NGT 73 3 175-197.Pdf
Marine-lacustrine stratigraphy of raised coastal basins and postglacial sea-level change at Lyngen and Vanna, Troms, northern Norway
GEOFFREY D. CO RNER & ERIK HAUGANE
Corner, G. D. & Haugane, E.: Marine-lacustrine stratigraphy of raised coastal basins and postglacial sea-level change at Lyngen and Vanna, Troms, northem Norway. Norsk Geologisk Tidsskrift, Vol. 73, pp. 175-197. Oslo 1993. ISSN 0029-196X.
Lithostratigraphic and diatom analysis of core samples from 10 raised lake basins from an inner (Lyngen) and outer (Vanna) coastal area of Troms, northem Norway, was made in order to reconstruct relative sea-level change during the Holocene and Late Weichselian. A variety of facies types and facies sequences, controlled primarily by sea-level change and inftuenced also by climatic factors, is recognized. Main facies types are: (I) Marine (mud and sand), (Il) Transitional (laminated gyttja or gyttja and silt), (Ill) Lacustrine (gyttjajplant detritus), and (IV) Mixed (gyttja, mud and sand/gravel). Laminated transitional facies li, in nearly all cases, is interpreted as having formed under meromictic limnic conditions following basin isolation from the sea, whereas heterolithic mixed facies IV forms usually under littoral inftuence during ingression. Sea-level displacement curves are constructed for Lyngen and Vanna based on radiocarbon-dated isolation and ingression contacts, elevation/inferred-age data for prominent raised shorelines, and other data,. The evidence suggests that the Tapes transgression at Lyngen had a minimum amplitude of 2-3 m and peaked at ca. 7000 BP. Average rates of pre-Tapes (before 8500 BP) and post-Tapes (after 6000 BP) regression are approximately 15 and 3 mm/year respectively at Lyngen, and lO and 1.5 mm/year respectively at Vanna.
Geoffrey D. Corner, Department ofGeology, IBG, University of Tromsø, N-9037 Tromsø, Norway; Erik Haugane, University of Tromsø - Present address: Nopec a.s., Pirsenteret, N-7005 Trondheim, Norway.
The pattern of postglacial relative sea-levet change in fore concerned with establishing a comparative basis for northern Norway is known in broad outline based on a evaluating use of the method in this region. number of constructed shoreline diagrams (Marthi Two main areas were chosen for study (Fig. 1): (l) nussen 1960, 1974; Anderson 1968, 1975; Møller & Sollid Lenangsbotn-Jægervatn on the Lyngen peninsula (Fig. 1972; Sollid et al. 1973; Møller 1985, 1987) and sea-levet 2A; referred to below as Lyngen) which has an inner displacement curves (Marthinussen 1962; Donner et al. intermediate position on the coast relative to the centre 1977; Corner 1980; Hald & Vorren 1983; Møller 1984, of postglacial uplift; (2) the istand of Vanna, which 1986, 1987; Vorren & Moe 1986). However, for large occupies as an outer coastal position. Because of the areas, no direct dating evidence exists as to the age of paucity of suitable, accessible basins in the region, two former postglacial sea-leve1s. In Troms, only two dis subareas on Vanna (Skipsfjorddal and Vannareid, Figs. placement curves før the Holocene have been constructed 2B, 2C), lying 8 km apart, were studied. (Corner 1980; Hald & Vorren 1983) and both draw This paper presents the main stratigraphic results of heavily on regionally interpolated ages rather than site the study and derived sea-levet displacement curves for specific data. Among major questions that remain to be the two areas. More general aspects relating to sedimen answered are the rate of postglacial relative uplift prior tary facies, identification and interpretation of the isola to the Holocene, and the precise timing and geographical tion contact, and a model for basin isolation, will be (landward) extent of the Tapes transgression. treated in a separate paper (Haugane & Corner in prep.). In an attempt to obtain more precise data on shoreline displacement in the region, two areas in Troms were investigated using the method of identifying and dating Regional setting and shorelines isolation and ingression contacts in sediment cores re trieved from raised coastal takes (Hafsten 1960; Suther The coastal area around Vanna was probably deglaciated land 1983; Kjemperud 1986). The method, used between 13 000 and 15 000 BP, whereas Lyngen at successfully in southern Norway (Stabell 1980; Kjempe Lenangsbotn was probably deglaciated shortly before the rud 1981, 1986; Hafsten 1983; Lie et al. 1983; Krzywinski Skarpnes readvance of 12 000-12 500 BP (Andersen & Stabell 1984; Kaland 1984; Anundsen 1985; Svendsen 1968, 1979; Vorren & Elvsborg 1979). Local glaciers & Mangerud 1987, 1990) and other glacio-isostatically existed nearby in both areas during the Late Weichselian, raised areas, has not previously been applied systemati and exist today immediately east of the investigated area cally in northern Norway. Part of the study was there- in Lyngen. 176 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT 73 (1993)
•••••••• Tapes terrace/ridge
·-·-· Main shoreline ---- Marginal/hummocky moraine limit
Skips fjord
Fig. /. Map of north Troms showing the location of the three investigated subareas on Vanna and in Lyngen (cf. Fig. 2) and isobases for the Main (Younger Dryas) shoreline ( continuous and dashed lines; after Marthinussen 1960; Andersen 1968) and the Tapes transgression maximum shoreline (dotted lines; Møller 1967). Isobases for the Main shoreline refer to shore features formed near high· tide leve l (ca. 1.5 m a. mean s.l.) whereas those for the Tapes shoreline refer to the contemporaneous mean sea leve! (Møller 1989). The isobases should nevertheless be considered approx.imate (±1-2 m) at this scale; in Lyngen the plotted Tapes isobase is slightly too low ( see text).
The marine limit, assumed to have formed at the time of deglaciation, Iies approximately 57 m, 47 m and 40 m a.s.l., at Lyngen, Skipsfjorddal and Vannareid, respec tively. In all three areas, the 'Main' (Younger Dryas) and 'Tapes' (Middle Holocene) raised shorelines are distinct and form important morphostratigraphic markers (cf. Marthinussen 1960; Andersen 1968; Møller 1985, 1987, 1989). The Tapes shoreline, as referred to here, is the shoreline formed during the Tapes transgression maxi mum (TIM). At Lyngen, where detailed studies were carried out dose to the TIM level, the Tapes shoreline consists of either a terrace or notch at 20.5-21.5 m a.s.l., or a gravelly beach ridge at ca. 22.5 m a.s.l. These shoreline features Iie ca. 0.5 m higher in the slightly more exposed northern part of the area. The general elevation of this shoreline at 21-22 m a.s.l. is estimated to represent a contemporaneous mean sea-level of 20-20.5 m a.s.l. At Skipsfjorddal, the Tapes shoreline forms a broad, sandy beach-ridge complex (Fig. 3C) reaching ca. 12 m a.s.l. The present, normal limit of wave action in the area, as indicated by the upper limit of drifted seaweed, Iies ca. 1.3 and 1.8 m a. mean s.l. at Lyngen and Vanna, respec (C) tively. Mean spring high-tide level is 1.25 m a. mean s.l. Fig. 2. Maps showing topography, basin Iocation, distinct raised shorelines and Vegetation at Lyngen consists of bog, heath and scat other features in the investigated areas: (A) Lenangsbotn-Jægervatn area, Lyn· tered birch and pine stands. Bog is prevalent in the gen, sbowing basins L2-L5 which are situated on hummocky marginal moraine, Vanna area which Iies dose to the tree line. The bedrock and coring stations (crosses) in basin LI (Lake Jægervatn); (B) Skipsfjorddal, Vanna, sbowing basins SI-S4 and radiocarbon-dated palaeosol site (x) in sand consists predominantly of schist and gabbro at Lyngen, dune/blowout area (vertical shading); (C) Vannareid, Vanna, showing basin VI and gneiss at Vanna. (Lake Litlevatn). Bog shown by horizontal shading. Altitude in metres. NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 177
Figs. Ja and Jb. 178 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT 73 (1993)
Fig. 3. Views of the investigated areas at Lyngen and Vanna: (A) Lyngen alps viewed towards the southeast, showing ice-covered Lake Jægervatn (basin LI) and adjacent Late Weichselian local moraines; (B) basin L5 at Lenangsbotn, Lyngen, showing morainic substrate with partial peat cover (foreground); (C) Skipsfjorddal showing the position of basin Sl and palaeosol locality 'x' in raised beachfdune area. The Main (M) and Tapes (T) shorelines are indicated by arrows.
