Characteristics, Age and Significance of Buried Podzols in the Grangemore Sand Dunes, CoLondonderryAuthor(s): Peter WilsonSource: The Irish Naturalists' Journal, Vol. 24, No. 12 (Oct., 1994), pp. 475-480Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25535866 .

Accessed: 15/06/2014 13:08

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.

.

Irish Naturalists' Journal Ltd. is collaborating with JSTOR to digitize, preserve and extend access to The IrishNaturalists' Journal.

http://www.jstor.org

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

THE IRISH NATURALISTS' JOURNAL

Vol. 24 October, 1994 No. 12

CHARACTERISTICS, AGE AND SIGNIFICANCE OF BURIED PODZOLS IN THE GRANGEMORE SAND DUNES,

CO LONDONDERRY

Peter Wilson

School of Environmental Studies, University of Ulster at Coleraine, Cromore Roady Coleraine, Co Londonderry BT52 ISA

Buried soils occur frequently within sand dunes around the coast of Ireland and may be useful chronostratigraphic markers with which to establish local and regional patterns of dune development. They are evidence of land-surface stability and vegetation "growth following a phase of dune construction; their subsequent burial representing a renewal of dune sand accumulation at the site. In addition, they can provide valuable information

concerning soil-forming processes that operated previously in the dunes, improve our

understanding of the evolutionary stages through which sand dune soils progress, and may yield organic material suitable for age determination by radiocarbon dating. Such soils have been described in considerable detail from Murlough, Co Down (Cruickshank 1980) and

Magilligan and Portstewart, Co Londonderry (Wilson and Bateman 1986, 1987, Wilson

1991) and form the basis for dune chronology at these locations (Wilson 1990). This paper reports on the characteristics and age of buried podzolic soils in sand dunes

at Grangemore, Co Londonderry, and assesses their significance with respect to the

previously established local dune chronology (Wilson 1990, 1991) and the evolutionary stages of sand dune soil development (Wilson 1992).

The Grangemore Buried Podzols

At Grangemore (Fig. 1, C806345), on the south side of the estuary of the River Bann, a

small area (c35ha) of relatively subdued dune topography contrasts with the high dune forms of neighbouring Portstewart and Castlerock. At two sites within the dunes buried soils with morphological characteristics (i.e. horizon sequences and colours) indicative of

podzolization are exposed. The first site (profile 1) is a blowout alongside the railway line that passes through the dunes; sand erosion to a depth of 3m has revealed the buried soil

which now forms a step across the floor of the blowout. The second site (profile 2) is a small

exposure in the flanks of a dune 170m east of profile 1. The sequence of soil horizons identified for profile 1 is shown in Fig. 2; chemical data

and Munsell soil colours for both profiles are listed in Table 1. Four horizons, overlain by a veneer of loose sand recently eroded from the walls of the blowout, were recognized in

profile 1. The former surface organic-rich horizon (bAh) of the podzol, at 7.72m O.D., consists of a thin layer of very dark grey (10YR3/1) humic sand and is probably the remnants of a former;thicker horizon that was eroded during blowout formation. The

overlying sand and the bAh horizon are absent at the right-hand side of the section (Fig. 2). The underlying eluvial horizon (bEa) is pinkish grey (7.5YR7/2) and, relative to the bAh

horizon, is deficient in organic matter and both pyrophosphate-extractable (Fep) and dithionite-extractable (Fed) iron. A very dark greyish brown (10YR3/2) illuvial horizon

(bBhs), enriched in both translocated organic matter and iron, is present beneath the bEa horizon. The boundary between the bEa and bBhs is distinctly wavy, while that between the

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

476 Ir. Nat. J. Vol. 24 No. 12 1994

\j* Grangemore

g km 1 ^

Figure 1. Sand dunes (stippled) at the Bann estuary and location of sites mentioned in the text.

bBhs and the underlying brown to dark brown (10YR4/3) illuvial horizon (bBh) is very irregular. Organic enrichment is again evident in the bBh horizon. Within the bEa, bBhs and bBh horizons occur thin, undulating lines containing slightly more organic matter than the host sand. The profile is acidic throughout. A 14C date of 2580 ? 60 years B.P.

