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MSc thesis Geology
PHYSICAL PROPERTIES OF GLACIAL SEDIMENTS FROM THE LANDSORT DEEP
Raisa Alatarvas
2017
UNIVERSITY OF HELSINKI FACULTY OF SCIENCE
DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY GEOLOGY
Tiedekunta/Osasto Fakultet/Sektion – Faculty
Faculty of Science Laitos/Institution– Department
Department of Geosciences and Geography Tekijä/Författare – Author
Raisa Alatarvas Työn nimi / Arbetets titel – Title
Physical properties of glacial sediments from the Landsort Deep Oppiaine /Läroämne – Subject
Geology Työn laji/Arbetets art – Level
MSc thesis Aika/Datum – Month and year
December 2017 Sivumäärä/ Sidoantal – Number of pages
55 Tiivistelmä/Referat – Abstracthttp://www.helsinki.fi/webmail/
The Landsort Deep is the deepest part of the Baltic Sea. It is located just south from the postulated
margins of the early Weichselian glacial, and the deep displays a high-resolution sediment
sequence from late Weichselian and Holocene. The physical properties and characterisation of
late and postglacial sediments from the Landsort Deep enabled the interpretation of the sediment
responses to late Weichselian and Holocene glacial settings. The sediment stratigraphy of the
Landsort Deep reflects variations of salinity in the Baltic Sea Basin, and it enables the
identification of four major stages in the history of the Baltic Sea: Baltic Ice Lake, Yoldia Sea,
Ancylus Lake and Littorina Sea.
The samples studied are from cores from Hole M0063C. The cores were recovered during the
Integrated Ocean Drilling Program (IODP) Expedition 347, “Baltic Sea Paleoenvironment”. Site
M0063 is divided into seven lithostratigraphic units, and the samples are from Unit VI (54–93
ambsf) and Unit V (48–54 ambsf). Sediment analyses and the interpretation of the sedimentary
environment of Units VI and V are based on grain-size analysis by laser diffractometry, loss on
ignition (LOI) determination, and on the IODP Expedition 347 physical properties dataset. The
uniquely long varved glacial clay sequence of Units VI and V gives indications of the
Scandinavian Ice Sheet and the sedimentation of the Baltic Sea Basin responded to climate
fluctuations. The lowermost part of the thick sediment column comprising Units VI and V,
displays ice-proximal settings, and the upper part represents ice-distal settings. The correlation of
the sedimentary features to well-known geological events in the Baltic Sea region enabled the
relative age determination of the Units VI and V. The sediments are deposited during the Baltic
Ice Lake stage and the transition into the Yoldia Sea stage, roughly estimated between 13.5 and
11.5 ka. Comparison to different late and postglacial settings e.g. marine and terrestrial, illustrated
conformities in various glacial sedimentary settings.
Avainsanat – Nyckelord – Keywords
Landsort Deep, Baltic Sea Basin, Scandinavian Ice Sheet, glacial sediments, grain size, clay
varves Säilytyspaikka – Förvaringställe – Where deposited
Helda Muita tietoja – Övriga uppgifter – Additional information
This study is a part of the CISU project funded by Academy of Finland and Russian Foundation
for Basic Research (RFBR).
Tiedekunta/Osasto Fakultet/Sektion – Faculty
Matemaattis-luonnontieteellinen tiedekunta Laitos/Institution– Department
Geotieteiden ja maantieteen laitos Tekijä/Författare – Author
Raisa Alatarvas Työn nimi / Arbetets titel – Title
Physical properties of glacial sediments from the Landsort Deep Oppiaine /Läroämne – Subject
Geologia Työn laji/Arbetets art – Level
Pro gradu -tutkielma Aika/Datum – Month and year
Joulukuu 2017 Sivumäärä/ Sidoantal – Number of pages
55 Tiivistelmä/Referat – Abstracthttp://www.helsinki.fi/webmai
Itämeren syvin kohta, Landsortin syvänne sijaitsee Varhais-Veikselin-kauden oletetun
jäätikkörajan eteläpuolella. Syvänteen sedimentit edustavat korkean resoluution
sedimenttisekvenssejä Myöhäis-Veikselin ja holoseenin kauden ajalta. Landsortin syvänteen
glasiaalisedimenttien ominaisuuksien tutkiminen ja luonnehdinta mahdollistaa tulkitsemaan
Myöhäis-Veikselin ja holoseenin aikaisen glasiaaliolosuhteiden vaikutusta niihin. Landsortin
syvänteen sedimenttistratigrafia heijastaa Itämeren suolapitoisuuden vaihteluja, joka
mahdollistaa neljän suuren vaiheen tunnistamisessa Itämeren historiassa: Baltian jääjärvi,
Yoldiameri, Ancylusjärvi ja Litorinameri.
Tutkitut näytteet ovat kairareiästä M0063C ja ne kairattiin Itämeren syväkairaushankkeen
(IODP:n Expedition 347, ”Baltic Sea Paleoenvironment”) aikana. Kohde M0063 on jaettu
seitsemään litostratigrafiseen yksikköön ja näytteet ovat yksiköistä VI (54–93 ambsf) ja V (48–
54 ambsf). Sedimenttianalyysi ja sedimentaatioympäristön tulkinta perustuvat raekokoanalyysiin,
hehkutushäviön määritykseen ja IODP Expedition 347:n raportin fysikaalisten ominaisuuksien
aineistoon. Yksiköiden VI ja V muodostama ainutlaatuisen pitkä glasiaalisavilusto-sekvenssi
indikoi Skandinaavian jäätikön ja Itämeren altaan sedimentaation ja ilmastonvaihteluiden
vuorovaikutusta. Sekvenssin alin osa edustaa jäätikön proksimaaliosaa ja ylempi osa jäätikön
distaaliosaa. Yksiköiden sedimenttien korrelaatio tunnettuihin geologisiin tapahtumiin Itämeren
alueella mahdollisti niiden suhteellisen iän määrityksen. Sedimentit ovat kerrostuneet Baltian
jääjärven aikana, sekä sitä seuraavan Yoldiameri-vaiheeseen siirtymisen alkuaikoina, karkeasti
arvioiden 13.5 ja 11.5 ka välillä. Sedimenttien vertaaminen erilaisiin glasiaaliympäristöihin,
kuten mariinisiin ja terrestriaalisiin, vahvisti erilaisten glasiaalisedimenttien
kerrostumisympäristöjen yhdenmukaisuuksia.
