Marine Geology, 83 (1988) 159-191 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
159
A STRATIGRAPHIC STUDY OF LATE QUATERNARY SEDIMENTS ON THE VQRING-PLATEAU, EASTERN NORWEGIAN SEA MOGENS RAMM Institute of Geology, University of Oslo, Postbox 1047, Blindern, N-0316 Oslo 3 (Norway) (Received November 3, 1987; revised and accepted April 8, 1988)
Abstract Ramm, M., 1988. A stratigraphic study of Late Quaternary sediments on the Voring Plateau, eastern Norwegian Sea. Mar. Geol., 83: 159-191. Four gravity cores from the Voring Plateau, west of the Nordland coast in N o r t h e r n Norway have been studied. About 250,000 yrs of continuous hemipelagic sedimentation is represented in the cores. This period has been divided into seven lithostratigraphic units and four planktonic foraminiferal assemblage zones. To improve the reliability and precision of the isotopic stratigraphy, a graphic comparison with several isotopic records previously described in the literature has been performed. A taxonomy of 36 isotopic events is established following Prell's* technique. The majority of these events seem to be recognizable in the isotopic records from the Norwegian Sea. During the glacial stages, however, several local events are caused by influxes of isotopically light meltwater. Comparisons between the records indicate a general trend toward decreasing sedimentation rates with increasing distance from the c o n t i n e n t a l margins for isotope stages 2, 3, 4 and 6. Only small variations in sedimentation rates are observed during stages 5 and 7. Comparisons with the land-based stratigraphy of Northwest Europe indicate t h a t the main glacials and interglacials as well as the F a n a and the Torvaldstad interstadials are recognizable in the marine sequences. Correlations to the Bolling and Allerod interstadials and the Younger Dryas stadial is obscured by a period of rapid influx of meltwater at about 15 14 Ka, followed by a period of high influx of clastic material.
Introduction
Several publications have, during the last decade, provided insight into the Late Quaternary palaeo-oceanographic development of the Norwegian Sea. However, a great number of controversies concerning the triggering mechanisms, timing and magnitude still exist, as well as the effects of the major oceanographic changes. The purpose of this paper is to establish a stratigraphic framework for the Late Quaternary Norwegian Sea sediments. A more detailed treatment of the palaeo-oceanographic *Prell et al. (1986). 0025-3227/88/$03.50
development of this area is left for a subsequent paper. Previous workers on this area have based their stratigraphic investigations on several criteria. Kellogg (1975, 1976) discussed six cores correlated mainly on the basis of distributions of calcium carbonate and planktonic foraminifera, a few radiocarbon dates and on correlations to dated ash layers. In somewhat more recent studies, age determinations have been based mainly on the distribution of oxygen isotopes in planktonic foraminifera (e.g., Duplessy et al., 1975, 1980; Kellogg et al., 1978; Belanger, 1982; Grousset and Duplessy, 1983; Jansen et al., 1983; Jansen and Erlenkeuser, 1985). Four gravity cores from the Voring Plateau
© 1988 Elsevier Science Publishers B.V.
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a r e s t u d i e d i n t h i s p a p e r ( F i g . 1 a n d T a b l e 1). These cores, which were collected during the A r c t i c I c r u i s e o f R.V. Polarstern ( A u g s t e i n et al., 1984), w e r e a n a l y z e d f o r c a l c i u m c a r b o n a t e and total organic carbon content. The distribution of planktonic foraminifera was studied in two cores, while the distributions of carbon TABLE 1 Location, length and depth of studied cores Core
Lat.
Long.
Depth (m)
Length (cm)
GIK-23199 GIK-23202 GIK-23205 GIK-23209
68°22.64'N 68°01.84'N 67°36.58'N 67i18.39'N
05°13.51'E 05°30.34'E 05°44.48'E 06°44.83'E
1968 1517 1411 1362
636 636 601 551
a n d o x y g e n i s o t o p e s in t e s t s o f Neogloboquadrina pachyderma w e r e d e t e r m i n e d in o n e c o r e . Three radiocarbon dates of planktonic foraminifera are given. Emphasis has been put on an attempt to correlate isotopic events to other records from the Norwegian Sea and the northeastern A t l a n t i c (Fig.2, T a b l e 2). C o r r e l a t i o n s b e t w e e n i s o t o p i c r e c o r d s f r o m n i n e c o r e s h a v e presented the possibility of comparing relative sedimentation rates and of checking the validity of the location of stratigraphic boundaries.
Methods Downcore analyses of total calcium carbona t e (TCC) a n d t o t a l o r g a n i c c a r b o n ( T O C ) content were carried out by a gasometric
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Lat.
Long.
Depth (m)
Reference
T w o cores, GIK-23199 a n d GIK-23205, w e r e tlsed for studies of p l a n k t o n i c f o r a m i n i f e r a l d i s t r i b u t i o n . S a m p l e s of a p p r o x i m a t e l y 12 g of w e t s e d i m e n t w e r e weighed, dried a t 50°C for a i l e a s t 24 h a n d t h e n w e i g h e d again. T h e dried s a m p l e s w e r e t h e n w e t sieved on a 63 pm sieve. T h e c o a r s e f r a c t i o n was dried a n d weighed. T h e f o r a m i n i f e r a l a s s e m b l a g e w a s studied in t h e size f r a c t i o n 150-500 pm. T h i s f r a c t i o n w a s r e p e a t e d l y split u n t i l 1000-3000 g r a i n s remained. T h e s e w e r e e q u a l l y s p r e a d on a c o u n t i n g p l a t e divided into 45 squares. G r a i n s in all, e v e r y second, third, f o u r t h or fifth s q u a r e s w e r e c o u n t e d until, if possible, at l e a s t 300 p l a n k t o n i c f o r a m i n i f e r a w e r e counted. In this process, p l a n k t o n i c f o r a m i n i f e r a w e r e identified a t t h e species level, while all b e n t h i c f o r a m i n i f e r a w e r e c o u n t e d as one g r o u p (for r a w d a t a , see R a m m , 1986). T h e p o r o s i t y (¢), t o t a l c o a r s e f r a c t i o n (TCF) a n d t h e t o t a l n u m b e r of p l a n k t o n i c foraminif e r a in t h e size f r a c t i o n 150-500 pm/g dried sediment, r e f e r r e d to as the p l a n k t o n i c foram i n i f e r a l n u m b e r (PFN), w e r e c a l c u l a t e d u s i n g eqns.(1-3): q~ =
(Mw-
T C F = Mcf/Md'. 100(%) PFN =
GIK-23199 GIK-23205 K-11 V27-60 V27-86 V28-14 V28-56 CH73-110 CH73-139c
68°22'64"N 05°13'51"E 67°36'35"N 05°44'29"E 71°47'00"N 01°36'00"E 72°11'00"N 08°34'48"E 66°36'24"N 01°07'06"E 64°47'00"N 29°34'00"E 68°02'00"N 06°07'00"W 59°30'2"N 08°56'3"W 54°38'2"N 16°21'3"W
1968 1411 2900 2525 2900 1855 1968 1366 2209
A B C C C D D C C
References: A - - This paper; B - - Haake and Plaumann (1987); C - - Labeyrie and Duplessy (1985); D - - Kellogg et al. (1978) (¢~180records only). m e t h o d a n d b y u s i n g a L E C O 5344 f u r n a c e , respectively. Multiple analyses and estimates of t h e " p o o l e d e s t i m a t e of v a r i a n c e " i n d i c a t e u n c e r t a i n t i e s in t h e r a n g e of + 0 . 5 % for t h e CaCOa a n d + 0.01% for t h e T O C c o n t e n t (Ramm, 1986).
