Introduction.
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| Tromso |
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| Location of Tromso/Langnes |
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| Detail of Tromso and Langnes in their fjord setting. |
Several sites have been recorded for evidence of glacial activity in the Tromso area, beginning at Langnes.
Fig. 8. Gravel pit in shore deposits near the Skarpnes end moraine at Langnes.
A: sand, well sorted.
B: gravel, poorly sorted with large erratics and numerous shells of Mya truncata [1] and [2] Macorna calcarea.
The shells were radiocarbon dated at 12,000-12,500 years R.P. (T-490 a, b, c).
C: sand, stratified with scattered boulders.
Scale: large boulder in "B" is l m.
The pit Iies 7O m-78 m above sea level, immediately above the Main shore line.
Fig. 13a. Cross-section of the proximal Tromsø-Lyngen end moraine at Giævernes on Tromsø, exposed in two grave! pits.
A: Beach-washed gravel with several large erratics.
B: Bouldery till with some clay.
C: Glacio-fluvial gravel and sand, strongly folded beds in upper part. Scattered fragments of Astarte elliptica [3], Chlamys islandicus [4], Mya truncata[1] Macoma calcarea [2], Hiatella arctica [5] and Balanus sp. [6] Iie in this section. They were radiocarbon dated at 11,500 ± 350 years B.P. (T-112).
D: Stratified marine sand, well sorted. The upper beds are folded.
D1: Stratified silt and clay, about 0.5m, with unbroken shells of Portlandia arctica [7], Leda pernula ]8], Thyasira flexuosa [9] and Nucula tenuis ]10]. Section D1 is Probably younger than bed E.
E: Glacio-marine blue clay with scattered cobbles and shells of the same species that were found in bed C. The shells were mostly unbroken.
They were radiocarbon dated at 11,480 ± 150 years B.P. (T-436 B).
F: Medium sand.
Filled circles: stratigraphic positions of radiocarbon dated samples.
Frame: Beds in fig. 13 b Iie within the frame.
Sketch of the two Tromsø--Lyngen end moraines and the marine terraces on the eastern side of Tromsøsund.
A: Sand (Yz m-1 m) with shells of Mya truncata [1] and Macoma calcarea. [2].
B: Glacio-marine clay with scattered pebbles to boulders and shells of Macoma calcarea,[2] Macoma torelli,[11], Nucula tenuis,[10] Yoldiella (Portlandia) lenticula, [12], Yoldia hyperborea [13] etc. About 4 m of clay was exposed. Shells from the middle part of the section ( x) were radiocarbon dated at I0,200 ± 35O years B.P. (T -113) .
Altitudes in metres above sea level.
Fig. 16. Cross-section of the outwash delta at Bjorelv.
Beds exposed in the gravel pit: 2 m topset beds, mainly of gravel with boulders. 20 m foreset beds, mainly of well sorted sand. However, beds of poorly sorted bouldery sand to gravel exist particularly 6m-10m below the exposed part of the topset beds. The foreset beds dip 20°-25° NW. Unbroken shells of Macoma calcarea [2] and Mya truncata [1] Iie within several beds. I, Il and Ill show the statigraphic positions of collected shell samples radiocarbon dated at respectively 10,500 ± 400 years B.P. (T-50), 11,250 ± 319 years B.P. (T-511 B) and 11,200 ± 500 years B.P. (T-174).
Altitudes in metres above sea level
Fig. 18. Cross-section of the Tromsø-Lyngen end moraine at Rensaa.
A: Beach grave!, 0.5m-1.5m.
B: Foreset beds, mainly gravel with large boulders.
The beds dip 15°-20°.
Shell fragments of the following species lie scattered within the beds: Mya truncata,[1] Hiatella (Saxicava) arctica, [5], Chlamys (Pecten) islandicus [14], Arctica (Cyprina) islandica [15] and Astarte elliptica. [3]. The shells fragments probably originale from older beds. They were radioarbon dated at 11,100 ± 300 years B.P. (T-111) and 11,650 ± 220 years B.P. (T-437 B).
C: Stratified marine sand and silt.
D: Interbedded silt and clay, with scattered pebbles and cobbles. Shells of Portlandia arctica [7] Iie in some of the beds. The shells were radiocarbon dated at 11,100 ± 800 years B.P. (T -17 5).
E: Marine blue clay, well sorted with no stratification.
F: Glacio-marine clay, 2m exposed. Numerous pebbles to cobbles and unbroken shells exist. The shells were of the same species as the shells in section B. They are large, and their radiocarbon age is 11700 ± 21O years B.P. (T -43 8 B); 11,990 ± 250 years B.P. (T-438 A).
Filled circles: radiocarbon dated samples.