Avainsanat – Nyckelord – Keywords
Landsort Deep, Baltic Sea Basin, Scandinavian Ice Sheet, glacial sediments, grain size, clay
varves Säilytyspaikka – Förvaringställe – Where deposited
Helda Muita tietoja – Övriga uppgifter – Additional information
Tämä tutkielma on osa Suomen Akatemian ja Venäjän perustutkimusrahaston (RFBR)
rahoittamaa CISU- projektia
CONTENTS
1. INTRODUCTION ...................................................................................................4
2. GEOLOGICAL SETTING AND DEVELOPMENT OF THE STUDY AREA ...5
2.1. The geography and hydrology of the Baltic Sea ........................................................................... 5
2.2. Sedimentation of the Baltic Sea Basin ........................................................................................... 6
2.3. The development of the late and postglacial Baltic Sea Basin ...................................................... 6
2.3.1 The Baltic Ice Lake .................................................................................................................... 8
2.3.2. The Yoldia Sea ....................................................................................................................... 10
2.3.3. The Ancylus Lake and the Littorina Sea .................................................................................. 11
2.4. The Landsort Deep ...................................................................................................................... 11
3. MATERIALS AND METHODS ........................................................................... 13
3.1 Site M0063 .................................................................................................................................... 13
3.2. Physical properties measurements .............................................................................................. 14
3.3. Age determination, depth scale adjustment and correlation ...................................................... 14
3.4. Grain size analysis ....................................................................................................................... 15
3.5. LOI determination ...................................................................................................................... 17
4. RESULTS .............................................................................................................. 18
4.1. Lithostratigraphy of Units VI and V ........................................................................................... 18
4.2. Physical properties of Units VI and V ......................................................................................... 25
4.3. Grain size analysis ....................................................................................................................... 30
4.3.1. Clay, silt and sand content ...................................................................................................... 30
4.3.2. Distribution and d-values ....................................................................................................... 33
4.4. Carbon and LOI values, and water content ................................................................................ 39
5. DISCUSSION ........................................................................................................ 41
5.1. Sources of errors.......................................................................................................................... 41
5.2. Physico-stratigraphic zonation of Units VI and V ...................................................................... 41
5.2.1. Subunit VIa 87.5–93.3 ambsf .................................................................................................. 43
5.2.2. Subunit VIb 67.7–87.5 ambsf .................................................................................................. 44
5.2.3. Subunit VIc 54–67.7 ambsf ..................................................................................................... 44
5.2.4. Subunit Va 48–54 ambsf ......................................................................................................... 45
5.3. Reconstruction of the sedimentation environment of Units VI and V ........................................ 46
5.3.1. Relative age determination ..................................................................................................... 46
5.3.2. Sediments, processes and deposition environment ................................................................... 47
5.3.3. Correlation ............................................................................................................................ 49
6. CONCLUSIONS .................................................................................................... 51
REFERENCES .......................................................................................................... 53
4
1. INTRODUCTION
The location of the Baltic Sea Basin (BSB) in a glaciation-sensitive latitude high in the
northern hemisphere, has led to a very dynamic development during the seas geological
history (Andrén et al. 2011.) The BSB sediments have been affected by the waxing and
waning of the Scandinavian Ice Sheet (SIS) (Andrén et al. 2015a). The recurring
Quaternary glaciations covered repeatedly the whole basin or parts of it, and the
interglacial/glacial cycles and subsequent deglaciations led to widely differential impacts
and uplift in the Baltic Sea region and in its drainage area (Andrén et al. 2011).
The deepest part of the BSB is the Landsort Deep, reaching to the depth of 459 m. It is
located just south from the postulated margins of the early Weichselian glacial, and the
deep displays a high-resolution sediment sequence from late Weichselian and Holocene
(Andrén et al. 2015b). The sediments of the Landsort Deep reflects variations of salinity
in the BSB and it enables the identification of four major stages in its history: Baltic Ice
Lake (BIL), Yoldia Sea (YS), Ancylus Lake (AL) and Littorina Sea (Böttcher and
Lepland 2000).
The Site M0063 in the Landsort Deep was recovered during the IODP Expedition 347.
The Site M0063 is divided into seven lithostratigraphic units (Andrén et al. 2015b), and
the samples are from Hole M0063C from Unit VI (54–93 ambsf) and Unit V (48–54
ambsf). Sediment analyses include grain-size analysis by laser diffractometry, loss on
ignition (LOI) determination, and the interpretation of the IODP Expedition 347 physical
properties dataset. The relative age determination for analysed cores is based on
knowledge of certain geological events in the BSB history.
The focus of this study is on the physical properties and characterisation of late and
postglacial sediments from the Landsort Deep and interpretation of the sediment
responses to late Weichselian and Holocene glacial settings. The interpretation is
complemented with correlation to different late and postglacial sedimentation settings
e.g. marine and terrestrial.
5
2. GEOLOGICAL SETTING AND DEVELOPMENT OF THE STUDY AREA
2.1. The geography and hydrology of the Baltic Sea
The Baltic Sea is a shallow inland sea and it consists of several sub-basins which all have
different physical and topographic features. Baltic Seas bedrock comprises of
Paleoproterozoic crystalline basement rocks that appear locally on the seafloor.
Sedimentary rocks are present in the southern areas, in the Gulf of Finland, and in tectonic
depressions in the Bothnian Bay and central Bothnian Sea. The bedrock is divided into
blocks by several fracture zones and ancient tectonic lineaments. The most notable
features are probably the pre-glacial originated depressions and troughs (Kaskela et al.
2012.).
Geographical position is between approximately 53° and 66°N, and the sea lies between
temperate and subarctic climate. The Baltic Sea is connected to the North Atlantic through
narrow straits between Denmark and Sweden, which leads to a restricted water exchange.
The Baltic Sea is one of the world's largest epicontinental and brackish water seas
(Kaskela et al. 2012), and it has an area of 377 000km². Björck (1995) reviewed that the
annual fresh-water input is 660 km³, annual discharge of brackish-water is 940 km³, and
the estimated annual inflow of saline bottom-waters is ca. 475 km³. The water depths of
the Baltic Sea are generally 25–75 m in the south, 100–200 m in the central part, and 50–
100 in the north. The salinity of the surface waters in the Baltic Sea basin varies between
ca.1‰ in the northern part and ca. 10‰ in the south (Andrén et al. 2000a). According to
Myrberg et al. (2006) the salinity of the Baltic Sea is one-fifth of average oceans salinity.
The drainage area is 1.7·10⁶ km² and it expands between 49–69°N, and the water
exchange time is about 50 years. One of the Baltic Seas special features is the absence of
tides (Björck 1995).
