Shell and pebble pavements on beaches: Examples from the north coast of Ireland

CA T E NA

VOL. 5, 365 - 374

BRAUNSCHWEIG 1978

SHELL AND PEBBLE PAVEMENTS ON BEACHES: EXAMPLES FROM THE NORTH COAST OF IRELAND

R.W.G. Carter & C.L. Rihan School of B i o l o g i c a l and Environmental Studies The New U n i v e r s i t y of U l s t e r , Coleraine Co. Londonderry, Northern I r e l a n d BT52 1SA (manuscript accepted for publication December 7, 1978)

SUMMARY Extensive s h e l l and pebble pavements occur on many beaches in N.W. I r e l a n d , and exercise an important r o l e in the geomorphological s t a b i l i t y of the c o a s t l i n e by p r o v i d i n g l i m i t s to erosion. Pavements form through the segregation of d i f f e r e n t grain sub-populations by bed shear stress under uniform f l u i d f l o w s , probably in some instances by the overpassing mechanism described by EVERTS (1973). Pebble pavements tend to u n d e r l i e the foreshores, and apart from small areas where fresh c l a s t s are a v a i l a b l e , are not a c t i v e l y forming at present. Shell pavements form under both wind and moderate wave attack and u s u a l l y develop on beach or berm surface. Reworking or b u r i a l of e o l i a n s h e l l pavements may r e s u l t in thickened u n i t s or complex s t r u c t u r e s . I t is c a l c u l a t e d t h a t r e s o r t i n g of between 3 and 6 m of beach sand was required to produce the pebble pavement at White Park Bay, but only about 0.4 m to produce a s h e l l one at M a g i l l i g a n . Some comparisons are drawn w i t h other recent and ancient examples. ZUSAMMENFASSUNG An v i e l e n KUsten in Nordwest-lrland sind Muschel- und G e r ~ l l p f l a s t e r h~ufig und sind w i c h t i g f u r die S t a b i l i t ~ t der KUste. Doe P f l a s t e r b i l d e n sich i n f o l g e der Korngr~Bensegregation als Folge von Scherkr~ften in gleichf~rmigen FlieBvorg~ngen und v e r m u t l i c h s t e l l e n w e i s e auch durch den von EVERTS (1973) beschriebenen Oberholmechanismus. G e r ~ l l p f l a s t e r l i e g e n o f t unter dem Vorstrand und b i l d e n sich auBer in kleineren Gebieten heute n i c h t neu. M u s c h e l p f l a s t e r bilden sich unter Wind- und m~Bigem W e l l e n a n g r i f f . Aufarbeitung oder Oberdeckung von ~olischen Mus c h e l p f l a s t e r n fUhrt zu komplexen Strukturen. Absch~tzungen zeigen, dab 3 - 6 m Strandsand a u f g e a r b e i t e t werden mu~ten, um das G e r ~ l l p f l a s t e r von White Park Bay zu b i l d e n , aber nur 0.4 m f u r das M u s c h e l p f l a s t e r von M a g i l l i g a n . 1.

INTRODUCTION

On beaches where sediment comprises mixtures of s h e l l or pebble plus sand, component sub-populations tend, in time, to separate, as various s i z e s , shapes and dens i t i e s respond to d i f f e r e n t parts of the process spectrum. Examples of segregated beach deposits include beach laminae (CLIFTON 1969), heavy mineral placers (MAY 1973) and s h e l l layers (NELSON 1977). This paper concentrates on l a t e r a l l y extensive sheet u n i t s composed of pebbles and s h e l l s , which commonly occur on beaches in N.W. I r e l a n d . These deposits, c a l l e d "pavements" (SHAW 1929) are formed by both 365

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wind and wave processes, and appear capable of reducing beach erosion rates. Some c r i t e r i a are proposed to a l l o w r e c o g n i t i o n of ancient examples, and to avoid confusion between s i m i l a r deposits. 2.