(Mw - Md')" P g • 100(%) M d ' ) " P k - Md" Ppw
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w h e r e Mw, Md a n d M c f a r e t h e m a s s of the w e t a n d dried s e d i m e n t s a m p l e a n d of t h e c o a r s e f r a c t i o n , r e s p e c t i v e l y , a n d Md' is the m a s s of the dried s e d i m e n t s a m p l e c o r r e c t e d w i t h r e s p e c t to p o r e - w a t e r s a l i n i t y ( M d ' = M d (Mw - M d ) . 0.035). P g a n d P p w a r e t h e densities of t h e s e d i m e n t g r a i n s (2.65 g/cm 3) a n d t h e p o r e w a t e r (1.02 g/cm3). T h e b e n t h i c f o r a m i n i f e r a l n u m b e r (BFN) is defined in a s i m i l a r m a n n e r to t h e P F N . T h e b e n t h i c p l a n k t o n i c (B/P) r a t i o is defined as the o b s e r v e d n u m b e r of b e n t h i c f o r a m i n i f e r a divided by t h e n u m b e r of p l a n k t o n i c foraminifera m u l t i p l i e d by 100 (i.e., BFN/PFN" 100). A f t e r w e t s i e v i n g in the 63 pm sieve, t h e fine f r a c t i o n f r o m core GIK-23199 w a s dried a n d
162 analyzed for the CaCO 3 content. The CaCO3 content in the <63 pm fraction as a weight percent of the total dried sediment (TCCf) and the CaCO3 content in the > 63 tJm fraction as a weight percent of the total dried sediment (TCCc) are estimated using eqns. (4 and 5): TCCf = TCCf*. (1 - TCF/100)
(4)
TCCc = TCC' - TCCf = T C C ' M d ' / M d - T C C f
(5) Where TCCf* is the measured CaCO 3 content in the fine fraction and TCC' is the bulk CaCO3 content corrected for pore-water salinity. Tests of the planktonic foraminifer N. pachyderma from GIK-23199 were analyzed for stable isotope composition. About 30-40 tests from the 200-250 ~tm fraction were picked from each sample where a sufficient number was present. The narrow size fraction was used in order to select tests from analogous growth phases in each sample. The tests were crushed and carefully washed with methanol. A Finnigan Mat 251 mass spectrometer combined with a fully automated carbonate preparation device (14C laboratory, University of Kiel) was used for the isotopic analyses. Radiocarbon dating was performed on tests of N. pachyderma from three sediment levels in GIK-23199 and GIK-23205. Approximately 10 mg of foraminifera were collected from the 150-500 ~m size fraction. The material was dated at the Tandem Accelerator L abor a t or y at the University of Uppsala with the use of accelerator mass spectrometry.
Lithostratigraphy Studies of CaCO3 and organic carbon content, in addition to evidence from X-ray photographs of the four cores, yielded eight distinguishable lithostratigraphical units (LI-LVIII), which in t ur n have been divided into a number of subunits (Figs.3a-d). Unit LI includes the upper " r e c e n t carbonate high" and consists of a yellowish brown clay. The unit is characterized by a high CaCO 3 content, low densities of coarse detrital clasts, high densities of biogenic material,
intense bioturbation and a modest organic carbon content decreasing from the top. The base of the unit is defined where the CaCO~ content shows a distinct increase upwards. Unit LII is an interval with a low CaCO3 content (about 5%) and high densities of coarse detrital clasts. It is composed of a yellowish brown sandy clay. In all cores, this unit contains a horizon with elevated organic carbon contents. Bioturbation is generally less intense than in LI. Unit LIII shows quite uniform sedimentation with a CaCO 3 content at about 10% and a high to moderately high density of coarse detrital clasts. It consists of greenish grey silty sandy clays. The TOC content is nearly stable throughout the unit in each core but varies between the cores. The lowest contents (0.15-0.20%) are found in the westernmost core GIK-23199, while the highest contents (0.3-0.4%) occur in the easternmost core GIK-23209. This unit may further be divided into two subunits where the upper subunit shows somewhat higher CaCO~ contents than the lower one. Unit LIV consists of heterogeneous sandy clays. In each core a horizon of dark olivegreen sandy clay is observed above a horizon of dark grey or black sandy clay. These two intervals are marked by high TOC content (> 1%) and a low CaCO 3 content (,~0%). The lower boundary of the unit is defined where the CaCO 3 content shows a marked downward increase to the penultimate carbonate high. The upper boundary is defined where the CaCO 3 content decreases with depth from values of -~ 10% to 4-5% or lower. Unit LV is characterized by high and variable CaCO 3 contents and includes the penultimate carbonate high. It consists of yellowish brown or greenish silty foraminiferal clays. In all the cores except GIK-23209 this unit shows a threepeaked pattern which may provide a division into five subunits. The subunits LVa, c and e show CaCO3 contents well above 25%, whereas LVb and d are the intervening carbonate lows. Unit LVI consists of sediments analogous to those found in units LII, LIII and LIV. It is fully represented only in the westernmost core
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LITHOSTRATIGRAPHY: GIK-23202 CoCO3 (bulk)
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(GIK-23199) but the upper parts are also present in GIK-23202 and GIK-23205. A number of sequences of olive-green or dark grey sandy clays having increased organic carbon and decreased CaCO 3 contents show oscillating organic carbon and CaCO3 distributions. Due to these variations it is possible to divide this unit into seven subunits. Subunits LVb, d and f show sediments analogous to those found in
Kellogg (1975, 1976, 1980) described the distribution of Recent and Late Q u a t e r n a r y planktonic foraminifera in a number of surface sediment samples and in six piston cores from the Norwegian and Greenland Seas. In this paper, the taxonomic nomenclature used by Kellogg is adopted; however, "Globigerina" pachyderma is referred to as "Neogloboquadrina" pachyderma as suggested by Collen and Vella (1973) and Srinivasan and K e n n e t t (1976). Ericson (1959) showed that two faunal indices are especially useful for palaeo-oceanographic studies of sediment samples from the Norwegian Sea. These indices are (1) the percent dextral N. pachyderma of the total number of N. pachyderma and (2) the percent "warm-water" species (i.e., all other species except N. pachyderma) of the total number of planktonic foraminifera. By using these two faunal parameters and the PFN, four assemblage zones have been established. These four zones have been further divided into a number of subzones. In Figs.4a and b these three parameters, the BFN, the B/P ratio and the division into biozones are shown.
165
LITHOSTRATIGRAPHY:
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CoCO3 { b u L k }
0 r g o n c c Corbon
Porosctg
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Zone AI is represented in the uppermost 40 and 20 cm of cores GIK-23199 and GIK-23205, respectively. The lower boundar y is marked by a minor increase in both warm-water species and the percentage of dextral N. pachyderma. A peak in both faunal indices is apparent near the base. The P F N is moderately high throughout the zone, except in the lower part of the zone in GIK-23205. Zone AII is found at 40-308 cm in GIK-23199 and at 20-540 cm in GIK-23205 and is charac-
terized by 95-100% sinistral N. pachyderma and generally less t han 1% warm-water species. This zone has been divided into four subzones. AIIb is characterized by a somewhat higher content of warm-water species (1-4%), AIId yields high PFN's, while AIIa and c are characterized by "cold-water" faunal associations and low PFN's. Zone AIII is found at 308-330 cm in GIK23199 and at 540-546 cm in GIK-23205. The planktonic foraminiferal fauna is analogous to
166
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within two sediment i n t e r v a l s not t h i c k e r t h a n 3 5cm. Zone AIV is found at 330-636 cm in GIK23199 and at 546 601 cm in GIK-23205. The faunal composition resembles zone AII h a v i n g a total d o m i n a n c e of left-coiling N. pachyderma. S o m e w h a t h i g h e r c o n t e n t s of warmw a t e r species and h i g h e r p l a n k t o n i c foraminiferal n u m b e r s in an i n t e r v a l between 570 and 615 cm in GIK-23199 justify the definition of three subzones.
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Fig.3. Downcore sedimentological properties and subdivision into lithostratigraphic units in GIK-23199 (a), GIK23202 (b), GIK-23205(c) and GIK-23209(d). The distribution of/~lsO is shown for GIK-23199and GIK-23205.Dashed and dotted lines represent boundaries between lithostratigraphic units and subunits as defined in the text.
