The last interglacial-glacial period on spitsbergen, Svalbard

Quaternary Science Reviews, Vol. l 1, pp. 633-664, 1992.

0277-3791/92 $15.00 © 1992 Pergamon Press Ltd

Printed in Great Britain. All rights reserved.

THE LAST INTERGLACIAL-GLACIAL

PERIOD ON SPITSBERGEN,

SVALBARD

Jan M a n g e r u d and John Inge Svendsen* University of Bergen, Department of Geology, Section B, Allegt. 41, N-5007 Bergen, Norway

The glaciation history of Svalbard (78°N) and the NW Barents Sea is reconstructed for the last 130 ka, based on studies of sediments exposed in coastal cliffs at the head of Isfjorden. Four different till beds separated by marine sediments are recognized. The lowest marine formation, containing Mytilus edulis, reflects warmer conditions than at present, and is correlated with the last interglacial, the Eemian of Europe and Oxygen Isotope Substage 5e in the deep sea. The post-Eemian tills are inferred to represent major glaciations around 110 ka BP, 75-50 ka BP, and 25-10 ka BP. During the intervening intervals the glaciers on Svalbard were not significantly larger than at present and the NW Barents Sea was probably ice-free. The ice-free periods, named Phantomodden and Kapp Ekholm interstadials, lasted from about 110 to 75 and from 50 to 25 ka BP respectively. The marine fauna from both these interstadials indicate seasonally ice free conditions. The ages of the recorded glaciations coincide with, or are slightly younger than, periods with insolation minima, which at this latitude is determined by a low tilt of the Earth's axis. Thus we postulate that the Quaternary glaciations of Svalbard were driven by orbital variations with the 41 ka tilt period, in contrast to the lower-latitude glaciations of Scandinavia that were partly driven by the precession cycle with a periodicity of around 23 ka.

INTRODUCTION Svalbard, reaching more than 80°N, is the northernmost land along the eastern seaboard of the North Atlantic Ocean (Fig. 1). During the Quaternary, Svalbard and the shallow Barents Sea were repeatedly covered by one of the northernmost ice sheets on earth (Denton and Hughes, 1981). Approximately 60% of the land area is currently covered by glaciers (Fig. 2). The Svalbard archipelago presently-experiences an anomalously mild climate compared to its latitude, due to northward heat transport of the Atlantic Current (Fig. 1). The growth and decay of the great Quaternary ice sheets were forced by perturbations of the Earth's orbital parameters (Berger et al., 1984). This astronomical - - or Milankovitch - - forcing varies strongly with latitude. Thus the glacial history of Svalbard, situated at such a high latitude, will be an important element in the interpretation of the Earth's response to the external forcing. The main purpose of the investigation presented in this paper was to study the glacial history of the last interglacial-glacial (Eemian-Weichselian) cycle on Svalbard. We present results from stratigraphical studies of coastal cliffs along Billefjorden, an inner branch of Isfjorden, which cut into the central part of the main island, Spitsbergen (Fig. 2). The main locality consists of a series of profiles at Kapp Ekholm, but some additional observations from Nidedalen are also presented (Fig. 3). Kapp Ekholm is the only known section in the central part of the Svalbard archipelago that has several till beds interlayered with marine sediment. *Present address: University of Bergen, Centre for Studies of Environment and Resources, HiB-ThormChlensgt. 55, N-5020 Bergen, Norway.

This section is located only 14 km from the fjord head, which is occupied by the large tide water glacier Nordenski61dbreen. This implies that during periods when Kapp Ekholm was ice free, glaciers on Spitsbergen were not much larger than at present. Indirectly, the site has also monitored major glaciations of the NW Barents Sea by means of high relative sea levels during degiaciation phases, due to the glacio-isostatic depression of the archipelago. Kapp Ekholm is therefore a key site in identifying periods when central Svalbard and the Barents Sea were deglaciated. The Kapp Ekholm section has been described previously by Lavrushin (1967, 1969), Boulton and Rhodes (1974), Boulton (1979) and Troitsky et al. (1979). Mangerud and Salvigsen (1984) pointed out that some of the earlier descriptions and dates from this section are inconsistent. In order to clarify these conflicting observations a more detailed description of the lithostratigraphy along the entire exposure is presented in this study. This reinvestigation leads us to significant new interpretations of the site. Several other sites with sediments of EemianWeichselian age have been described from Svalbard (Boulton, 1979; Troitsky et al., 1979; Miller et al., 1989; L0nne and Mangerud, 1991; Lindner and Marks, 1991; Mangerud et al., 1992; Landvik et al., 1992). It has been a common view that only one large glacial advance occurred during the Weichselian. For example, Miller et al. (1989) and Larsen et al. (1992) concluded that only one glaciation, dated to > 80 ka BP, reached the shelf off western Svalbard after the Eemian. Recently, however, Mangerud et al. (1992) and Svendsen et al. (1992) have demonstrated that an ice sheet also extended seaward of Svalbard during the Late Weichselian. A major problem associated with Quaternary studies in the high Arctic environments of Svalbard is

633

634

1. Mangerud and J.I. Svendscn

•

;~-.L~eenal nd__~,_~ -

/

~",.. Norwegian~a /

\

~

,Biernoya Barents / Sea

(J/

//

o

'3

co S

.~

FIG. 1. An oblique north polar map projection, showing the high latitude location of Svalbard. The two main surface currents flowing in and out of the Norwegian Sea are schematically shown. The minimum sea-ice extent (September) based on a 75% concentration limit is shaded (Hibler, 1989).

that there is no well-suited method available for accurate correlation or age assessment of sediments older than the range (40-50 ka) of radiocarbon dating. This implies that reconstructing the glacial history for the pre-Late Weichselian period by combining several localities is problematic. The advantage of the Kapp Ekholm section is that more Weichselian depositional events occur in stratigraphic superposition than at any other known site on Svalbard (Fig. 6). Thus a more or less complete glacial history for the Weichselian can be reconstructed from this single site (Fig. 22). METHOD

Location and Surveying of the Sections The Kapp Ekholm sections are situated in the bay between Kapp Ekholm and Phantomodden in Billefjorden, 1 km south of the present delta from Mathisondalen (Figs 3 and 4). The sediments are exposed in up to 30 m high coastal cliffs which are dissected by broad gullies, leaving a series of isolated sections. The studied sections are numbered I to VI from south to north (Fig. 5). We measured horizontal distances along the foot of the sections with a tape measure (Figs 4 and 5). Most observations are referred to the nearest 10 m.

For elevations we used the approximate mean tide level as the zero point. The top of the present day beach is around 1.5 m above our reference level along the sections. Among the different exposures at Kapp Ekholm, Section II was studied in most detail. This section was levelled and marked every 5 m in the outcrop. Vertical distances between marks were measured with a ruler. The other sections were less precisely measured, but in all sections at least a few points were levelled. Heights above the present sea level marked on the photos (Figs 9, 12, 13 and 14) were all levelled. Errors for elevations given in the text are in most cases less than 1 m. The Kapp Ekholm sections were investigated for five weeks during the summer of 1988. Only two days were spent studying the section at Nidedalen (Figs 3 and 19).