(Beta-62957) was obtained from the organic matter in the bAh horizon (Fig. 2). This and

subsequent 14C dates quoted in the text are in uncalibrated 14C years B.P. Profile 2 differs from profile 1 in several respects. First, it extends to the present-day

ground surface and incorporates a modern dune soil consisting of a single dark yellowish brown (10YR4/4) Ah/Cu horizon that is 55cm thick. Second, it includes two buried soils of which only the lowermost is podzolized. The uppermost buried soil consists of a very dark

grey (10YR3/1) bAh horizon that is enriched in organic matter and underlain by a brown to dark brown (10YR4/3) bAh/Cu horizon. This buried soil occupies a profile thickness of

only 15cm. Third, the buried podzolized soil has a solum thickness considerably less than that in profile 1 and displays a slightly different profile morphology. The very dark grey (10YR3/1) bAh horizon, at 7.44m O.D., is underlain by a dark grey (10YR4/1) bAh/Ea horizon containing less organic matter and iron. Two bB horizons are present and both

qualify as bBhs horizons on the basis of their contained amounts of translocated organic matter and iron, even though their colours differ (Table 1). The remainder of the excavated section consists of a bBCu and a bCu horizon.

Both of the buried podzolized soils meet the morphological and chemical criteria established by Avery (1980) for classification as humoferric podzols; in profile 2 the

uppermost buried soil and the modern soil are both typical sand rankers. Particle size analyses of four samples from the humo-ferric podzol in profile 1 show

that the sand has a mean grain size range from +2.37 to +2.410 (0 = ?

log2 diameter in

mm); between 89% and 92% of the grain size distributions are in the fine sand category (+2 to +30). Sorting coefficients range from 0.25 to 0.270, indicating very well-sorted sand.

Discussion

A preliminary chronology of coastal dune formation for sites on either side of the Bann

estuary was presented by Wilson (1990). Subsequent work at Portstewart (Wilson 1991) and the information given above for Grangemore has allowed construction of a more detailed chronology, which is discussed below and outlined in Fig. 3.

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

Ir. Nat. J. Vol. 24 No. 12 1994 477

. A, 2580 ?60 DAh (Beta-62957)

Figure 2. Sequence of horizons exposed in profile 1 and location of radiocarbon-dated sample.

From a sand-cliff exposure in a meander of the Articlave River, on the western edge of the Grangemore dunes (Fig. 1), Hamilton and Carter (1983) described a silt-rich organic deposit interbedded in dune sands. A 14C date of 5315 ? 135 years B.P. (UB-937) was obtained from macro-fossils within the organic bed and is compatible with the pollen spectrum. The date is the earliest minimum age for dune formation in Ireland. Above the

organic bed, Hamilton and Carter (1983) recorded the presence of two distinct buried soils

displaying immature podzolic characteristics, but these were not dated. Nevertheless,

together the l4C-dated organic bed, the buried soils and the modern soil testify to four

phases of dune sand accumulation and subsequent stability at Grangemore. On the north side of the Bann estuary, in the dunes that back Portstewart Strand (Fig.

1), stratigraphical and archaeological information obtained from several sites by Coffey and

Praeger (1904) and May and Batty (1948) suggests that four phases of sand accumulation occurred here also; one pre-dating and one post-dating the Neolithic period, one post-dating the Bronze Age and another post-dating the Iron Age. Buried organic horizons reveal that the dunes were stabilized during parts of these cultural periods and probably also during the

Mediaeval period. The pre-Neolithic dunes may be correlated with those identified by Hamilton and Carter (1983) as pre-dating c5300 years B. P., but cross-estuary correlation of other dune sand units has proved difficult in the absence of absolute age determinations. Elsewhere at Portstewart, Wilson (1991) recognized four phases of aeolian sand deposition from detailed analyses of an exposure at the site of the former Strand Hotel (Fig. 1). Two of these phases were of relatively small scale and added sand to pre-existing soil organic horizons, the other two were of larger scale and were dated to after c4800 years B.P. and after c525 years B.P. respectively.

The presence of buried podzols in the Grangemore dunes indicates that a significant period of land-surface' stability prevailed during the course of dune development. Furthermore, the 14C date from the bAh horizon of profile 1 locates this stability phase at c2600 years B. P., which is considerably later than the stability phase identified by Hamilton and Carter (1983) and probably corresponds with one of the buried soils they identified above their 14C-dated organic bed. However, from this single age determination it is not

possible to define the initiation or termination of the stability phase nor to define its length.

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

478 Ir. Nat. J. Vol. 24 No. 12 1994

Table 1. Properties of the Grangemore soils.