Field and laboratory methods parts of each core was x-radiographed. The organic minerogenic sediment proportions in the cores were Basin threshold elevations, lake water-levels and raised estimated visually and, in some cases, recorded by tone shorelines were levelled using tide-leve!, reduced to mean density measurements on radiographs. Grain-size analy sea-leve!, as base leve!. Levelled profiles started and sis was carried out by standard wet and dry sieving, and ended at the same point in order to correct for closing pipette analysis, using a modified U dden-Wentworth errors, except at Vannareid where a single profile was grade scale with the clay-silt boundary defined at carefully levelled. 0. 002 mm. Samples of ca. 5 mm3 volume were taken at Coring was carried out mainly on ice-covered !akes in various intervals, to as small as lO mm, for diatom winter, usually at the deepest part, using a simple 'Rus analysis. Samples were treated with 30% hydrogen per sian'-type sampler to locate the depth of the organic oxide, the residue being mouiited on glass slides using minerogenic sediment transition, and a Geonor K-200 NAFRAX cement, and studied under the microscope piston corer with l-2 m long, 110 mm diameter, p1astic using phase-contrast illumination at x 1000 magnifica tubes, or l m long, 54 mm diameter, steel tubes for tion. Photographs were taken for reference purposes. sample collection. Reconnaissance coring to find the Identification of different taxa (and classification accord organic-minerogenic sediment interface was carried out ing to salinity to1erance) was made mainly with reference at several places in each lake in order to find the most to Hustedt (1930, 1957), Cleve-Eu1er (1951-55) and suitable, flat-bottomed part of the lake for sampling. Hendey ( 1964), as well as Florin ( 1982) and Foged During the coring procedure, prenetration length was ( 1978, 1982). compared with core length in order to check for and avoid disturbance. In the 1aboratory, cores in steel tubes were extruded Diato ms mechanically and halved longitudinally, whereas those in plastic tubes were halved directly. After describing core Diatoms are sensitive to chemical and physica1 changes lithology, a lO mm thick longitudinal slice of selected in the water. A change from a marine to a 1acustrine NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 179
environment, and vice versa, has a drastic effect upon Facies I (Marine) - bioturbated, occasionally weakly existing species. Although diatoms have been used with a laminated mud and sandy mud, usually containing scat high degree of confidence, as salinity indicators, it is not tered ( ice- or seaweed-rafted) clasts, shells and marine always possible to determine the precise environmental diatoms. Single, thin, sand or gravelly sand beds may affinity of any given species. For several species, contra occur. dictory reports have been given as to what kind of environment they inhabit. In addition, the diversity of Fa cies Il (Transitional) - finely laminated, alternating the environment in the shore zone may confuse the fossil layers of gyttja, gyttja and silt, or gyttja, silt and fine record. In particular, the role of sea spray in transporting sand, usually occurring at the transition between minero diatoms or affecting the salinity of small lakes may be genic (facies l) and organic (facies Ill) units. Diatoms in important. Consequently, any change in the diatom flora this facies usually show an upward transition from is significant, but should be interpreted in conjunction marine to freshwater flora. The facies is interpreted as with other environmental indicators (Palmer & Abbott having formed immediately after isolation of the basin 1986). from the sea, in nearly all cases during a relative1y In this work diatoms have been classified conservatively short-1ived meromictic ( sa1inity-stratified) limnic p hase into salinity classes according to Hustedt (1957) and (Haugane 1984; Haugane & Corner in prep.; cf. Strøm plotted alphabetically on the frequency diagrams. The 1936; Anderson et al. 1985). The isolation contact, which salinity classes are: polyhalobous (prefer salinity > 30o/oo), represents the moment at which the basin threshold loses mesohalobous (salinity 30-0.2o/oo), oligohalobous halo regu1ar contact with the sea, is therefore placed at the philous (prefer slightly saline water), oligohalobous in base of this unit. This interpretation of the laminated different (prefer freshwater, tolerate slightly saline water), transitional unit and placement of the isolation contact halophobous (exclusively freshwater, salinity <0.2o/oo). differs from that employed in previous studies (e.g. Sta Abbreviations 'cf.' and 'ssp.' refer to slight divergence hell 1980; Kjemperud 1981, 1986; Lie et al. 1983; Kaland from species characteristics or uncertain identification et al. 1984; Svendsen & Mangerud 1990) where common owing to poor preservation, and to subspecies, respec practise has been to interpret the laminated unit as tively. Sampled levels are indicated by thin horizonta1 representing a brackish phase occurring immediately be lines on the frequency diagrams. The diatom data are also fore isolation, and to place the isolation contact at the presented as summary diagrams in which taxa belonging top of this unit. Sea-level curves constructed using to each of the five salinity classes are grouped into three present and previous interpretations of the isolation con major groups: marine (polyhalobous and mesohalobous), tact will generally be displaced in time by an amount brackish (ha1ophilous) and freshwater (indifferent and equivalent to the duration of deposition of the laminated halophobous). This grouping differs slightly from previ unit. In two cases (basin S4 and probably also basin VI), ous practice but relates hetter to the hydrology of coastal facies Il sediment comprising laminated gyttja and silt waters in Troms where salinity values range from 33- sand, apparently formed under fully lacustrine conditions 29o/oo for full y marine water, through ca. 29-3o/oo for and represents episodes related to climatic factors rather surface waters in fjords and sounds, to < ca. 0.4o/oo in than sea-level change. lakes (Nordgård et al. 1983 and own measurements; cf. also Bøyum 1970). The pioneer freshwater Fragilaria spp., Fa cies Ill (L acustrine) - generally massive gyttja and which can tolerate a wide range of salinity conditions plant detritus, occasionally weakly laminated and con (Hendey 1964) and occur in large numbers at the transi taining some silt or fine sand, and possessing a domi tion from marine to lacustrine conditions, is plotted nantly freshwater diatom flora. Plant detritus is defined separately on the frequency diagrams, except in the case as organic material containing identifiable plant material. of F. viresens var. subsalina which is assumed to be a It commonly occurs in the upper, less humified part of typical brackish species (Stabell 1981). the lacustrine unit.
Fa cies IV (M ixed) - heterolithic, stratified organic (gyt Facies and isolationjingression contacts tj a, plant detritus) and minerogenic (silt, sand, gravet) sediment, containing both marine and freshwater di Four main facies types (I-IV), differing in lithology, atoms or only freshwater diatoms. The facies is inter structure and fossil content, and related to predictable preted as indicating wave influence at the threshold, depositional environments controlled by sea-1evel either during an episodic storm surge, or during an change, are distinguished. A number of variants, which ingression into the basin as a result of a transgression, in may owe their 1ithological character to factors other than which case the ingression contact is placed at the base of sea-level change, are also distinguished. These are as the unit. In one case (basin L4), a variant of this facies is signed to a group of miscellaneous facies (V), except interpreted as having formed as a result of slumping. where they lithologically resemble one of the main facies types. Figs. 8 and 16 illustrate examples of the main Fa cies V (D iverse) - facies of diverse character and ori facies types. gin comprising gravet (basin S2), sand and organic-rich 180 G. D. Corner & E. Haugane NORSK GEOLOGISK TJDSSKRJFf 73 (1993) sand (basin S3), sandy mud (S4) and laminated sandy quence having clear isolation contacts, one (Sl) contains mud (V I) and interpreted as being related mostly to high a variant (facies I-IV-Ill) of the simple regressive se rates of ( terrestrial) sediment influx. quence, one (L3) contains a syngressive-regressive, IV-Il Ill facies seqeunce, one (L2) contains a compound, transgressive-regressive, I-IV-I-Il-Ill facies sequence hav Radiocarbon dating ing ingression and isolation contacts, and one (VI) con tains a compound I-Il-V-II-Ill facies sequence thought Radiocarbon dating was carried out mostly on gyttja/ to reflect both climatic and sea-level change. The remain plant detritus using the NaOH-soluble fraction, preferen ing four basins (L4, S2, S3, S4) contain sequences in tially, in order to avoid problems caused by which isolation contacts are absent or difficult to identify contamination with younger root material (Kaland et al. precisely. A brief description of the stratigraphy in these 1984). Shell dates are corrected for isotopic fractionation basins is given since they provide additional information (to -25o/oo PDB) and a marine reservoir age of 440 years on facies variations and palaeoenvironment. in accordance with the standard used for the Norwegian coast (Mangerud & Gulliksen 1975). Dates from marine shells and freshwater gyttja should therefore be compara Basin L l (Jægervatn), Lyngen, 2. 6 m a.s.l. ble. However, some of the dated gyttja samples, particu Lake Jægervatn (basin LI) is a large, 50 m deep, glacial larly those having low negative {)1 3C values (e.g. samples basin with a bedrock threshold (Fig. 3A). The lake is fed from basins Sl and Vl; Table 1), may contain material by several small streams, including glacial meltwater of brackish (or mixed marinejfreshwater) rather than streams. Two 1.8 m long cores, taken 20 m apart from a purely freshwater origin (cf. Gulliksen 1980). Dates from 7 m deep, flat bench on the northem side of the lake, these samples may be too old by an amount equivalent show identical stratigraphy comprising a regressive, I-Il to some, presently unknown, proportion of the marine Ill facies sequence (Fig. 5). reservoir age (S. Gulliksen pers. comm. 1993).
