Boreasr8l-Lql
Total Page：16
File Type：pdf, Size：1020Kb
The E,arlyand Middle Weichselian in Norway: a review JAN MANC;tiRUD Mangerud. Jan l9ltl ll01: The Earlyand MiddleWeichsclian in Norxay: a revicw.Borca.r. Vol. t0. nn. BOREASr8l-lql. C)rlrr.ISSN 0100-q4X-1 All knonn 'non sites with lirssilsand till sediments of possibleEarl1, and Midtile Wcichselr.rnage rn Nlrrual'', are dircusscd. Along the $e\t coasr there are many sitcs *ith nrarincshells which have oeen drted b! nreans rtl- radiocarbon. amino acids and thorium/uranium methods. Somc sitcs are itlso correlatedby meansof undcrl-vingEcmian :cquenccs.A tentativeglaciation curvc fgr $cstern N()ru.a! indicalcs a first glaci:rladvance soon alier thc end of the Ecmian. There are indications oi another '10.000 rc-adl:rnce around 8.P.. and the Late Wcichselianmaxrmum {ntaxrma.,)occurred somewhcre 10.(X)0 bct*een B.t'. and 1.1.000B.P. Partsofthc coast mitJ,have been ice free for most ofthc rctrlarnrng pcrlods. Fronl thc central parts ofthe countr-vare known bones (c.g. mammoth). glaciolacusrrrneano lluvial scdiments.peat. ctc. Thc netl.v discovcred site with peat at Brumunddal can ver_vprobably'be corrclated trith thc Jamtland Interstadialin Swedcn. and the Brorup Intcrstadialin t)enmark. Ifrhis is corrcct. nelrl! the u'hole of southernScandinavia must have been dcglaciatedduring that interstadial. ql .lttrr 'llunqcnrd. oeril.gi:k instirutt. u\'(1.B, Attigt. l;-50H Bt,rgen Llnit,trsitcr. Norr.ar.; No\.(,nlb(r. An increasingnumber of sites with fbssils or stratigraphicalunits. 'non-till is used simply for a period sediments'of possibleor probableEarly (except interglacials)when the described site and Middle Weichselian age have been found in was ice-fiee. -l'hese Norway in recent years. sites are impor- tant piecesin the complicatedpuzzle to establish the Weichselian stratigraphy and glacial history of Norway. which is gcnerallyassumed to have Northern Norway provided the nucleus from which ice sheets spreadover Europe. The Tromsl rcgiotl In this review I have tried to compile all the Vorren (1979)described a shellytill from Kval- known sites with possible Early or Middle sundet(nearly 70'N) with a radiocarbondate of Weichseliannon-till sedimentsand fossilsfronr (T-2177) 40.700 lillili e p. He interpreted rhe the Norwegian mainland (sites tiom Svalbard molluscsand foraminiferaas indicatinglow arctic and the continental shelf are not discussed). conditions.but later (Vorren e1al. l98l) con- Refcrencesto the original descriptionsare given. cluded that the fbssils representedmixed faunas and my current opinion of their age. In the final of different ages. section some conclusictnsand correlationsare At Slettaelva.some l0 km from Kvalsundet. given. The locationof sites(Fig. l)to a consider- Vorren et al. (1981)described a similarfossilifer- ablc extent reflectsareas which have been in- ous till. The radiocarbon dating gave 41,900 vestigatcd by Quaternary stratigraphersduring 1jllill o.. with two srandarcldeviations. >38.000 the last decade.Pre-Late Weichselian sediments. B.P. The species.especially of the foraminif-era, are therefore certainll, much more liequent than and the amino acid D/L ratios. strongly suggest apparentfrom Fig. l. that lbssils of different ages arc incorporated in Stratigraphical nomenclature follows that ol' the till. Below the till there is a laminated (1974) Mangerud et al. except for rhe Middle/ lacustrineclay. and beneath that another till. Late Weichselianboundary. which is placedat Vorren et al. assume that the lower till was (Mangerud c.2,5.000 vears B.P. & Berglund depositedby a local glacier during the Early 1978).as recommendedby the Subcommission Weichselian.which disappearedbefbre thc de- for European Quaternary Stratigraphy (Chaline position of the laminatedclay. Later the area 'interstadial'. et al. 19t30).In Norwav the term was covered by a continental ice sheet which both informally and formally in defined climato- eroded Eemian and Early Weichselian marine 382 Jun Mungerud BOREASl0 0981) p 34,330 I iliil B (T-2670). With the sparse in_ formation available, it is difficult to evaluate whether this date reflects the true age or a mini- mum age. o' Foildat ! . '%c,Ernbu B, Western \ Norway "-&-%' , Sunnm0re u*sdi:.jq ta. n-Q -. 1 n^: nn, In the Alesund (Fig. " aD! area l) there are many --lbr Ftang 2 "f,4)"' \. localities with fossil-bearing tills which Man_ o..Blrulddrl / et al. (1979, !,q irvrlvual Serud I98lb) assumed to be the \ A . t\ same as Rogne Till (Fig. a vossestrand i.. \. \.i 2). Fifleen radiocarbon rand '; \* -trvos '\" datings on shell fragments from these sites all !. 