Radiocarbon Dating Samples were dated at two laboratories. At the Trondheim Laboratory for Radiological Dating (prefix T- on samples) dating is performed by proportional counting, using CO2 gas, under the supervision of R. Nydal and S. Gulliksen. Small samples were submitted to the T. Swedberg Laboratory, Uppsala University (prefix Ua-), for accelerator mass spectrometry (AMS) dating, supervised by G. Possnert. For samples with

635

Interglacial-Glacial Period on Spitsbergen 9*

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FIG. 2. Map of Svalbard. Glaciers are white, ice free land areas are shaded. Contour lines show the equilibrium line altitude on present day glaciers, according to O. Liest¢l (cited from Kristiansen and Sollid, 1987). Figure 3 is shown by the box near the head of Isfjorden.

prefix TUa- the target was prepared in Trondheim, and the AMS measurements performed in Uppsala. All finite samples are reported as recommended by Stuiver and Polach (1977), including a correction for isotopic fractionation to - 2 5 %0 6~3C on the PDB scale (Tables 1-4), A reservoir age of 440 years is subtracted for all samples that have obtained their carbon from sea water (shells, seaweed, whalebones, etc.). This is a standardized value used by the Trondheim laboratory for the coasts of Norway including Svalbard, and is based on measurements of many preindustrial shells from these waters (Mangerud and Gulliksen, 1975). For samples with activity close to the background radiation ('non-finite old' samples) we have given some more details (as recommended by Stuiver and Polach, 1977) in order to evaluate which of the dates are finite (Tables 2 and 3). Generally, samples that are of nonfinite age on the two standard deviation criteria should be cited as such.

Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) Dating All samples are dated by V. Mejdahl at the Nordic Laboratory for Luminescence Dating, Ris~, Denmark, using sand sized feldspars (Mejdahl, 1985, 1986). The ages for TL dates are calculated by using the plateau method (Mejdahl, 1988), and assuming a water content of 14% (given as weight of water relative to weight of minerogenic matter). This was found to be a mean water content of the samples when saturated with water. As indicated for some of the samples (Table 5), the TL age would be considerably higher if one postulated that they had been completely zeroed (bleached) during deposition. Thus, the age assessments are entirely dependent of the validity of the plateau method. As mentioned above, The Nordic Laboratory use the sand fraction method, whereas Forman and Ennis (1992) in their methodological study of TL dating of sediments from Svalbard used the finegrained technique. The OSL dating (Aitken, 1992)

636

J. Mangerud and J.l. Svendsen

17°E

Pyramiden

Section

Kapp sectic ~ 0

1

Phantomodden 2

3

4

5km

FIG. 3. The inner part of Billefjorden (from map sheet Bille]}orden 1 : 100 000, Norsk Polarinstitutt, Oslo, 1984). Contour intervals are 50 m, with an additional contour at 25 m a.s.l. Glaciers are shown in white. Pyramiden is a Russian coal-mining town. The location of the sections south of Kapp Ekholm and the section near Nidedalen are marked.

followed the procedures given by B~tter-Jensen et al. (1991). We collected samples for TL and OSL dating from sand lenses or sand matrix from gravel foresets. It was assumed that these sand grains had been washed back and forth on the beach, and therefore bleached by daylight, before they were deposited in the foresets. We postulated that these grains had been exposed to light for longer periods than sand particles in the sand or silt formations. However, two OSL dates from the present beach yielded ages of some few thousand years (Table 5), and two out of three Early Holocene samples yielded OSL ages that were a few thousand years too old. This shows that the collected sediments at Kapp Ekholm are not ideal for T L or OSL dating. Individual dates on samples from the same formation may vary by more than 50 ka. We therefore obtained several dates from each formation (Table 5), and, when assessing the age, outliers were omitted. For example, for Formation F six samples yielded ages between 38 + 5 and 59 _+ 3 whereas two samples that yielded ages of 104 and 80 ka were disregarded. Amino Acid Diagenesis Amino acid diagenesis measured in the protein matrix of molluscs (Miller and Brigham-Grette, 1989) was used for three purposes: (1) To correlate between

individual sections. (2) For estimating the duration of glacial ice cover and/or inundation of the site by the sea. (3) For a first order age estimate of samples of nonfinite radiocarbon age. All samples were analyzed at the Bergen laboratory (prefix BAL-) under the supervision of H. P. Sejrup, according to methods described by Miller and Mangerud (1986). In this paper we mainly use the epimerization of isoleucine to alloisoleucine for the total fraction, expressed as D/L ratios (by some labelled aIle/ lie); the D/L ratios measured for the free fraction are also given for most samples (Tables 6-11). All reported D/L ratios are from the species Mya truncata or Hiatella arctica, which have approximately similar epimerization rates (Miller, 1982). However, recently it was found that the epimerization for Mya is around 15% slower than for Hiatella in the initial phases (D/L for total fraction < 0.1) (D. Kaufmann and G. H. Miller, oral commun., 1991). This slightly different reaction rate is compatible with the ratios we obtained for the two species from samples of the same age. For paleotemperature estimates we have used a D/L ratio of 0.011 for living shells, and the Arrhenius parameters 28.1 kcal/mol for the activation energy and 16.45 for the intercept (Miller, 1985). It should be noted that the epimerization reaction is extremely slow in this cold arctic environment, and the resolution is

Interglacial-Glacial Period on Spitsbergen

637

FIG. 4. Vertical air photo of the study area at Kapp Ekholm. The individual sections are marked with roman numerals. The horizontal distances along the shore are given in metres, compare with Fig. 5. To the north-east of the sections are Holocene terraces, up to 90 m a.s.l. Strike and dip, that indicate they were deposited by long-shore drift, are shown for foresets in some of these terraces. The ornamented lines show karst depressions that are younger than the terraces (Salvigsen et al., 1983). The present fan-delta deposited by the river from Mathisondalen is seen to the north of the hut. Photo: Norsk Polarinstitutt $61 2958 (August, 1961).

therefore low in both estimates.

age and

paleotemperature

S E D I M E N T FACIES The entire section at K a p p E k h o l m consists of a few sediment facies in a typical deglaciation sequence: tillmarine silt-sand-gravel. This sequence is stratigraphically repeated (Fig. 6).