Un it A (m arine fa cies l) - > 1.5 m bioturbated, cal Raised basin sites and stratigraphy careous silty, fine to very fine sand, having a high content of bivalve shells and calcareous algae (Lithothamnion) A total of 10 lake basins lying at various elevations which comprise the bulk of the sediment. The upper 5 cm between the marine limit and present sea-leve] were of unit A is rich in organic material and lacks Lithotham investigated (Fig. 2). The lakes mostly occupy morainic nion fragments. Diatoms occur near the top of the unit depressions and generally have reliable uneroded where marine species and the salinity indifferent pioneer thresholds. Basins in Lyngen occupy moderately shel species Fragilaria spp., dominate. At lower levels (7.5- tered sites, whereas those of Vanna, especially in Skips 8 m depth) diatoms are partially dissolved and only fjorddal, are more exposed. Nitzschia punctata could be identified. The basins show considerable variation in facies and The Lithothamnion flora is symptomatic of stable facies sequences (Fig. 4). Six of the ten basins provided marine, wave-protected, tidally-inftuenced conditions datable evidence of sea-level change. Among these, two (Freiwald 1991). Its absence in the upper part of the unit (L I, L5) contain a simple, regressive, I-Il-Ill facies se- may have been caused by temperature or salinity
Table l. Radiocarbon dates from (a) raised basin sediment cores and (b) a palaeosol from Skipsfjorddal, and their relationship to former sea leve!. Sample depth ('Unitjdepth') in basins is given relative to lake leve!. Lab. ref. suffixes 'A' and 'B' refer to dated NaOH-soluble and insoluble fractions, respectively. Calibrated ages are according to Stuiver & Reimer (1986). 'Max' and 'Mean' sea level refer to estimated spring high-tide leve! and mean sea-leve!, respectively.
Sea leve! ( m. a present s.l.) Unit/ Sam ple Samp le 613C Radiocarbon Calibrated Locality depth (m) Lab. ref. material wt(g) %o date (BP) date Event Max Mean
Basin LI A/7.1 T-4867 shells 3 +1.0 830 ±90 ADI095-1290 Isolation1> �2.6 �l Basin LI B/7.0 T-4866A + B gyttja 4 -21.3 1660 ± 160 AD200-570 Isolation 1> <2.6
1 Dates inverted. T-4866 probably too old. 2 lsolation history uncertain. Dates probably also too old. NORSK GEOLOGISK TIDSSKRIFf 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 181
3.9 4.1 5.1 4.3 3
t Mixed (facies IV) t t t � Ill Lacustrine (facies Ill) a Transitional (facies 11) Marine (facies l) 2 O I Diverse (facies V) .c O c, c 1.7 <1 lsolation contact � 0.8 Q) lngression contact o <1 o 14 1.7 l C-dating (ka)
3. 7 1····· l o Basin/ threshold L3 L4 L5 S1 S2 S4 V1 (m.a.s.l) 2.6 20.0 21 24.4 30.0 7.8 22.3 25.3 46.3 24.8
Fig. 4. Summary diagram of the stratigraphy of lake basin cores showing sediment thickness, facies types, position of isolation and ingression contacts, radiocarbon datings and basin threshold elevations.
changes, or by the influx of a predatory marine fauna as which the samples were taken. The isolation contact is isolation approached and conditions changed. therefore placed below facies Il, dose to the top of facies I (unit A). Radiocarbon-dated gyttjajplant detritus and Unit B (transitional facies II) - 0.07 m weakly laminated shell fragments from above and below this level gave gyttja having a variable content of plant detritus and dates of 1660 ± 160 and 830 ± 90 BP, respectively (Table minerogenic material. The unit has a diffuse lower 1). These dates are mutually inverted indicating that at boundary and contains the same diatom flora in its lower least one of them is erroneous. It is possible that the part as in the underlying marine unit. A transition from dated gyttja contains some marine or brackish-water marine to freshwater diatom species is seen at the very material which would give too high an age. However, the top of the unit. The typical marine minerogenk sediment age difference between the two samples is much greater and macrofauna of unit A is absent in this unit, which is than any potential error caused by the marine reservoir interpreted as representing a meromictic transition to full effect. The gyttja date is thought to be too old on lacustrine conditions at the sampling site. account of the presence of resedimented plant material in the sample, a common source of error in lacustrine l Unit C (lacustr ne facies /Il) - 0.2 m sandy-silty gyttja, environments (Olsson 1979). The date of 830 ± 90 BP, containing more minerogenic material than the underly from unit A, probably represents a dose maximum age ing unit. lts lower part is laminated and contains a bed for the isolation contact and dates a threshold isolation of the remains of the freshwater calcareous green alga level dose to 2.6 m a. present mean s.l. Chara sp. Diatoms consist predominantly of freshwater species, with a small brackish component. Diversity is highest in the laminated lower part of the unit. The Basin L2, Lenangsbotn, Lyngen, 20.0 m a.s.l. relatively high content of minerogenic material may This 120 m diameter lake Iies in a broad morainic depres reflect glacial meltwater input. sion just 1.5 m below the Tapes shoreline and at the same level as the estimated Tapes mean sea level. Two 2.9 m Isolation. - At present, sea water intrudes into Jæger long cores (A and B), taken 10 m apart from slightly vatnet only under exceptional circumstances (cf. report northwest of centre of the basin, at a depth of 3.4-3.5 m, in 'Nordlys' daily newspaper, 13 January, 1993), and in show essentially similar stratigraphy comprising a com quantities insufficient to significantly affect the hydrology pound, transgressive-regressive I-IV-I-Il-Ill facies se of this large lake. However, following isolation and the quence (Figs. 6, 7, 8). inevitable establishment of a meromictic hydrology in a basin of this size, a marine fauna and flora would · be Unit A (marine facies I) - >0.6 m bioturbated sil ty fine expected to persist for a short time on the bench from sand containing plant material, scattered dropstones, and 00- N
0 � g � �rtr �tfr "" ;;; o .... [JJ] -o .(J � -$§ �· �� fbttr �(l)�(j � Leg end LITHOLOGY: DIATOMS: · Gyttja Bioturbation Barren Mud Sand � [I] L:=J o Halophobous Muddy gyttja Laminated .....___[il[]]]]] Freshwater �:;:;:;:� � o Indifferent -- z ���a:��� ich B Distinct boundary "' Halophilous --� Brackish o [&!+l o Mesohalobous �:><: Gradational bound. --� Marine Cl Calcareous G • Polyhalobous ---� silty sand � Low diversity El (lithothamnion) Shells '' [I] � < 3 species) r;; ( §:><: ::l Sl � "' �;:;l i Fig. 5. Lithostratigraphy and diatoms from basin LI (Lake Jægervatn), Lyngen. The isolation contact is indicated by a triangle. � NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 183 o 30% L.u..J •• • o O O 6 • e ODD • • e o• O O O • o• e OD D e ee O .. . l .. l ....: l ...... , ,.... ,.. """"" • � ...... J , , l L � L ."... i-- � t------l r r �- ...... � ..... ' l l il l -- l 11 l l l l l l l l l l l l l l l l l Ill l l; :l: l lil l l li ill il B l I l Core l' i l ' l l 'li '' l ' l, ; ill 'll l l'l, , I ll l Core A l l l :l lo Mud Sand Gv Legend UTHOLOGY: DIATOMS: lB Plant detritus Thin gyttja Laminat ed Bar.ren E3 � o Halophobous D Gyttja Scattered clasts Weakly laminated ---OF Freshwater a El El o Indifferent- Q Muddy gyttja Shells Distinct boundary 6 Halophilous --[g Brackish [I] El o Mesohalobous Mud and sand Bioturbation Gradational bound. ....__. Marine l.tJl El • Polyhalobous------ Fig. 6. Composite diatom diagram for adjacent cores (A and B, 10m apart) from basin L2, Lyngen. A slight gap or overlap in the stratigraphy between the two cores rnay exist (cf. Fig. 7). 73 (1993) 184 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFf SEA-LEVEL CHANGE � DIATOMS/ o -- - - SALINI TY lsolation Q) a: o o D Marine DIATOMS/ - SALINITY -- - - -?