STUDY AREA

The north coast of I r e l a n d (Fig. I ) is composed of a series of sandy beaches and dunes separated by rocky headlands. A l l beaches are formed of w e l l - s o r t e d sands derived l a r g e l y from marine reworking of g l a c i a l d e b r i s , plus a small but v a r i a b l e proportion of biogenic carbonate (mainly recent comminuted skeletal m a t e r i a l ) . Composite sediment samples often reveal polymodal grain p o p u l a t i o n s , w i t h peaks r e l a t e d to p a r t i c u l a r s i z e , shape or d e n s i t y f a c t o r s . As far as possible Table i summarises these data f o r the f i v e beaches discussed in t h i s paper. The c o a s t l i n e is exposed to a wide spectrum of i n c i d e n t waves, with extreme nearshore wave heights (Hmax) around 4.5 m, and swell wave periods exceeding 15 s during storm decay. Spring t i d a l range varies from about 3.5 m at C u l d a f f , to 3.0 m at Naran and M a g i l l i g a n , to 1.5 m at Runkerry and White Park Bay. Tidal streams are g e n e r a l l y weak (< 0.3 m s - I ) and reverse from W + E to E ÷ W over the flood/ebb cycle (ADMIRALTY 1968). Although l i t t l e or no sediment passes longshore between beaches, extensive onshore/offshore t r a n s p o r t occurs over several time scales in response to changes in both wave climate and nearshore geometry. Spectacular episodes of beach s t r i p ping and dune c l i f f i n g occur every 3 to 4 years (CARTER 1975), followed by gradu a l , but almost complete recovery. Eolian processes cause continuous, but s p a t i a l l y i r r e g u l a r , sediment t r a n s f e r s across the beach. Sediment volume entrained by wind stress depends not only upon wind v e l o c i t y and d i r e c t i o n , but also on the moisture content of both a i r and sand, presence of vegetation and concentrations of s a l t n u c l e i . Although about 50 % of winds recorded on the north coast are S.W. or W., there is l i t t l e persistance or s e a s o n a l i t y , and winds of a l l strengths from a l l 366

DATA

C935

C660

C538

B725

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~aran, :o. D o n e g a l

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423

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SEDIMENT

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i: B A S I C

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Tab.

Schist Quartz

pebbles sand

Shell sand Quartz sand

Shell sand Quartz sand

Basalt pebbles Quartz sand Magnetite sand

Basalt pebbles Chalk pebbles Quartz sand Magnetite sand

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% ~

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0.56 O.45

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-5.28 O.81 1.56 0 . 3 8 3.07 -

-5.78 0.72 -5.21 0.65 1.86 0 . 3 4 3.15 -

Size ~ ~, g cm

2.64-2.90 2.61-2.65

1.80-2.95 2.61-2.65

1.80-2.95 2.61-2.65

2.75-2.80 2.61-2.65 5.18

2.75-2.80 2.55-2.65 2.61-2.65 5.18

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-3 - roundness

Well-rounded Well-rounded

Angular Well-rounded

Angular Well-rounded

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d i r e c t i o n s are not uncommon. In a d d i t i o n , local a i r f l o w , p a r t i c u l a r l y near high dunes, is often s h o r e - p a r a l l e l regardless of general c o n d i t i o n s (CARTER 1977), and land and sea breezes occur in summer. 3.