1 gave agesbetween 'r. I 28,000and 38,000years B.p. HApDA\(rFo o4 ,-"""*1 \ A Middle Weichselian o o, de1^f Y / age is independentlysug_ 'o gested VIDDA._ by amino acid D/L ratios in shells.The ice o iio/nes free period s is named the Alesund Interstadial. and the fauna suggestsarctic conditions with the o\vl\ Atlantic water possibly I present during the war_ mest period. So far, no undisturbed sequencesbelow till have been found. Possiblythe radiocarbondates should only be regarded as minimum ages, t although Sedimentswirh marine sheits Mangerud et al. (l98lb) give several a Peat,soiLg organic sediment, woo., argumentswhy . Mammolh remarns they could reflect the true ase. o Otkr bones, and anliers tr Slrairlied m nerogenrc sedimenls, w lhoulh tossrLsor wr Inner Socn Fig. l. A map of southern possible Norway with Earlv and Vorren (1972) described glaciotectonically dis- Middle Weichsclian sites indrcaled. The di.cu.sed rite: irr (Tromsd turbed laminated silts in a core from Kroken northern Norway and Glomfiord) are north of the in maD area. Inner Sogn (Fig. l). There are redeposited in_ terglacial,probably Eemian, pollen grains in the sediments.The other pollen spectrafrom the silt suggesta birch-herb vegetation. If the interela_ sediments,and deposited the shelly tills at both cial pollen really is of Eemian age. the silr m;st Kvalsundet and Slettaerva. be of Early or Middle Weichselian ase. as con_ The mixed faunas indicate, as concluded bv cluded by Vorren: any closer dating iiat present Vorren. that the radiocarbon dates at both site.s impossible. did not reflect the true ages.However. if there is no contamination of even younger carbon, the Vos.r youngest shell population must be of Middle Weichselian age, probably some few thousanc Mangerud & Skreden (1972) described a se_ years younger than suggestedby the dates. quence with a sandbed (the Lundarvatn Sand)at the base, overlain successivelyby a lower till, Glom.fjord stratified sand. silt and clay (the Voss Clav and Siltt. and an upper till becl. Wedge structures At AmOy and Vassdal in the western part of penetratingthe three lower units were originallv Clomljord. Nortlland lc. 66.50,N1, Rasmussen interpreted as ice-wedge casts, but are relcentlv (1979)has described tills with small il-20 mm) re-interpretedto be injectedclastic dikes (Man_ shell fragments. of which Myu trun(.uto and gerud et al. l98la). Very few pollen were found Balanus sp. are identified. A radiocarbon datins in the sediments,and no dates obtained.Man_ on shellfragments from the Vassdal sectioneave gerud & Skreden therefore discussed some BOREAS l0 (l981) Early and Middle Weichselian in Norwav 383 SUNNMORE SANDN ES KARMOY r0000 AL \A Rogne AI Stovonger flo ugesu \A AI nd TilI AI Dio mic ton \A Diomicton E AI -o t/L j:;+le"Austrdtt )3' A tc Iesund coo Sond t: Hioius? In tersiod io I lo GonnCloy c 50000 Nygoord Grovel ooo ooo \ -? ooo FJOSANGER Till D Kormpy k'' Siodio I VOSSE- BOnesTill STRAND Eikelund ooo Fono Inierstodio + Gulstein looo noP - ooo oo ooo Fipsongerion .9.c. (in terg lo c io I) too Stoge LEGEND TitI GroveI Sond Siit C loy Fig. 2. A correlation of some sequencesfrom western Norway. References:Sunnmpre-Mangerud et al. 0981b), Vossestrand- (in Sindre & Eide prep.), Sandnes-Anderseneral.0981). Fjgsanger_Mangeruderal.0981a), Karm/y_Andersen etal.098t): from the Nygaard Gravel and upwards the Nygaard section, below the Nygaard Gravel the B/ II section, thejoint ofthe two sections being uncertain. The names refer partly to lithostratigraphical, and partly to climato- or chronostratigraphical units. alternative ages based on the lithostratigraphy. and the peat. In the middle part of the pollen The lower till bed was correlated with the oldest diagram from the peat, Pi(ea (spruce) consti- glacial striae in the area by means of fabric tutes approximately 70% of the pollen. The analysis. These striae were supposed to be of closed forest at this latitude (nearly 6l"N) and Late Weichselian age, or older, so the Lundar- altitude (320m above sealevel) strongly suggests vatn Sand is of Middle Weichselianor older age. a correlation with an interglacial, and not an The Voss Clay and Silt may be of Allerpd (ca. interstadial; and the Late Eemian is clearly the l1,000 B.P.) or Middle Weichselianage, or old- most likely alternative, as concluded by Sindre & Eide. Above the peat there is 3 m laminated silt. with Vosse.strand a demonstrable hiatus at the boundary between the two beds. The topographical situa- Sindre ( 1979) and Sindre & Eide (in prep.) tion indicatesthat the silt must have been deoo- describeda sequenceat Vossestrand(Figs. I and sited in an ice-dammecllake. and since many 2) with a till or a till-like sediment at the base. pieces of peat and wood have been found in the overlain by a two cm thick, highly compacted silt, this lake was probably dammed by the very peat. Sindre assumesan hiatus between the tilt first glacier approachingthe site. BOREASl0 ( 1981) 384 Jttn Mangerud Above the silt follows a basal till of unknown ice-covered, based on the difference in and age, and the top sedimentsdeposited during the epimerizationbetween Fj@sangersite shells deglaciationin EarlY Holocene. 12,000years B.P. They concluded that Fi@san- ger was ice-covered less than 50% of the time, and thus that the coast of western Norway FjQsanger remained unglaciated throughout much of the At Fjgsanger(Fig.