- --- �li��+l ���,..,.,;1-..,.CX) 1'-- ' ' o 50 100% ------Hiatus - Unit B (mixed facies IV) - ca. 0.4 m heterolithic unit -E comprising altemating, irregular laminae and lenses of I gyttja, plant detritus, sand and pebbly sand (Fig. 8). The I plant material mostly comprises mosses and wood frag Cl. ments. Fragments of Mya truncata were found in the w o unit. The diatom flora consists of a mixed assemblage containing the same marine species as in the underlying 3.5 unit, as well as several freshwater species. Unit B evidently contains resedimented material derived from a variety of sources and represents an abrupt change in depositional conditions. Slumping seems unlikely as a sole explanation for the characteris tics of this unit. Rather, the unit is thought to have formed during a marine incursion into the basin causing erosion, transport of plant material and littoral sand into the basin, and disturbance of lacustrine gyttja on the floor of the basin. Accordingly, any previously deposited 5.0 transitional facies Il sediments, formed during prior iso lation, must have been removed creating a hiatus be tween units A and B. Unit C (marine facies I) - ca. 1.3 m bioturbated fining upward unit of silty fine sand - sandy silt, containing shell fragments and scattered, coarse sand grains. Weak 5.5 lamination is preserved in the slightly coarser lower part of the unit, and the degree of bioturbation increases upwards. Apart from a few freshwater diatoms at the base, the unit is dominated by marine species. Unit D (transitional facies Il) - 0.2-0.3 m laminated 6.0 gyttja containing fine sand laminae (Fig. 8). The diatom flora changes from a marine assemblage in the lower part, similar to that in the underlying unit, to a freshwa ter assemblage in the upper part. Freshwater, calcareous algae (Chara sp.) occur at the top. Unit E (lacustrinefacies Ill) - 1.3-1.65 m gyttja grading 6.5 into dy (gel-mud) towards the sediment-water interface. Freshwater diatoms dominate. Isolationfingression. - The stratigraphy of basin L2 indi cates what are probably two episodes of isolation, with an intervening ingression represented by marine unit C. 7.0 The first isolation is recorded indirectly by the presence, in unit B (mixed facies IV), of resedimented lacustrine gyttja and plant detritus. These sediments must have formed originally when the threshold level was situated above the limit of storm-surge tides. Mean sea-level at that time probably lay below 17 m a.s.l. Unit B was Fig. 8. X-radiographs showing facies l-IV in basin L2, core A (cf. Fig. 7). Altema ting organic·rich (dark) and minerogenic {light) layers show high con trast deposited during a subsequent ingression, when storm in laminated units B and D. waves overtopped the threshold at 20 m a.s.l., corre sponding to an estimated mean sea-level of ca. 18-19 m partially dissolved shells. The diatom flora (Fig. 6) is a.s.l. A radiocarbon date of 7880 ± 100 BP, from resedi dominated by marine species, but some freshwater spe mented plant detritus from unit B, gives an approximate eies also occur. The unusually high content of plant age for the pre-ingression lacustrine phase and a maxi detritus and freshwater diatoms in this marine unit may mum age for the marine ingression. Unit C represents an be due to the location of the basin near the former outlet extended period during which sea leve) was situated of a stream some 400 m to the north. above the threshold. The ingressiveftransgressive event 73 (1993) 186 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT leading up to deposition of unit C most likely correlates with the forma ti on of the Tapes shoreline at 21-22 m a.s.l., in which case sea level probably lay only mar GRAIN-SIZE ginally above the threshold at that time. The slight DIS TRIBUTION fining-upwards texture in the lower part of unit C may md sd gv•• reflect the changing process-regime at the threshold dur [:..:::r···· .·3· , ing the transgression, or possibly basin stabilization dur l ing the following syngression. Final isolation of the basin o 100% is placed at the boundary between marine unit C and transitional unit D. A radiocarbon dating from the base - en>- w of unit D gave an age of 6480 ± 90 BP, which corre ��-- _.J sponds to a threshold isolation level of 20.0 m and an oz a.. estimated mean sea level of ca. 18.5 m a.s.l. � �::i_<( <( Cl Cf) Cf) • Basin LJ, Lenangsbotn, Lyngen, 21m a.s.l. • • Basin L3 is a small 20 x 50 m diameter, bog-encircled, • 1.2 m deep lake situated in a sheltered morainic depres sion lying immediately behind the Tapes beach ridge. • The threshold is obscured by bog, but is thought to consist of Tapes beach gravel lying just below the level of • the lake (21.3 m a.s.l). No radiocarbon dating was made • from the 4.2 m long core recovered from this lake, but l the stratigraphy, a compound IV-11-III facies sequence (Fig. 9), is interesting on account of the lake's proximity to the Tapes shoreline. • • Unit A (mixed facies IV) - > l m complex, irregularly bedded, partly laminated, partly bioturbated, partly de l formed (folded) unit comprising predominantly silty • • sand with dispersed plant material, gravet and sand lenses, and some thin gyttja beds. Diatoms in the silty • sand and gyttja suggest marine conditions. • Unit B (transitional facies Il) 0.32 gyttja contammg scattered pebbles. Distinct lamination- at the base of the o 100% unit becomes less distinct upwards and eventually disap pears. Marine diatoms dominate. The upper boundary coincides with an abrupt colour change from light to Leg end dark brown, as well as a transition from dominantly LITHOLOGY: marine to dominantly freshwater diatom species, includ Plant detritus Scattered clasts ing a small brackish component. mm @] Gyttja [l] Bioturbation Unit C (lacustrinefacies Ill) 2.9 m gyttjafplant detritus � - Mud and sand Laminated containing mostly freshwater diatoms. l t I j � Grave! and sand Distinct boundary Isolationfingression. - Heterogeneous unit A (facies IV) lao;:ol B resembles unit B in basin L2 (interpreted as an ingressive � Thin gyttja O Gradational bound. unit), except that it contains only marine and brackish diatoms, and is much thicker. The unit is interpreted as DIATOMS: a littorally-influenced deposit, formed during the Tapes CJ Barren transgression and TIM syngression which gradually Halophobous raised the level of the threshold at this basin. Unit B --- ITTTTFffiTll Freshwater Indifferent -- lllJJ.1J..l.ll. Halophilous --� Brackish Mesohalobous --� Marine Fig. 9. Lithostratigraphy and diatom summary diagram for basin L3, Lyngen, Polyhalobous ---� showing the position of the isolation contact. NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 187 (facies Il) was formed following isolation; the unusual tion contact was not precisely located in this basin and persistence of marine diatoms in this unit may be due to only a minimum age for isolation was obtained. Strati marine water infiltrating through permeable gravels m graphic correlation of the different units in the two cores the threshold ridge. is based on lithology and diatom assemblages (Haugane 1984). Basin L4, Lenangsbotn, Lyngen, 24.4 m a.s.l. Units A and B (marine facies /) - >0.75 m bioturbated, This small, 40 x 60 m diameter, 3.2 m deep, moram1c silty fine sand containing many pebbles, cobbles and basin Iies ca. 3 m above the Tapes shoreline. Two 5.1 m shells, including Mya truncata in life position, capped by long co res (A and B, Fig. l 0), taken 5 m apart, show a thin, possibly uncomfortable, layer of plant detritus. considerable differences (aberrant 1-III/I-IV-III facies se The marine diatom flora can be divided into two assem quence), suggesting disturbance by slumping. The isola- blage zones (l and 2) dominated by marine species, with /L4/ Core A - .----- Core B ------. E I DIATOMS o6' 1- � a.. w >- 1- w_J er� �V o '<� 3.2 z a.. s .§ ::i � DIATOMS N <( <( <( C/) C/) • >- 1- _Jw z a.. _J � F Lacustrine N <( <( 5 <( C/) C/) • • 7.0 • • • t---1:>7:=�".,..".,. • - - t------f...r'-.+.,L.,'.,I+-----L l • 7.5 ' ' f o 100% '--+---,.---� • ' o 100% ', ...... ? Mud Sand Legend DIATOMS: LITHOLOGY: W Shells Plant detritus Barren Bm Bioturbation O � Halophobous F Gyttja --._IITTT'fTTTTTl reshwater æ J J Weakly laminated Indifferent -- llJ.ilEJillll Mud and sand Halophilous Brackish �m::::::J Distinct boundary --� B Mesohalobous Thin gyttja ----� Marine � G Gradational bound. Polyhalobous--- Scattered clasts EJ B Hiatus Fig. JO. Litho- and diatom stratigraphy iri adjacent cores (5 m apart) in basin L4, Lyngen. The suggested stratigraphic correlation, based on lithology and diatom assemblages, indicates a major hiatus in core A and a slumped unit (C) in core B. The radiocarbon date provides a minimum age for basin isolation. 73 (1993) 188 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT a barren zone between. Zone l is found in both cores, whereas zone 2 is found only in core B, indicating the g:- ��· 6- presence of a hiatus above unit B in core A. �� 0 0 ;:f,S GRAIN SIZE t ! Jit::: DISTRIBUTION el sl sd J M - ' DIA O S/ Unit C (mixed facies IV) 0.35 m heterolithic unit, Ø (j ,"!