GENERALSITING OF PAVEMENTS

Pebble and s h e l l surfaces or horizons occur at several p o s i t i o n s in beach deposits (Fig. 2) dependent upon both the r e l a t i v e p r o p o r t i o n of movable to immovable mater i a l and the entrainment processes i n v o l v e d . In these examples lack of primary pebble sources u s u a l l y r e s u l t s in pebble surfaces (pavements) being exposed only at times when beach l e v e l s are at t h e i r lowest. At other periods pavements are covered by sand. Usually t h i s sand is devoid of pebble c l a s t s unless supplied by a secondary pebble source - most l i k e l y from the erosion of o l d e r pavements in nearby raised beach deposits. T y p i c a l l y pebble u n i t s are only one or two c l a s t widths in thickness (30 - 200 mm) and dip g e n t l y seaward (Photo IA) at the same angle as planar beach lamina ( I - 3o). Pebbles tend to be w e l l - s o r t e d both in shape and size (RIHAN in p r e p a r a t i o n ) , and at White Park Bay the smaller and more angular chalk c l a s t s are often higher on the foreshore than the l a r g e r w e l l - r o u n ded basalts. In the densest and most compacted sections of the pebble pavement (up to 240 c l a s t s m-2) s l i g h t seaward dipping i m b r i c a t i o n may occur. This is esp e c i a l l y apparent among elongate s c h i s t s at Naran. Sometimes at White Park Bay and Runkerry the pebble pavement is i n f i l l e d and o v e r l a i n by a t h i n u n i t (5 - 10 mm) of black magnetite sand (Photo IB). Pebble pavements are r a r e l y exposed f o r long, or over the e n t i r e beach at one time, as swash action q u i c k l y replaces foreshore sand (Photo IC). Shell pavements are found in many environments (CARTER 1976), but in these examples are commonly d e f l a t i o n lags on the upper beach. Periods and rates of formation vary according to marine accretion a c t i v i t y , wind c o n d i t i o n s and moisture l e v e l s . The e o l i a n s h e l l pavement has no s t r u c t u r e unless one is i n h e r i t e d from previous mar i n e episodes, i n d i v i d u a l s h e l l valves occur l o o s e l y in a l l p o s i t i o n s (convex, concave and on edge) w i t h no preferred o r i e n t a t i o n , and u n i t s are commonly 3-25 mm in thickness. A n g u l a r i t y and r e l a t i v e l y small size (compared to pebbles) of shell material renders the pavement l i a b l e to frequent reworking, p a r t i c u l a r l y during H.W. Spring t i d e s and surges. Between t i d a l l i m i t s wave-formed shell pavements, c l o s e l y analogous to pebble types in appearance, may form on the beach face slope. 368

Photo i: A. Pebble p a v e m e n t at White Park Bay, J a n u a r y 1976. (Sand apron fronting dune (top left) is d e r i v e d from c l i f f i n g and o v e r l i e s pavements.) B. Scour patterns, e t c h e d in m a g n e t i t e sand over a p a r t i a l l y e x p o s e d p a v e m e n t (Same location and date as A.) C. T e m p o r a r y exposure of pebble p a v e m e n t u n d e r l y i n g a swash bar at Runkerry, caused by an intermittent stream. (The upper bar surface has been d e s t r o y e d by cattle.) D. Deflation p a v e m e n t of shells at Magilligan, June 1973. E. R a i s e d pebble pavem e n t in dune cliff c o l l a p s i n g onto the b e a c h (White Park Bay). Note the b e a c h lamination under the pavement, and dune lamination above. F. Exp o s u r e of 3 d i s t i n c t b u r i e d p a v e m e n t s at the foot of a dune cliff at Naran. (Scales in all p h o t o g r a p h s = i m.)

369

Such pavements form under moderate wave a c t i v i t y and can be d i s t i n g u i s h e d from e o l i a n ones as (a) they are h i g h l y compacted (b) almost a l l s h e l l s (except at the s t r a n d l i n e ) are convex-up and (c) many species, e s p e c i a l l y i f i n e q u i l a t e r a l , e.g. Donax, Venerupis, Ensis, show a strong preferred seaward o r i e n t a t i o n . In a d d i t i o n , s h e l l hash u n i t s may form as i n t e g r a l parts of more complex t i d a l - s e d i m e n t a t i o n u n i t s as OTVOS (1965) among others has demonstrated. Shell material is r e a d i l y a v a i l a b l e at M a g i l l i g a n and C u l d a f f . Beach strandings of whole and fragmented s h e l l s r e g u l a r l y occur in post-storm periods, when cons t r u c t i o n a l sediment accumulations are made up of sand/shell mixtures. On these I r i s h beaches the most extensive s h e l l pavements form by d e f l a t i o n on beach r i d g e , swash bar and berm surfaces. M u l t i p l e or coalesced pavements occur where newer beach forms override e x i s t i n g pavement margins. F i n a l l y two f u r t h e r occurrences of pavements must be noted. F i r s t l y e o l i a n d e f l a t i o n lag deposits of both pebble and s h e l l form w i t h i n dune systems, p a r t i c u l a r l y in blow-outs. Secondly o l d e r pavements (Photo IE and F) often occur in raised beach m a t e r i a l , and erosion of these deposits may c o n t r i b u t e s i g n i f i c a n t l y to newer formations. 4.

