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Earth Science Conservation Review
| Roddan's Port | Down |
| Site number: | 5 | File Number: | J66 |
| ESCC: | IS | ||
| Locality Type: | Coastal section | Status: | ESCR |
| Grid Reference: | J641658 Approximate | ||
| Google maps: | 54.51445,-5.466 | ||
| County: | Down | Council area: | Ards & North Down Borough Council |
| Period: | Quaternary | ||
| Stages: | Pleistocene | ||
| Site Description | |
|---|---|
| Highlights: | |
Sequence from a former interdrumlin depression embracing the classical European late-glacial events of the Older and Younger Dryas with the intervening milder Allerod oscillation. This sequence is sandwiched between a late glacial marine clay and a later post glacial transgression. The stratigraphy demonstrates the interactions between isostatic uplift and eustatic changes of sea level following ice withdrawal from east County Down. | |
| Introduction: | |
The area around Roddan's Port consists of drumlins which rest upon an irregular rock basement of folded Ordovician and Silurian slates and grits. Drumlins vary in shape and are up to 30m in height. The site is located in a former interdrumlin hollow and was orginally surveyed at low tide along the foreshore. The site was described originally by Praeger (1897) who recorded several lithologies including the post-glacial peat beds and trunks of Scotch Fir. He recognised that the basal pink clays were in a similar stratigraphic position to those at Killough. Later the site was investigated in detail by Morrison and Stephens (1965) who recognised deposits of two marine transgressions separated by a late glacial terrestrial sequence. It is emphasised that the sequence is not visible unless excavated through the present gravelly accumulations on the foreshore. | |
| Description: | |
At Roddan's Port the lowest late glacial unit recorded was red clay which occurred between +1.83m and -2.79m O.D. Locally this clay forms a drape on the drumlins up to about 12m O.D. It is massive to faintly-laminated and contains thin stringers of gravelly detritus. Few fossils were recovered from the red clay except several ostracods species which are all living North Atlantic species. The red clay is overlain by grey clay which is stoneless, massive to faintly-laminated. Pollen analysis was only carried a short distance into this unit due to the paucity of pollen grains. Algae especially the coenobia of Pediastrum were recorded. Towards the top of this clay Betula, Pinus, Juniperus and Salix pollen begin to appear together with disseminated organic detritus. The overlying organic mud occurs as thin horizontal slabs. The surface of these compressed slabs were threaded through in all directions by cyperaceous and graminaceous fragments and there was a network of skeltons of Characeae. In some sections there were well-marked, thin seams of freshwater shells. There were chiefly Lymnaea peregra and several species of Pisidium together with a few specimens of Planorbis. The change in sediment type is accompanied by rising curves of Betula, Juniperus and Empetrum and high values of Romex. There is no evidence of distinctly thermophilous species and instead, the occurrence of oceanic plants such as Artemisia, Helianthemum and Potamogeton pectinatus is noted. Finally the top of the organic mud is marked by increasing values of Graminae and dimishing values of Juniperus and Empetrum. The organic mud is overlain by a grey, sandy deposit with numerous small, angular to rolled pebbles of shale. The latter are generally random with no preferred fabric. There are well- defined thin seams of organic detritus containing leaves of Salix herbacea and Polytrichum especially in the lower part of the 90cm sequence. It is almost devoid of pollen and results were obtained with difficulty (Morrison and Stephens, 1965). The pollen however contains the interesting Ephedra distachya which has a wide distribution in southern Europe. The list of water plants does not indicate a barren landscape and identifications suggest certain floristic similarities with the lower grey clays. Rananculus achenes are present. The organic seams also contain many tetsons of the freshwater notostracan Lepidurus arcticus which has now a circum-polar distribution (65° to 80°N) where it occurs in ponds and lake margins. The grey sand is overlain by a clearly-defined band of clay mud rich in seeds of Potamogeton and Myriophyllum. This is overlain by up to 22cm of highly-compacted Phragmites peat with fragments of birch bark. These post glacial muds and peats terminate in a grey-marine silt which is capped by coarse beach deposits. The radiocarbon dates obtained from Roddan's Port span late glacial time from around 12ka B.P. | |