6
2.2. Sedimentation of the Baltic Sea Basin
Four significant factors influence the stratigraphic characteristics and properties of the
BSB sediments. The source material and variations in the salinity contribute to grain size
mineralogical composition and organic components of the deposits. The bedrock of the
sea floor and the land areas surrounding it affects the sediments and the resulting
morphology of the sea floor. Sea floor topography and bathymetry in relation to
prevailing air pressure and wind fetch conditions, along with depth to wave base and near
bottom currents govern sedimentation, non-deposition and erosion balance. Biological
factors, such as bioturbation, have also influenced the BSB sediments. (Winterhalter
1992.)
The strong variability in bedrock lithology and the distribution of deformable Quaternary
sediments made the Baltic region favourable for the development of a thin and mobile ice
sheet (Lambeck et al. 1998). Various internal and external factors have affected the
climate in the Baltic Sea region during the Holocene. Changes in the Earth's orbit and
variations in incoming seasonal solar radiation, changes in the land surface, volcanic
activity and the concentration of atmospheric greenhouse gases were the main external
climate drivers during the deglaciation (Borzenkova et al. 2015). Intensive water-table
fluctuations characterized the different stages of the BSB. The subdivision of the BSB
into four different stages is related to water exchange between the Baltic Sea and the
world ocean (Lepland and Stevens 1998). River discharge and meltwater caused the
balance between water-table and glacio-isostatic uplift to rise, which led either to a
temporary connection between the BSB and the world ocean, or to isolation of the BSB
(Lampeck et al.1998).
2.3. The development of the late and postglacial Baltic Sea Basin
The Baltic Sea region had an interstadial sequence with occasional glaciation and boreo-
arctic proglacial fjords between ca. 40.0 and 30.0 ka (Houmark-Nielsen and Kjær 2003).
7
This was followed by a Last Glacial Maximum (LGM) sequence at ca. 30.0–20.0 ka, with
the closure of subsequent ice streams and fjords (Houmark-Nielsen and Kjær 2003). After
25.0 ka the expansion of the ice sheet occurred mostly along the southern and eastern
terrestrial margins (Hughes et al. 2015). The estimated extent of the ice sheet between
25.0 and 18.0 ka is illustrated in Figure 1, based on the reconstructions by Hughes et al.
(2015). Uncertainty estimates of the extent of the ice sheet area are presented by
maximum, minimum and most-credible lines.
Figure 1. The extent of the ice sheet in the Baltic region between 25.0 and 18.0 ka. Three lines represent
the uncertainty in the data. Dashed line: maximum ice sheet area, dotted line: minimum ice sheet area, solid
white line and shaded white area: most-credible ice sheet area. Figures modified from Hughes et al. (2015).
8
According to Hughes et al. (2015), a peak in the total ice sheet area and volume occurred
at 21.0–20.0 ka. Three ice-margin fluctuations of the south-eastern margin of the SIS
were identified between 25.0 ka and 12.0 ka (Rinterknecht et al. 2006). Deglacial
millennial-scale climate variability, along with its effect on surface mass balance,
influenced strongly to the rates of SIS margin retreat (Cuzzone et al. 2016). Lambeck et
al. (2010) summarised that the ice sheet advanced and retreated several times and the
maximum advance was not simultaneous in Scandinavia at the time of the LGM. The
advance of Baltic ice streams, the retreat of the Swedish ice, and the transgression of
arctic waters lead to interstadial conditions, which are indicated by a deglaciation
sequence between ca. 20.0 and 15.0 ka (Houmark-Nielsen and Kjær 2003). The glaciers
advanced and reached the largest extent in the Baltic region ca. 18.0 ka ago (Houmark-
Nielsen and Kjær 2003).
2.3.1 The Baltic Ice Lake
The first embryo of the BIL formed at ca. 16.0 ka (Houmark-Nielsen and Kjær 2003).
The BIL was most likely at sea level during its initial stage, and the updamming of the
lake possibly started due to uplift of the Öresund threshold area, which lifted the lake area
above sea level at ca. 14.0 ka (Andrén et al. 2011). The BIL captured meltwater from the
retreating ice sheet and the drainage of most river systems from Europe and western
Russia (Patton 2017). Andrén et al. (2011) concluded that the first drainage of the BIL is
estimated to have taken place 13.0 ka ago, due to the altitudinal difference between the
gradually risen sea and the level of the BIL. The drainage was possibly caused by the ice
recession at Mt. Billingen and at the northern part of the south Swedish highlands (Andrén
et al. 2011). Figure 2 demonstrates the deglaciation of the Baltic region and different
stages of the retreating ice sheet between 14.0 and 11.0 ka. At the time of the Younger
Dryas (YD) cooling at ca. 12.8 ka, the ice sheet re-advanced, blocking the northern
drainage of the BIL which led to transgression (Andrén et al. 2011).
9
Figure 2. The retreat of the ice sheet and deglaciation of the Baltic region between 14.0 and 11.0 ka. Three
lines represent the uncertainty in the data. Dashed line: maximum ice sheet area, dotted line: minimum ice
sheet area, solid white line and shaded white area: most-credible ice sheet area. Figures modified from
Hughes et al. (2015).
Figure 3 illustrates the BIL at ca. 11.7 ka prior to the maximum extension and final
drainage, which took place when a new passage opened in south central Sweden
(Bergsten and Kjell 1992). The water level of the BIL was abruptly lowered – ca. 25 m
over a period of 1–2 years – down to sea level (Andrén et al. 2011). The final drainage of
the BIL is estimated to occur at ~11.7 ka (Andrén et al. 2015a). It had a great impact on
the BIL environment e.g. changes in fluvial systems, reworking of sediments, and
exposure of large coastal areas (e.g. Andrén et al. 2011, Hyttinen et al. 2011).
10
Figure 3. Paleogeographic map of the Baltic Ice Lake (light grey area) at ca. 11.7 ka, prior to the maximum
extension and final drainage. Figure modified from Andrén et al. (2011).
2.3.2. The Yoldia Sea
According to Andrén et al. (2011) the onset of the YS stage coincides with the beginning
of the Holocene epoch at ~11.7 ka, and the rapid warming related with that. The lowering
of the BIL down to the YS level possibly was as rapid as the warming, and 25 m
displacement of the shores led to emerged zones rich with clay and silt, and most likely
the YS deposits consist of reworked BIL clays (Björck 1995). Björck (1995, according to
Brunnberg 1998) concluded that a distinct change from a brown clay, to a rather thick-
varved dark grey clay might indicate abrupt increase of deglaciation and sedimentation
rates, which correlates to the transition from the BIL to the YS.