t h a t found in AI, with high values for both the w a r m - w a t e r species and the n u m b e r s of N. pachyderma. Nevertheless, the faunal composition in this zone shows a s o m e w h a t different development. In GIK-23199, w h e r e this zone is best developed, the two faunal indices c h a n g e first from a fully glacial to a fully interglacial composition and t h e n from a fully interglacial to a fully glacial composition
isotope
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The o x y g e n isotopic composition of the oceans is a f u n c t i o n of the volume of freshw a t e r locked up in w a t e r r e s e r v o i r s or as inland ice on the continents. Thus, ~180 records from deep-sea cores are well suited for s t r a t i g r a p h i c c o r r e l a t i o n s between cores from different localities (e.g., S h a c k l e t o n and Opdyke, 1973, 1976). The r e s o l u t i o n for such c o r r e l a t i o n s is limited by the mixing time of the o c e a n w a t e r s (500 yrs) (Stuiver, 1983). At least t h r e e o t h e r factors, however, affect the ~lsO composition in the tests of m a r i n e organisms. These are: (1) species- and sized e p e n d e n t f r a c t i o n a t i o n d u r i n g metabolism and g r o w t h ("vital effects") (e.g., V i n c e n t et al., 1981; Wefer et al., 1981), (2) f r a c t i o n a t i o n as a result of t e m p e r a t u r e v a r i a t i o n s (e.g., Emiliani, 1955; S h a c k l e t o n , 1967) and (3) local or regional isotope anomalies resulting from abn o r m a l e v a p o r a t i o n , p r e c i p i t a t i o n or freshw a t e r inflow (e.g., Epstein and Mayeda, 1953; Craig and Gordon, 1965). F a c t o r s affecting the 613C distribution in c a r b o n a t e tests are less well established. Vital effects h a v e been well d e m o n s t r a t e d m a i n l y a m o n g benthic species (e.g., Zahn et al., 1986). Local v a r i a t i o n s in pH, 0 2 s a t u r a t i o n and flow of o r g a n i c c a r b o n from organisms or from h y d r o c a r b o n s influence the t o t a l a m o u n t of dissolved i n o r g a n i c CO2 and affect the ~13C distribution. However, global changes in the c a r b o n isotope distribution in o c e a n w a t e r TCO2 (total dissolved i n o r g a n i c carbon, i.e., dissolved CO2 + H C O 3 + C O 3 2 - ) have taken
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169
place (e.g., Shackleton, 1977; Broecker, 1982; Berger and Keir, 1984). Labeyrie and Duplessy (1985) were, against this background, able to identify a set of isochronous/513C transitions in high-latitude sediments. Downcore variations in GIK-23199 and GIK-23205
In GIK-23199, light 5'sO values are found in two intervals, at 0-60cm and 308-360cm, which are correlated to isotope stages 1 and 5e, respectively (Fig.5a). Duplessy et al. (1981) showed t h a t the transition between stages. 2 and 1 is made up of two steps. This transition, termination I (Broecker and Van Donk, 1970), was divided into terminations Ia and Ib. This division is also useful in GIK-23199 where Ia starts at 65 cm while Ib is located between 29-43 cm. Kellogg et al. (1978) showed that the /5180 distribution in cores from the Norwegian Sea indicates short-lived reversals towards heavier 5~80 values after the initial decreases in amounts both at terminations I and II. On this basis it seems reasonable to divide termination II into two substeps also. In GIK-23199, this makes sense as a slight reversal is observed at about 340 cm followed by a transition into lighter values just below the changes in lithology and foraminiferal fauna which occur with the approaching interglacial conditions. On this basis terminations IIa and IIb are defined at 365-357 and 340-333 cm in GIK23199, respectively. The ~1sO distribution in planktonic foraminifera shows further intermediate values in the upper penultimate carbonate high, during the third carbonate high and in a series of levels at 130, 210, 372, 451 and 526 cm. This may indicate that stages 5a-d are characterized by ~180 values of about 4.2-3.8%0 between 260 and 308 cm. The third carbonate high may represent sedimentary settings analogous to the upper part of the penultimate carbonate high so that the intermediate ~180 values at this level may reflect oxygen isotope stage 7. Thus, termination III may be located at 626-618cm where both the (~180 and 5~3C
values show major shifts. This is also supported by the lithology of lithostratigraphic zone LVIII which indicates glacial conditions t h a t may correspond to stage 8. The interval between 65 and l l 3 c m is characterized by stable ($180 values between 4.62 and 4.79%o reflecting a glacial maximum probably corresponding to isotope stage 2. The transition between stages 2 and 3 is indicated by a distinct reduction to lighter 6180 at 131 cm (3.9%o). Light ~13C values observed immediately above the penultimate carbonate high, help to identify the upper boundary of stage 4 (Labeyrie and Duplessy, 1985). The light 5~sC values above and below the interval barren of planktonic foraminifera may reflect stage 4, while the intermediate values at 142-200 cm may reflect stage 3. The observed ~ 8 0 minimum at 210 cm is interpreted as a result of regional reduced surface water salinities and does not correspond to a global 5~80 minimum. The distribution of ~ 8 0 is characterized by several such local minima (e.g., 58, 210, 372, 451 and 526 cm), all occurring just above horizons with dark olive green or blackish sandy clays with reduced CaCO s and elevated organic carbon contents. Epstein and Mayeda (1953) showed that a linear relationship between salinity and ~180 in the North Atlantic region occurs. The differences were accounted for by mixing of various bodies of fresh and marine water, both with fixed salinities and /5180 distribution. Following this argument it can be shown t h a t the decreases in ~ 8 0 values from 4.63 to 3.47%0 (482-451 cm) and from 4.62 to 3.25%o (65-58 cm) can be explained by assuming mixing with isotopically light meltwater leading to reductions in salinities of about 1.3 and 1.6%o, respectively (Ramm, in prep.). In GIK-23205, low 5180 values corresponding to oxygen isotope stages 1 and 5e were found at 28-45 and 535-590 cm respectively (Fig.5b). Termination Ib falls within an unmeasured interval above 28 cm. Comparisons between GIK-23199 and GIK-23205 with respect to ~ 8 0 , /51sC, organic carbon, CaCO3 and planktonic foraminiferal distribution indicate that termi-
170
ISOTOPIC RATIOS IN GIK-23199 5toO vs. PDB
Iso{opeS£age e-=
'
~,o o.o .
4.o ~
3.o
6~C vs. PDB
%° 2.o
-0 .S O.B
0 .B
2
t00.[}
~O0.0
ZO0.O
~°0.
S
4
m,I
SO0.0
5e
O&
B E 50Q.[
ILl El:: C3 (D z
-/ £:3
Q
400,0 /~
400.0
~o
\
SO0,O.
0 .S
~o 1,0
171
ISOTOPIC RATIOS IN GIK-23205
5toOvs.
I sot_opeSLoge
s.o 0.0 .
O.,O
4.o ~
PDB ~.o
2.0 % "
5~C vs. PDB %° -0.5
D.O
O.'S
I
!
0.0
! .El
f
IW.0.
~00.D
t00.I)
~mj
200.0
208.0.
~0.0
400,0.
400.0
400.0 -
5OO.O
500.0 -
/
4 O -
- -
m
era.!
C~ O Z
-r t---
m-d .
.
.
.
.
Se
CL L-J
gB.0-" "8" -
"~o,'O"
-~o-:o i
Fig.5. Distribution of oxygen and carbon isotopic ratios of Neogloboquadrina pachyderma in GIK-23199 (a) and GIK-23205 (b). Isotopic data from GIK-23205 are adapted from Haake and Pflaumann (1987).
172
nations IIa and IIb may be located at 585-595 and 550-545 cm respectively. Intermediate 51sO values are also found between 475 and 545 cm, probably corresponding to stages 5a-d, and in one level at 230 cm, probably corresponding to a low-salinity event in the upper part of stage 3. As in core GIK-23199, the boundaries between stages 4 and 3 and stages 3 and 2 are difficult to locate from the ~'sO distribution alone. With one exception at 100 cm, consistent and high d180 values (4.55-4.67%0) are found between 45 and 155cm. The slight decrease in ~180 values from 4.60%0 (150 cm) to 4.31%o (180 cm) probably reflects the transition from stage 2 to 3. The boundary between stages 4 and 3 is most probably located at 415cm where the (~3C distribution shows a major change towards higher values.
Radiocarbon dating Low concentrations of carbon-bearing matter constitutes a major problem in dating deepsea sediments. Standard radiocarbon dating is therefore usually carried out on bulk sediment
samples (e.g., Mangerud and Gulliksen, 1975; Sarnthein et al., 1982). This opens up the possibility t hat contamination by reworked fine-grained carbonate may yield ages t hat are too high. Ultrasensitive, high-voltage tandem mass spectrometers allow analyses on a few (500-1000) tests of foraminifera, as only small amounts of carbon ( ~ 2 mg) are required (Muller, 1977; Purser et al., 1982). Assuming that these tests are not reworked and that the precipitation of carbonate occurred in equilibrium with atmospheric CO: with respect to the initial I4C concentration, it is plausible to accept the 14C ages as being correct. Uncertainties are, however, introduced by the measurement, by changing production rates of 14C in the atmosphere and by mixing of the sediment due to bioturbation. Three ~4C age determinations were carried out (Table3). In addition, one date from Pedersen (1987) was available. The 14C age at 37 cm in GIK-23199 (9390 _+ 340 yrs B.P.; Pedersen, 1987) is in good agreement with the age expected from an interpretation of the 5180 distribution. Term±-
TABLE 3 ~C ages from selected levels in GIK-23199 and GIK-23205 Depth in core (cm) Core GIK-23199 37.5 36.5
14C age (yrs B.P.)