Horizon Depth Munsell pH Organic Fep Fed (cm) colour matter %. % %

(dry) Profile 1

bAh 3-6 10YR3/1 4.7 5.2 0.22 0.34 bEa 6-17 7.5YR7/2 4.8 0.3 0.02 0.19

bBhs 17-37 10YR3/2 5.0 1.4 0.41 0.64 bBh 37-53+ 10YR4/3 5.1 1.0 0.05 0.36

Profile 2 Ah/Cu 0-55 10YR4/4 4.2 1.5 0.10 0.33 bAh 55-65 10YR3/1

' 4.6 4.3 0.28 0.38

bAh/Cu 65-70 10YR4/3 4.7 1.4 0.16 0.29 bAh 70-79 10YR3/1 4.5 3.3 0.24 0.32

bAh/Ea 79-87 10YR4/1 4.5 1.4 0.12 0.21 bBhsl 87-91 10YR3/3 4.4 2.2 0.55 0.69

bBhs2 91-95 7.5YR3/4 4.4 1.5 0.47 0.60 bBCu 95-125 10YR5/6 4.7 0.9 0.10 0.26

bCu 125-155+ 10YR6/6 4.8 0.6 0.04 0.26

The 14C date provides only a minimum age estimate for stability initiation and a maximum

age estimate for stability termination. Given that the upper part of the bAh horizon has been

eroded, the date may be a closer estimate of stability initiation than termination. The most

rapid rate of podzolization reported for Irish sand dunes is c600 years at Murlough (Cruickshank 1980), and the Grangemore buried podzols are considered to have needed at least the same length of time to acquire their morphological and chemical characteristics.

Thus, dune stabilization at Grangemore is believed to have begun prior to 3200 years B.P. and to have ended sometime after 2400 years B.P. These age estimates correspond with the latter half of the Bronze Age (Mallory and McNeill 1991) and are in broad agreement with the evidence presented by May and Batty (1948) for dune stability at Portstewart Strand

during the Bronze Age. Therefore, the early history of dune development on either side of the Bann estuary is becoming clearer and seems to have followed a similar time-course (Fig. 3).

It is interesting to note that the buried podzols at Grangemore occur at heights of 7.7m and 7.4m O.D., suggesting the presence of an extensive near-horizontal land surface at the time of podzolization. At Portstewart Strand, the Bronze Age surfaces identified by May and Batty (1948) occur at 7.9m and 8.8m O.D. again suggesting the existence of a

near-horizontal land surface. As yet the significance of this surface is not clear. It may have been a surface associated with primary sand deposition, in which case sand sheet

topography (near-horizontal or very gently undulating) rather than dune topography (strongly undulating) existed. Alternatively, a primary dune topography may have been

eroded to a planar surface prior to human occupation and pedogenesis. Because of the broad chronological agreement shown by the early dune stability and

instability episodes on either side of the Bann estuary, it is tempting to extend the

chronology by correlating the uppermost buried soil in profile 2 with the Iron Age dune

stability phase recognized by May and Batty (1948) at Portstewart Strand. Correlation of the

post-Iron Age phase of sand accumulation with the surface sand unit at Grangemore is more

difficult, however, due to the contrasting topographic and sedimentary characteristics of these sands. At Portstewart the sand is rich iri CaC03 and forms steep-sided dunes with a

maximum amplitude of c20m; at Grangemore the dunes lack CaC03 and the maximum

amplitude is less than 8m. The Grangemore buried podzols are indicative of free drainage and favourable

conditions for the mobilization and translocation of iron and organic matter at the time of

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

Ir. Nat. J. Vol. 24 No. 12 1994 479

0 vi. 0 9 wiw?w Portstewart

">^< ?">*?* Strand Hotel

?.?.->* Neolithic ^-V Bronze Age **V J

^....? sf/aS?*"1

?.->- -<? ? ? -<?- ? Grangemore

I-!-1-1-1-1-1-1-1-1-1-1-1 6000 5000 4000 3000 2000 1000 0 14C years BP

+ u ? Phase of sand deposition, question mark indicates C date ? 2o -<? . ?

uncertainty about length of phase

Figure 3. Sand accumulation phases and land-surface stability phases for sites at the Bann estuary.

their formation. This suggests that they progressed through a series of development stages similar to those outlined by Wilson (1992) for soils in freely-drained sites on calcareous

(shelly) sand. The absence of CaC03 in the dunes may be because of pedogenic leaching, but the possibility exists that for some reason as yet undetermined CaC03 was never present at Grangemore. Even the modern soils, developed in the uppermost sand unit, lack shell

fragments and are anomalous in the context of dune sands and soils on the north coast of

Ireland.

More examples of buried podzols have been reported from Irish sand dunes than modern podzols. This could be due to either more conducive environmental factors in the recent past favouring podzol development or a shorter time period for modern soil formation. Whatever the reason, there are few sites where podzolization is currently active.