The brackish phase of the YS is documented by the varve lithology, along with
geochemistry and marine/brackish fossils. An occasional show up of sulphide banding
implies a halocline, which gives an estimation of 350 years as maximum duration of the
brackish phase (e.g. Heinsalu et al. 2000, Andrén et al. 2011). The high uplift rate caused
11
rapid shallowing of the strait area, and this prevented the saline water inflow to the Baltic,
turning the YS into a freshwater basin. (Andrén et al. 2011.) The end of the YS stage is
marked by the shallowing of the outlets in the west of Lake Vänern, caused by isostatic
rebound around the lake, which led to large outflow from the Baltic (Andrén et al. 2011).
2.3.3. The Ancylus Lake and the Littorina Sea
The AL began after the water level raised due to shallowing of the outlets in the west of
Lake Vänern. The melt water input from the final deglaciation of the ice sheet, and the
quite immaculate soils of the deglaciated drainage area, consequenced to organic-poor
sediment deposits in the large freshwater lake. This led to an aquatic environment, which
had low nutrient input and productivity. The AL stage ended when the lake was at
approximate level with the sea in the west and saltwater possibly entering the lake.
(Andrén et al. 2011.)
The first signs of saline water entering the basin, and a minor increase of brackish-
freshwater diatom taxa is recorded at ca. 9950–9750 ka (Andrén et al. 2000a). This period
with low saline influence is called the Initial Littorina Sea (Andrén et al. 2000b). The
Littorina Sea stage is characterized by lithological changes, apparent increase in organic
content, and abundance of brackish marine diatoms (Andrén et al. 2011).
2.4. The Landsort Deep
The Landsort Deep is the deepest part of the Baltic Sea and it is located at the western
part of the Gotland basin, between the southeast coast of Sweden and the island of
Gotland (Figure 4). The Landsort Deep is a crescent-shaped crack with very steep walls
(Myrberg et al. 2006). It is a comparatively narrow trench, with a width of 3.2 km and
length of 20 km, and the location of the deep is along a major fault line, which is deepened
12
by glacial erosion (Lepland and Stevens 1998). The geometry of the Landsort Deep
enables protection to sediments from subsequent glacial erosion (Andrén et al. 2015b).
Figure 4. Map showing the location of the Landsort Deep in the central Baltic Sea.
The salinity of the water at the western part of the Gotland basin is 6.3–7.7‰ at the
surface, 8.7–10.3‰ beneath the halocline in the depth of 100 m, and 10–11.5‰ near the
seabed at Landsort Deep (Myrberg et al. 2006). The intense stratification of the basin and
great depth cause oxygen problems in the water near the seafloor (Myrberg et al. 2006).
The halocline of the water-column is at about 50 to 80 m, separating surface waters with
a salinity of 7–8‰, from the bottom waters with a salinity varying between 8‰ and 13‰
(e.g. Lepland and Stevens 1998, Böttcher and Lepland 2000,). The limited inflow of
oceanic water and the stratification of the water column leads to depletion of oxygen in
the bottom waters (Böttcher and Lepland 2000). Landsort Deeps water column is
stratified into three different zones: oxic, suboxic and anoxic (Berndmeyer et al. 2014).
13
Landsort Deep has a high sedimentation rate of 100–500 cm kyr–1 (Andrén et al. 2015b),
and it has varied between 100 and 650 cm kyr–1 from 11.0 ka ago to present day (Obrochta
et al. 2017). Sediments of the deep display the transition from low-organic glacial clay
deposits to organic-rich Holocene clay deposits, and this transition indicates the
changeover from glacial to interglacial, and from freshwater to brackish marine
conditions (Andrén et al. 2015b).
3. MATERIALS AND METHODS
3.1 Site M0063
The cores studied here were recovered during Integrated Ocean Drilling Program (IODP)
Expedition 347, “Baltic Sea Paleoenvironment”, at the Baltic Sea. The drilling occurred
at Site M0063 (58°37.34ʹN, 18°15.25ʹE, water depth 437 m), in the Landsort Deep. Five
holes were drilled at the site: Hole M0063A, M0063B, M0063C, M0063D and M0063E.
The average site recovery was 97.9%. Materials used in this study are from cores
recovered from Hole M0063C, as it has the greatest continuous penetration (Andrén et al.
2015b).
Details of the operations at Hole M0063C are described in the Expedition report 347
(Andrén et al. 2015b), and summarised here. The recovery was 99.29% at Hole M0063C.
For gaining the maximum recovery of the expanding sediments, before firing the piston
corer system (PCS), it was pulled back 1.3 m from the base of each washed-out interval.
The bottom-hole assembly (BHA) was advanced 2 m after each PCS sample run. The
procedure provided the most complete sequence within the expanding sediment package.
The coring continued until diamicton was encountered at 93.3 adjusted meters below
seafloor (ambsf). This nonoverlapping depth scale for each hole was constructed by
Obrochta et al. (2017) by calculating a new depth scale for all cores. The ambsf depth
14
scale took account of the expansion that the cores experienced due to degassing during
decompression. The hole was opened 3 m, and a hammer sample was taken. The sample
confirmed that the coring had encountered diamicton, and the hole was terminated.
Altogether 40 cores were successfully recovered from Hole M0063C, including one open-
hole section. The maximum depth reached was 96.40 ambsf
3.2. Physical properties measurements
The condensed method description is based on the Expedition 347 report (Andrén et al.
2015b). All physical parameters were measured in one run from core sections shortly after
recovery. During the whole analytical process, all sections were handled in the same way
to guarantee consistency in treatment. Measuring device was automated GEOTEK®
Multi-Sensor Core Logger (MSCL). Standard - MSCL track outfitted with four primary
sensors was used for measuring P-wave velocity, gamma density, magnetic susceptibility
(MS) and non-contact electrical resistivity. Fast Track – MSCL track outfitted with two
primary sensors were working offset measuring magnetic susceptibility. For a complete
lithological sample information, visual examination and written descriptions were
produced from all the cores and core catcher material, along with images of the core
archive halves.
3.3. Age determination, depth scale adjustment and correlation
Age determinations of the studied sediments were derived from different types of
methods, or compilation of those methods. The different stages of the BSB and phases of
the SIS were determined for example by geochronological data from varves (e.g. Andrén
et al. 2002, Stroeven et al. 2015a), radiocarbon, 14C, (e.g. Obrochta et al. 2017,
Rinterknecht et al. 2006), optically-stimulated luminescence, OSL (Houmark-Nielsen
15
and Kjær 2003) and cosmogenic nuclide,10Be dating (e.g. Cuzzone et al. 2016,
Rinterknecht et al. 2006).
15 samples from Hole M0063C (43–86 ambsf) were radiocarbon dated at the University
of Tokyo for age model and determination (Obrochta et al. 2017). The calibrated
radiocarbon ages of 12 cores from Units VI and V (49.408–85.836 ambsf) vary between
21533 and 24820 cal BP and they are not consistent in relation to depth. The reworked
material of the units strongly affected the radiocarbon ages and the resulted radiocarbon
dates are older than the construed age of deglaciation at Landsort Deep and not in relation
with the known knowledge of the geological events in the Baltic region (Obrochta et al
2017).