9390 ± 340*
Associated s t r a t i g r a p h i c levels
T e r m i n a t i o n Ib S t a r t of t e r m i n a t i o n Ia LII-LI boundary BII BI b o u n d a r y
43 65 40 40
-29 cm ± 3 cm _4- 2 cm _+ 2 cm
65 70 61 79
± ± ± ±
65.5 64.5
15820 ± 215
S t a r t of t e r m i n a t i o n Ia LIILLII boundary BIIb BIIa b o u n d a r y BIIe--BIIb b o u n d a r y
113.5 112.5
22050 ± 360
Stage 3 2 b o u n d a r y LIIIb L I I I a b o u n d a r y
123 103 cm 108 ± 4 cm
Core GIK-23205 160.5 159.5
21520 ± 350
Stage 3 2 b o u n d a r y LIIIb LIIIa b o u n d a r y
180 150 cm 170 ± 5 cm
*Pedersen (1987)
3 cm 3 cm 3cm 4 cm
173 nation ib was located between 43 and 29 cm. As this termination has been dated at 10-8 Ka (Duplessy et al., 1981; Sarnthein et al., 1982; Jansen et al., 1983; Kellogg, 1984), an age close to 9.0 Ka is expected for the midpoint at 36 cm. The 14C age found at 65 cm in the same core (15,820 +215 yrs B.P.) fits the age of 16Ka given in a series of earlier papers for the onset of termination Ia (Duplessy et al., 1981, 1986; Sarnthein et al., 1982; Kellogg, 1984). However, it contradicts the time scale introduced by Mix (Ruddiman and Duplessy, 1985) and Berger et al. (1985) which puts the initiation of the latest deglaciation after 14 Ka. The two datings, at l l 3 c m in GIK-23199 (22,050_+ 360 yrs B.P.) and at 160 cm in GIK23205 (21,520__ 350 yrs B.P.), confirm the correlation of the boundary between isotope stages 2 and 3 as suggested above. However, the datings are somewhat younger than the accepted age for this transition (24 Ka; e.g., Imbrie et al., 1984). This discrepancy may have several origins, such as erroneous radiocarbon ages due to bioturbation, recrystallization or other contamination, or a displacement of the 5180 change due to salinity or temperature effects. In the following discussion, the radiocarbon dates are assumed to be correct.
Graphic correlation of isotopic records In many cases, stage boundaries show rapid monotonic 5~80 shifts. As a result, most authors dealing with stable isotope chronology have presented their results in terms of stage boundaries. This method has some disadvantages when applied to the Late Quaternary sediments of the Norwegian Sea. As described above, some stage boundaries are ambiguously located. Further, both the 5180 and the 513C distribution yield more stratigraphic information than is actually used when dividing the isotopic records into stages. To improve the reliability and applicability of the isotopic records, the stratigraphic system introduced by Prell et al. (1986) is adopted here with some modifications. Here, GIK-23199
is used as a reference section, and both the oxygen and carbon isotopic records are used. Major recognizable events in these records are identified and given a decimal notation. These isotopic events are tentatively recognized in the records from GIK-23205 and in records from the cores listed in Table 2. Correlation diagrams are constructed and an inspection of the lines of correlation is carried out to verify the identification of these events in different records, and to test the validity of correlation between records. Finally an attempt is made to correlate these Norwegian Sea isotopic events with the standard composite units of Prell et al. (1986) and with ages given by the SPECMAP time scale (Imbrie et al., 1984).
Isotopic nomenclature The defined isotopic events were assigned to a numerical code system analogous to that given by Prell et al. (1986). The standard isotopic stage numbers of Emiliani (1955) are kept in the integer position of the code, while individual isotope events are indicated by decimals within their respective stage. This is performed in such a way that even numbers will, as a rule, refer to local 51sO highs and 513C lows while local 51sO lows and 513C highs are indicated by odd decimal numbers. A prefix letter "N" is added to indicate that the highs, lows and rapid changes refer to events in isotope records from the Norwegian Sea. As previously described, terminations I and II appear in two distinct steps in GIK-23199. Furthermore, the upper boundary of substage 5e appears as a distinct change-over from light to intermediate values. In order to include this information in the code system, these events are given names in a somewhat different manner: (1) Termination I, which by Prell et al. (1986) was coded as event 2.0, is here split into events N2.0 T M and N2.0 Tlb, (2) termination II is analogously referred to as event N6.0 T M and N6.0 T2b and (3) termination III is referred to as N8.0 z3. (4) The returns from the peak intergla-
174 c i a l - i n t e r s t a d i a l v a l u e s i n s t a g e s 5 a n d 7, w h i c h a r e r e f e r r e d t o as i n i t i a t i o n s I a n d II a r e g i v e n t h e n o t a t i o n N5.0 '1 a n d N7.0 '2. (5) T h e r e t u r n from p e a k i n t e r g l a c i a l 6~so v a l u e s in s u b s t a g e 5e t o p e a k g l a c i a l v a l u e s i n s t a g e 4 is c o n s i d e r e d to h a v e o c c u r r e d i n t w o s t e p s a t t h e t r a n s i t i o n b e t w e e n s u b s t a g e s 5e a n d 5d a n d b e t w e e n s u b s t a g e 5a a n d s t a g e 4, a n d a r e t h u s
r e f e r r e d to as respectively.
events
N5.0 'in
and
A t o t a l o f 36 i s o t o p i c e v e n t s a r e d e f i n e d a n d listed in T a b l e 4 . D i s c r e t e l y sampled d a t a c a n n o t be c o n s i d e r e d t o c a p t u r e t h e c o m p l e t e character of the isotopic records. The events are t h e r e f o r e a s s i g n e d to d e p t h r a n g e s limited on the basis of the i n t e r v a l s a c t u a l l y sampled.
TABLE 4 Definition of isotopic events and their location in GIK-23199 Events
Event boundaries in GIK-23199 (cm)
N5.0 'lb,
Comments
Lower
Upper
NI.1
25.5
13.0
The 51sO minimum peak somewhat below the core top. It is worth noticing that the core top itself shows even lower values
N2.0Ti b
43.5
29.0
A distinct fall in 5lSO values measured over four samples. The 613C record shows rather stable values
N1.2
58.0
47.5
A maximum level in the 6~80 record which may be correlated to the Younger Dryas chronozone (e.g., Jansen et al., 1983; Berger et al., 1985)
N1.3
65.0
53.0
A very pronounced 61sO low which may be explained by supply of meltwater due to ice retreat. This interval also shows rapid changes in the 613C record
N2.0rla
65.0
58.0
A rapid change from high glacial 51s0 towards intermediate values probably due to ice retreat and meltwater supply
N3.0
123.0
103.0
The boundary between stages 3 and 2, showing a slight increase in 6180 values toward high stable glacial values
N3.1
142.0
123.0
A marked negative 5180 peak and a corresponding negative peak in the 613C record
N3.2
157.0
142.0
A marked 6J80 peak below 3.1 which corresponds to a broad 513C maximum
N3.3
178.0
164.0
An event characterized by negative peaks in both 6180 and 613C records
N3.4
186.0
172.0
A marked 5180 maximum at a level which is also characterized by the highest 613C values found in stage 3
N4.0
210.0
202.0
This stage boundary is recognized by an increase in 613C values as expected, but also shows an increase in the 6180 record. This may be interpreted to result from high influx of meltwater during the upper part of stage 4 which reduced the 180 concentration in the surface waters
N5.0,1 b
263.0
254.0
An interval characterized by increasing 51sO and decreasing 613C values (initiation Ib)
N5.1
279.0
263.0
A minor narrow negative peak in both 6180 and 613C records (substage 5a?)
N5.2 N5.3 N5.4 N5.0l'a
307.0
272.0
311.0
307.0
This level is divided into three events despite the stable values because of the existence of a two-spiked pattern corresponding to this level in a series of other 6180 records An interval characterized by rapidly increasing 5180 values (initiation Ia)
175 TABLE 4 (continued)
Events
Event boundaries in GIK-23199 (cm)
Comments
Lower
Upper
N5.5
324.0
314.0
This distinct negative (5180 peak represents the lowest 51so level below NI.1. 513C shows low but increasing values (upper substage 5e)
N6.0r2b
340.0
333.0
A distinct drop in 5180 values after the local maximum in N5.6 (termination IIb).