PAVEMENTDEVELOPMENTAND MAINTENANCE

Pavements develop by s e l e c t i v e entrainment and d e p o s i t i o n under uniform f l u i d flows. I n d i v i d u a l grains of d i f f e r e n t c h a r a c t e r i s t i c s become sorted w i t h absolute v a r i a t i o n s in bed shear stress (~b). Within a mixed sediment each grain sub-population initially becomes entrained at a c r i t i c a l bed shear stress (~c). I n c i p i e n t motion is s t a t i s t i c a l depending upon both scalar and vector p r o p e r t i e s of i n d i v i d ual grains. I f the actual l e v e l of ~b is below some required values of ~c then s e l e c t i o n and segregation occurs. Smaller, less dense or more angular grains are r e l a t i v e l y easy to disentangle and dislodge from the bed, leaving a residue of coarser, denser or more angular m a t e r i a l , which may remain elevated on pedestals above the mean surface level (CARTER 1978). These form proturbances in the f l u i d f l o w , e v e n t u a l l y breaching any laminar sublayer present, causing collapse or i n creased turbulence. During development of the s h e l l pavement at M a g i l l i g a n pedest a l s are r a r e l y over 14 mm in h e i g h t , a f i g u r e which j u s t exceeds c a l c u l a t e d thickness (from wind v e l o c i t y p r o f i l e s ) f o r the boundary l a y e r . Above 14 mm the s h e l l caps are unstable and may be 'launched' downwind f o r several meters. A f t e r t h i s the pedestals r a p i d l y d i s i n t e g r a t e . While t h i s sequence of events is best observed under e o l i a n c o n d i t i o n s , i t seems l i k e l y t h a t s i m i l a r , but more r a p i d , processes occur under wave uprush. Where many values of ~c are never a t t a i n e d the pavement w i l l form as a collapsed chaotic s t r u c t u r e i n v o l v i n g l i t t l e h o r i z o n t a l displacement of m a t e r i a l . Most e o l i a n pavements take t h i s form. However where the m a j o r i t y of ~c values are surp r i s e d , a l b e i t p r o g r e s s i v e l y , pavements develop as a r e s u l t of 'overpassing' mechanisms. EVERTS (1973) has shown e x p e r i m e n t a l l y how changes in ~b r e l a t i v e to values in ~c create overpassing c o n d i t i o n s which become muted i f e i t h e r Tb increases or values of ~c are s i m i l a r . The overpassing mechanism a f f e c t s grains both l a r g e r and smaller than the bed, so t h a t anomalous p a r t i c l e s w i l l move u n t i l they assume a stable p o s i t i o n w i t h i n the bed. P a r t i c l e s a c t u a l l y undergoing overpassing should, by v i r t u e of t h e i r unstable p o s i t i o n , have lowered values of ~c. S t a b i l i t y under wave uprush probably occurs when e i t h e r a p a r t i c l e is p a r t i a l l y b u r i e d , or presents a convex p r o f i l e to the f l o w . The s h e e t - l i k e persistence of some pebble pavements is almost c e r t a i n l y caused by v e r t i c a l and h o r i z o n t a l s o r t i n g derived from overpassing. In the s h e l l and pebble examples described in t h i s paper grain size would seem to be the most important sedimentological d i f f e r e n c e promoting segr e g a t i o n , although at other scales shape i s important in forming shell hash u n i t s (MOSS 1963, 327), and d e n s i t y in producing heavy mineral placers (MOSS 1963, 322; MAY 1973). Domination of the bed by a p a r t i c u l a r sediment type may encourage f u r 370

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A is o n t h e l o w e r f o r e s h o r e , a n d t h e p a v e m e n t i s o n l y e x p o s e d by maprocesses. S i t e B is o n t h e b a c k s h o r e and pebbles may be exposed by marine ( J a n u a r y 1976) a n d e o l i a n ( J u n e / J u l y 1976) p r o c e s s e s . Similar-