Results from this study's analyses are compared with former analyses from the Baltic Sea
area and Holocene marine sedimentation. The relatively age determination for sediments
of Units VI and V between 48 and 93 ambsf are based on the existing knowledge of the
geological history of the BSB, interpretation of the lithostratigraphy of the units and
educated guesses.
3.4. Grain size analysis
The 76 samples (Figure 4) studied are from the depths of Units VI (54–93 ambsf) and V
(48–54 ambsf). Before the laser diffractometer analysis, the samples were oxidized to
reduce the amount of organic matter. The oxidation was carried out with aliquots of 30%
hydrogen peroxide (H2O2) and with an addition of hydrochloride (HCl). Before the laser
analysis, the samples were also chemically treated with 300 mg of sodium pyrophosphate
(Na4P2O7) to prevent particles from flocculating. The samples were also mechanically
treated with 10µm amplitude ultrasound (Figure 5) for 30 seconds before measurements.
16
Figure 5. Two samples from the 76 samples from Hole M0063C, Units VI and V, and Soniprep 150 ultrasound
device at the Department of Geosciences and Geography at the University of Helsinki.
The samples were analysed using the Department of Geosciences and Geography
Malvern Mastersizer 2000G device (Figure 6). The necessary amount of material from
the samples was used to achieve a beam obscuration of 15–20% on the laser equipment.
Each sample was measured three times with 750rpm stirrer speed and 2000rpm pump
speed.
Figure 6. Malvern Mastersizer 2000G laser diffractometry device at the Department of Geosciences and
Geography at the University of Helsinki.
The analysis of grain size statistics from the laser diffractometry results is derived from a
computer program called GRADISTAT (Blott and Pye 2001). The program runs within
the Microsoft Excel spreadsheet package.
17
3.5. LOI determination
The loss on ignition (LOI) is a method used in estimating the organic matter and water
content of sediments. The samples were heated in a muffle furnace to determine the
weight percent of organic material by means of LOI (Heiri et al. 2001). The technique is
commonly used in reconstructions of Holocene glacier variations, especially with
glaciolacustrine sediments.
29 samples were chosen to be studied with the LOI method. Heating the samples in the
hot air oven removed pore water from the samples. By igniting the samples in furnace,
the amounts of organic matter and crystallization water could be estimated. First the
empty ceramic crucibles were weighted, and then the crucibles and samples were
weighted. Samples were dried in the oven at 105°C overnight and then cooled in
desiccator. Dried samples and the crucibles were weighted and placed in a muffle furnace
and kept at 550° C for 2 hours. After that, the samples were cooled again in desiccator
and weighted. The weights of crucibles were subtracted to determine the mass loss, and
the result reported was LOI%. LOI was calculated using the following equation from
Heiri et al. (2001)
LOI550 = ((DW105–DW550)/DW105)*100
In the equation DW105 represents the dry weight of the sample before combustion, and
DW550 is the dry weight of the sample after heating to temperature of 550 °C In addition,
total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC) and sulphur
(S) measurements from Units VI and V (Expedition 347 Scientists 2014a) were used.
18
4. RESULTS
4.1. Lithostratigraphy of Units VI and V
The description of the lithostratigraphy of Units VI and V is based on the report by
Andrén et al. (2015b), visual images are from Expedition 347 Scientists (2014b), and
these are supplemented by grain size concentration of 76 samples derived from
GRADISTAT.
Unit VI is more than 40 m thick and it is the thickest unit at Site M0063. The unit consists
of finely laminated varved clay, and is featured by a down-core increase of silt and sand
content, which is indicated by dispersed pebble content and thicker laminae. Well-sorted
sand laminae and dispersed clasts occur in the lower parts of the unit, and the percentage
of very coarse sand is 1–2 vol% at 72.58, 75.38–75.88, 76.88, and 86.75 ambsf, and 14
vol% at 70.33 ambsf. Coarse sand is present in a few samples between 68.83 and 82.45
ambsf, with a maximum concentration of 1 vol%.
The concentration of very coarse silt varies from 1 to 11 vol% at depths between 66.67
and 90.08 ambsf. Mostly brown and weak red coloured clay-silt-sand interlaminations
are present upward from ~85 ambsf in thicker units. Occasional internal mm-scale silt
laminae and slumping, packed to cm-scale, within 2–20 cm thick clay laminae is also a
common feature of Unit VI. At 82.45 ambsf medium and fine sand are present with a
percentage of 4–5 vol%. Very fine sand with a concentration of 1–3 vol% appears only
in few depths in Unit VI. Scattered cm-scale carbonate concretions within mm-scale silt
laminae can be identified upward from ~75 ambsf.
The percentage of very fine silt varies between 14 and 28 vol%, with the lowest values
concentrated below ~68 ambsf. The percentage of coarse silt varies between 1–19 vol%,
with the highest values (>10 vol%) concentrated below ~67 ambsf. There are several
distinct fining-upward couplets present with depth, as well as mm-scale sand laminae and
19
pockets. The share of fine silt varies between 12–25 vol%, with values >20 vol%
appearing below ~62 ambsf. The concentration of medium silt varies between
13– 23 vol%, with the highest values (>10 vol%) appearing also below ~62 ambsf. The
uppermost part of the unit is presented by mm- to cm-scale dark grey-brown clay, and it
is interlaminated by mm-scale silt laminae. Very coarse silt with a concentration of
0– 2 vol% is present only at various depths in Unit VI. Very coarse silt with a
concentration of 18 vol%, along with very fine sand with a concentration of 9 vol% are
present at 58.43 ambsf.
Unit V is distorted, convolute bedded clay which varies from dark grey to greyish brown
in colour and is very well sorted. In parts the internal structures show a massive
appearance, although contorted silt laminated intervals with clear convolute bedding are
visible. At the lower parts of the unit cm-scale laminated clay is displaced by microscale
transverse faults. Very coarse silt with a concentration of 0–2 vol% and very fine sand
with a concentration of 1–3 vol% occur only in a few depths in Unit V.
The lithostratigraphy of Unit VI and V is illustrated in Figure 7. The lowest section
between 92.12 and 93.02 ambsf has a massive, diamictic and homogeneous structure, and
it is moderately or highly disturbed, and poorly sorted. The sections from 77.37 to 92.12
and between 54.5 and 77.37 ambsf have laminated structure, and they are slightly
disturbed. The lower section (77.37–92.12 ambsf) of this continuous unit is well or very
well sorted, and the upper section (54.5–77.37 ambsf) very well sorted. The section from
50.0 to 54.5 ambsf has also laminated and slump bedding structure, with an addition of
homogeneous structure. These sections are slightly or moderately disturbed and very well
sorted. The lithology of the units is mainly of clay and silt content, with a small amount
of sand content at the depth of 55–92 and 48–50 ambsf. The uppermost section between
48 and 50 ambsf is laminated, and has a convolute and slump bedding structure.