(' � found only in core B, consisting mainly of a deformed 45. ' �-==l�;:;ql SALINITY Q � " " l l l bed of sandy plant detritus overlain by a cyclic set of o 100% o 100% three, laminated, coarsening-upward beds of mud to fine sand with gyttja. Marine diatoms dominate at all levels 6.0 in the unit except in the gyttja layers, which contain freshwater species. Unit C shows characteristics which are not found in facies IV or facies Il sediments in other basins. The cyclic bedset and presence of both marine and freshwater diatoms indicate mixing and resedimenta tion of material, possibly by a tidal or storm influenced marine incursion into a previously isolated basin, or by repeated turbidite deposition caused by slumping within an already isolated basin. Unit D (lacustrine facies Ill) - ca. 4 m predominantly plant detritus consisting mostly of mosses. Thin beds of gyttja and compact plant detritus occur at the base. · Scattered, coarse sand clasts occur in the lower part in both cores. Two different diatom assemblages, compris ing a diverse freshwater flora in core B (zone 4) and a freshwater flora in core A (zone 5), indicate the presence of a hiatus and slumping in this unit too. 7.0 Isolation. - The stratigraphy shows a rather abrupt change from marine to lacustrine conditions, represented primarily by an erosional hiatus in core A and a slumped unit (unit C) in co re B. Cyclic beds of uncertain genesis in unit C, containing marine and freshwater diatoms, were formed same time after isolation. A radiocarbon Fig. 11. Lithostratigraphy and diatom summary diagram for basin LS, Lyngen, date of 7580 ± 130 BP from a bed (possibly displayed) of showing the position of the isolation contact. Legend in Fig. 12. freshwater gyttja immediately overlying unit C, indicates that the basin was isolated at this time. Unit C (transitional facies Il) - O. l m laminated gyttja containing same sand and silt laminae. A transition from Basin L5, Lenangsbotn, Lyngen, 30.0 m a.s.l. a marine to a freshwater diatom flora is seen at the base Basin L5 is 100 m in diameter, 4.5 m deep, partly covered of the unit. by floating peat mats, and Iies 8.5 m above the Tapes shoreline (Fig. 3B). Reconnaissance coring revealed cob Unit D (lacustrine facies Ill) - 1.5 m thick gyttjajplant bles or boulders at a depth of ca. 7.5 m. Above this is a detritus. The unit contains a freshwater diatom flora, 3m thick, simple, regressive, I-Il-Ill facies sequence including halophobous species, similar to that in the (Fig. 11). underlying unit. lsolation. - A radiocarbon dating from the base of unit Units A and B (mixed facies l) - 1.15 m coarsening upward sequence consisting of a unit (A) of pebbly clay C which represents isolation of the basin, gave an age of lacking shells or diatoms, overlain by a unit (B) of 8960 ± 130 BP. This corresponds to a threshold isolation altitude of 30.0 m a.s.l., and an estimated mean sea-levet bioturbated, partly laminated, sandy clayey silt with of 28.5 m a. present s.l. scattered pebbles and a bed of gravelly sand. Organic material in the upper l cm is probably derived by inflltra tion from overlying gyttja. Diatoms first appear in the Basin Sl, Skipsjjorddal, Vanna, m a.s.l. upper lO cm of unit B, being represented by distinctly 7.8 marine species (Fig. 12). The sequence is interpreted as a This 100 m diameter, 1.3 m deep lake occupies a shallow marine, shallowing-upward sequence. morainic hollow (Fig. 3C). It contains an estimated NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 189 0.5 m of postglacial sediment, comprising what is inter raised into the upper intertidal zone. Unit B is therefore preted as a regressive I-IV-Ill facies sequence (Fig. 13). interpreted as having been deposited when the basin lay between neap high-tide level and the storm limit. Unit A (marine facies I) - 0.2 m well-sorted, bioturbated fine sand containing dispersed organic material, scattered Unit C (lacustrinefacies Ill) - 0.03 m brown gyttja. The pebbles, and a gravelly sand bed near the top. The unit diatom assemblage is dominated by freshwater species, contains no diatoms, but its lithology suggests a wave but also contains brackish and marine species, despite inftuenced marine origin. the fact that this unit extends to the present sediment surface and is obviously lacustrine. Unit B (mixed facies IV) - O.l l m weakly laminated heterogeneous unit of black gyttjafplant detritus and Iso/ation. - The succession indicates a transition from sand, containing two beds of matrix-supported sandy marine to lacustrine conditions. The unusual lithology grave!. The unit contains no diatoms. The organic mate and diatom assemblage of units B and C (facies IV and rial probably consists of marine, brown-algae detritus Ill) is probably related to the relatively high degree of washed into the basin by storms. The grave! is inter wave exposure, with facies IV (unit B) replacing the preted as having been deposited by storm waves onto more normal transitional facies Il. The isolation contact, winter ice covering the lake, and subsequently metting placed at the base of unit B and dated to 3680 ± 180 BP, out causing only minor disturbance to the loose, lake represents a threshold isolation altitude of ca. 7.8 m a.s.l. bottom detritus. At this exposed locality, winter ice The obtained date may be slightly too old on account of would normally form only once the basin had been the marine reservoir effect. -� � 4.�0� 20% ,w Legend Mud Sand LITHOLOGY: DIATOMS: - Plant detritus [ZLJ Bioturbation c=J Barren o Halophobous ---- � Gyttja Laminated Freshwater m � o Indifferent -llllltJuru Mud and sand E;d Load east A Halophilous --� Brackish l i\ j o Mesohalobous ----� Gravel and sand Distinct boundary Marine JOo::;l B • Polyhalobous --� Scattered clasts Gradational bound. Low diversity @ G - ( < 3 species) Fig. 12. Diatom diagram for the upper part of the stratigraphy in basin L5 (cf. Fig. Il). 73 (1993) 190 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT Barren ti on o 100% Leg end LITHOLOGY: Scattered o !mim Plant detritus B clasts Bioturbation Gyttja 1. 6 f � [l] �\\\:\:\: ;l Mud and sand � Laminat ed Org rich Dis tinet Gv l\\:;t%\l ;��d boundary � Gravel and sand B DIATOMS: C=:J Barren o Halophobous -..._ITTTfFTITTTl Freshwater o Indifferent -- lll.J..lL:J..ll LJ. Halophilous --� Brackish o Mesohalobous ----� Marine • Polyhalobous--- . Fig. 13. Litho- and diatom stratigraphy of basin Sl, Skipsforddal, Vanna, showing the position of the isolation contact. Basin S2, Skipsfjorddal, Vanna, 22.3 m a.s.l. Unit A (facies V) - O.l m subrounded, sandy gravel containing a sparse freshwater diatom flora. This 150 m diameter, 1-1.5 m deep, boulder-strewn, morainic basin Iies within the inferred tidal zone of the Main shoreline. A 0.7 m sediment cores shows a V-III. Unit B (/acustrinefacies Ill) - 0.6 m gyttja/plant detritus facies sequence (cf. Fig. 4). No radiocarbon dating was containing lenses of fine sand and scattered pebbles. A made. 2 cm thick layer of black jelly-like gyttja occurs at the NORSK GEOLOGISK TIDSSKRIFT 73 (I993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 191 base. Diatoms in the ana1ysed lower 20 cm of the unit Basin VI (Litlevatn), Vannareid, Vanna, 24.8 m a.s.l. comprise freshwater species, except for a single brackish This 250 m diameter, mostly shallow, up to 3.6 m deep species. basin Iies at a levet 10 m above the Main shoreline and 15 m below the marine limit. It Iies upvalley from and Iso/ation. - Unit B is clearly lacustrine whereas unit A just 0.5 m above a much larger lake (Storvatn), near the may represent littoral sediment. The abrupt facies transi head of the valley. The lake is fed by small streams and tion suggests the presence of a hiatus representing the seepage. Two 2 m long cores from the lake showed a period during which this shallow basin became isolated similar, compound I-II-V-II-III facies sequence (Fig. 14- and before organic lacustrine deposition became estab 16) which most likely represents a regressive sequence lished (see discussion for basin S4). The sand lenses and modified by climatic factors. scattered pebbles in unit B are probably of windblown and/or ice-rafted origin. Unit A (marine facies l) - 0.55 m silty fine sand contain ing intermittent laminae of slightly coarser sand and, near the top, two thin beds of medium sand and gravelly Basin S3, Skipsfjordda/, Vanna, 25.3 m a.s.l. sand, respectively. The lower part of the unit contains many well-preserved shells and fragments of Hiatella This l m deep, bog-enclosed basin is situated centrally on the flat floor of the valley. It contains more than 1.6 m of arctica and Mytilus edulis, including the periostracum of sand (facies V) which is laminated with organic material Mytilus. Unit A lacks diatoms. The coarser sandy layers in its upper part and overlain by 0.3 m of gyttja (facies near the top of the unit suggest shallowing-upward Ill). The lithology, and a freshwater diatom flora, sug marine conditions and the influence of storms. gest a purely fluvial/lacustrine origin for these sediments. Unit B (transitional facies Il) - 0.17 m finding-upward unit of mainly finely laminated silty gyttjafplant detritus Basin S4, Skipsfjorddal, Vanna, 46.3 m a.s.l. This 100 x 200 m diameter, 2m deep basin consists of a littoral-ridge dammed lake situated on the side of the valley at the marine limit. The ridge consists partly of GRA IN-SIZE rounded, littoral cobbles and boulders, and partly of DISTRIBUTION� �DIATOMS/ bouldery diamicton of presumed iceberg-rafted or sea-ice ALINITi rafted origin. A 2.5 m long sediment core contained a o 100% o 100 % VII-Ill facies sequence (cf. Fig. 4). 