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ther s i m i l a r deposition (MOSS 1963) or a s s i s t in moving discrete grain populations (BAGNOLD 1954, EVERTS 1973), although in t h i s study paucity of incoming sediment appears to preclude such processes. The pebble pavements at White Park Bay, Runkerry and Naran have not been seen to develop, thus we may only speculate about the stages involved. A 32 month survey at White Park Bay showed that the position of the pavement, both on the foreshore and backshore was fixed (Fig. 3) and changes in beach level at two sites are shown as examples. In both cases the beach is eroded to pavement level (Fig. 3A - February 1975, May 1976; Fig. 3B - December 1974, January 1976 and June 1976), but never below i t . This pattern was repeated over the e n t i r e beach except where pebbles were being a c t i v e l y eroded from older higher pavements exposed in the dune c l i f f . Here a combination of wind and wave work rapidly established in additional pavement - a photograph of t h i s appears as Plate IC in CARTER (1978). At some locations seemingly unsorted pebble and sand mixtures underlie pebble u n i t s . Using the e~cavation technique described in CARTER (1976), the number of pebble clasts per m was calculated at three s i t e s in White Park Bay to be 10, 17 and 35. (Lack of s u i t a b l e exposures accounts for such a small sample.) This represents about i0 20 % by volume of each m3 of undisturbed beach sand. As f u l l y exposed pavement surfaces contain between 45 and 100 % clasts per m2, t h i s suggests that between 3 and 6 m thickness of mixed beach sand would need to be sorted to produce a basal pavement. At present, at White Park Bay, a maximum thickness of 1.5 m sand may cover the pavement, so that general conditions of sediment a v a i l a b i l i t y must have a l t e r e d . The most obvious explanation is that much of the former beach sand is now stored as dunes or offshore bars. At White Park Bay average clast size is 52 mm (B axis),although occasional boulders up to 2000 mm occur. Very l i t t l e pebble motion has been seen to occur when the pavement is exposed to swash processes although some material is transported 371

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following

t o - a n d - f r o by higher swash v e l o c i t i e s on the lower foreshore. Also the somewhat r e s t r i c t e d periods when waves break d i r e c t l y onto the pavement cause only minor dislodgement once sand-sized m a t e r i a l s have been s t r i p p e d . The p o s i t i o n of a photograph showing the White Park Bay pavement taken by CHARLESWORTH (1936) was easil y relocated in 1976 as many of the more prominent boulders were s t i l l in place. Although the e f f e c t s of i n f r e q u e n t storm a c t i v i t y are d i f f i c u l t to assess they appear to make l i t t l e l a s t i n g impression upon the p o s i t i o n of the pavements. In theory, the f i n a l pavement l e v e l should be when e i t h e r ( i ) a completely immovable residue remains or ( i i ) the lowest l i m i t of beach s t r i p p i n g has been reached. Obviously i f ( i ) is a t t a i n e d before ( i i ) then maximum beach s t r i p p i n g is never achieved. In c o n t r a s t to the pebble pavements, the shell pavements at M a g i l l i g a n and Culdaff are ephemeral by nature. CARTER (1976, 1977) has discussed formation and geomorphological aspects of e o l i a n s h e l l pavements. At M a g i l l i g a n the sequence of pavement formation takes between 14 and 40 days and the beach is lowered by up to 0.4 m by d e f l a t i q n . There may be as many as 2000 shell valves or fragments (> 0.4 mm) per m° of beach sediment, so t h a t d e f l a t i o n w i l l be l i m i t e d . One hundred percent surface cover of s h e l l remains requires d e n s i t i e s of up to 700 fragments per m2. Shell pavements are subject to constant reworking or b u r i a l . A f t e r marine reworking d e f l a t i o n rates are i n i t i a l l y rapid (0.05 m per day) but decrease a s y m p t o t i c a l l y in time (Fig. 4). 5.