20
Figure 7. Lithostratigraphy of Units VI and V at 48–93 ambsf. Data from Expedition 347 Scientists (2015).
Figure 8 represents visual examples of lithostratigraphy features from Figure 7 of Unit
VI and V. Core 39–1 (90.8–93.3 ambsf) shows massive, moderately or highly disturbed
diamict and sandstone (Figure 8a). Silt is more dominant in core 37–1 (84–87.5 ambsf)
and the sediment is laminated by grain size and colour and slightly disturbed (Figure 8b).
Cores 33–2 (71–74.3 ambsf), 32–2 (67.7–71 ambsf) and 30–2 (61.1–64.4 ambsf) are silt
dominated, and, also laminated by grain size and colour (8c, d, e). There is also a clear
carbonate concretion in core 33–2, and a massive clay interbed in core 32–2. Core 27–2
(52–54.5 ambsf) shows a clayey and silty homogenous structure, and core 26–2
(50– 52 ambsf) slightly or moderately disturbed lamination and slump bedding. Figure
8h illustrates convolute bedding and slumping in moderately disturbed and deformed
sediment in core 25–2 (48–50 ambsf).
21
a) 39–1 b) 37–1 c) 33–2 d) 32–2 e) 30–2 f) 27–2 g) 26–2 h) 25–2
Figure 8. Examples of diamict and sandstone (a), clay and fine sand-silt laminated by color and grain size
(b, c, d, e), carbonate concretion (c), massive clay interbed (d), homogeneous grey clay and silty clay (f),
slumping, deformation and disturbance (g and h). Images modified from Expedition 347 Scientists (2014b).
The recovered cores were described in detail and photographed by the Expedition 347
Scientists. The description of the cores is based on Expedition 347 Scientists (2015) report
and the core images are modified from Expedition 347 Scientists (2014b). The lowermost
part of Unit VI, Core 39 (90.8–93.3 ambsf) is brown, poorly sorted, and clast poor sandy
diamict and sandstone with pebbles (Figure 8a and 9a). There is also slightly disturbed
22
interlamination by grey/brown silt and clay, with few dispersed pebbles. Core 38 (87.5–
90.8 ambsf) is well sorted grey clay and silty clay, with fine sand-silt laminations
throughout the core at varying intensities (Figure 9b). Figures 8b and 9c show that core
37 (84.2–87.5 ambsf) is grey clay with mm-scale fine sand-silt and color laminations
throughout the core at varying intensities and mm-cm-scale spacings.
a) b) c)
Figure 9. Core images from Hole M0063C: a) 39/90.8–93.3 ambsf, b) 38/87.5–90.8 ambsf, c) 37/84.2–87.5
ambsf. Images modified from Expedition 347 Scientists (2014b).
Core 36 (80.9–84.2 ambsf) is greyish brown clay, which is interlaminated by silt laminae,
and they are occasionally bundled (Figure 10a). Grey clay with mm-scale fine sand-silt
and color laminations at varying intensities and spacings is the dominant feature
throughout core 35 (77.6–80.9 ambsf) (Figure 10b). Core 34 (74.3–77.6 ambsf) is greyish
brown clay, which is interlaminated by silt laminae (Figure 10c). Grey clay and silty clay
varies in core 33 (71–74.3 ambsf). It is well sorted with mm-scale color and fine silt-sand
laminations occurring in cm-scale in unequal distributions (Figure 8c and 10d). There is
also a carbonate concretion at 120 cm in section 2.
23
a) b) c) d)
Figure 10. Core images from Hole M0063C: a) 36/80.9–84.2, b) 35/77.6–80.9 ambsf c) 34/74.3–77.6 ambsf,
d) 33/71–74.3 ambsf. Images modified from Expedition 347 Scientists (2014b).
The content of core 32 (67.7–71 ambsf) is mainly dark grey clay, which is planar, parallel
laminated by color (Figure 8d and 11a). There is also a massive clay interbed in section
1 at 45–55 cm, and in section 2 at 65–85 cm. Section 4 (CC) is highly disturbed by coring.
All though core 31 (64.4–67.7 ambsf) is dark grey clay, which is mostly laminated by
color and grain size, there are also homogeneous parts in section 2 and 3 (Figure 11b).
Planar, parallel laminated dark grey clay is the main feature of core 30 (61.1– 64.4 ambsf)
but there are silt laminae with uneven thickness and distribution throughout the sections,
and section 3 also has a massive homogeneous dark grey clay interbed (Figure 11c). Core
29 (57.8–61.1 ambsf) is dark grey clay with lamination by color and grain size (Figure
11d).
24
a) b) c) d)
Figure 11. Core images from Hole M0063C: a) 32/67.7–71 ambsf, b) 31/64.4–67.7 ambsf, c) 30/61.1–64.4
ambsf, d) 29/57.8–61.1 ambsf. Images modified from Expedition 347 Scientists (2014b).
The main feature of core 28 (54.5–57.8 ambsf) is dark grey clay with faint lamination by
color (Figure 12a). Section 3 has visible layers, and there are also dispersed sand grains
in sections 2 and 3. Core 27 (52–54.5 ambsf) is dark grey clay with lamination or faint
lamination by color (Figure 8f and 12b). There are dispersed intraclasts and slumping
features, and sections 1 and 2 are slightly deformed and disturbed. Interlaminated dark
grey and dark greyish brown clay is the main feature of core 26 (50–52 ambsf) (Figure
8g and 12c). Bedding is strongly contorted in sections 1 and 2, and there are also micro-
faults and steep inclining and disturbance by slumping. Core 25 (48–50 ambsf) is dark
grey clay with intraclasts (Figure 8h and 12d). There occurs soft-sediment deformation
and convolute bedding or slumping. The sediment is moderately or highly disturbed.
25
a) b) c) d)
Figure 12. Core images from Hole M0063C: a) 28/54.5–57.8 ambsf, b) 27/52–54.5 ambsf, c) 26/50–52
ambsf, d) 25/48–50 ambsf. Images modified from Expedition 347 Scientists (2014b).