| Importance: | |
The Roddan's Port site is of national significance and is one of possibly two sites which record a terrestrial, late-glacial sequence sandwiched between marine deposits. Future research on isostatic and eustatic interactions will probably focus on detailed evaluation of this and other similar sites. | |
| Interpretation: | |
The red clay which contains ostracods at the base of the section is part of a regional drape of marine clay resting on drumlin forming tills (Stephens, 1963; Stephens and McCabe, 1977; Eyles and McCabe, 1989). It is probable that the clays span a period between deglaciation (~16ka B.P.) and subsequent isostatic uplift (~12ka B.P.) since they are interbedded with glaciomarine outwash at Killard Point (McCabe, Dardis and Hanvey, 1984). The overlying sequence of grey clay, organic mud and grey sand is typical of Jessen's (1949) classic tripartite late glacial stratigraphy. However Watts (1985) has pointed out that changes in vegetation cover do not necessarily correlate exactly with changes in sediment type and that there were too many distinct events in the vegetation history to be fitted into these three units. The following summary of floristic elements should therefore be viewed within the context of conventional radiocarbon years. Undoubtedly, the elements of late Quaternary history involve events which are time transgressive owing to measurable lags between the causative force and the geological response (Watts, 1985). The vegetation after deglaciation is poorly-known but probably consisted of very sparce, scattered herbs in a landscape in which base soil still predominated. The grey clay was therefore moved downslope by mass flow in a setting where few plants had time for migration into deglacierised areas. A radiocarbon date (Q360) from organic matter near the top of the grey clay at the Salix pollen maximum confirms an older Dryas Age (Zone 1) of 12,110 ± 150 years B.P. The change of sediment from soliflucted clay to organic mud is accompanied by rising curves of Betula, Juniperus and Empetrum and suggests a shift towards warmer conditions. Traditionally, the organic muds were thought to represent an abrupt climatic amelioration (Zone II) which has been termed the Allerod oscillation (eg. Watts, 1963). The three phases of vegetational development originally outlined by Morrisson and Stephens (1965) are recognised from other sites in Ireland which are dominated by open herb-rich vegetation. Dates from the top of the organic mud are 11,450 ± 150 (Q363), 11,770 ± 150 (Q364) and 11,480 ± 150 (Q365). Watts (1985) however suggests the grass phase ended around 10,900 years B.P. Perhaps a major non-sequence is present at the top of the organic mud at Roddan's Port. The overlying grey sand is interpreted as a soliflucted slope deposit with poorly preserved pollen. Soil instability is generally cited as a major factor in the change of vegetation and minerogenic sedimentation. Tundra vegetation dominated and Jessen named this phase the Younger Salix herbacea (dwarf willow) or Zone III. Watts (1985) prefers the term younger Dryas. A 14C date of 10,070 ± 150 was obtained from the basal part of the organic mud overlying the solifluction clay (Q370). Morrison termed this the Zone III/IV transition. The Zone III/IV transition is marked by an end of solifluction and the expansion of Betula woodland with an intervening period characterised by open habital genera (eg. Koenigia, Artemisia, Rumex). The late glacial strata at Roddan's Port are succeeded by post- glacial muds and peats which terminate in a grey marine silt capped by beach deposits. The peats may be subzone IVG or VIC. Dates from the Phragmites peat range from 10,210 ± 150 to 9,090 ± 150 (Q368, Q367). However deposition of the overlying postglacial beach could have occurred well after these dates which do not constrain the timing of the post-glacial transgression in this area. | |