Grey Diamicton (Till) These are massive grey diamictons which occur as sheet formed sediment bodies, normally 0.5-3 m thick. The lower contact of each diamicton is an erosional unconformity. The diamictons are matrix supported, non-sorted, and characterized by a high content of stones and boulders of different sizes. In contrast to the other facies present in the sections, glacially striated stones are c o m m o n . A few abraded shell fragments occur occasionally. The diamictons are compacted, and in most sections they protrude as low vertical cliffs from the m o r e gentle slopes of sediments at the angle of repose. All the grey diamicton facies look similar, except for varying amounts of inclusions of underlying sediments. We a t t e m p t e d to distinguish the different diamictons by silt, clay and carbonate content of their matrix, but without success. The CaCO3 content is very high (around 70%) in all of the diamicton units,

indicating that the local Permian limestones are the main source. These greyish diamictons are all confidently interpreted and referred to as basal tills. We are in full a g r e e m e n t with Lavrushin (1967, 1969) and Boulton (1979) on this interpretation.

Brown Diamicton On top of the grey tills at some sites, lenses, or a thin sheet (less than 30 cm) of a silty, reddish brown diamicton occurs. The texture varies along the sections. In the field descriptions we did not normally distinguish between this diamicton and a reddish brown silt that occurs at the same stratigraphic level. They were both registered as a reddish brown, transitional zone between the grey till and the grey silt above. The colour is caused by red sandstones. The brown diamicton was not studied in detail, and the genesis is not clear. At some stratigraphic levels it may form the uppermost part of the grey till, but in most levels it probably represents the base of the marine sediments. Silt This facies is c o m m o n l y massive, but in a few instances it is laminated in the lower part, just above the tills. It contains varying amounts of clay and sand, generally it becomes m o r e coarse grained upwards. Some stones of varying sizes occur, often covered by a crust of marine carbonate algae. Paired molluscs,

FIG. 5. Mosaic photo of the Kapp Ekholm sections. The valley to the left is Mathiesondalen, compare with Figs 3 and 4. Section numbers and horizontal scale (m)~ as employed in the text, are also shown on the photo.

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Interglacial-Glacial Period on Spitsbergen

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FIG. 6. Composite stratigraphy of the Kapp Ekholm sections. The thickness of formations A and B are measured in Section II, Formations C, D and E in Section IV, Formations F and G in Section V, and Formation H in Section VI. Each of the coarsening upward sequences are marked with a wedge-like symbol to the fight in the lithological column. The radiocarbon dates are given in Tables 1-3. Within each formation the dates are plotted from the oldest to the youngest obtained age. For the Holocene only some radiocarbon dates from the base of the formation are included. The TL and OSL dates are given in Table 5, and the amino acid D/L ratios in Tables 6-9. Horizontal lines between TL and OSL dates indicate that the ages were obtained from the same sample.

sometimes in living positions, and also other fossils, demonstrate a marine origin. As mentioned above, the lower part of the silt is characterized by a reddish brown colour, contrasting to the more dull greyish colour of the rest. The silt beds are generally less than 0.5 m thick and grade into sand facies upward.

blocks occur sporadically. Paired molluscs, sometimes in living positions, and also other marine fossils are more common in the sand than in the silt facies. The sand facies is interpreted as having been deposited in a marine environment, below the wave base.

Sand This facies consists of sand, generally fine in the lower part and coarse in the upper. The sand is nearly massive. However, a crude bedding occurs. Stones and

Marine Diamicton This term is here used to distinguish a sediment that consists of nearly equal amounts of sand and silt/clay, with frequent (rounded) stones. A crude, nearly horizontal bedding is visible. It contains numerous

640

1. Mangerud and J.l. Svendscn T A B L E 1. Radiocarbon dates from Formation H (Holocene) at Kapp Ekholm

Lab. No.

Age

Material

Locality

Field sample No. and description

Ua-972

1l.(15(t _+ 15(1

Shells

I, 110

Svalbard 1988-696. Onc shell fragment from the base of a 21) cm thick reddish brown silt overlying till. The sample was collected just above sample -695 described below. Sample TUa-69, -70, -71, and -72 were subsequently dated to test if the age of Ua-972 could be reproduced

"FUa-70

97311 _+ 1811

Shells

I, 1 1 1 )

Svalbard 1988-695b. One shell fragment from a less than one cm thick sand layer beneath stones along the boundary between the underlying till an the reddish brown silt, described above

TUa-69

37,400 _+ 16011

Shells

I, 1 1 1 )

Svalbard The date has been 2500 ka

1988-695a. A thick fragment from the same sample collection a TUa-70. shows that this fragment has been redeposited from older beds. The age calculated on the basis that non-finite old calcite yields an age of 42 _% BP with the same chemical preparation

TUa-71

94711 +_ 1411

Shells

1, 110

Svalbard 1988-697. One gastropod from exactly the same site as sample -696

1"-8322

9730 _+ 120

Shells

1, 130

Svalbard 1988-235. Paired Hiatella arctica in sorted sand, 5 cm above a 10-20 cm thick bed of reddish brown silt

T-8330

98111 +__ 70

Shells

I, 160

Svalbard 1988-698. Balanus balanus sitting on a boulder in a 10 cm thick lens ol reddish brown silt at the transition between thc (interglacial) gravel lk)resets anti the Holocene sand above

T-8319

96911 _+ 711

Shells

11, 2811

Svalbard 1988-78. Three paired Hiatella arctica from the transition between a brownish silt and overlying fine sand. Sample collected less than 10 cm above a bed of angular pebbles that are thought to be the base of the Holocene at this locality

'1'-8335

89311 _+ 711

Shells

II, 300

Svalbard t988-733. Paired Mytillus edulis from the lower part of the Holocenc gravel

T-8323

8740 _+ 100

Shells

IV, 5 5 t )

Svalbard, 1988-317. One large Mya truncata from a boulder bed. This bed is interpreted as an erosional lag at the base of the Holocene

T-8333

8610 _+ 120

Shell

IV, 550

Svalbard 1988-323. One whole, large shell of Zirphea crispata, lound on tile surfacc of slumped material

Ua-974

9910 +_ 130

Shells

V, 650

Svalbard 1988-447. One Lepeta from a laminated silt with reddish and greyish laminae, at the base of the Holocene sequence

T-8326

8560 _+ 60

Shells

V, 7411

Svalbard 1988-438. Onc large paired Mya truncala from the base o1 thc Holocene. The underlying till is missing at this site

TUa-72

9760 +_ 140

Shells

VI, 870

Svalbard 1988-758. Overlying tile youngest till is 20-30 cm reddish brown silt. Small Lepeta from the base of the silt

T-5666

9531/ +_ 110

Shells

V1, 8711

Sa 81-08. Paired Mya lruncuta from the basc ol the sand above the reddish brown silt described under sample 1988-758. This sample was collected by Salvigsen and Mangerud in 1981, but can easily be plotted into the section measured in 1988

I"-8534

908(] _+ 110

Shells

VI, 8911

Svalbard 1988-522. Two large Mya truncata in living position, from a zone rich in large Mw~, 1.5 m above the till

In "Fables 1-3, the roman numbers in the column 'Locality" relcr to the section number, and arabic numbers give metres along the horizontal scale (Fig. 7). Samples are listed from south towards north along the section.

