the rest of the constituents of the deposit, may indicate a primary compositional difference. Remaining clast types include rounded, primarily glassy lava fragments, small sub-rounded flint clasts and small angular quartz crystals and fragments. | |
| Conclusions: | |
The section of the Clay-with-Flints formerly exposed in Gibson’s Quarry could be divided into three layers with the distinctive character of each one emphasised by variations in the proportion of reworked flint clasts and by the concentration of volcanic lapilli. Sedimentological evidence seems to indicate that the middle, lapillirich and flint-poor, layer occupies a channel that eroded into the top of the underlying flint-rich and lapilli-poor basal layer. Petrographical analysis shows that Sample 1 originated as a volcaniclastic deposit while Sample 2 is a lapilli tuff with a volcanogenic origin. Geochemical analysis, using immobile element ratios, of the volcanic component of the clay matrix in the three layers indicates a transition from rhyodacitic or andesitic composition in the basal layer to basaltic andesite in the middle and upper layers. | |
| 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 7), Cornamucklagh Townland [Grid Ref: H981 546], 3.3km WNW from the Bann Bridge in Portadown, Co. Armagh (Figures 9 and 10). |
| Restrictions: | Private land |
| Record type: | ESCR report | ||
| Entered by: | I J Enlander | ||
| Last updated: | 28 Mar 2019 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Gibson’s Quarry, Portadown – Clay-with-Flints, County , site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=1302. Accessed on 2026-11-06. |
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