4.2. Physical properties of Units VI and V
Natural gamma ray (NGR) data shows that, regardless of the expansion of the sediment
and coring disturbances, the sediment record recovery was nearly continuous (Andrén et
al. 2015b). The NGR values remain relatively high (~20cps) and constant through Units
VI and V, and there are also meter-scale peaks of lower values throughout the units
(Figure 13) The distortion between 45–53 ambsf is caused by expansion of the sediment
(Andrén et al. 2015b). Discrete P–wave velocity in Unit VI is typically ~1500 m s–1, and
~1250 m s–1 in Unit V. Zero values are due to distortion at the top and bottom of the core
(Andrén et al. 2015b). Dry density increases downhole and through Unit VI it is generally
>1 g cm³. There is a general declining trend of density from bottom of Unit VI to the top
of Unit V, which is positively related to a decrease in sample wet density
(Andrén et al. 2015b). Large excursions in magnetic susceptibility (MS) are limited to the
lower portion of Unit VI.
26
Figure 13. Natural gamma radiation, P-wave velocity, density and magnetic susceptibility values of Units VI
(54–93 ambsf) and V (48–54 ambsf). Dashed lines marking the changes in physical properties trends. Data
from Expedition 347 Scientists (2014c).
48
53
58
63
68
73
78
83
88
93
10 15 20 25
DE
PT
H (
am
bsf)
NATURAL GAMMA RADIATION (cps)
48
53
58
63
68
73
78
83
88
93
0 400 800 1200 1600 2000
DE
PT
H (
am
bsf)
P-WAVE VELOCITY (m s–1)
48
53
58
63
68
73
78
83
88
93
0,8 1,2 1,6 2 2,4
DE
PT
H (
am
bsf)
GAMMA DENSITY (g cm³)
48
53
58
63
68
73
78
83
88
93
0 50 100 150 200 250 300
DE
PT
H (
am
bsf)
MAGNETIC SUSCEPTIBILITY (IUs)
27
The MS, density, P-wave velocity and NGR values of Units VI and V are divided into
sections of certain depths and are illustrated in Figures 14–17. There are larger excursions
in MS at the lower parts of Unit VI between 81 and 93.3 ambsf, and the values vary from
40 to 160 10–5 instrument unit (IUs). The average value between 68 and 81 ambsf is 60
IUs. The values are quite constant from 48 to 68 ambsf, settling between 30 and 40 IUs,
with the addition of a few peaks of higher values.
Figure 14. Magnetic susceptibility of cores from Unit VI and V from depths between 48 and 93 ambsf. Data
from Expedition 347 Scientists (2014c).
87
88
89
90
91
92
93
60 160 260
am
bsf
IUs
81
82
83
84
85
86
87
40 80 120 160
am
bsf
IUs
75
76
77
78
79
80
81
40 60 80 100
am
bsf
IUs
69
70
71
72
73
74
75
20 40 60 80
am
bsf
IUs
63
64
65
66
67
68
69
20 40 60 80
am
bsf
IUs
58
59
60
61
62
63
20 40 60 80
am
bsf
IUs
53
54
55
56
57
58
20 40 60
am
bsf
IUs
48
49
50
51
52
53
0 60 120 180
am
bsf
IUs
28
Figure 15 shows that density decreases upward in the units. Density is ~2 g m3 from 87
to 93 ambsf, and the highest value (>2 g m3) appears at 92–93 ambsf. Peaks of lower
values also occur at 90.5 and 93 ambsf. At 75–87 ambsf the values vary between 1.8 and
2 g m3, and at 50–75 ambsf between 1.6 and 1.8 g m3. Upward from 49 ambsf the density
decreases to 1.4 g m3.
Figure 15. Density of cores from Unit VI and V from depths between 48 and 93 ambsf. Data from Expedition
347 Scientists (2014c).
P-wave velocity varies approximately between 1000 and 1500 m s-1 throughout Units VI
and V, with an exception of few peaks of lower values (Figure 16). A relatively constant
value of 1500 m s-1 is present at 81–83, 78.5–80.5, 61–63 and 59–60.5 ambsf. There are
frequent variations of velocity in relation to depth between 48 and 53 ambsf.
87
88
89
90
91
92
93
0,8 1,4 2 2,6
am
bsf
g m3
81
82
83
84
85
86
87
1,6 1,8 2 2,2
am
bsf
g m3
75
76
77
78
79
80
81
1,6 1,8 2 2,2
am
bsf
g m3
69
70
71
72
73
74
75
1,4 1,8 2,2
am
bsf
g m3
63
64
65
66
67
68
69
1,6 1,8 2
am
bsf
g m3
58
59
60
61
62
63
1,4 1,6 1,8 2 2,2
am
bsf
g m3
53
54
55
56
57
58
1,4 1,6 1,8
am
bsf
g m3
48
49
50
51
52
53
1,2 1,4 1,6 1,8
am
bsf
g m3
29
Figure 16. P-wave velocity of cores from Unit VI and V from depths between 48 and 93 ambsf. Data from
Expedition 347 Scientists (2014c).
Figure 17 illustrates that the NGR values vary between 15 and 20 cps at 87–93 ambsf,
and from 69 to 87 ambsf the values are ~20 cps, with a few peaks of lower values. From
61 to 69 ambsf, there is a slight increase of values to >20 cps, and between 48 and 61 the
values settle again at ~20 cps. The lowest value (10 cps) occurs at 52 ambsf.
87
88
89
90
91
92
93
500 1500
am
bsf
m s-1
81
82
83
84
85
86
87
500 1000 1500
am
bsf
m s-1
75
76
77
78
79
80
81
750 100012501500
am
bsf
m s-1
69
70
71
72
73
74
75
0 500 10001500
am
bsf
m s-1
63
64
65
66
67
68
69
250 750 1250
am
bsf
m s-1
58
59
60
61
62
63
750 1500
am
bsf
m s-1
53
54
55
56
57
58
500 1000 1500
am
bsf
m s-1
48
49
50
51
52
53
500 1000 1500
am
bsf
m s-1
30
Figure 17. Natural gamma ray of cores from Unit VI and V from depths between 48 and 93 ambsf. Data from
Expedition 347 Scientists (2014c).
4.3. Grain size analysis
4.3.1. Clay, silt and sand content
The mean grain size of the 76 samples from Unit VI and V from depths between 49
and 90 ambsf is described by using a scale in which the grain size of <2 µm is classified
as clay, 2–63 µm is silt, and >63 µm is sand. Figure 18 shows the change of the clay-silt
ratio in relation to depth. The silt content decreases and clay content increases upward,
87
88
89
90
91
92
93
10 15 20 25
am
bsf
cps
81
82
83
84
85
86
87
15 20 25
am
bsf
cps
75
76
77
78
79
80
81
10 15 20 25
am
bsf
cps
69
70
71
72
73
74
75
10 15 20 25
am
bsf
cps
63
64
65
66
67
68
69
15 20 25
am
bsf
cps
58
59
60
61
62
63
15 20 25
am
bsf
cps
53
54
55
56
57
58
15 20 25
am
bsf
cps
48
49
50
51
52
53
10 15 20 25
am
bsf
cps
31
and between 66 and 90 ambsf the clay content is 20–30 vol% and silt content 70–80 vol%.