molluscs in living positions, and it is undoubtedly of marine origin. This diamicton facies occurs only in (the interglacial) Formation B, where it forms a thick unit between the sand and gravel in the coarsening upward sequence. Gravel In general this facies consists of clast supported, rounded gravel in steeply inclined (15-25 °) foresets. The exception is Formation F where the gravels partly occur as large lenses with glaciotectonic boundaries to sand and silt. Shells and seaweed occur sporadically; most often within sand lenses between the gravel foresets. In some sections the foresets interfinger with the underlying sand and silt, showing that the gravel represents prograding sequences. Facies Relations and Interpretations Most of the sections of Kapp Ekholm are wave cut

cliffs parallel to the shore (Fig. 7). The most complete cross section occurs along the gully at 500 m (Fig. 8). The top of the sections consists of a Holocene beach terrace which is nearly horizontal in cross section. The underlying bedrock surface is part of the valley side that slopes towards the sea, and therefore the entire deposit is wedge-shaped in cross section (Fig. 8). The vertical succession of the facies is similar in most of the sections and stratigraphic levels (Fig. 6). The tills (grey diamicton) are overlain by brown diamicton or silt, followed by grey silt which grades into sand. Alternating beds of silt and sand were also found, and in Formation B the marine diamicton takes the place of the sand. The sands interfinger with the overlying gravel foresets. This succession of sediment facies, starting with till and followed by marine mud, sand and gravel is typical for emerged sequences on Svalbard (Boulton, 1979, 1990; Miller, 1984). The first order interpretation is simple: Each glaciation was succeeded

Interglacial-Glacial Period on Spitsbergen

641

TABLE 2. Radiocarbon dates from Formation F, at Kapp Ekholm Lab. No.

, Age

+ 1o

+ 2 o

Material

Locality

Field sample No. and description

T-8320

45,900

+2400 -1900

+5900 -3400

Shells

I[, 280

Svalbard 1988-86, -87, -88, -89, and -90. Five paired Mya truncata from gravel, collected less than 10 cm from each other and 160 cm below the boundary to the post-glacial sediments

Ua-975

37,000

+2000

Shells

II, 280

Svalbard 1988-18. One paired Hiatella arctica from massive sandy gravel, 1 m below boundary to Holocene sediments

Ua-973

17,700

_+300

Shells

IV, 530

Svalbard 1988-309. One Mya truncata from deformed gravel (Mangerud and Svendsen 1990). See further comments under next datings

Ua-1174

> 40,000

Shells

IV, 530

Redating of the same individual as Ua-973, because of the surprisingly young age. Inner 50% of 'thick' fragment was dated

Ua-1175 T-8433

> 40,000 > 29,400

Shells Shells

IV, 530 IV, 530

As Ua-l174. Inner 50% of thinner fragment. Sameindividual as Ua-973. The reason why it gave lower nonfinite age than other samples from Trondheim is that it was measured in a very small counter. With these redatings we conclude that sample Ua-973 was contaminated during preparation, and that the real age is > 40 ka

T-8324

51,400

+6610 -3560

> 45,400 Shells

IV, 570

Svalbard 1988-325, -328, -329, -331, -332, and -335. Six paired Mya truncata from silty sand, all collected less than 50 cm above a till

T-8325

45,000

IV, 570

44,000

+7500 -3800 +5400 -3200

Shell

T-8318

+2900 -2100 +2300 -1800

Whalebone

IV, 580

Svalbard 1988-360. Several individuals of Serripes grenlandica from fine sand, 2 m above sample 1988-325 Svalbard 1988-252. Large bone of Greenland whale (Balena mysticetus) from just beneath the boundary to Holocene sediments. Approximately same level as sample 1988-360, but there occur glaciotectonic thrustplanes between them

T-8331

48,100

+4200 -2700

Shell

V, 650

TUa-63

36,500

+1800 -1500 +1800

Seaweed

V, 650

T-8327

42,000

+1900 -1500

+4400 -2800

Shell

V, 730

T-8533

46,100

+3200 -2300

+8700 -4080

Shell

VI, 870

by m a r i n e i n c u r s i o n following glacial retreat. D u e to glacio-isostatic r e b o u n d , which causes a falling relative sea level, each m a r i n e f o r m a t i o n is c o m p o s e d of a coarsening upwards sediment sequence, grading from silt to gravel. T h u s , each s e q u e n c e of t i l l - s i l t - s a n d gravel r e p r e s e n t s a m a j o r glacial cycle. C o n t i n u o u s m a p p i n g of the u n i t s is i m p o s s i b l e b e c a u s e of the gully incision b e t w e e n the sections (Fig. 7) a n d the stratigraphic r e p e t i t i v e n e s s of similar sedim e n t a r y facies m a k e s it difficult to c o r r e l a t e b e t w e e n the i n d i v i d u a l sections. I n S e c t i o n I V (Fig. 7) s e d i m e n t facies f r o m f o u r d i f f e r e n t glacial cycles o c c u r in s u p e r p o s i t i o n , which a c c o r d i n g to o u r lateral correlations is the total n u m b e r of cycles p r e s e n t (Fig. 6). H o w e v e r , r e m n a n t s of e v e n o l d e r m a r i n e s e d i m e n t s occur as a n i n c l u s i o n (lens) in the l o w e r till (Fig. 6).

STRATIGRAPHY I n this s e c t i o n we focus o n the lithostratigraphic

Svalbard 1988-716, -717, and -718. Three paired Mya truncata in a recumbent fold of sand Svaibard 1988-724, -725. From the same beds as 1988-716, etc. This sample was first burned for conventional dating. When it turned out to be too small it was precipitated as CaCo3 and prepared as a target for AMS-dating. Thus it has been through a long preparation process, and contamination might be expected Svalbard 1988-471, -472, -473, -474, -475,-476, -459, -460. All samples are paired Mya truncata in gravel directly beneath the upper till Svalbard 1988-240, -245, -247, -249. Hiatella arctica: two individuals were paired, the other two were halfs. Beneath the till is 2 m of gravel. The specimens were collected in sand, 1-1.5 m below the gravel

d e s c r i p t i o n s of the s t u d i e d sections at K a p p E k h o l m , b u t o b s e r v a t i o n s of fossils are also i n c l u d e d . W e have s u b - d i v i d e d the e n t i r e s e q u e n c e into i n f o r m a l lithostratigraphic f o r m a t i o n s d e s i g n a t e d with letters, starting with A at the base a n d e n d i n g with H for the H o l o c e n e (Figs 6 a n d 7). W e use the s a m e letter for each f o r m a t i o n in all sections, a s s u m i n g that o u r c o r r e l a t i o n s b e t w e e n the sections are correct. H o w e v e r , a f o r m a t i o n in a single s e c t i o n m a y be identified as a s e p a r a t e u n i t by c o m b i n i n g the section n u m b e r a n d the f o r m a t i o n letter; for e x a m p l e F o r m a t i o n I - B a n d F o r m a t i o n I V - B ( T a b l e s 1-9). T h e s e d i m e n t facies described a b o v e ate used to d e f i n e the lithostratigraphic units. W e have labelled each of the grey tills as a f o r m a t i o n (Fig. 6), most o f t e n r e f e r r e d to as till A , till C, etc. E a c h c o a r s e n i n g u p w a r d s s e q u e n c e of till, sand, m a r i n e d i a m i c t o n , a n d gravel facies is also d e f i n e d as o n e single f o r m a t i o n (Fig. 6). I n s o m e of the sections these f o r m a t i o n s are s u b - d i v i d e d into a lower s i l t - s a n d m e m b e r a n d a n

642

J. Mangerud and J.l. Svendsen T A B L E 3. Radiocarbon dates from Formation B, at Kapp Ekholm

Lab. No.