( rough sketch).
A: Marine blue clay, mostly unstratified.
B: Marine silt and clay, partly laminated.
C: Marine silt and fine-sand, stratified.
D: Foreset beds of sand and grave!.
E: South-dipping sand and grave! beds.
F: Topset beds of grave! with large boulders.
A1: Marine clay, mostly unstratified.
B1: Marine silt and clay, partly laminated, with shells of Macoma calcarea [2] and Mya truncata. [1]
D1: Gravel
x: Location of shells radiocarbon dated at approximately 9,150 years B.P.
(T-510 A, B).
Altitudes in metres above sea level.
Fig. 20. Cross-section of the terraces immediately inside (east of) the moraine at Moen in Gratangen Fjord (rougb sketch).
A: Sand and gravel
B: Silt and fine-sand, stratified with scattered pebbles. Small shells of Mya truncata [1] and Macoma calcarea [2] were collected and radiocarbon dated at 9,520 ± 190 years B.P. (T -63 O).
C: Bouldery gravel, poorly sorted~ in parts till-like, with many large striated erratics.
D: Stratified silt and sand, about 4 m. Pebbles and cobbles lie in some of the sand beds, pariicularly in one bed which is very fossiliferous. Shells of Macoma calcarea, [2] Mya truncata, [1] Hiatella (Saxicava) arctica, [5], Chlamys islandicus [4] were collected and radiocarbon dated at 9,740 ± 160 years B.P. (T-512 B).
E: Bouldery gravel, l m.
Altitudes in metres above sea level
Conclusion
The photograph of the town of Tronso at the head of this article demonstrates the proximity of the high mountains of northern Norway with their snow cover, towering over the region. In addition the plan of the local area presents the fjords that criss-cross the region, each with higher ground either side of them.
No evidence is presented that the molluscs that were catalogued were live in-situ. These are therefore likely to be redeposited, along with the the material in which they were found.
It is demonstrated elsewhere that when the ice sheets melted they did so producing meltwater in quantities measurable in cubic kilometres per day. These volumes would have literally moved mountains, and churned up neighbouring fjords bringing up deep dwelling molluscs to the surface and dumping them on land that is now above sealevel.
[1] Mya truncata, A deep burrower in sand and sandy mud. From low in the intertidal to shallow shelf depths of about 70m.
[2] Macoma calcarea, A burrower in muddy sands, offshore. Subfossil in North Sea and off northern Scotland. Living in Norway, Iceland and circum-Arctic Depth Range, Continental Shelf (to 200m)
[3] Astarte elliptica, Lives in a range of clean, silty and muddy sands and gravels from the near sub-littoral towards the mid-shelf, depth range c.5m - >150m, but most frequently in depths <50m.
[4] Chlamys (Pecten) islandicus, Byssally attached to stones and rocks from low in the intertidal to shelf edge. Present here only as post glacial subfossil shells. Living in Faroes, Iceland and Norway south to Bergen. Intertidal Continental Shelf (to 200m)
[5] Hiatella arctica, A nesting species attached by a weak byssus in crevices on hard substrates and among coarse ground and Modiolus beds and in kelp holdfasts. From the low intertidal to the shelf edge and upper slope. Widespread. Continental Shelf (to 200m), Continental Margin Zone (200 - 500m)
[6] Balanus sp. (Barnacles)
Balanus crenatus is primarily a sublittoral species that can sometimes be found under stones or overhangs on the lower shore. Balanus crenatus colonizes cobbles, shells, bedrock, molluscs and artificial substrata. It is found at a wide range of wave exposures and it can tolerate salinities as low as 14 psu
[7] Portlandia arctica, A high arctic species living in Greenland, Svalbard and northern Norway but not in Iceland. Records further south are most likely subfossil. The status of the single record from the Minch, NW Scotland (see NBN Gateway) is uncertain.
Continental Margin Zone (200 - 500m), Bathyal (500 - 2000m), Abyssal Rise (2000 - 4000m)
[8] Leda ( nuculana) pernula, northern species ranging south to to the northern North Sea at outer shelf and shelf edge depths. Also recorded from greater depths on the slope off Ireland but these may be based on valves only or subfossil shells. Depth Range, Continental Shelf (to 200m), Continental Margin Zone (200 - 500m)
[9] Thyasira flexuosa, Widely distributed from the intertidal and shelf to over 150m.
[10] Nucula tenuis. Occurs all around Britain and Ireland but is absent from the English Channel and southern North Sea. Mud and substrates such as sand and gravel which have a muddy element. Occurs from inshore in c. 10m to the outer continental shelf in depths of up to 200m.