N5.6
348.0
333.0
An event showing a short-lived return against higher (5180 values after the onset of stage 5 (lower substage 5e)
N5.7
357.5
340.0
The first (5180 low correlative to the lowest part of stage 5
N6.0T M
365.0
357.5
Boundary between stages 5 and 6 (termination IIa). This event marks the major part of the transition from glacial to interglacial (5'80 values at the onset of the penultimate interglacial period
N6.2
372.0
357.5
The uppermost positive event in stage 6, showing both a positive (5180 and a positive 513C peak
N6.3
390.0
365.0
A (5180 low, correlative to the upper part of a sediment layer with no calcareous fossils
N6.4
415.0
390.0
The upper part of a broad (5180 high also showing a local (513C high
N6.5
482.0
443.0
A pronounced local negative 5180 peak also showing low (513C values
N6.6
498.0
451.0
High 5180 and low (513Cvalues below a sediment layer with no calcareous fossils
N6.7
534.0
518.0
An event showing a local low in (5180 but no distinct patterns in the 513C record
N6.8
568.0
534.0
A 5180 high just above the lowermost barren zone
N7.012
575.0
568.0
Boundary between stages 6 and 7 (initiation II), showing a rapid rise in (5180 and a fall in (513C
N7.1
583.0
568.0
An upper minor 6180 peak just below the boundary between stages 6 and 7
N7.2
588.0
575.0
A minor (5180 low showing the highest (51~C values found within stage 7
N7.3
594.0
583.0
A distinct negative (5180 event also showing high (513C values
N7.4
610.0
594.0
An intervening narrow (5t 80 high between N7.3 and N7.5 showing low (513C values
N7.5
618.0
602.0
The lowermost negative 5180 peak found within stage 7
N8.0T3
626.0
618.0
Boundary between stages 7 and 8 (termination III) showing a fall in (5180 parallel to a rapid rise in 513C
Correlation between selected cores Assuming that the isotopic events described a r e c o r r e c t l y r e c o g n i z e d i n a l l c o r e s ( T a b l e 5) and reflect isochronous oceanographic and climatological changes, a correlation line may be d r a w n t h r o u g h the defined c o r r e l a t i o n boxes. Relative changes in sedimentation rates
and/or the presence of hiatuses or depositional pulses are the only processes that may cause offsets or changes in the slope of this line. The d r a w i n g o f t h e l i n e b e t w e e n c o r e s is, h o w e v e r , a subjective procedure and may be subject to criticism and further discussion. The proced u r e u s e d h e r e is t o d r a w s t r a i g h t l i n e s b e t w e e n s t a g e b o u n d a r i e s (indicated by solid
176 rectangles) (Fig.6). These events are considered to represent periods of major changes in the oceanographic settings and to represent levels where changes in the sedimentation rates are likely. (cm) qoo i
DEPTH 6oo
. . . .
I
IN
5oo
. . . .
i
G IK-25
~oo
. . . .
i
~oo
. . . .
i
(cm) 7oo
DEPTH 600
I N
500
G I K-2..~
400
~oo
i
2o0 i
~oo
. . . .
i
o
/I
o
. . . .
1oo
i
t99
. . . .
199
200
o
/
O Pl 1) --t I
too
2Do
~oo < f~ -J
400
I
01 o
5o0
/
5Do
G7
60o
I
400
"700 OW
Y
0
(1
(cm)
6OO
qoo i
(cm)
IN
DEPTH
G I K-2~;
DEPTH 600
. . . .
i
I N
SO0
. . . .
I
G I K-2~
~-00
. . . .
I
500
. . . .
,
'199
:200 . . i ....
qO0 i ....
J /
.199
~?? 6,o0. .??? ??? ??? 2 7 7 ,??...? O
11"1 "O -H -[
o
O in "0
too
I z
<
z / I
O1 S-O)
< rd -4 ' ~ 0 0 --
I
O0 O)
(cm} qoo i
. . . .
DEPTH 600 J
,
I N
~oo •
. J
. . . .
G I K-2~
400 i
. . . .
500 i
. . . .
(cm)
t99 200 i
. . . .
ioo i ....
"zoo
o
i
0
. . . .
OEPTH 600 i
. . . .
I N
sod i
. . . .
G I K-25
.~oo i
500
. . . .
i
. . . .
t99 20o i
. . . .
~oo i ....
o m
too
0 m "0 --{
qoo
"0 1"
I 2oo
200
z ~oo
2~
[
~0o
5oo E
C
~oo ~
< N O3
/
-~oo
f
600
I
3
177
lcm) 700
DEPTH
6O0
SO0
IN
GIK-2$
~00
~00
Interpretation of the correlation lines
499 200
0
100
100
1°
200
S00
£3 I 4
400
I
SOD
5
600
700
800
900 n
g
Icm) "TOO I ....
DEPTH SO0 i ....
SO0 t ....
IN ~00 i ....
4000
GIK--2$199 3O0 i ....
200 i . ,
100 ,
0 ....
0
~O0
O m
"~
--I -r 200
fl .j I
"~00
SO0
to 0
GO0
-TOO
h
g 80O
Fig.6a-h. Graphic correlation of selected cores compared to the standard section from GIK-23199 (see text for discussion).
Cores GIK-23199 and GIK-23205 show comparable sedimentation rate fluctuations between events N1.3 and N4.0 and events N4.0 and N5.7 (Fig.6a). The sedimentation rate during stage 1 was apparently slower in GIK23205 t h a n in GIK-23199. It also seems evident t h a t GIK-23205 indicates low sedimentation rates during stage 5e compared to GIK-23199. It is further evident t h a t all six cores from the central and eastern Norwegian Sea and the one from the southern Denmark Strait (V28-14) show comparable patterns of systematic, and close to isochronous, changes in sedimentation rates (Figs.6a-f). During stages 5 and 7, nearly identical sedimentation rates are found in al~ seven cores. During the glacial stages 2, 3, 4 and 6, a general trend of decreasing sedimentation rates with increasing distance to the continental margin is present. Thus, relative to GIK23199, we find lower sedimentation rates especially in V28-56 and somewhat lower or analogous rates in V27-86 and K-11. The sedimentation rates in GIK-23205, V27-60 and V28-14 are higher than in GIK-23199. These observations support the general trends described by Thiede et al. (1986). They found t h a t during isotopic stage 5, the linear sedimentation rates were lower than during the later stages and relatively constant throughout the eastern Norwegian Sea. Moreover, Thiede et al. (1986) also described a general trend of decreasing sedimentation rates with increasing distance to the continental margins during stages 2, 3 and 4. The two cores from the northeastern Atlantic (CH73-110 and CH73-139c) show some distinct deviations from the general trends observed in the Norwegian Sea records. Especially apparent are high sedimentation rates relative to GIK-23199 during stages 2, 3, 5a-d and 6 (in CH73-110), while low rates are found in levels corresponding to stage 4. These observations suggest that the sedimentation rates within the Norwegian Sea were strongly depressed during the upper parts of stages 5 and 7, while during stage 4 the
178 TABLE 5 Identified isotopic events in selected cores. All depths in centimetres Event
GIK-23199
GIK-23205
Lower
Upper
N1.1 N2.031 ~ N1.2 N1.3 N2.0 Tl~ N3.0 N3.1 N3.2 N3.3 N3.4 N4.0 N5.0 ~Ib N5.1 N5.2 N5.3 N5.4 N5.0 'la N5.5 N6.012b N5.6 N5.7 N6.0 T M N6.2 N6.3 N6.4 N6.5 N6.6 N6.7 N6.8 N7.0 'a N7.1 N7.2 N7.3 N7.4 N7.5 N8.0 T3
25.5 43.5 58.0 65.0 65.0 123.0 142.0 157.0 178.0 186.0 210.0 263.0 279.0 307.0 307.0 307.0 311.0 324.0 340.0 348.0 357.5 365.0 372.0 390.0 415.0 482.0 498.0 534.0 568.0 575.0 583.0 588.0 594.0 610.0 618.0 626.0
13.0 29.0 47.5 53.0 58.0 103.0 123.0 142.0 164.0 172.0 202.0 254.0 263.0 272.0 272.0 272.0 307.0 314.0 333.0 333.0 340.0 357.5 357.5 365.0 390.0 443.0 451.0 518.0 534.0 568.0 568.0 575.0 583.0 594.0 602.0 618.0
sedimentation
rates
were particularly
the area where GIK-23199 was obtained.