Age

+_ t o

_+ 2 o

Material

Locality

T-8532

43,800

+ 1100 - 1000

+2300 - 1800

Wood

I, 150

Svalbard 1988-237. Piece of wood, 5 cm in diameter, and 70 cm long. It was found on the surface near the boundary between the silt and gravel members of Formation B. It could have slided downwards, but according to our interpretation there are no younger sediments above this site. except Holocene

T-9644

56,000

+9700 -4300

> 49,000

Shell

II, 270

Svalbard 1988-544, -545 and -546. Three paired Mya truncata from the "Mytilus zone"

T-8321

49,000

+2300 -1800

+5600 -3300

Shell

II, 280

Svalbard 1988-113. Paired, large Mya truncata, from the lowest part of the sand (Fig. 10). 5 cm above the reddish brown silt

T-8535

60,000

> 53,901/> 50,400

Shell

IV. 570

Svalbard 1988-665, -667, -672. Three paired Mya truncata from the marine diamicton

T-9645

61,600

> 52,900 > 48,900

Shell

IV, 570

Svalbard 1988-677. Mya truncata from the marine diamicton

> 60,900

Shell

V, 650

Svalbard 1988-682, -683, -684, and -685. Paired Mya truncata from marine diamicton, around 5 m a.s.l.

T-9646

Field sample No. and description

T A B L E 4. Radiocarbon dates from the section near Nidedalen Lab. No.

Age

+ 1 o

+ 2 o

Material

T-8329

43,300

+4000 - 2600

+ 12,000 - 4600

Shell

Svalbard 1988-6311, -633, -640. Three Hiatella arctica from sand just above the lower till

T-8328

9180

+_120

Shell

Svalbard 1988-615. Several paired Chlamys islandica from gravel foresets. 3-4 m above the upper till

Field sample No. and description

upper gravel member. The brown diamicton facies, which sporadically occurs on top of the till units, has been included in the marine silt-sand member. In the field the formations were correlated from section to section by means of sediment facies, fossils, style of glaciotectonic deformation, and stratigraphic position. The field correlations were later tested and confirmed by radiocarbon dates, TL-dates and by the amino acid D/L ratios measured on shells. The inferred ice free periods are given informal climatostratigraphical names (Nystuen, 1989). These are defined by the marine sediments deposited during the first part of the ice free periods. Kapp Ekholm interstadial is defined by Formation F, Phantomodden interstadial by Formation D, and interglacial B (Eemian) by Formation B (Fig. 6). During latter parts of the ice free periods it is assumed that the sections were sub-aerially exposed and these periods are not represented by sediments in the sections. The glaciations during which the tills A, C, etc. were deposited, are referred to as glaciation A, glaciation C, etc.

Formation A (Till) This formation was recognized in Sections I and II (Fig. 7). The following description is from Section II

where it was exposed along the base of the cliff (Figs 9 and 10). In Section I this unit was for the most part covered by slumped material (Fig. 12) and north of Section II it dips underneath the present shoreline (Fig. 7). The dip apparently reflects the descending bedrock floor. The sediments form a typical grey diamicton facies as described above. The matrix is sandy in some parts and in others more silty, the variation is apparently random. Several isolated pockets of gravel, probably derived from older shore deposits, occur in the till. The thickness of the formation varies between 1.3 and 4 m. Glacial striae occur on the underlying bedrock surface, oriented 226 ° at 300 m and 210 ° at 270 m, showing ice flow parallel with the fjord. The underlying bedrock is sharply cut by the till. At 280 m there is a 20 cm thick and 3 m long lens of a reddish brown silt/diamicton at the base of the formation which contains frequent small shell fragments, obviously from molluscs that lived during a preceding ice free period (Figs 6 and 10). The lens has a transitional boundary to the grey diamicton above, and is covered by slumped masses from the steep cliff at both ends. Its lateral extension was therefore not determined exactly. However, this unit was not seen exposed elsewhere along the section.

80 + 7

902501

93 + 3

76 + 2

99 + 10

103 + 5

89 + 4

902503

902502

902510

902505

902504

902507

6.7 + 0.8

4.5 + 0.5

42 + 1

902514

902515

902508

40 + 4

36 _+ 5 310--470

370-500

32~460

330-500

320-350

250-410

270-460

200-410

210--470

300-440

260~40

140

76

130

215

168

168

138

132

94

205

123

143

VI-H

VI-H

VI-H

II-B

I-B

1-13

IV-D

IV-D

IV-D

IV-D

V-F

V-F

IV-F

IV-F

II-F

Max. T L age (ka) Formation

Nidedalen

Nidedalen

900

900

1070

1020

890

280

150

115

570-580

570-580

500

500

740

730

570-580

500

280

Locality

1988-741

1988-739

1988-750

1988-748

1988-754

1988-752

1988-519

1988-479

1988-513

1988-515

1988-500

1988-502

1988-511

1988-509

1988-491

1988-493

1988-498

1988-503

1988-487

Field No. Svalbard

1 m above sample 1988-739. More sandy

A thin sand bed in gravel foresets. 5 m below the till. 15 m a.s.l.

Sample collected between high and low tide on present beach. The top layer was removed before sampling. T h e apparent age indicates that it is not fully zeroed

Sample from the present beach. T h e apparent age indicates that it is not fully zeroed

A s sample 1988-752

Early Holocene gravel foresets. Sand matrix sampled

Sand beneath gravel foresets. Radiocarbon age 9080 + 110 (T-8534)

Lower part of foresets, 5 cm above sand (Fig. 10). T h e OSL m e t h o d yielded three different ages

Foresets, 1.5 m below upper boundary. 19.5 m a.s.l.

Sandy gravel in the foresets, 2 m below the upper boundary. A g e plateau very short

C o m p a c t sand, 35 cm below the base of the foresets

Sand matrix in middle part of the gravel foresets

5 cm thick sand bed. 20 cm above sample 1988-509

Sand matrix in gravel. Lower part of gravel foresets

Sand in upper part of Formation F

Gravel, 1.5 m below the till G. 20 m a.s.l.