4.0 Unit A (facies V) - 0.14 m relatively poorly sorted, predominantly sandy silt having a variable content of dispersed organic material and poorly preserved fresh 4.5 water diatoms. Unit B (facies Il)- 0.06 m laminated gyttja and fine sand containing dominantly freshwater diatoms. Unit C (lacustrine facies Ill) - 2.5 m gyttja containing numerous, very thin, fine-sand laminae in the 1ower part, 5.0 and a diatom flora similar to that in the underlying unit. Palaeoenvironment. - The sediments are interpreted as having formed in a lacustrine environment in which early colluvial deposition of minerogenic sediment was later replaced by deposition of organic material. The transi 5.5 tion (unit B) was dated to 8200 ± 160 BP. This date is much younger than the expected age close to the date of basin formation around the time of deglaciation at ap proximately 13000 BP. The pollen stratigraphy, however, Fig. 14. Lithostratigraphy and diatom summary diagram for basin VI (Lake suggests that the date is reliable and marks a period of Litlevatn), Vannareid, Vanna. The favoured interpretation of the sequence places increased vegetation growth and substrate stabilization the isolation contact at the base of unit B and correlates units C and D with a Yo unger Dryas lacustrine p hase. An alternative interpretation suggesting ingres of this northeast-facing slope, following a climatic ame sion (shaded dashed triangle) and renewed isolation ( open dashed triangle), seems lioration (K.-D. Vorren pers. comm. 1993). less likely (see text). Diatom sampling interval and legend is given in Fig. 15. 73 (1993) 192 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT o 50% L..u...u..l o OD ODD DO O • OD O O o o o o r1 l l ' r ,. � � � � � .. • • • � ·"'' Legend LITHOLOGY: DIATOMS: og Plant detritus @] Scattered clasts � Laminated c=J Barren � Gyttja W Shells B Distinct boundary o Indifferent -[].l[]Jll!] Freshwater Muddy gyttja Bioturbation Gradational bound. • Mesohalobous Marine � l .i./l G -� Mud and sand Low diversity I,::I:: :n (c 3 species) Fig. 15. Diatom diagram for basin VI (Lake Litlevatn), Vannareid, Va':lna (cf. Fig. 14). and fine sand (Fig. 16). The lower boundary is grada sediment transport were high and organic production tional and the organic content increases upwards. At the low. top is a thin silt bed overlain by a thin bed of plant detritus containing mostly moss (Campyliun stel/atumf Unit C (laminated facies V) - 0.27 m finely, evenly lami polygamum). The unit contains scattered, probably ice nated, sandy mud, being slightly coarser at the base (Fig. rafted, sand and pebble clasts. A poor flora of freshwater 16). The unit contrasts lithologically with the underlying diatoms dominated by Fragilaria spp. occurs in the upper unit but the boundary between the two does not appear half of the unit. A sample from the lower part contained to be erosional. Sporadic, thin ( < l mm), subvertical, resting spores ( cysts) of a marine dinoflagellate ('Hys pyritized tubes are interpreted as burrows. A sparse, trix'), (Vorren 1985). partly corroded diatom flora occurs in the upper and The lamination and virtual absence of bioturbation, as lower parts of the unit. It consists of freshwater species, well as the first appearance of freshwater diatoms in unit except for a single species identified as the mesohalobous B, suggest that the basin had become isolated from the Navicula cf. crucigera typica, which is relatively abundant sea at this time. The unusually high content of minero near the top. genic material in this unit compared with facies Il sedi The sparse diatom flora in unit C does not allow a ment in other, younger sequences, may reflect the Late reliable environmental interpretation. The unit differs Weichselian environment in which rates of subaerial from normal transitional facies Il and lacustrine facies NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 193 E material consists of algal material an d plant detritus con tainin g well preserved leaves of Salix polaris. The un it Cf) con tains a rich diatom flora comprising freshwater spe UJ eies. Both the relatively high organic con ten t an d the () u..<( diatom flora in dicate that un it D was deposited in a lacustrine environment. The presence of Salix suggests that a substan tial vegetation cover existed at the time. The un it resembles transitional facies Il in other basins with regard to its laminated structure, but ditfers with regard to the absence of marine diatoms. Unit E (/acustrine facies Ill) - ca. 3.2 m gyttjafplant detritus with scattered sand an d pebble clasts an d an in creasing proportion of plant detritus, in cluding Phrag mites sp., towards the top. The unit contains a diatom flora similar to that in the un derlying un it an d is clearly lacustrine in origin. Isolation and palaeoenvironment. - The stratigraphy of basin VI in dicates a transition from marine (unit A) to lacustrine (unit E) con ditions, but the isolation con tact is difficult to define precisely. Units B, C an d D all show lamination, but they contain few diatoms an d the se quence ditfers from that found in other basins. In itial isolation of the basin probably occurred during deposi tion of un it B as suggested by the in crease in organic matter an d first occurrence of freshwater diatoms. The overlying minerogenic-rich sequence ( units C an d D) may be in terpreted in two alternative ways: (l) marine in gression an d subsequent isolation, (2) climatically in duced increase in sediment supply to an already isolated lacustrine basin. The evidence for a marine in gression is not compelling. It con sists of sporadic bioturbation traces an d a single diatom species, both of presumed marine origin. A climatic control on the sediment supply seenis feasible, however, in view of the Late Weichselian age of the sediments. Radiocarbon dates obtained from shells at the base of un it A an d from gyttja in units B an d D, gave ages of 12 140 ± 300, Il 480 ± 290 an d Il 140 ± 130 BP, respec tively (Fig. 14). Pollen stratigraphic evidence from the core suggests that the gyttja dates are too old (K.