Lower
28.0 30.0 158.0 220.0 250.0 310.0 320.0 400.0 470.0 480.0 500.0 52O.0 530.0 540.0 540.0
580.0
560.0
high in Devia-
variations.
Correlation to absolute age The oxygen isotopic Prell et al. (1986) were
events described by u s e d b y I m b r i e e t al.
(1984)
to
in
an
attempt
correlate
Upper
40.0 50.0 162.0 240.0 270.0 330.0 340.0 410.0 480.0 500.0 520.0 540.0 550.0 550.0 560.0
tions from straight-line correlation between cores are probably caused entirely by sedimentation-rate
K-11
oxygen
isotope
Lower
V27-60 Upper
18.0 23.0 30.0 70.0 90.0 100.0
15.0 16.0 25.0 55.0 80.0 90.0
180.0 210.0 240.0
170.0 200.0 220.0
280.0 290.0 290.0 298.0 305.0 305.0 320.0
270.0 282.0 285.0 285.0 298.0 300.0 305.0
380.0 410.0 450.0 460.0 470.0
360.0 390.0 420.0 440.0 460.0
490.0 504.0 520.0 530.0
470.0 480.0 500.0 520.0
records
Lower
Upper
80.0 140.0 150.0 170.0 180.0 210.0
60.0 100.0 130.0 150.0 160.0 200.0
270.0
250.0
332.0 370.0 435.0 446.0 475.0 495.0 510.0 515.0 532.0 532.0 535.0 555.0 565.0 575.0 58o.0 650.0
310.0 360.0 420.0 435.0 440.0 480.0 495.o 505.0 510.0 525.0 525.0 535.0 560.0 560.0 565.0 620.0
to the Milankovitch
mechan-
ism. Imbrie et al. (1984) were able to develop a geological time scale by considering the isotopic records as a single exponential system forced by variation in the earth's orbit. The first step in the following discussion is to correlate the isotopic events introduced in this p a p e r t o t h o s e d e f i n e d b y P r e l l e t a l . (1986). Some additional dates have been introduced after correlating to the stratigraphic system of N o r t h w e s t E u r o p e ( M a n g e r u d e t al., 1974) a n d
179
Lower 19
30.0 110.0 130.0 150.0
215.0 246.0 255.0 280.0 295.0 300.0 310.0 320.0 321.0 325.0 330.0 330.0
CH73-139c
CH73-110
V27-86 Upper
Lower
Upper
5.0
50.0 70.0 80.0 90.0 100.0 240.0
20.0 60.0 60.0 70.0 80.0 220.0
480.0 500.0 600.0 650.0 660.0 700.0 720.0 830.0 850.0 860.0 860.0 870.0 880.0 900.0 960.0 1000.0
450.0 460.0 590.0 630.0 640.0 650.0 690.0 770.0 820.0 840.0 850.0 850.0 860.0 880.0 940.0 950.0
19.0 100.0 110.0 120.0
210.0 235.0 240.0 255.0 275.0 290.0 300.0 310.0 315.0 315.0 321.0 325.0
V28-56
V28-14
Lower
Upper
Lower
Upper
Lower
Upper
90.0
70.0
30.0
20.0
160.0 260.0
140.0 230.0
50.0 120.0
40.0 100.0
99.0 129.0 141.0 141.0 190.0 240.0
90.0 109.0 119.0 129.0 170.0 220.0
310.0
290.0
500.0 540.0 580.0 620.0 640.0 680.0 680.0
490.0 530.0 530.0 580.0 610.0 630.0 670.0
730.0
740.0
145.0 169.0
139.0 159.0
389.0 431.0 460.0
360.0 421.0 441.0
205.0 225.0 235.0 244.0 249.0 259.0
199.0 209.0 229.0 229.0 235.0 254.0
511.0
505.0
545.0
535.0
309.0
289.0
389.0
379.0
439.0
431.0
by m a k i n g s o m e a s s u m p t i o n s c o n c e r n i n g fluctuations in sedimentation rates. I m b r i e e t al. (1984) e s t i m a t e d t h a t t h e 9 5 % confidence i n t e r v a l for c o n t r o l points in the
N2.0 Tla is t h e r e b y
d a t e d a t 15 ___ 1 K a w h i l e
SPECMAP t i m e s c a l e is + _ 2 K a . A s e a c h i s o t o p i c e v e n t is d e f i n e d h e r e a s a d e p t h r a n g e , no further uncertainties are added due to s a m p l i n g d e n s i t y . T e r m i n a t i o n I a ( e v e n t N2.0 Tla) a n d t h e s t a g e 2 - 3 b o u n d a r y ( e v e n t N3.0) m a y , h o w e v e r , be d a t e d s o m e w h a t m o r e p r e c i s e l y by a c c e p t i n g the r a d i o c a r b o n dates as a c t u a l ages.
p e r f o r m e d * . A g e s f o r e v e n t s N2.0 Tlb, N1.2, N1.3, N5.0 Ha a n d N6.0 T:b a r e i n t r o d u c e d b a s e d
N3.0 is d a t e d a t 22 +_ 1 K a . As a first a p p r o x i m a t i o n , d i r e c t c o r r e l a t i o n s to events from the SPECMAP time scale are
on the following criteria: *N5.0lib = 5.0; N6.0T M = 6.0; N7.012 = 7.0; N8.0v3 = 8.0. Events ,N6.4-N6.8 are correlated to events 6.2-6.6 in the SPECMAP time scale.
180
(1) N2.0 T~b is equivalent to termination Ib (Tlb) and is dated to 10-8 Ka (e.g., Duplessy et al., 1981; Sarnthein et al., 1982; Berger et al., 1985). This age is also indicated by the radiocarbon dating at 37 cm in GIK-23199. (2) N1.2 parallels or slightly predates the Younger Dryas chronozone and is dated at 12-10 Ka (Mangerud et al., 1974). (3) N1.3 begins slightly before the Bolling chronozone and is dated at 14 12 Ka (Mangerud et al., 1974). (4) Nh.0 ua is equivalent to the boundary between substages 5e and 5d and is dated at 117 113 Ka (Shackleton, 1969; CLIMAP, 1984). (5) N6.0 T2b is dated at 127-123 Ka. This is justified by assuming oceanographic settings and sedimentation rates during this period analogous to those between events N2.0 T~R and 2.0 T~b. Figure 7 gives a graphical illustration of core depth against age in GIK-23199 based on ages given in Table 6. Straight lines are drawn between stage boundaries (solid boxes). DEPTH
(cm) TOO
6OO
SO0
IN
GIK-23
~00
500
t99 200
IO 0
j,/
/ /
/
/
o o ~o so
/ SO 6O Wo
B~ ~o
>
~o 2o so ~e t~o 6o To ~o 2OO
/
2 ~,~ 22o 2~ ~ -2-,o 2se
Fig.7. The depth-age correlation in GIK-23199. Plotted values are from Table 6.