Sand in upper part of Formation F, 21.5 m a.s.I. Acceptable plateau. However, also short plateau corresponding to a T L age of about 155 ka

Massive sand, 90 cm below the boundary to the Holocene gravel. 24 m a.s.i.

Gravel at the top of Formation F; 12 m east in Fig. 15

Comments

Lab. No. refers to the Nordic Laboratory for Luminescence Dating. Plateau indicates the t e m p e r a t u r e intervals for the T L plateau. Max. age is the age obtained if one postulates that the T L signal was completely zeroed during deposition. Locality gives metres along the shore at Kapp E k h o l m (Fig. 7).

892509

16 + 2

9.5 + 1

19 + 2

902511

902513

76 + 10

54/84/104

902509

902512

104 + 10

892506

114 + 10

122 _ 10

107 + 10

53 +__7

44 _+ 5

50 + 2

892504

38 + 5

11)4 + 10

230-480

44 + 5

59 +__ 3

892503

Plateau (°C)

T L age (ka)

902506

Lab. No. OSL age R (ka)

T A B L E 5. T L and OSL dates from the Kapp E k h o l m and Nidedalen Sections

O',

O

O e~

644

J. Mangerud and J.l. Svendsen T A B L E 6. A m i n o acid D/L ratios from Formation H, the Holocene, at Kapp Ekholm

BAL-No.

D/L-ratio Total

Sp.

Locality

Field sample

Comments

1820A 1822A 1823A 1824A Mean

0.022 0.020 0,017 1~.022 0.020 +__0.002

H I- 130 235 H II-280 78 H 11-28(I 78 H 11-280 78 for Hiatella arctica from the Early Holoeene

Paired shells radiocarbon dated to 9730 _+ 120 ('1"-8322) BAL-1822, -1823, and -1824 are from 3 paired shells, radiocarbon dated to 9691) +_ 70 (T-8319)

1825 A 1829A 1830A 1831A Mean

0.018 0.014 0.017 0.012 0.015 _+ 0.003

M M M M for Mya truncata

Radiocarbon dated to 8710 _+ 100 (T-8323) BAL-1829, -1830, and -1831 are from three shells in living position, one was radiocarbon dated to 8590 + 60 (T-8326)

1V-550 317 V-740 438 V-740 438 V-740 438 from the Early Holocene

Note for Tables 6--11 of amino acid results: BAL-No. is the sample n u m b e r at the Bergen amino acid laboratory. Postscripts A and B m e a n s independent preparations and m e a s u r e m e n t s of the same specimen. W h e n more than one D/L ratio is given under the same n u m b e r and letter, a prepared sample is remeasured. Sp. m e a n s species, where M is Mya truncata and H is Hiatella arctica. The full designation for the field sample is Svalbard 1988-No. D/L ratios given in ( ) are not included in the calculated mean values and standard deviations.

Formation B (Interglacial B) This formation was studied in most detail in Section II, which is described below (Figs 9 and 10). The lower member of formation B in this section includes several beds of silt, sand, and a marine diamicton (Fig. 10). In several places a thin layer of a brown diamicton facies was observed along the transition between Formations A and B; possibly it occurs continuously along the entire Section II. The diamicton grades upwards into a 20 cm thick brownish silt which contains many shells. The gradational boundary to the marine silt above, compared with the sharp boundary to the till below, suggests that the brown diamicton was also deposited as a marine sediment. Between 260 and 285 m there is a shallow depression in the surface of the underlying till (A), presumably a channel (Fig. 10). It is filled with faintly bedded silty sand, 2.2 m thick in the centre. Paired Macoma calcarea and Mya truncata occur in this sand facies. Probably it was deposited by gravity flows from the sloping sea shore. The sand does not extend laterally, but a similar facies was exposed at the base of Section IV (at 500 m). Over the channel fill there is a 30 cm thick gravelly zone (Fig. 10) which cuts the underlying sand. In this zone we found several fragments, and also whole shells, of Mytilus edulis (Fig. 11). This is the only site and stratigraphic level where we found pre-Holocene Mytilus in the sections. Also Lavrushin (1969) has earlier reported fragments of Mytilus from this section, as far as we understand from the channel fill. Mytilus edulis requires warmer sea surface temperatures than at present, indicating that formation B is of interglacial age. The gravelly zone with Mytilus represents the lower part of a nearly 5 m thick bed of a distinctive marine diamicton facies (Fig. 10). Paired molluscs in living positions occur frequently in this diamicton, including exceptionally thick and large shells of Mya truncata.

Macoma calcarea, Serripes groenlandicus, Hiatella

arctica, and Astarte sp. are also common. The many individuals of Mya in upright, living positions, show that the bed has not been disturbed after these molluscs burrowed into the sea floor. The high content of mud in the sediments indicates quiet water environment during deposition, which requires a water depth of some 15-20 m or more. In conformity with Boulton's (1979) interpretation, we assume that most of the stones have rolled down the steep slope from the shore, others may have been dropped from sea ice. Due to the distinctive appearance of the marine diamicton as compared to the other sediment facies, Formation B could be recognized in the different sections by visual correlation (Fig. 7). A similar lateral correlation of these diamicton sections was undertaken by Boulton (1979). Above the marine diamicton there is a thick sequence of foresets consisting of well rounded gravel. In some of the sand lenses which are interbedded in the gravel foresets, seaweed and shell fragments occur. Rust staining of the gravel was seen many places, especially along the boundaries of the more finegrained sediments. We were not able to determine whether the rust staining is 'old' or Holocene in age. The sequence of gravel foresets becomes considerably thicker (12 m) in Section I (Figs 7 and 13) whereas to the north of Section II it appears to wedge out (Fig. 7). Thus, at the southern end of Section III there is only a small pocket of gravel above the marine diamicton. However, Section III is only a low ridge that was heavily covered by slumped material, and no sedimentary unit was confidently identified between the marine diamicton and Formation F at this particular exposure. In the upper part of the marine diamicton in Section IV (570 m) there is a 2.5 m thick gravel lens with a crude bedding, which is probably a remnant of the same gravel member as in Section II. There are also pockets of gravel in the till above, which may derive from Formation B. Boulton (1979) correlated a till (his unit 3) into a

645

Interglacial-Glacial Period on Spitsbergen

TABLE 7. A m i n o acid D/L ratios from Formation F, the Kapp Ekholm interstadial, at Kapp Ekholm D/L-ratios

BAL-No.

Total

Free

Sp.