-D. Vorren 1985, pers. comm. 1993). Un it C shows an Fig. 16. X-radiographs fr om basin VI, Vannareid, showing well-laminated sedi Artemisia peak which is preceded an d succeeded by an ments (facies Il and V) in the transition zone between marine (unit A) and lacustrine (unit E) sediments. Laminated unit D (right-hand radiograpb) is Oxyria peak in un its B an d D, respectively. Compared particularly distinct. The apparent density difference between the two images is with regional evidence (Vorren 1978, 1985: Fimreite not directly comparable since different exposure times were used. 1980; Pren tice 1981, 1982; Vorren et aL 1988; Alm 1990; Vorren et al. in press) this vegetation pattern suggests that un it C formed un der arctic steppe conditions during Ill in lackin g organic materiaL It ditfers from marine the early part of the Y o un ger Dryas Chronozone (ca. facies I in having distinct lamination, an d lacking strong lO 500-11 000 BP), whereas un its B and D formed un der bioturbation. The dominan tly minerogenic lithology sug more humid an d part1y milder conditions during Allerød gests either a marine or estuarine environment, or a an d late Younger Dryas, respectively (K. -D. Vorren climatic control on sediment supply to a lacustrine en vi pers. comm. 1993). This correlation, if correct, implies ron ment. that the older an d younger gyttja dates are ca. 300 years an d 600-700 years too old, respectively. For the older Unit D (transitional facies Il) - 0.09 m laminated gyttja date, the age discrepancy could be largely explained by containin g several, very fine sand laminae. The organic the marine reservoir etfect. For the younger date, it is 194 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT 73 (1993) thought to be related to the presence, in the sample, of Each curve has been drawn as a smooth interpolated fit old resedimented organic matter derived from eroded soil to the data using a minimum of assumptions regarding and solifluction material, as reported elsewhere (Suther its shape. The curves are based on the following evi land 1983; Vorren 1985). The reinterpreted age of unit C dence: corresponds well with a dimatic interpretation of the sequence, since the Younger Dryas dimatic fluctuation (l) Radiocarbon-dated stratigraphic sequences and iso would be expected to cause a noticeable increase in the lation contacts in 6 out of 10 investigated raised minerogenic-organic sediment ratio (cf. Svendsen & basins (Table 1). Mangerud 1987, 1990), and such a change is not seen (2 ) A radiocarbon-dated palaeosol from Skipsfjorddal higher in the sequence (unit E.) (Table 1). The sample (locality 'x', Figs. 2B, 3C) was To condude, the compound sequence at basin V1 is taken from the lowermost of several, superimposed, considered to represent a simple regression, rather than palaeosol horizons in dunes covering beach ridges at transgression-regression. The shell date of 12 140 ± 300 7. 1 m a. s.l., just below the Tapes shoreline. The BP provides a maximum age for basin isolation. The dated NaOH-soluble and insoluble fractions gave isolation contact near the base of unit B has an estimated fairly similar results and probably provided a reliable age of between ca. Il 600 BP ( estimated from uncor minimum age for the beach ridges. rected radiocarbon date) and ca. Il 300 BP (pollen (3) The elevation of the Tapes shoreline, which is as stratigraphic age). sumed to mark the peak of the TIM. Regarding the occurrence of Mytilus edulis in unit A, (4) The elevation and inferred age of the Main shoreline. dated to 12 100 BP, this musse! was obviously living in This shoreline corresponds with the Tromsø-Lyngen the bay at the time, and is the oldest recorded postglacial (Yo unger Dryas) moraines (Andersen 1968) but its occurrence of this circumpolar, relatively temperate exact age and genesis is uncertain. For present pur (mid-arctic to boreal) species at this latitude. M. edulis poses, it is assumed to have an age of ca. 10 500 BP, has been found in early Bølling (ca. 12 400-12 700 BP) although in inner areas dose to the Tromsø Lyngen sediments from Hordaland in western Norway (Man moraines, an age doser to lO 300 BP may be more gerud 1977), but not from Late Weichselian (ca. 10 000- correct (Corner 1980). 12 500 BP) sediments from inner (glacier-proximal) (5) The altitude and estimated age of the marine limit at coastal areas of Troms (Andersen 1968). Because larvae Vannareid. This is placed at approximately 40 m of M. edulis have a limited life span (Seed 1976), the a. s. l. based on the elevation of the highest beach occurrence of this mollusc at Vanna at this early date ridge at 39 m s. a.l. and Hansen's ( 1966) marine limit suggests the presence of a strong coastal current which determination of 41-42 m a.s.l. lts maximum age could transport the larvae from more southerly locations. corresponds to the date of general deglaciation in the The source is likely to have been western Norway since area which, judging from regional data (Andersen much of the intervening coast of Nordland was glaciated 1968, 1979; Corner 1978; Vorren & Elvsborg 1979) at the time (Andersen 1975, 1979; Andersen et al. 1981; probably occurred between 13 000 and 15 000 BP. Rasmussen 1981). The evidence from Vanna supports (6) The gradient of the present rate of relative uplift previous indications (Mangerud 1977; Vorren et al. 1978) which, according to reconstructed isobases (Sørensen that the Polar Front had a relatively northerly position et al. 1987) has a general (regional) rate of ca. l and (north of Troms) during the Bølling and Allerød 2 mmjyr at Vanna and Lyngen, respectively. Chronozones. (7) The age and amplitude of the Tapes transgression at Vanna, derived from comparison with localities far ther south in the region (between Tromsø and Lo foten) which have a similar position relative to the Sea-level displacement curves for Lyngen and isobases (H ald & Vorren 1983; Møller 1984, 1987). Vanna An amplitude of 10 m and a starting and ending date of 8500 and 60 00 BP, respectively, are presumed. Construction Sea-level displacement curves have been constructed for Lyngen and Vanna (Fig. 17) based on dated isolation Discussion contacts and other data. The curve for Vanna consists of separate halves (Vannareid and Skipsfjorddal) for which Of the dated isolation contacts, five (Ll, L2 , L5, Sl, Vl) the altitude scale has been mutually adjusted, using the lie dose to expected values and appear to be relatively gradient of the Main shoreline (0 .9 mjkm), in order to reliable. Two dated transitions (L4, S4 ) are dearly too make them broadly comparable. young and represent lacustrine depositional phases. In The curves refer to high-tide leve! (ca. 1.5 m a. mean consistencies appear in two basins (Ll, Vl) where more s.l. ). This corresponds approximately to the water plane than one dating was made, and introduce a small degree at the time of isolation at the basin threshold, and to the of uncertainty; in both cases gyttja dates may be too old approximate altitude of contemporaneous shore terraces. by several hundred years. NORSK GEOLOGISK TIDSSKRIFT 73 (1993) Marine-lacustrine stratigrap hy at Lyngen and Vanna, Troms 195 LEGEND co r--60 Lynge "C j !!]_Main - 14C-dating (±1o-), isolation contact "C .. � s o . horeline , lacustrine ·--- ...... " " - .. , marine (/) ...... " " r--50 40_ Marine . o. . , palaeosol limit ...... _S4 � " " � "C . en .. . <> Undated syngressive sequence Q) .. � . .. . + co .. r--40 · . . c c 30- · ., · Q) c C) co \ > V1 *\? c 3' - \._ L5 r--30 - 20- \. (/) . - L4 . \ (/) co Main · . \ -· E Tapes co shoreline .. \- _ --L3 r---20 ---"··· . 7,.:s -..... _j - 10- . - .:::�� oreline E . Q) . . . - - "C . . .. Q) .. . :::J .. . . . "C - ...... · .. . :::J - . . ···· . ·· r- 10 0- Vannareid/ / . · S - l ··. 1··...._-..:::::::.� Palaeosol - l Skipsfjorddal/ L�� -- �-��-��-��-��-��-���==,r===��==T=I==�, -�,-��-�,-��o 14 13 12 11 10 9 8 7 6 5 4 3 2 1 o 14 B.P. 1000 C-yrs x Fig. 17. Shoreline-displacement curves for Lyngen (Lenangsbotn-Jægervatn) and Vanna (Vannareid-Skipsfjorddal), based on dated isolation contacts in lake basin sediment cores, and other data. The curve refers to high-tide leve l (threshold isolation level). Dashed and continuous parts of the curve indicate relative degree of uncertainty; dotted parts are interpolated or based on regional data. Question marks beside data points for basins V l and LI denote gyttja dates that appear to be too old. The sea-level curves (Fig. 17) indicate a relatively western Norway, where they are interpreted as tsunami rapid pre-Tapes (before 8500 BP) and relatively slow deposits formed about 7000 BP (J. l. Svendsen, J. post-Tapes (after 6000 BP) rate of regression, in accor Mangerud & S. Bondevik pers. comm. 1993; cf. also dance with results from previous work in the region Svendsen & Mangerud 1990). This hypothesis could (Corner 1980; Hald & Vorren 1983; Møller 1984, 1987). provide an alternative interpretation of facies IV sedi Average rates of regression for the two periods are of the ments at Lyngen and negate the need for a transgression order of 15 and 3 mm/yr at Lyngen and lO and 1.5 mm/ to explain the sequences in basins L2 and L3. However, yr at Vanna. Rates obtained using calibrated ages (Table in the absence of evidence supporting the tsunami hypo l) are slightly ( 15%) lower. thesis, it is thought that a transgression best explains the The Tapes transgression appears on both sea-level stratigraphic sequences in basins L2 and L3 and their curves, based on local data at Lyngen and