SIGNIFICANCE OF PAVEMENTS

Both s h e l l and pebble pavements impose a l i m i t on the amount of sediment t h a t may be eroded from a beach by wind or wave processes. While not n e c e s s a r i l y f i x e d in p o s i t i o n , they are, at l e a s t in the short term, e f f e c t i v e in sealing the beach 372

from c o n t i n u i n g erosion, so m a i n t a i n i n g the beach p r o f i l e and reducing s u s c e p t i b i l i t y to f u r t h e r r e t r e a t . Also the r o l e of the beach as a s u p p l i e r of dune sand is diminished. A stable pavement may a l l o w the preservation of f a i r w e a t h e r sediment a r y sequences and s t r u c t u r e s which would normally be destroyed during storm a c t i vity. Presence of a shell or pebble pavement a f f e c t s the f l u i d motion over the beach surface. CARTER (1977) showed t h a t the thickness of the boundary l a y e r over a shell pavement is 2 to 6 times t h a t found over sand. S i m i l a r l y increased f r i c t i o n a l drag on swash uprush across a pavement w i l l r e s u l t in a drop in run-up height s i g n i f i c a n t l y reducing the l i k e l i h o o d of backshore erosion. This is c l e a r l y v i s i b l e a f t e r storms; the average rate of dune recession at White Park Bay behind the pebble pavement is less than 0.05 m per year, compared with unprotected s i t e s nearby where r e t r e a t is up to 4 m per year. 6.

SUMMARYDISCUSSION

Pavements are l a t e r a l l y p e r s i s t e n t deposits produced by the reworking of sediment mixtures. CLIFTON (1973) has o b j e c t i v e l y d i s c r i m i n a t e d between coastal and a l l u v i a l pebble beds on the basis of l e u t i c u l a r i t y , but c l a s s i f i e s a l l p e r s i s t e n t l a y ers with a low ' l e u t i c u l a r i t y index' score as wave-worked. From the evidence presented here i t is obvious t h a t t h i s c l a s s i f i c a t i o n is too broad to account f o r the v a r i e t y of pavement types found at the s h o r e l i n e . Each pavement u n i t corresponds to a d i s t i n c t sedimentological c h a r a c t e r i s t i c (shape, size or d e n s i t y ) of a sub-population. Separation i n t o coarse and f i n e u n i t s is confirmatory evidence t h a t there are two or more grain populations r a t h e r than a s i n g l e poorly sorted one. I f the l a t t e r case e x i s t e d s i m i l a r processes would produce u p w a r d - f i n i n g or coarsening sequences, which are not found in these beach sediments. Pebble pavements provide lower, and at l e a s t semi-permanent l i m i t s to beach erosion. They probably form r a p i d l y during periods of beach s t r i p p i n g . KUMAR & SANDERS (1976) have described somewhat s i m i l a r deposits from depths of 5 - 21 m, of basal lag gravels o v e r l a i n by laminated sands, r e s u l t i n g from a l t e r n a t i o n s of storm and f a i r w e a t h e r processes under o s c i l l a t o r y wave a c t i o n . The beach examples described in t h i s paper d i f f e r from those of KUMAR & SANDERS in the f o l l o w i n g ways: (i) the u n i t dips seaward at a low angle (ii) the pebbles may show s l i g h t i m b r i c a t i o n (such an observation may not have been possible in KUMAR & SANDERS' examples, but i t is not to be expected under o s c i l l a t i n g wave motion) ( i i i ) the o v e r l y i n g " f a i r w e a t h e r " u n i t on the beach is a d i s t i l l a t i o n of several d e p o s i t i o n a l phases extending over some months, r a t h e r than the rapid (hours) s e t t l i n g of suspended sand during c o n d i t i o n s of high bed shear. Also i t should be emphasised t h a t sub-aerial pebble pavements may form by d e f l a t i o n or i n h e r i t a n c e , but show i r r e g u l a r persistence, no s t r u c t u r e or preferred o r i e n t a t i o n s , a l l of which occur in the marine examples. Despite the wide environmental range of shell pavements (CARTER 1976) i n t e r p r e t a t i o n of such deposits in ancient rocks is somewhat narrow. NELSON (1977) assumes t h a t most shell sediment u n i t s on beaches are storm deposits, and l i k e w i s e KUMAR & SANDERS (1976) accept t h a t coarse shell debris replaces gravel in s h e l f storm sequences. These authors assume a s i m i l a r pattern in a n c i e n t sediments. POWERS & KINSMAN (1953) observed l a t e r a l l y p e r s i s t e n t convex-up s h e l l u n i t s forming at the base of the t r a c t i o n zone in storm and swell dominated s h e l f environments, and BRENNER & DAVIS (1973) assume t h a t such processes are responsible f o r shell u n i t s in Jurassic sandstones. While a l l these observations may be c o r r e c t , i t must be emphasised that shell layers are not u n i q u e l y i n d i c a t i v e of high-energy, l o w - f r e quency processes. However careful observation of s t r u c t u r e , o r i e n t a t i o n and per373

sistence should provide c r i t e r i a u n i t has formed under.