Excluding stages 3, 5e and 6, all dated intervals fall on or close to the line segments between stage boundaries. The hypothesis that these events correspond to the same events as those defined by Prell et al. (1986) is therefore acceptable. Offsets from these line segments may be due to significant shifts in sedimentation rates or to incorrect assignments of absolute age. It is suggested here that the events within stages 3 and 6 were caused by local anomalies in surface salinities (or temTABLE 6
Suggested ages for isotopic events compared to core depth in GIK-23199 Event
NI.1 N2.0 v i b N1.2 N1.3 N2.011a N3.0 N3.1 N3.2 N3.3 N3.4 N4.0 Nh.0 llh Nh. 1 N5.2 N5.3 N5.4 Nh.011~ N5.5 N6.0 T2~ N5.6 N5.7 N6.0 T M N6.2 N6.3 N6.4 N6.5 N6.6 N6.7 N6.8 N7.0 ~2 N7.1 N7.2 N7.3 N7.4 N7.5 N8.0 T3
Depth (cm)
Age (Ka)
Lower
Upper
25.5 43.5 58.0 65.0 65.0 115.0 142.0 157.0 178.0 186.0 210.0 263.0 279.0 307.0 307.0 307.0 311.0 324.0 340,0 348.0 357.0 365.0 372.0 390.0 415.0 482.0 498.0 534.0 568.0 575.0 583.0 588.0 594.0 610.0 618.0 626.0
13.0 29.0 47.5 53.0 58.0 111.0 123.0 142.0 164.0 172.0 202.0 254.0 263.0 272.0 272.0 272.0 307.0 314.0 333.0 333.0 340.0 357.5 357.5 365.0 372.0 443.0 451.0 518.0 534.0 568.0 568.0 575.0 583.0 594.0 602.0 618.0
Lower
Upper
8.0 10.0 12.0 14.0 16.0 23.0 30.0
4.0 8.0 10.0 12.0 14.0 21.0 26.0
55.0
51.0
61.0 73.0 82.0 89.0 101.0 109.0 117.0 124.0 127.0
57.0 69.0 78.0 85.0 97.0 105.0 113.0 120.0 123.0
130.0
126.0
137.0 148.0 153.0 173.0 185.0 188.0 196.0 207.0 218.0 230.0 240.0 247.0
133.0 144.0 149.0 169.0 181.0 184.0 192.0 203.0 214.0 226.0 236.0 243.0
181 perature). Hence, they are not equivalent to the events introduced by Prell et al. (1986). A slight offset during stage 5e indicating younger ages for events N6.0 TEb and N5.5 is, however, assumed to be caused by high sedimentation rates early in this stage. The events within stages 3 and 6 fall on the correlation lines in Figs.6a-h. This suggests that they represent actual regional changes in oceanographic settings such as variations in salinity and temperature and not ice volume effects. Ages for these events are estimated by assuming linear sedimentation rates during stages 3 and 6 in GIK-23199 (eqn.(6); see below). In Fig.8, the 51aO records from the nine cores are plotted with the stacked global record presented by Imbrie et al. (1984). Dating of single 5lsO observations is performed by assuming linear sedimentation rates between dated isotopic events.
Dating o f lithostratigraphic units and biozones The chronostratigraphic framework introduced, is used to calculate ages for the biozones and lithostratigraphic units in GIK23199 and GIK-23205 (eqn.(6)). By assuming isochronous shifts in sedimentation patterns and ecological settings in the area along the cored traverse line, absolute ages may be estimated for corresponding levels in GIK23202 and GIK-23209. A, = A a + (D, - Da).(A b - A a ) / ( D b - D~) = Aa - (D b - D,). (A b
-
-
A,)/(D b -
D~)
(6) where A, and D n are the age and depth for the isotopic event t h a t is to be dated, Aa and D, are the age and depth for the nearest dated isotopic event above, and A b and Db are age and depth for the nearest dated isotopic event below. Absolute uncertainties in the estimated ages may be calculated using eqn.(7):
,4'+
,,o./'-..,4'+
For these calculations, only major isotopic events (i.e., stage boundaries) are used. The midpoints of all age and depth ranges are used as actual ages and depths, while half the ranges are used as uncertainties. Uncertainties in the depths of the boundaries of interest (Son) are assumed to equal half the sample interval. Tables 7A-D list the resulting ages together with the dated levels used for each calculation. Comparisons between Tables 7A and B and between 7C and D verify the assumption that the majority of the litho- and biostratigraphic boundaries are isochronous within the expected uncertainties. The boundaries between LI and LII and between AI and AIIa are, however, doubtfully dated in GIK-23205. Henrich (1987) discussed the CaCO a and 51sO distribution between 0 and 37 cm in a boxcore (GIK-23201) located close to GIK-23202. Termination Ib in this core is located at 20-27 cm while the base of LI may be located between 13 and 16 cm from the CaCO 3 distribution. Thus, the base of LI in this core is younger than 8 Ka. As the upper part of the three cores, GIK-23202, GIK-23205 and GIK-23209, show sediments analogous to those in GIK-23201, it is likely that the base of LI is younger in these three cores than in GIK-23199. This observation may be explained by enhanced carbonate dissolution at the Voring Plateau in the Early Holocene (Henrich, 1987). Also, low sedimentation rates or nondeposition during the Holocene in the area where GIK-23205 was extracted may contribute to this discrepancy.
Correlation to the onshore stratigraphy Mangerud et al. (1979) and Miller and Mangerud (1986) showed that Eem interglacial correlates to isotope stage 5e. The distribution of planktonic foraminifera in GIK-23199 (Fig.4a) indicates t h a t the general warming of
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183 TABLE 7 Estimated ages for boundaries between l i t h o s t r a t i g r a p h i c u n i t s and planktonic assemblage zones Unit
Depth, D,(cm)
Age, A , (Ka)
Dated levels with a s s u m e d c o n s t a n t s e d i m e n t a t i o n rates A a (Ka)
A b (Ka)
D~ (cm)
Db (cm)
Sediment rate (cm/Ka)
9±0.5
15± 1
36± 3
62± 3
~4.3
15 ± 1
22 ± 1
62 ± 3
113 ± 3
~7.3
59±2
71±2
206±4
259±4
~4.4
71 ± 2
115 ± 2
259 ± 4
309 ± 3
~1.1
115 ± 2
128 ± 1
309 ± 3
360 ± 4
~3.9
128 ± 2
186 ± 2
360 ± 4
186 ± 2
~3.7
186 ± 2
245 ± 2
572 ± 4
622 ± 4
~0.8
7.A. L i t h o s t r a t i g r a p h i c units, GIK-23199 LI 40± 3
10± 1
LII 70 ± 4
16 ± 1
108 ± 5
21 ± 1
213 ± 3
61 ± 2
239±6
67± 2
258 ± 4
71 ± 2
273 ± 3
83 2 4
286 ± 4
94 ± 5
299 ± 4
106 ± 5
309 ± 2
115 ± 4
LIIIa LIIIb LIVa LIVb LVa LVb LVc LVd LVe 331 ± 2
120 ± 2
353 ± 4
126 ± 2
375 ± 3
132 ± 2
411 ± 3
142 ± 2
455 ± 4
154 ± 2
478 ± 4
160 ± 2
538 ± 4
177 ± 2
565 ± 3
184 ± 2
588 ± 3
204 ± 5
603 ± 4
222 ± 6
614 ± 4
236 ± 6
LVIa LVIb LVIc LVId LVIe LVIf LVIg LVIIa LVIIb LVIIc LVIII 7.B. L i t h o s t r a t i g r a p h i c units, GIK-23205 LI 5 ± 1
2 ± 1
0±0
15± 1
0±0
50±3
~3.3
60± 5
16± 1
15± 1
22± 1
50± 3
165± 3
~16
22 ± 1
59 ± 1
165 ± 3
410 ± 4
,~6.6
59 ± 2
71 ± 2
410 i 4
480 ± 4
~5.8
71 ± 2
115 ± 2
480 ± 4
540 ± 4
~1.4
115 ± 2
128 ± 1
540 ± 4
590 ± 4
~3.9
LII LIIIa 170 ± 5
23 ± 2
430 ± 2
62 ± 2
440 ± 1
64 ± 2
465 ± 5
68 ± 2
495 ± 5
82 ± 5
515 ± 5
97 ± 5
525 ± 5
104 _+ 5
535 ± 5
111 ± 5
LIIIb LIVa LIVb LVa LVb LVc LVd LVe LVIa
545 ± 2
116 ± 2
585 ± 5
127 ± 2
184 TABLE 7 (continued)
Unit
Depth, D,(cm)
Age, A. (Ka)
Dated levels with assumed constant sedimentation rates A~ (Ka)
Ab (Ka)
Sediment rate (cm/Ka)
Oa (cm)
Dh (cm)
15 ± 1
36 ± 3
62 ± 3
~4.3
22 ± 1
62 ± 3
113 ± 3
~7.3
7.C. Biostratigraphic (planktonic assemblage) zones, GIK-23199 AI AIIa AIIb AIIc AIId AIII AIVa AIVb
40 ± 3
10 ± 1
61 ± 3
15 ± 1
79_+ 4
17 ± 1
15 ± 1
9 ± 0.5
255 ± 2
70 ± 2
59_+ 2
71 ± 2
206_+ 4
259 + 4
~4.4
308 ± 2
114 ± 4
71 ± 2
115 ± 2
259 ± 4
309_+ 4
~1.1
331 + 2
121 ± 2
115 + 2
128 ± 2
309 ± 4
360 ± 4
~3.9
568 ± 3
185 ± 3
128 + 2
186 ± 2
360 ± 4
572 ± 4
~3.7
622 ± 4