regional data predictable relationship to the Tapes shoreline. at Vanna. At Lyngen, mixed facies IV units occur in The age (ca. 7000 BP) indicated for the postulated basins L2 and L3 at an elevation just below the Tapes TIM at Lyngen is somewhat older than that derived for shoreline. They belong to sequences interpreted as ingres more distal (outer) areas in northern Norway, where an sive and ingressivejsyngressive, respectively, formed dur age close to 6000 BP is relatively well established (Møller ing the Tapes transgression. Comparing the sea level 1984, 1986, 1987; Bergstrøm 1973). The age of the TTM necessary for initial isolation of basin L2 , with the TIM at ioner areas is more uncertain, but appears to be older sea-level as indicated by the Tapes shoreline, indicates a than 6000 BP at two localities where dates have been minimum amplitude of 2-3 m for the Tapes transgres obtained; in northern Nordland and eastern Finnmark, sion at this locality. The age of the TIM peak is esti respectively (Dahl 1968; Donner et al. 1977). These mated at ca. 7000 BP, based on bracketing pre-ingression dates, together with the present date from Lyngen, sug and isolation dates from basin L2, of 7880 ± 100 and gest that the TTM is older in ioner areas than in outer 64 80 ± 90 BP, respectively. areas (cf. Fig. 17). This is in accordance with previous Facies similar to facies IV sediments in basins L2, L3 geometric reconstructions of the Tapes shoreline complex and L4 at Lyngen, have been found in raised basins in in northern Norway as a curved, diachronous feature 196 G. D. Corner & E. Haugane NORSK GEOLOGISK TIDSSKRIFT 73 (1993) (Tanner 1930; Marthinussen 1960) rather than a dorni ( 5) The Tapes transgression maximum is dated to ca. nantly synchronous shoreline (Møller 1987). The evi 7000 BP at Lyngen, based on bracketing dates of dence from Lyngen also suggests that the Tapes 7880 ± 100 and 6480 ± 90 BP from a basin (L2) transgression in Troms reached well inland beyond the lying just below the Tapes shoreline. The evidence 20 m isobase, in accordance with previous indications suggests that the Tapes transgression amplitude was from other parts of northern Norway that it reached the at least 2_:_3 m at Lyngen, that the transgression 25-30 m isobase (Tanner 1930; Donner et al. 1977; extended inland to at least the 25 m isobase, and that Møller 1987). More dates are needed, however, before it peaked earlier in inner areas than in outer areas. the age and geometry of the TTM and Tapes shoreline can be defined precisely. Acknowledgements. - The fieldwork and analyses were carried out in 1981 and The reconstruction of pre-Tapes sea-level change at 1982 as part of E.H's cand. real. thesis. We thank Bjørg Stabell, University of Vanna is rather uncertain on account of the limited Oslo, for teaching one of us (E.H.) the fu ndamentals of diatom analysis and for help with identification. We also thank: Karl-Dag Vorren and Elsebeth Thomsen, number of data points, which include derived ages for University of Tromsø, for identifying plant remains and shell fragment taxa, the marine limit, Main shoreline and Holocene regression respectively: Marit Bernsten, Geir Elvebakk, Geir B. Larssen, Roald Olsen, minimum. The sequence in basin Vl is interpreted as a Hermod and Hilbert Thomassen, and Hans Vasseng for field assistance; Hilkka Falkseth, Frøydis Strand and Liss Olsen for drafting the figures; Gunvor Granaas probable climate-influenced regressive sequence, rather for photographic reproduction; and Bjørg Stabell and John Inge Svendsen for than a transgressive-regressive sequence. A transgression critical review. Radiocarbon dating and calibration was carried out at the at this level also seems unlikely considering the timing of Radiocarbon Dating Laboratory in Trondheim. The work was financed by the University of Tromsø. possible causa) factors such as a glacier readvance (cf. Late Weichselian transgression in western Norway; Anundsen 1978, 1985; Kaland 1984; Krzywinski & Sta Manuscript received March 1993 hell 1984; Svendsen & Mangerud 1987, 1990). For the period before 12 000 BP, following deglaciation, the sea leve) curve for Vanna indicates a relatively low rate of References uplift, in accordance with previous tentative curves con Alm, T. 1990: Late Weichselian vegetation and terrrestrialflacustrine environ structed for the outermost areas (Marthinussen 1962; ments of Andøya, northern Norway - a paleoecological study. Unpublished Andersen 1968; Vorren et al. 1988). thesis, University of Tromsø, 263 pp. Andersen, B. G. 1968: Glacial Geology of western Troms, North Norway. Norges geologiske undersøkelse 256, 1-160. Andersen, B. G. 1975: Glacial geology of northern Nordland, north Norway. Norges geologiske undersøkelse 320, 1-74. Conclusions Andersen, B. G. 1979: The delgaciation of Norway 15 000-10 000 BP. Boreas 8, 79-87. (l) A lithostratigraphic and dia tom study of co res from Andersen, B. G., Bøen F., Nydal, R., Rasmussen, A. & Vallevik, P. N. 1981: raised, postglacial, coastal basins situated between Radiocarbon dates of marginal moraines in Nordland, North Norway. Geo 2.6 m and the marine limit in an inner (Lyngen) and grafiska Annaler 63(A}, 155-160. Anderson, R. Y., Dean, W. E., Bradbury, J. P. & Love, D. 1985: Meromictic outer (Vanna) area of Troms, northern Norway, !akes and varved lake sediments in North America. US Geologica/ Survey provided reliable evidence of sea-level change in 6 Bulletin 1607, 1-19. out of lO cases. Dated isolation contacts range in age Anundsen, K. 1978: Marine transgression in Younger Dryas in Norway. Boreas from ca. 800 to ca. l l 500 14C BP. 7, 49-60. Anundsen, K. 1985: Changes in shore-level and ice-front position in Late (2) Four major facies {l-IV) characteristic of deposi Weichsel and Holocene, southern Norway. Norsk Geografisk Tidsskrift 39, tional environments related to sea-level change are 205-225. distinguished and form the basis for recognizing a Bergstrom, E. 1973: Den prerecente lokalglaciationens utbredningshistoria inom Skanderna. Naturgeografiska institutionen, University of Stockholm. Forsk variety of simple regressive, syngressive-regressive ningsrapport 16, 212 pp. and compound tran sgressive-regressive sequences. Bøyum, A. 1970: Some physical and chemical properties of Jak es in north-eastern The isolation contact is generally placed at the base Norway. Schweizerische Zeitschriftfor Hydrobio/ogie 32, 299-327. Cleve-Euler, A. 1951-55: Die diatomeen von Schweden und Finland. Kung/. of transitional laminated facies Il, interpreted as Svenska Vet. Akad. Hand/. Stockh. 4, ser. 1-5. having formed, in most cases, during a meromictic Corner, G. D. 1978: Deglaciation of Fugløy, Troms, North Norway. Norsk phase of basin evolution following isolation from the Geografisk Tidsskrift 32, 137-142. Corner, G. D. 1980: Preboreal deglaciation chronology and marine limits of the sea. Lyngen-Storfjord area, Troms, North Norway. Boreas 9, 239-249. (3) Climatic fluctuations during the Late Weichselian Dahl, R. 1968: Late-glacial accumulations, drainage and ice recession in the and Early Holocene appear to have influenced the Narvik - Skjomen district, Norway. Norsk Geografisk Tidsskrift 22, 101-165. Donner, J., Eronen, M. & Jungner, H. 1977: The dating of the Holocene relative pattern of deposition in two of the basins (S4 , Vl). sea-leve! changes in Finnmark, North Norway. Norsk Geografisk Tidsskrift 31, (4) Sea-level displacement curves are constructed for 103-128. Lyngen and Vanna, based on radiocarbon-dated iso Fimreite, S. 1980 Vegetasjonshistoriske og paleolimnologiske undersøkelser i Tromsø, Nord-Norge fra Sen Weichsel og Holocen. Unpublished thesis, Uni lationjingression con tacts, a dated palaeosol, and the versity of Tromsø, 179 pp. elevationjestimated age of regionally prominent Florin, M. B. 1982: Light microscopical studies of Cymbella diluviana (Krasske) shorelines. The curves show a rapid (l0-15 mm/yr) Florin. In: Håkansson, H. & Gerlolf, J. (eds.): Diatomaceae Ill. Nova Nedwi gia, 73. pre-Tapes regression (before 8500 BP) and a slow Foged, N. 1978: Diatom analysis. The Archaeo/ogy of Svedbord, Denmark l, ( 1.5-3 mmjyr) post-Tapes regression (after 6000 BP). Odense. NORSK GEOLOGISK TIDSSKRIFT 73 (I993) Marine-lacustrine stratigraphy at Lyngen and Vanna, Troms 197 Foged, N. 1982: Diatoms in Bornholm, Denmark. Bibl. phyco/ogica 59, Cramer, Møller, J. 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