capable of resolving what environment a shell

ACKNOWLEDGEMENTS One of us (CLR) acknowledges the receipt of a New U n i v e r s i t y of Ulster postgraduate studentship (1974 - 1977). John Shaw k i n d l y drew the diagrams and Mrs. Edna Doherty typed the manuscript. BIBLIOGRAPHY ADMIRALTY (1968): I r i s h Coast P i l o t . 566pp, Hydrographer to the Navy, London. BAGNOLD, R.A. (1954): The physics of blown sand and desert dunes.(2nd e d i t i o n ) , 265 pp., Chapman & H a l l , London. BRENNER, R.L. & DAVIES, D.K. (1973): Storm generated coquinoid sandstone: genesis of high energy marine sediments from the upper Jurassic of Wyoming and Montana. B u l l e t i n of the Geological Society of America 84, 1685 - 1698. CARTER, R.W.G. (1975): Recent changes in the coastal geomorphology of the M a g i l l i gan Foreland. Proceedings of the Royal I r i s h Academy 75B, 469 - 497. CARTER, R.W.G. (1976): Formation, maintenance and geomorphologTcal s i g n i f i c a n c e of an aeolian shell pavement. Journal of Sedimentary Petrology 46, 418 429. CARTER, R.W.G. (1977): Rate and pattern of sediment t r a n s f e r between beach and dune. In: TANNER, W.F. ( e d . ) : Coastal Sedimentology, Coastal Research, Tallahasseee, F l a . , 3-34. CARTER, R.W.G. (1978): Ephemeral sedimentary structures formed during the eolian d e f l a t i o n of beaches. Geological Magazine 115, 379 - 382. CHARLESWORTH (1936): Large boulder of A i l s a Craig Microgranite, White Park Bay, Co. Antrim. I r i s h N a t u r a l i s t s ' Journal 6, 94 - 95. CLIFTON, H.E. (1969): The o r i g i n and nature of #each lamination. Marine Geology 7, 553 - 559. CLIFTON, H.E. (1973): Pebble segregation and bed l e u t i c u l a r i t y in wave-worked versus a l l u v i a l gravel. Sedimentology 20, 173 - 187. EVERTS, C.H. (1973): P a r t i c l e overpassing on f l a t granular boundaries. Journal of the Waterways, Harbours and Coastal Engineering Division ASCE, 99 WW4, 425 - 438. KUMAR, N. & SANDERS, J.E. (1976): C h a r a c t e r i s t i c s of shoreface storm deposits. Modern and ancient examples. Journal of Sedimentary Petrology 46, 145 162. MAY, J.P. (1973): Selective transport of heavy minerals by shoaling waves. Sedimentology 20, 203 - 212. MOSS, A.J. (1963-~: The physical nature of common sandy and pebbly deposits. Part I I . American Journal of Science, 261, 297 - 343. NELSON, C.S. (1977): Grain-size parameters of insoluble residues in mixed t e r r i genous-skeletal carbonate sediments and sedimentary rocks: some New Zealand examples. Sedimentology, 24, 31 - 52. OTVOS, E.G. (1965): Sedimentation-erosTon cycles of single t i d a l periods on Long Island Sand beaches. Journal of Sedimentary Petrology 35, 604 - 609. POWERS, M.C. & KINSMAN, B. (1953): Shell accumulations in underwater sediments and t h e i r r e l a t i o n to the thickness of the t r a c t i o n zone. Journal of Sediment a r y Petrology 23, 229 - 234. RIHAN, C.L. (in prepara~on): The coastal geomorphology of two small embayments in Co. Antrim, Northern Ireland. Ph.D. Thesis, The New U n i v e r s i t y of Ulster. SHAW, C.F. (1929): Erosion pavement. Geographical Review 19, 638 - 641.

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