56 Dag Ottesen, Reidulv Bee & Kari Gresfjeld NGU. BULL 427. 1995
Carbonate sand deposition along the coast of southern Norway
DAG OTTESEN, REIDULV B0E & KARI GR0SFJELD
Dag Ottesen, Reidulv Bee & Kari Grestjeki, Norges geologiske undersoke tse, P.O.Box 3006-Lade, N-7002 Trondheim, Norway.
In spite of extensive exploitation of marine carbo 5' E r E 9'E 11' E nate sand (as fertilizers for agricultural purposes) along the western coast of Norway, little attenti on has been drawn to these cool-water carbona te deposits in the geologica l literature. Some work has been carried out on their geochemica l composition and quality as soil fertilizers (Sve et al. 1990), but there has been little work dealing with the sedimentology and sedimentation rates of carbonate sand deposits. Carbonate sand is a designation commonly used for both carbonate sand and carbonate gra vel. For convenience, we will continue to use this term even though some of the deposits have the grain size of gravels. The examined carbonate sand is bioclastic, usually composed of bivalve fragments making up more than 90 % of the sediment, with gastropods , serpulids, barnacles and echinoids in minor amounts. The calcareous red algae Lithothamnium is also present, but rarely in large quantities in southern Norway. Occurrence Cool-water, modern carbonate deposits in Europe are described from the coast of Brittany in northwestern France, from the western part of the English Channel and in Cornwall, along the western coast of Ireland and from the western and northern coasts of Scotland. Regional mapping by the University of Bergen (Haye & Russenes 1984) and the Geological Survey of Norway (Bee & Ottesen 1994) has shown that carbonate sand deposits occur in a Fig. 1. Carbonate sand and gravel deposits along the coast of Norway from Lindesnes to Lysoya. The stippled line represents narrow coastal belt with thousands of islands the approximate landward boundary of areas with large carbo and skerries along the outermost part of the nate sand deposits. Dots show major carbonate sand deposits southern and western coasts of Norway (Fig. 1). to the south of Stadt. The boundary line between areas with and wit hout carbonate sand deposits swings into the Methods Boknafjord near Stavanger, but is otherwise The mapping of carbonate sand resources by remarkably restricted to the outermost coastal the Geological Survey of Norway has been carri belt. The sea bed within this coastal belt has an ed out using high-resolution seismic equipment irregular relief, and commonly drops down to the (Topas and Geopulse). Approximately 4500 pro fjord bottom at several hundred metres water file kilometres have been acquired, and 1000 depth. Carbonate sand deposits are normally grab samples have been taken to verify the type situated between 0 and 50 metres water depth. and quality of the bottom sediments. These data, Due to a moderate land uplift of the coastal are together with detailed bathymetric maps from the as after the deglaciation (Kaland 1984), carbona Norwegian Hydrographic Service, have been te sand is rarely located above sea level in sout used to draw boundaries of individual carbonate hern Norway. sedime nt areas. In two areas along the western NGU · BULL 427,1995 Dag Ottesen, Reidulv Bee & Kari Grasfjeld 57 coast of Norw ay, Sund and Austevoll (Fig. 1), LYS0YA kyr SUND kyr carbonate sand has been sam pled by vibroco ring (Gro sfjeld 1991, Boe & Ottese n in prep.) m 5, 6, ? 8 ? ' ,0 1,' m 1 2 3 4 5 6 7 and dated, and sediment accumul ation rates I have been calculated . An additional locality at , ~ l J Lysoya in Bjugn, Central Norway, has also been studied. 2J 2 ~ a>-.STORE YAROOY I ~ STORERlSOY Description and results 3J Q!i F..E: ROY The shoreline along the western coast of Norway 31 'g \ faces the North Sea, and is exposed to westerly 4 - winds. There is little input of terrigenous material I AUSTEVOLL kyr from major rivers to these coast al areas, and this m , 2 3 4, ~ 6, 7, ~ ' favours the growth of lime-secreting organisms. 5i ~ Skeletal grains accumulate to form carbo nate \. ,I ~4 sand and gravel dep osits. The carbonate pro 61 duction sites in Sund and Austevoll vary from 21 '$ exposed areas with a rocky substrate (resistant
bottom to top: (1). 0.5 m of glaciomarine clay with dropstones and a few mollusc fragments. (2). A 2 m-thick transition zone with layers of non-calcareous sand and gravel with an upward increasing content of carbonate fragments (mostly molluscs and serpulids). (3). 10 m of almost pure, stratified carbonate sand and gravel with erosive troughs up to 20 cm deep infilled with cross -bedded sand and gravel in the uppermost 3 m of the sect ion.