| Conclusions: | |
The Roddan's Port site was surveyed in 1965 and clearly demonstrates the major events and sedimentary environments following deglaciation of the coast of east County Down (Morrison and Stephens, 1965). The early late-glacial transgression is recorded by red clay which drapes the drumlins in the area. Elements of late-glacial climatic oscillations are recorded by soliflucted clays and organic muds which have been traditionally known as the Older Dryas, Allerod interstadial and Younger Dryas. Recent work suggests that this lithostratigraphic subdivision needs updating (eg. Watts, 1985). The top of the preserved sequence documents elements of post-glacial peat formation on the foreshore and post-glacial beach gravels. However it is difficult at present to determine how much of the original 1965 post- glacial peat now remains due to beach sands and cobbles. | |
| Notes: | |
This site is also a Site of Local Nature Conservation Importance. See Key Site 749 - Roddan’s Port. | |
| Keywords | |
|---|---|
| Rocks: | Clay, Gravel, Sand |
| Fossil Groups: | Ostracods |
| Structures: | late-glacial sequence, post-glacial pollen zone |
| Relations: | Beach deposit, Late-glacial deposit, Marine deposit |
| Access | |
|---|---|
| Approach: | Roddan's Port is approximately 3km south of Ballywalter. |
| Management: | |
The state of the exposure is poor but probably most of the stratigraphic succession is preserved beneath the present beach sediments. There is little that could be done to enhance the value of the site in terms of shore protection. Future work on the site would require excavation and the site can withstand reasonable geological sampling. Notifiable operations include: 1- Any modification of the beach surface. 2- Use of vehicles on the beach. 3- Extraction of any deposits on the surface or subsurface. 4- Dumping, spreading, discharge or storage of any materials. | |
| Threats: | Dumping |
| Uses | |
| Uses: | The site is located on the foreshore seaward of the modern shingle beach. There are no obvious signs of any intensive use of the beach area for extraction of materials though there has been some dumping of waste towards the southern end of the beach. |
| References (9) | |||
|---|---|---|---|
| Eyles, N. & McCabe, A.M., 1989. The late Devensian (< 22,000 B.P.>) Irish Sea Basin: The Sedimentary record of a collapsed ice sheet margin. Quaternary Science Reviews, vol. 8, pp.307-351. | |||
| Jessen, K., 1949. Studies in Late Quaternary deposits and floral history of Ireland. Proceedings of the Royal Irish Academy, vol. 52B, pp.85-290. | |||
| McCabe, A.M., Dardis, G.F. & Hanvey, P.M., 1984. Sedimentology of a Late-Pleistocene submarine moraine complex, County Down, Northern Ireland. Journal of Sedimentary Petrology, vol. 54, pp.716-730. | |||
| Morrison, M.E.S. & Stephens, N., 1965. A submerged late-Quaternary deposit at Roddans Port on the north-east coast of Ireland. Philosophical Transactions of the Royal Society, London, vol. B249, pp.221-255. | |||
| Praeger, R.L., 1897. Post Tertiary beds at Ballyhalbert, Co. Down. Irish Naturalists Journal, vol. 6 numb. 306. | |||
| Stephens, N., 1963. Late glacial sea levels in north-east Ireland. Irish Geography, vol. 4, pp.345-359. | |||
| Stephens, N. & McCabe, A.M., 1977. Late-Pleistocene ice movements and patterns of Late- and post-glacial shorelines on the coast of Ulster, Ireland. Special Issue of the Geological Journal, numb. 7 In The Quaternary History of the Irish Sea., pp.179-198. | |||
| Watts, W.A., 1963. Late-glacial pollen zones in western Ireland. Irish Geography, vol. 4, pp.367-376. | |||
| Watts, W.A., 1985. Quaternary vegatation cycles. In The Quaternary History of Ireland, pp.155-185 Academic Press, London. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 21 (Strangford Lough) Discoverer Series. | ||
| Record type: | Environment Serv. GIS, ESCR report, J. Preston l | ||
| Entered by: | Crowther, P.R. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Roddan's Port, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=5. Accessed on 2026-11-08. |
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