Locality

Field sample

1800A B 1651A B 1652A B Mean

0.023 0.023 0.021 0.019 0.017 0.021 0.021 __. 0.002

0.347

M

11-280

43

Paired. From sand 60 cm above till

0.352 M 0.232 0.320 M 0.343 0.319 ± 0.050

I1-280

48

Paired. From sand 30 cm above till

I1-280

51

Paired. From sand 30 cm above till

0.183 0.208 0.268 0.241 0.232 0.243

Comments

for Mya truncata from Formation I I - F Thrusted sand, just above till Lens of gravel. Same individual yielded non-finite C-14 ages (Ua-I174/I175, T-8324) Samples 329, 331,332, and 335 are four paired shells. In sand less than 50 cm above till. Radiocarbon dated to > 45,400 (T-8324)

M M

IV-530 IV-530

302 309

M M M M

IV-570 IV-570 IV-570 IV-570

329 331 332 335

IV-570

338

Paired. In sand one m above sample 329

IV-570

344

As 338

1808A 1821A B 1826A 1827A 1828A 1792A B 1802A B 1793A B Mean

0.024 0.019 0.029 0.024 0.024 0.022 0.031 0.027 0.027 0.028 0.028 0.026 ± 0.003

1834A 1835A 1796A B 1832A 1833A 1797A 1794A B 1804A B 1795A B Mean

0.028 0.026 0.029 0.029 0.026 0.025 0.027 0.026 0.034 0.032 0.023 0.031 0.033 0.028 __. 0.003

M M M

V-650 V-650 V-730

716 717 460

0.146 M 0.215 M 0.136 M 0.187 M 0.228 0.215 M 0.220 (0.669) M 0.265 0.184 __. 0.049

V-730 V-730 V-730 V-765

472 475 476 402

V-765

403

V-765

406

2450

0,184 H 0,183 0,173 H 0,162 0,177 H 0,183 0,117 ± 0,008

V-765

410

V-765

411

Samples 410-411 are paired shells in sand, 70-80 cm above the underlying silt where samples 402, 403, 406 listed above were collected

V-765

412

As sample 410, but not paired

Mean

0,031 0,030 0,032 0,033 0,028 0,026 0,030 + 0,002

1817A 1818A 1819A Mean

0.042 0.035 0.027 0.035 ± 0.008

0.190 H 0.215 H 0.118 H 0.174 ± 0.050

VI-870 240 Samples 240, 247, and 249 are three paired shells. From VI-870 247 sand 3 m below till. Radiocarbon dated to 46,100 (T-8533) VI-870 249 for Hiatella arctica from Formation VI-F

Mean Mean

0.026 ± 0.004 0,031 _+ 0,005

0.207 ± 0.075 0,176 ± 0,025

for Mya truncata from entire Formation F for Hiatella aretica from entire Formation F

2511 2512

0.146 0.234 M 0.206 0.208 M 0.174 0.205 __. 0.043 0.123 0.215 0.118

for Mya truncata from Fromation IV-F

Paired. From overfolded sand As 716 Samples 460, 472, 475, and 476 are four paired shells. From gravel 0.2-1 m below till. Radiocarbon dated to 42 ka (T-8327) Samples 402,403, and 406 are three paired shells. From 30 cm thick silt just above underlying till

for Mya truncata from Formation V - F

for Hiatella arctica from Formation V - F

postulated unconformity between the marine diamicton and the gravel foresets in Sections I and II. However, at the southern end of Section II (11-12 m a.s.l., Fig. 10) we discovered well-defined gravel foresets that clearly finger into the marine diamicton below. These gravel beds were mapped continuously along the cliff for more than 20 m within the upper part of the marine diamicton, and they gradually become more finegrained in the distal direction. We therefore conclude that the marine diamicton is a distal facies of the gravel foresets, and that there is no unconformity along the boundary between the two different units.

Formation C (Till) This till unit is mapped continuously along Section IV (Fig. 13), but it varies greatly in thickness and lithology. At 500 m it is only 1 m thick, and appears as a well-defined bed of compacted, homogeneous grey diamicton facies with numerous striated stones. At 550-570 m the same till unit is as much as 4-5 m thick; the upper half is massive, as at 500 m, whereas the lower part has incorporated large lenses of gravel and silt, and contains numerous shell fragments and stones that are covered with bryozoa. In some places the lower boundary is difficult to define.

646

J. Mangerud and J.I. Svendsen TABLE 8. Amino acid D/L ratios from Formation D, the Phantomodden interstadial, at Kapp Ekholm D/L-ratios

BAL-No.

Total

Free

2453

0.044 0.055 0.046 0.043 0.053 0.053 0.049 "4- 0.005

0.280 M 0.277 0.318 M 0.264 0.312 M 0.321 0.295 ± 0.022 0.349 0.297 0.366

1658A B Mean

0.075 0.076 0.079 0.078 0.068 0.066 0.070 0.070 0.073 + 0.005

Mean

0.063 ± 0.013

2517 2518 Mean

1657A B 1803A B

Sp.

Locality

Field sample

IV-500

256

IV-500

257

IV-500

259

Comments Samples 256, 257 and 259 are three paired shells. In 1.4 m thick sand just above reddish brown silt at the base of the formation

for Mya truncata for Formation D at 500 m

M

IV-565

384

M

IV-565

387

0.317 M 0.346 0.335 ± 0.028

IV-565

392

for Mya truncata from Formation D at 565 m

0.314 ± 0.029

for all Mya truncata from Formation D

Samples 384, 387 and 392 are three paired shells In sand just above reddish brown silt at the base of the formation

0.318

T A B L E 9. Amino acid D/L ratios from Formation B (Eemian interglacial), at Kapp Ekholm D/L-ratios BAL-No.

Total

Free

Sp.

Locality

Field sample

1801A B 1647A B 1648A B

0.072 0.077 0.073 0.069 0.068 0.068 0.071 0.071 ± 0.003

0.396 0.385 0.291 0.355 0.379 0.380

M

II-280

110

M

11-280

111

Samples 110, 111, and 113 are extremely large individuals, collected 5-11 cm above the reddish brown silt at the base of the formation

M

11-280

113

Radiocarbon dated to 49 ka (T-8321)

0 . 3 6 4 ± 0.035

for Mya truncata from the base of Formation l i b

0.332 0.335 0.297 0.288 0.339 0.352 0.291 0.307

M

II-280

127

Paired. Top of silt-sand member, 120 cm below gravel

M

II-280

128

As sample 127

M

II-280

129

As sample 127

M

I1-330

709

Paired. Top of sand member, 80 cm below gravel

1807A B 1650A

0.073 0.076 0.055 0.056 0.078 0.076 0.056 0.062 0.052 0.061 0.062 0.062

I1-320

710

Not paired. Otherwise as 709

11-320

711

Paired. 'Fop of sand member, 1 cm below gravel

B

(I.061

0.340 M 0.352 0.301 M 0.361 0.342 0.451 0 . 3 3 4 ± 0.040

Mean

2451 2513 2514 1649A B

Mean

0 . 0 6 4 ± 0.009

1653A B

0.071 0.060

1654A B

Mean

0.077 0.071 0.070 0.073 0.082 0.081 0.073 0.076 0.078 0.077 0.074 ± 0.006

Mean

0.069 ± 0.008

1806A B 1655A 1656A B

Comments

for Mya truncata from top of the silt-sand member of Formation II-B

0.344 0.366 0.266 0.257 0.337

M

IV-570

660

Paired. In silty sand 15 cm below deformed gravel at top of the formation

M

IV-570

662

As 660

0.394 0.374 0.306

M

IV-570

665

Samples 665,667 and 672 were paired. 2 m below gravel. Radiocarbon dated to > 50,400 (T-8335)

M

IV-570

667

0.335 0.346

M

IV-570

672

0.332 ± 0.044

for Mya truncata from Formation I V - B

0 . 3 4 0 ± 0.042

for Mya truncata from entire Formation B (all samples listed above)

647

Interglacial-Glacial Period on Spitsbergen TABLE 10. Amino acid O/L ratios from lens of reddish brown silt in lower part of till A, at Kapp Ekholm D/L-ratios BAL-No.