The sedimentary succession is interpreted as a shallowing-upward sequence. A mollusc frag ment from the clay near the bottom of the pit has been dated by the AMS method to 10,140±85 years BP (Fig. 2 and Tab le 3), which represents -=..=: GtaeiOm. clay L...=:J Carbo nate sand the latest part of the Youn ger Dryas cold period. 50m The sediments of the transition zone above the m E3 Bedrock 20 1 ~ Beach deposit clays were deposited during Preboreal time (10,000-9,000 years BP) (Fig. 2). Carbonate sand accumulation started in the beginning of the Preboreal, and increased throughou t the period. Near this pit, another section near the top of Akimskaret (x in Fig. 3b) shows glaciomarine clay overlain by cobbles and boulders with a matrix of sandy, gravelly carbonate (Fig. 3b). The glaciomarine clay can by correlated with the Fig. 3. a) Carbonate sand accumulation and production area at l ysoya. Altitudesare in metres above sea level. See Rg. 1for clayey sediments at the bottom of the dated sec location . b) Cross-section through Akim-skaret at l ysoya. For tion measured in the pit, while the coarse depos it location see Fig. 3a. with cobbles and boulders is a beach depos it representing the transition from offshore to fore shore conditions at this locality. The 14C method gave an age of 4,015±90 years BP (T-11167) for Table 3. 14C ages and averag e accumu lation rates from the l ysoya section. the shelly matrix in the beach deposit. This means that the shell production took place over a Sampleno Depth A~ e Lab. no. Aver. ace. rate (cm) (1 Cyrs BP) (cm/lOoo yrs) period of about 6,000 years , from about 10,000 years BP to about 4,000 years BP, when the 25 45 4995" 95 T-11 165 22 240 6065" 50 T-lll64 150 locality rose above sea level. The carbonate lys 8-88 380 6490" 90 T- 9174 310 sand accumulation rate at the Lysoya locality 635 71 20" 90 T- 8144 390 varies from 150 cm/1000 years to 390 cm/1000 lys 9·88 635 7260" 55 T- 9175 year (Fig. 2). 13 820 7800,, 11 5 T-11163 300 l ys 7·88 925 8075,,100 T- 91 73 360 3 1040 8660" 65 T-11162 210 2 1090 9630" 80 T-11272 50 Discussion 1 11 40 9920" 55 T-11271 170 During the maximum of the last glaciation (ea, 6 1255 101 40" 85 TUa-876 54 0 20,000 years BP), inland ice covered the whole of the Scandinavian peninsula and reached the shelf edge . During this period extensive erosion occur red, and most of the older deposits in the (Fig. 4), which makes it possible to estimate the coasta l areas were remov ed. Thus , it was not wate r depths during the time of deposition of the until the end of the glacial period that cond itions Lysoya carbonate sand depos it. When deg lacia were ~ u itab le for carbonate production and pre tion occurred about 12,000 years BP, the sea serva tion. The results obtained in our studies level was about 130 metres above the prese nt show that the majority of the Norwegian carbo sea level. After a period of relatively stable sea nate sand deposits are of Holocene age. level betwee n 12,000 and 10,000 years BP, a Kjemperud (1986) cons tructed a shoreline dis strong regression occurred between 10,000 and placemen t diagram for the Bjugn/Lysoya region 9,000 years BP (Kjemperud 1986). Thereafter NGU - BULL 427, 1995 Dag Ottesen, Reidulv Boe & Kari Grosfjeld 59
m 3a). Farrow et al. (1984) measured sedimenta I 120 "--... tion rates of carbonate sand on the Orkney shelf - t~I_- to be 10 cm/1000 years, and on the Scottish 100 - :-.. - shelf 3 cm/1000 years. The sedimentation rates 80 in Sund and Austevoll, on the western coast of r \ - 60 ,. - Norway, are 4-11 times higher than the sedimen Cl r tation rates on the Orkney shelf, while the sedi 40 :-- mentation rates at Lysoya are 15-40 times hig I 1 20 ~ l - - - , her. This difference in carbonate sand accumula ------+-- tion rates is due to the very efficient transport o 12 10 8 5 4 - ' o and concentration mechanisms, with high