245 ± 7
186 ± 2
245 ± 2
572 ± 4
622 ± 4
~0.8
21_+3
6+1
0±0
15 ± 1
0± 0
50_+ 3
~3.3
60 ± 5
16 ± 1
115 ± 5
19 ± 1
15 + 1
22_+ 1
50_+ 3
165 ± 3
~16
AIVc 7.D. Biostratigraphic (planktonic assemblage) zones, GIK-23205 AI AIIa AIIb AIIc AIId AIII AIVa
465_+ 5
68 ± 2
59 ± 2
71 + 2
410 ± 4
480 ± 4
~5.8
538 ± 1
113 + 4
71 ± 2
115 _+ 2
480 _+ 4
540 _+ 4
~ 1.4
545 + 2
116 ± 2
115 + 2
128 ± 2
540 ± 4
590 ± 4
~3.8
the surface waters occurred after termination II. T h e l o w e r p a r t o f s t a g e 5e i n c o r e GIK-23199 ( e v e n t s N5.6 a n d N5.7) s h o w s a g l a c i a l f a u n a l composition and relatively high sedimentation r a t e s . T h i s m a y be i n t e r p r e t e d to r e p r e s e n t a p e r i o d of h i g h m e l t w a t e r i n f l u x a n d e x t e n s i v e ice r a f t i n g w h i c h a l s o i n d u c e d t h e low 6~sO v a l u e s a n d t h e h i g h c o n t e n t of c o a r s e - g r a i n e d t e r r i g e n o u s m a t e r i a l . T h e l o w e r b o u n d a r y of t h e E e m i n t e r g l a c i a l m a y h e n c e be c o r r e l a t e d to e v e n t N2.0 ~2b ( t e r m i n a t i o n IIb). T h e g e n e r a l w a r m i n g of t h e s u r f a c e w a t e r s , w h i c h is i n d i c a t e d b y t h e c h a n g e i n f o r a m i n i f e r a l comp o s i t i o n , s e e m s to l a g b e h i n d t h i s t r a n s i t i o n b y a b o u t 1 2 Ka. O x y g e n i s o t o p e s t a g e 7, w h i c h p a r a l l e l s L V H a n d A I V b , w a s c o r r e l a t e d to t h e T r e e n i a n w a r m s t a g e b y S a r n t h e i n et al, (1986). S t a g e 6 t h e n , c o r r e s p o n d s to t h e W a r t h i a n (or E i d e r ±an) g l a c i a t i o n . Z o n e A I V b s h o w s o n l y a m i n o r
i n c r e a s e i n t h e p e r c e n t a g e of w a r m - w a t e r p l a n k t o n i c f o r a m i n i f e r a a n d low n u m b e r s of d e x t r a l N. pachyderma. T h u s , t h e c l i m a t e w a s apparently colder in stage 7 than in stages 1 a n d 5e, as is a l s o s u g g e s t e d b y K e l l o g g (1977) a n d S a r n t h e i n et al. (1986). Four interstadial episodes are described from s e d i m e n t s of W e i c h s e l i a n age in w e s t e r n N o r w a y . T h e s e a r e d a t e d a t a b o u t 30 K a , 6 4 - 4 0 K a , 85-71 K a a n d 1 0 1 - 8 7 K a ( S e j r u p , 1987). T h e l a t t e r t w o fall w i t h i n o x y g e n i s o t o p e s t a g e s 5 a - d a n d s e e m to c o r r e l a t e w i t h t h e l i t h o s t r a t i g r a p h i c u n i t s L V a a n d LVd. H e n c e , t h e F a n a i n t e r s t a d i a l m a y be e q u i v a l e n t to e v e n t N5.1, w h i l e t h e T o r v a l d s t a d i n t e r s t a d i a l m a y c o r r e s p o n d to e v e n t N5.3. I n t e r s t a d i a l p e r i o d s w i t h i n i s o t o p e s t a g e s 2, 3, 4 a n d 6 a r e n o t r e c o g n i z a b l e i n t h e f o u r cores. T h e r e f o r e , a c o r r e l a t i o n to i n t e r s t a d i a l d e p o s i t s of t h e A l e s u n d ( M a n g e r u d et al., 1981),
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0
189 K a r m o y (Sejrup, 1987) and S k j o n g h e l l e r e n (Larsen et al., 1987) areas is at p r e s e n t n o t possible. The d i s t r i b u t i o n of p l a n k t o n i c f o r a m i n i f e r a in GIK-23199 and GIK-23205 after the last d e g l a c i a t i o n i n d i c a t e s t h a t the t r a n s i t i o n from cold to t e m p e r a t e surface w a t e r s t o o k place at a b o u t 7 . 5 K a . T h e b o u n d a r y b e t w e e n the W e i c h s e l i a n and H o l o c e n e (10 Ka) is, however, recognizable as a n i n c r e a s e in the CaCO 3 c o n t e n t and a d e c r e a s e in the c o n t e n t of icer a f t e d d e t r i t u s at the b o u n d a r y b e t w e e n lithos t r a t i g r a p h i c units LI and LII. B e r g e r et al. (1985) a t t e m p t e d to c o r r e l a t e the first 61so m i n i m u m a f t e r t e r m i n a t i o n Ia to the Bolling and Allerod interstadials. It seems evident from the discussion above t h a t this 61so low in the N o r w e g i a n Sea (N1.3) must be explained by high inflow of m e l t w a t e r d u r i n g a n e a r l y stage of d e g l a c i a t i o n p r o b a b l y p r i o r to the Bolling interstadial. It seems, t h e r e f o r e , t h a t this m e l t w a t e r e v e n t and the period of high influx of clastic m a t e r i a l p r i o r to t e r m i n a t i o n Ib c a n n o t be easily r e l a t e d to the climatic c h a n g e s in N o r t h w e s t Europe. E v i d e n c e for significant m e l t w a t e r influx at a b o u t 15 K a f u r t h e r m o r e indicates t h a t the c o n t i n e n t a l ice sheets a d j a c e n t to the N o r w e g i a n Sea b e g a n to melt before the n o r t h e r n h e m i s p h e r e m a x i m u m of calorific r a d i a t i o n .
a t u r e ) influence N o r w e g i a n Sea isotopic records. Thus, a set of r e g i o n a l N o r w e g i a n Sea isotopic events c a n be defined. These events must be d a t e d i n d i r e c t l y by e x t r a p o l a t i n g b e t w e e n d a t e d levels. Isotopic signals c a u s e d by r e g i o n a l v a r i a t i o n s in salinity and tempera t u r e m a y f u r t h e r i n t e r f e r e with the global isotopic signals and m a y in some cases cause slight offsets. F i g u r e 9 sums up the complete s t r a t i g r a p h i c system i n t r o d u c e d in this paper. Here, all isotopic events are r e p r e s e n t e d by a r r o w s while s t r a t i g r a p h i c b o u n d a r i e s are r e p r e s e n t e d by lines. This disguises the fact t h a t all dates are s u r r o u n d e d by m a j o r u n c e r t a i n t i e s . Only f u r t h e r studies of h i g h - r e s o l u t i o n cores and more i n f o r m a t i o n on absolute dates m a y reduce these u n c e r t a i n t i e s .
Conclusions
References
T h e last 250,000 y e a r s of s e d i m e n t a t i o n in the e a s t e r n N o r w e g i a n Sea display a n u m b e r of p a l a e o n t o l o g i c a l and lithological changes. W i t h i n this r e l a t i v e l y limited area, it is probable t h a t these c h a n g e s are isochronous. T h e y may, t h e r e f o r e , serve as a set of m a r k e r h o r i z o n s for c o r r e l a t i o n b e t w e e n cores and to an absolute age scale. C o r r e l a t i o n s to an a b s o l u t e age scale are f u r t h e r a d v a n c e d by the use of stable isotope s t r a t i g r a p h y . The m a j o r i t y of the isotopic events defined by Prell et al. (1986) and d a t e d by Imbrie et al. (1984) also seem to be d e t e c t a b l e in the N o r w e g i a n Sea. H o w e v e r , regional v a r i a t i o n s in salinity (and temper-
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Acknowledgements R a i n e r Zahn kindly p e r f o r m e d the stable isotope analysis on core GIK-23199. P e r Kristian Egeberg and Girish Saigal c r i t i c a l l y r e a d an early m a n u s c r i p t and suggested m a n y i m p r o v e m e n t s . J o r n Thiede, E y s t e i n J a n s e n and H a n s P e t t e r Sejrup r e v i e w e d the p a p e r and helped to improve it. To these colleagues I express my sincere thanks.
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