Earth Science Conservation Review

Summary Full report
Killard Point
Site number:9File Number:J64
ESCC:IS
Locality Type:Coastal section Status: ASSI
Grid Reference: J627486,J613434,J558373 Centroid
County: DownCouncil area:Ards & North Down Borough Council
Period:Quaternary
Stages:Pleistocene
Site Description
Highlights:
The Late Midlandian sections at Killard Point illustrate the internal geometry of a coarse-grained, glaciomarine apron which fronts the drumlin swarms of east County Down. The facies sequence demonstrates that the high basal sediment flux which occurred during drumlinisation was resedimented in a tidewater setting. High relative sea level at this time is related to deep isostatic deflection in the northern part of the Irish Sea basin. The sedimentology clearly demonstrates variability in the processes which operate at a grounded, tidewater ice front. This was the first sedimentological study to demonstrate that the deglaciation of the Irish Sea basin was effected by tidewater processes and marine downdraw of the lowland ice sheet in the Late Midlandian (McCabe, Dardis and Hanvey, 1984). The sequence was also used to develop the theory that Late Pleistocene, mid-latitude sea-surface temperatures coupled with rising sea-levels provided a strong deglacial mechanism which was largely independent of climatic forcing.
Introduction:
The Killard Point moraine trends NE/SW, is 6km to 7km in length and 1km to 2km in width and occurs as hummocky topography between Ardglass (Ardtole Hill) and Killard Point. Topographically the morainic zone has a local relief of 10m to 15m and forms a well-defined depositional unit 1km to 2km in front of the erosional drumlin topography of east Co. Down. Drumlin orientations indicate a southeasterly ice flow during drumlinisation. The latter involved a high basal debris flux towards the ice margin which had grounded (re-equilibrated) along rock butresses or pinning points in this coastal zone. Excellent sections at Ballyhornan and Belderg Bays document a wide range of subaqueous processes during resedimentation from basal effluxes into deeper water (McCabe, Dardis and Hanvey, 1984). Earlier regional work by Stephens (1963) recognised that red marine clay and cliff notches associated with a late glacial marine transgression postdate the 'morainic gravel'. Sedimentological evidence from the current exposures indicate that the moraine is essentially a glaciomarine apron that prograded into deeper water.
Description:
The sedimentology and sediment geometries of the Benderg and Ballyhornan bay sections are similar. They consist of three major lithofacies associations. The diamict association overlies a rock pavement which has been moulded by ice flow to the southeast. The massive diamict is crudely bedded. Upwards the massive diamict grades over 0.5m into stacked beds of stratified diamict which tend to occur either in hollows or on the flanks of the massive diamict. Clast fabrics in the massive diamict are poorly- developed but those of the stratified diamict show strong preferred fabrics, subparallel to the bedding planes. Thin, discontinuous beds of red mud and mud intraclasts occur both within and drape the diamicts.
The top of the diamict association is undulating and possibly channeled. Resulting depressions are infilled by rhythmically- bedded muds and sands which pass upwards into parallel-laminated sands and finally more massively-bedded, medium sands. Isolated small cobbles are present together with small 'till pellets' and occasional dish-shaped water escape structures.
The junction between the sands and overlying gravel association varies from sharp to channelled with occasional soft-sediment deformation dikes and sills. The gravels occur as a nested set of fourteen channel infills. Channels are identified on the basis of well-defined margins, erosional junctions between adjacent infills and sedimentary contrasts between channel fills. Generally channel cross-sections range from 10m to 80m in width by 5m to 11m in depth though a magnificant example at the eastern end of the section is 250m in width by 15m in depth. Channel infills contain a wide range of stacked beds ranging from pebble to cobble gravel which show a wide diversity in sorting and grading patterns. Thick beds of massive to rhythmically bedded red muds occur within the gravelly sequences and occasionally drape erosional channel margins.
Importance:
The Ballyhornan and Belderg sites are highly important at local, national and possibly international levels. The scientific reasons are similar for all three categories. In addition at the local scale this is the only site showing deep coastal exposures in Pleistocene sequences in the whole of eastern Co. Down from Newcastle to Belfast.
The scientific concepts include:
1: The sequence is a signature for a substantial subglacial debris flux on an areal scale during the largely unresolved processes of drumlinisation (McCabe, 1993).
2: The moraine is situated about 1km in front of and is perpendicular to the drumlin swarms of east Co. Down and forms the output of an integrated glacial/proglacial system.
3: The position of parts of the moraine overlying, coastal bedrock highs it is a re-equilibration feature formed as the ice sheet margin withdrew from the Irish Sea basin as a tidewater front.
4: There is no other known site in the Irish Sea basin which illustrates clearly a prograded glaciomarine apron.
5: Sedimentologically the coarse-grained gravel association is an excellent example of high density mass flows and resedimentation into deep water. No other known site in the Irish Sea basin contains such a wealth of sedimentological evidence.
6: A broader view of the moraine is that it reinforces the concept that rising sea levels were largely responsible for the disintegration of the Irish Sea glacier. This, and the recognition that the areal processes of ice sheet downdraw into the marine environment (documented by drumlin lineation) indicate that climatic forcing cannot be used alone as a concept to explain ice sheet disintegration. This scenario also demonstrates that deep isostatic depression occurred in the northern part of the Irish Sea basin at this time and it can be inferred that local deglaciation bed global eustasy.
In summary it is argued that the exposures are part of an integrated glacial/proglacial system which document the nature of the main controls on deglaciation of the last ice sheet in the northern Irish Sea basin. It is therefore a national type site containing magnificant stratigraphic and sedimentological evidence.
Interpretation:
Although it rests on an abraided platform the sedimentary structures of the diamict association are not typical of basal tills. Stratification, winnowing, matrix variability, clast freighting, mud drapes, slump folds and interbedded sands within the diamicts are more suggestive of a continuum of processes during mass flow events. Interbedded pebbly muds suggest resedimentation and mud drapes testify to periodic phases of suspension sedimentation.
The apron of overlying laminated-sands are suggestive of flows of low to intermediate viscosity with variable rates of bed-load transport and suspension fallout. The general absence of structures within the massive sand suggests gravity flow of cohesionless sediment. Locally interbedded, disaggregated mud beds are associated with erosion during phases of strengthening bottom current activity.
Palaeographic considerations, a general coarsening-upwards trend and the orientation of channel axes indicate that the gravels prograded south and south eastwards from a glacial efflux. The channelled complex records repeated channel avulsion. Sharp junctions between stacked gravelly beds and intraformational mud drapes suggest that deposition occurred as a series of high energy pulses. The grading patterns within many vertical sequences are very similar to models for resedimented, deep-water conglomerates (Walker, 1975, 1983). In general the gravel sequences represent high-density turbidity flows.
Regional sea levels, lithofacies geometries and interpretation of associated processes indicate that the deposits at Killard Point were resedimented from a subglacial efflux into a glaciomarine environment. The flutes on the pavement occurred during ice flow into the Irish Sea basin. The diamict association reflects release of basal debris and resedimentation by mass flow with minimal sorting. Overlying sands are linked to increased bottom current activity with occasional ice rafting. The gravel association points to a vastly increased sediment flux which was resedimented by high density turbidity currents. Regional evidence from erosional drumlins farther inland suggest that the high rates of sediment flux are directly associated with the areal process of drumlinisation.
Conclusions:
The Killard Point moraine and associated sections at Ballyhornan and Belderg Bays mark the position of the ice margin when it withdrew from the Irish Sea basin and re-equilibrated on the coastline. It represents the output of the glacial system into a glaciomarine setting while the processes of drumlinisation occurred farther north below the main ice sheet. Sedimentologically it is unique in the Irish Sea basin showing extensive resedimentation of debris from a grounded tidewater margin into deeper water. It is clearly a type site of national importance showing both the importance of regional ice dynamics and fine sedimentological detail.
The moraine covers an area of about 4km / . The area around Ballyhornan and Benderg Bays is of critical importance because the thickest sequences are exposed and have not been quarried. The morphology is intact.
Notes:

The sands within the sequence are used as nesting sites.

Keywords
Rocks:Diamict, Gravel, Sand
Structures:glaciomarine apron
Relations:Glacial deposit
Geomorph:moraine, proglacial
Measurements
Length:250 mWidth:Height:18-20 m
Depth:Area:  
Access
Approach:Killard village is approximately 7km S of Strangford.
Management:The current rates of erosion in both small bays are essential to maintain not only the scientifically interesting exposures, but the topographic and aesthetic balance of this area. The crescent-shaped bays fronted by sandy beaches form an aesthetically pleasing view from many angles especially in association with the stepped outline of Guns Island immediately offshore. Coastal dynamics and sediment budgets of coastal beaches are complex. For example, if the Ballyhornan section was stabilized to protect the coast road, erosion of the beach would probably follow and lead to a more serious erosion problem than at present. As the current rates of coastal erosion are low, they keep the scientifically important sections clean and replenish the beach sediments. One serious problem has been dumping over the Ballyhornan cliff section from the coast road. Signs were erected but all types of rubbish end up on the back of the beach and drape the section. The sections can withstand sampling by responsible geologists. There are no shell beds or unique fossils or rocks which are sought after. However notifiable operations should include any modification of the land surface, engineering works, storage of materials, use of machineary, extraction, afforestation or tree planting, burning of waste material, dumping or discharge, or quarrying of any sort.
Threats:Increased erosion; irresponsible sampling; dumping.
Uses
Uses:The land over the defined sites is mainly used for silage and grazing. No quarries were found and the MOD have now removed their base. Remnants of the old MOD runway still exist along with huts and minor roads.
References
McCabe, A. M., Dardis, G. F. and 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
McCabe, A. M. 1993: The 1992 Farrington Lecture: Drumlin bedforms and related ice marginal depositional systems in Ireland. Irish Geography, vol. 26, pp.22-44
Stephens, N. 1963: Late glacial sea levels in north-east Ireland. Irish Geography, vol. 4, pp.345-359
Walker, R. G. 1975: Generalised facies models for resedimented conglomerates of turbidite association. Bulletin of the Geological Society of America, vol. 86, pp.737-748
Walker, R. G. 1983: Turbidites and associated coarse clastic deposits. Reprint Series of the Geological Society of Canada, vol. 1 In Facies Models., pp.91-103
Map(s): See the 1:50,000 O.S. Sheet 21 (Strangford Lough).
Rec Type Environment Serv. GIS, ESCR report, J. Preston l    
Enterer: Crowther, P.R.
Updates: 03 FEB 97 / 29 JAN 97 / 23 DEC 96 / 12 NOV 96 / 05
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