Total

Free

Sp.

Locality

Field sample

2508

0.130 0.126 0.126 0.125 0.109 0.109

0.448 0.431 0.480 0.467 0.366 0.429

M

11-270

122

M

11-270

122

M

II-270

122

0.121 --- 0 . 0 0 9

0.437 _ 0.37

2509 2510 Mean

Comments Sample 122 contains shell fragments collected 0-20 cm above bedrock

for Mya truncata p r e d a t i n g Till A

TABLE 11. Amino acid D/L ratios from the section at Nidedalen D/L-ratios BAL-No.

Total

Free

Sp.

Field sample

1805A

0.045 0.040 0.037 0.033 0.027 0.025 0.039 0.031

0.309

M

626

Paired shells, 3 m below till

M

617

Top of sub-till sediments

M

641

Paired shells from top of sub-till sediments

Mean

0 . 0 3 4 _+ 0 . 0 0 6

0 . 2 6 6 _.+ 0 . 0 3 3

for Mya truneata f r o m the sub-till sediments

1798A B 1799A B

0.055 0.056 0.050 0.051

0.228 0.223 0.246 0.200

H

638

Paired shells from base of sub-till sediments

H

639

As sample 638

Mean

0.053 + 0.003

0 . 2 2 4 __+ 0 . 0 1 9

for two individuals o f Hiatella aretica f r o m the sub-till sediments

2516

0.041 0.013

0.227 0.205

744

B 2452 2515B

0.304 0.312 0.225 0.242 0.262 0.272

M

Because the formation (D) above wedges out at both ends of Section IV, till C merges with the next younger till (E) in the adjacent sections (Fig. 7). Thus the lateral correlation of this till is not clear. In Section II (Figs 10 and 15) there is a till that can be bracketed between Formation B and F, and which can be either till C or E. This till unit sharply cuts the underlying gravel foresets, indicating that the lower boundary is erosive. Due to its compactness, it was easily recognized as a well-defined layer protruding from the exposures in Section II (Fig. 9). In the E - W section shown on Fig. 15, the till wedges out 5 m east of the cliff. However, it can be traced further as a horizon of striated boulders and isolated pockets of till until it re-occurs east of 15 m. Evidently the top of the till is eroded, and for stretches it is entirely removed. This indicates that the till unit in question represents Formation C and not E. Otherwise the erosional episode must have occurred after the deposition of Till E, but before Formation F, which is not very likely. In Section I the gravel foresets of Formation B are

Comments

From silt at the base of the Holocene

sharply cut by an erosional unconformity, on which there is a till of typical grey diamicton facies that can be mapped continuously from 100 to 130 m. From 130 to 180 m the till occurs as lenses or as a horizon of striated boulders, but for stretches it is completely missing. The till is a maximum 1 m thick at 100 m. It is stratigraphically bracketed between Formations B and H (Holocene) only, thus it could be correlated with any of the Tills C, E or G in the other sections (Fig. 7).

Formation D (Phantomodden Interstadial) This formation occurs in Section IV only (Figs 7 and 13). Above Till C there is a 20-60 cm thick bed of brown silt facies, which at 500 m appears as a thin layer of a brownish diamicton. There is a gradual transition from the brownish silt to sorted sand facies above. The sand contains frequent Mya truncata in living positions, especially at 560-570 m, and also paired Macoma calcarea and other molluscs. Above the sand there is a sequence of gravel foresets

648

.I. Mangerud and J.I. Svendsen ~i

ro°o° 4 Gravel Gravel foresets Sand ~__.~_ - Silt

Marine diamicton (in formation B)

Tm Glaciotectonic thrusts and folds L_ ] Covered by slamped material

South

North IV

V

Iti

[

II

3o

20

10

i

!

900m

700

I

300

500

100m

3O

20

o95

10

(--,,6

900m

700

500

300

I OOm

FIG. 7. The upper figure shows the lithostratigraphy of each section, and our correlations between the secUons. The vertical scale is exaggerated 20 ×. Most formations dip toward the sea (the viewer), and also increased in thickness in that direction. Thus elevations and thicknesses depend on how far back each section is eroded. The boundary between sand and gravel facies in the Holocene sequence was not mapped systematically, and in some places this line is drawn arbitrarily. The stippled top on Section IIl indicates a gentle slope with small sections behind the main cliff. On the lower figure radiocarbon (marked with X) and OSL/TL (marked with dot) dates are plotted in ka (thousands of years). For the Holocene one decimal is included. For samples dated with both the OSL and TL method, ages are given as OSL/TL. The OSL sample (R-902509) from Formation B (280 m) that yielded three different ages is omitted.

representing the upper member of this formation. The base of the planar foresets curves towards the lower sand. The gravel member decreases in thickness, from 10 m in the southern end of Section IV to only 2 m at the northern end (Figs 7 and 13). As seen in Fig. 8, it also becomes thinner towards the valley side. The top of the foresets are sharply cut by the overlying till (E), but they are hardly disturbed. Because this formation

was only found in Section IV we have considered the possibility that formation D might be a glaciotectonically upthrusted floe from Formation B. The obtained T L ages (Table 5) and amino acid D/L (0.063) ratios from this formation are not significantly different from the samples from Formation B (Tables 8 and 9). Thus, from the available dating methods alone, we were not able to prove that Formation D is in fact younger than

m a.s.I. West 40--

East

Stratigraphic

30

Terrace 28.5 m a . s . I .

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FIG. 8. A cross section showing the stratigraphy along the gully at the south end of Section IV (500 m in Fig. 7). The formations are marked with letters on the shore face cliff. The stratigraphic position of Till G is also marked, even though this formation is missing in this section. Note the wedge shape of the entire deposit, and that some formations wedge out towards the valley side.

649

Interglacial-Glacial Period on Spitsbergen

FIG. 9. Photo of Section II taken in 1981, and used for the field mapping in 1988, when the section was very similar. The horizontal scale in metres along the shore, and some levelled elevations are marked. The boundaries between the formations are marked with full lines. In Formation B the boundary between the silt-sand member and the gravel member is stippled. Some of the foresets that can be seen in the photo from Formation B are dotted.

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