[11]Macoma torelli, burrower in muddy sands, offshore. Not in the British fauna. Circum-Arctic Greenland and Svalbard. Continental Shelf (to 200m)
[12] Yoldiella (Portlandia) lenticula, Known from the West European basin mostly from a small geographic area from 43° to 48° N and 3° to 10° W in depths from 1400-2245m.
Panarctic, south to northern Norway and Iceland in depths of 10-300m. Also known from deep water north Atlantic basins (West European and Canary) in depths from 1400-2245m.
This species displays “equatorial submergence” being found at much greater depths in the south of its range.
[13] Yoldia hyperborea. A subarctic species extending southward to Iceland. Mostly taken from outer shelf depths beyond 100m. Not yet recorded from the British area. Continental Shelf (to 200m)
[14] Chlamys islandicus, Byssally attached to stones and rocks from low in the intertidal to shelf edge. Present here only as post glacial subfossil shells. Living in Faroes, Iceland and Norway south to Bergen
[15] Arctica (Cyprina) islandica, Arctica islandica is found at extreme low water level but predominately on sublittoral firm sediments including level offshore areas, buried (or part buried) in sand and muddy sand that ranges from fine to coarse grains. Depth range, 4-482 m
Mytilus edulis, Occurs from the high intertidal to the shallow subtidal attached by fibrous byssus threads to suitable substrata. Found on the rocky shores of open coasts attached to the rock surface and in crevices, and on rocks and piers in sheltered harbours and estuaries, often occurring as dense masses. Depth, intertidal to ca. 5m.
Turritella communis (Turretellinella Tricarinata). Abundant on muddy sediments in shallow water, more or less buried but maintaining contact with the water. This species is slow moving and sits on the seabed filtering seawater for particles of food. It may be gregarious, occurring in large numbers. It can be found down to 200 m.
Pecten, scallops 18m Free living sitting on the surface of bottoms of sand to fine gravel. From the sublittoral to mid shelf depths, Widespread from northern Norway to Iberian Peninsula. Continental Shelf (to 200m)Hiatella (Saxicava) arctica, A nesting species attached by a weak byssus in crevices on hard substrates and among coarse ground and Modiolus beds and in kelp holdfasts. From the low intertidal to the shelf edge and upper slope. Widespread. Continental Shelf (to 200m) Continental Margin Zone (200 - 500m)
Saxicava arctica , wrinkled rock borer , and hiatella arctica. Hiatella arctica, known as the wrinkled rock-borer, the arctic hiatella or the arctic saxicave, is a species of saltwater clam, a marine bivalve mollusc in the family Hiatellidae. The white shell of this mollusc is thick and more or less rectangular, but generally irregular in shape. It is up to 45 mm long.
Hiatella arctica is widespread and found in all the oceans, ranging from the Arctic and Antarctic to the subtropical and tropical zones. It occurs from the low water mark to depths of down to 800 m. It lives on hard substrates, often attached with byssus, for instance in mussel beds or nestling among kelp holdfasts, or hiding in rock crevices and also boring itself into soft rocks.
Bathyarca glacialis , An Arctic species extending south along the shelf edge and upper slope into the Faroe-Shetland Channel. Byssally attached to gravel, stones and deep water coral debris along the continental margin and upper slope. Continental Margin Zone (200 - 500m) Bathyal (500 - 2000m)
Similpecten greenlandicus Free living on fine sediments at outer shelf and bathyal depths. An arctic species not recorded from British waters, closest are records from the Faroes and Iceland. A dwarf form was recorded from Biscay but this is now S. oskarssoni. Continental Shelf (to 200m) Continental Margin Zone (200 - 500m) Bathyal (500 - 2000m)
Modiolaria nigra black mussel rocky shores
Lyonsia arenosa, Sandy Lyonsia
Benthic; depth range 0 - 360 m (Ref. 119523). Subtropical
Members of the class Bivalvia are mostly gonochoric, some are protandric hermaphrodites. Life cycle: Embryos develop into free-swimming trocophore larvae, succeeded by the bivalve veliger, resembling a miniature clam.
Natica clausa Cryptonatica affinis
Cryptonatica affinis is widely distributed in Arctic and sub-Arctic marine environments, occurring circumpolarly from the Pacific boreal-Arctic sectors to the Northern Atlantic, including areas like the Skagerrak and Norwegian coast. It is eurybathic, found from shallow shelf depths to 2650 meters, but predominantly on continental shelves in soft sediment habitats with strong bottom currents. In the Baltic Sea region (HELCOM area), records are sparse, limited to a single deep locality in the Öresund strait (Landskronadjupet) at soft bottoms mixed with sediments, with the most recent observation from 2007. This distribution suggests it functions as a southern outpost for Arctic species in transitional zones.
Jeffery Nicholls
Orkney
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