waves Kyr. BP and strong currents, along the western coast of Norway. Rg. 4. Shoreline displacement curve tor Bjugn. Modifi ed Irom Kjemperud (1986). Keary (1985) showed that there is a zone of high carbonate deposition along the Atlantic mar gin of Europe. Carbonate deposits are confined to areas which are open to the influence of undil the rate of regression diminished, and when uted Atlantic water. The results of the carbonate extensive carbonate production by benthic car sediment mapping along the coast of Norway bonate-secreting organisms started at about support this observation and show that a short 9,000 years BP, about two thirds of the shoreline distance to the east, where the Atlantic waters displacement had occurred. In Fig. sa, the pro are diluted by water from other sources, carbo duction areas of lime-producing organisms are nate sand deposits do not exist. indicated. From about 9,000 years BP, the fauna was dominated by the mussel Modiolus modiolus Acknowledqements and serpulids. Farrow et al. (1984) have obser We thank RolfSorensen, Anna Siedlecka and Oddvar l ongva lor their reviews of the manuscript and David Roberts lor cor ved from side-scan records that both live on bare recting the English text. rock. When extensive carbonate production star ted at about 9,000 years BP, the water depth in References the accumulation area was about 50 m above Boe, R. & Ottesen , D. 1994: Skjellsandundersokelser i today's sea level (Fig. 4). This means that the Rogaland . Del I. Omradene sor lor Boknafjorden. Nor . water depth in the production area varied betwe goo/. unders. report 94.00 1, 49 pp. Farrow, G. E., Alien, H. & Akpan, E. B. 1984: Bioclastic en 0 and 50 m, and that the water depth decrea Carbonate Sedimentation on a High-Latitude, TIde-domina sed through the whole production period. This ted Shell: Northeast Orkney Islands, Scotland. J. Sed. Petr. also implies that production took place in smaller 54 , 373-393 . and smaller areas, so that a constant accumula Grosljeld, K. 199/ : Skjellsan dkartlegging i Sund komm une, Hordaland. Supplerende undersokelser, 1991. Nor. goo/. tion rate in reality means an increasing carbona unders. report 91.210, 53 pp. te production. Haye , T. & Russenes, B.F. 1984: Skjelsandprosjektet i Sogn During the period of carbonate sedimentation, og Fjordane. Kartlegging av skjelsandlorekomstar i dei the lime-producing organisms were eroded, kystncere larvatna. Sogn og Fjordane fylkeskommune, Plan- og utbyggingssjefen , 197 pp. crushed and washed down from the production Kaland , P.E. 1984: Holocene shore displacement and shoreli areas and deposited on the lee side of Lysoya. nes in Hordaland, western Norway. Boreas 13,203·242 . The water depth in the accumulation area decre Keary, R. 1985: Carbonate sediments 01 the Irish coast. ased from 50 m to about 10 m. This is consistent Distribution and oceanographic inlluences. Interim Report, Geol. Surv. Ireland , 104 pp. with the occurrence of erosive troughs infilled Kjemperud, A. 1986: Late Weichselian and Holocene shoreline with cross-bedded carbonate gravels in the displacement in the Trondheimsljord area, central Norway. upper 3 m of the section. During deposition of Boreas 15,61-82 . this part of the section, extreme currents through Sve, D., Erstad, K.J. & lyngstad, I. 1990: Quality 01shell sand for agric ultural liming in Western Norway . Norsk the narrow bedrock-channel Akim-skaret (which Landbruksforskning 4,65-72. was formerly a narrow sound) (Fig. 3) generated during storms were strong enough to be erosive. The carbonate sand accumulation rates are between 2.6 and 9 times higher at Lysoya than in Sund and Austevoll. The high rates of depositi on at Lysoya might have resulted from high pro duction rates of calcium carbonate by organisms inhabitating an extensive, shallow, offshore plat form on the northwestern side of l.ysoya (Fig.