Conclusions

Although some advances have been made in recent years towards establishing a reliable dune chronology for sites at the Bann estuary, several problems still remain. For

example, the relationship between sand accumulation phases at the site of the former Strand Hotel (Wilson 1991) and those documented for Portstewart Strand and Grangemore needs to be resolved. In particular, sand accumulation after c525 years B.P. at the Strand Hotel

(Fig. 3), although consistent with widespread evidence for Mediaeval dune formation from

many other locations in Ireland, has no apparent equivalent at either Portstewart Strand or

Grangemore.

Furthermore, the forcing mechanisms for dune instability phases are not known with

certainty and to speculate here on the causes of sand accumulation at sites around the Bann

estuary would be premature. Several forcing mechanisms ?

sca-lcvel changes, climatic

changes, and human-induced environmental changes ? are frequently invoked, either

individually or in combination, as initiating periods of instability and sand movement but at

present for the Bann estuary there is insufficient information available to enable meaningful assessment of the causes.

The dune chronolqgy that has been established is based on relatively few sites (some of which are no longer exposed) and only four 14C dates. This chronology must continue to be

regarded as preliminary until such time as additional sites and dates are available that may

verify or refute the sequences of stability and instability as being representative of the dune

systems as a whole.

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions

480 Ir. Nat. J. Vol. 24 No. 12 1994

Acknowledgements

Assistance with field and laboratory work was given by Peter Devlin, Robert Stewart and Debbie Rainey, and the diagrams were prepared by Mark Millar and Kilian McDaid.

Funding for the radiocarbon date was provided by the late Bill Carter.

REFERENCES

Avery, B. W. (1980) Soil classification for England and Wales (Higher categories). Soil Survey Technical

Monograph 14. Soil Survey of England and Wales, Harpenden.

Coffey, G. and Praeger, R. L. (1904) The Antrim raised beach: a contribution to the Neolithic history of the north of Ireland. Proc. R. Ir. Acad. 25C: 143-200.

Cruickshank, J. G. (1980) Buried, relict soils at Murlough sand dunes, Dundrum, Co Down/r. Nat. J. 20: 20-31.

Hamilton, A. C. & Carter, R. W. G. (1983) A mid-Holocene moss bed from eolian dune sands near Articlave, Co.

Londonderry. Ir. Nat. J. 21: 73-75.

Mallory, J. P. & McNeill, T. E. (1991) The archaeology of Ulster from colonisation to plantation. Institute of Irish

Studies, Queen's University of Belfast.

May, A. McL. & Batty, J. (1948) The sandhill cultures of the River Bann estuary, Co Londonderry. J. R. Soc.

Antiq. Ir. 78: 130-156.

Wilson, P. (1990) Coastal dune chronology in the north of Ireland. In: Bakker, Th. W. M., Jungerius, P. D. and

Klijn, J. A. (eds) Dunes of the European coasts. Catena (Suppl.) 18: 71-79.

-(1991) Buried soils and coastal aeolian sands at Portstewart, Co Londonderry, Northern Ireland. Scott.

geogr. Mag. 107: 198-202.

-(1992) Trends and timescales in soil development on coastal dunes in the north of Ireland. In: Carter, R. W. G., Curtis, T. G. F. and Sheehy-Skeffington, M. J. (eds) Coastal dunes: geomorphology, ecology and management for conservation: 153-162, Balkema, Rotterdam.

-& Bateman, R. M. (1986) Nature and palaeoenvironmental significance of a buried soil sequence from

Magilligan Foreland, Northern Ireland. Boreas 15: 137-153.

-&-(1987) Pedogenic and geomorphic evolution of a buried dune palaeocatena at Magilligan Foreland, Northern Ireland. Catena 14: 501-517.

SEED BANK ASSOCIATED WITH STANDS OF HEATHER MOORLAND

D. M. McFerran and J. H. McAdam

Department of Applied Plant Science, Queen's University, Agriculture & Food Science Centre, Newforge Lane, Belfast BT9 5PX

W. I. Montgomery

School of Biology & Biochemistry, Division of Environmental and Evolutionary Biology, Queen's University, Belfast BT9 7BL

Summary

From preliminary investigation of mini-turves obtained from a north Antrim heathland it is suggested that these contained a viable seed bank which could facilitate representative regeneration following vegetation disturbance. Subsequent investigations of species presence and abundance over a 12 month period indicates that there are variations in the seed bank between different ages of Calluna stands. The rate of reappearance of individual

species is also variable.

This content downloaded from 91.229.229.44 on Sun, 15 Jun 2014 13:08:02 PMAll use subject to JSTOR Terms and Conditions