The sand content in the lower part has a maximum percentage of 5 vol%, and notable
peaks approximately at 58, 70 and 82 ambsf. Between 49 and 66 ambsf the clay content
is 40–60 vol%, silt 40–60 vol%, and sand 0–5 vol%. The percentage of clay and silt are
relatively equal in the upper part.
Figure 18. Clay, silt and sand content (vol%) of the 76 samples. The samples are from Units VI and V, from
different depths between 49 and 90 ambsf. Arrow pointing the boundary between Unit VI and V.
The grain size scale was divided into certain size fractions of silt and sand. This enabled
the construction of the volume percentage in each size fraction. The scale of sand grain
size fraction is divided between the ranges of 63–200 µm, 200–600 µm and 600–2000 µm
(Figure 19). Between 57 and 63 ambsf the content is fine/very fine and medium sand.
Below 68 ambsf the dominant size fraction of sand content varies from medium to
coarse/very coarse sand. The highest coarse content is approximately at 75 ambsf. A
notable factor is the absence of sand content at depths of 50–57 and 64–67 ambsf. The
silt grain size fraction is divided into 2–4 µm, 4– 16 µm and 16–63 µm (Figure 19). There
0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %
49
53
55
57
59
61
63
65
67
69
71
73
75
76
78
81
82
84
86
Depth
(am
bsf)
Content (vol%)
Clay < 2µm Silt 2-63 µm Sand 63-2000 µm
32
is a decrease of medium/coarse silt content and an increase of very fine silt/clay content
upward the units. A peak of coarser material appears at 58 ambsf.
Figure 19. The percentage of grains falling into each size fraction of sand and silt. The samples are from
different depths between 49 and 90 ambsf from Units VI and V.
0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %
49
53
55
57
59
61
63
65
67
69
71
73
75
76
78
81
82
84
86
Depth
(am
bsf)
Sand content (vol%)
63-200 µm 200-600 µm 600-2000 µm
0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %
49
53
55
57
59
61
63
65
67
69
71
73
75
76
78
81
82
84
86
Depth
(am
bsf)
Silt content (vol%)
2-4 µm 4-16 µm 16-63 µm
33
4.3.2. Distribution and d-values
Figure 20 illustrates the grain size distribution of the 76 samples. The type and textural
group of the samples is unimodal and poorly sorted mud, with an exception of three
samples, which are bimodal and very poorly sorted sandy mud. Sediment varies from
very fine, fine, and medium silt to medium sandy fine silt, very coarse sandy fine silt,
very fine sandy coarse silt, and mud.
Figure 20. Grain size distribution of the 76 samples from Unit VI and V.
Figures 21–24 provide visual images of 14 samples, as well as their grain size distribution.
Figure 21 shows samples from the lower part of Unit VI from depths between 87.5 and
93.3 ambsf. The sediment name of sample 38–2 is very fine silt and sample 37–2 is fine
silt. The content of these samples is 96–100 vol% mud and 0–4 vol% sand.
0
1
2
3
4
5
0,2 2 20 200 2000
Vol%
Grain size (µm)
34
Figure 21. Grain size distribution and cm-scale images of samples from Unit VI. Images modified from
Expedition 347 Scientists (2014b).
Samples from depths 67.7–87.5 ambsf are illustrated in Figure 22. Sample 36–2 is
medium sandy fine silt, sample 32–2 is very coarse sandy fine silt. These samples are
13– 16 vol% sand and 84–87 vol% mud. Sample 35–1 is very fine silt, and samples 34– 2
and 33–1 are fine silt. These samples are 96–100 vol% mud and 0–4 vol% sand.
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
38–2/108–110cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
37–2/105–107cm
35
Figure 22. Grain size distribution and cm scale images of samples from Unit VI. Images modified from
Expedition 347 Scientists (2014b).
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
36–2/5–7cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
35–1/82–84cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
34–2/8–10cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
33–1/57–59cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
32–2/113–115cm
36
Samples from Unit VI between 54 and 67.7 ambsf are presented in Figure 23, and samples
from Unit V between 48 and 54 ambsf are illustrated in Figure 24. The samples from
31– 1 to 25–2 are mud, with the exception of sample 30–2 beeing very fine silt. These
sample are almost all 100% mud, and the main grain size is clay with distribution between
31 and 57 vol%.
Figure 23. Grain size distribution and cm scale images of samples from Unit VI. Images modified from
Expedition 347 Scientists (2014b).
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
31–1/17–19cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
30–2/47–49cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
29–1/114–116cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
28–1/70–72cm
37
Figure 24. Grain size distribution and cm scale images of samples from Unit V. Images modified from
Expedition 347 Scientists (2014b).
The d-values were used to illustrate volume distribution of the 76 samples from depths
between 49–90 ambsf. The d-values are the intercepts for 10 vol%, 50 vol% and 90 vol%
of the cumulative mass. Figure 26 shows an increase of coarser material downward from
~67 ambsf, which is in line with Figures 17–19.
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
27–1/18–20cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
26–2/78–80cm
0
2
4
6
0,01 0,1 1 10 100 1000 10000
Vol%
µm
25–2/64–66cm
38
Figure 25. The d(10), d(50) and d(90) values based on a volume distribution from all 76 measured samples
from Unit VI and V.
A table of d(10), d(50) and d(90) values from four samples from Units VI and V displays
examples of the volume distribution of different sediment types (Table 1). Sample
36– 2/5–7cm (82.45–82.47 ambsf) is medium sandy fine silt, and sample 33–1/57–59cm
(71.57–71.59 ambsf) is fine silt. The latter represents the most common volume
distribution of the samples. Sample 32–2/113–115cm (69.93–69.95 ambsf) is very coarse
sandy fine silt, and the high d(90) value of the sample and the grain size variation is also
visible in the cm scale image of the sample in Figure 23. Sample
27– 1/18– 20cm (52.18– 52.20 ambsf) values represents the volume distribution of mud.
Table 1. The d(10), d(50) and d(90) values and depths from samples from Unit VI and V.
Sample Depth (ambsf) d (10) d (50) d (90)
36–2/5–7cm 82.45–82.47 1.202 6.535 124.3
33–1/57–59cm 71.57–71.59 1.270 6.167 23.3
32–2/113–115cm 69.93–69.95 1.363 8.084 1402.4
27–1/18–20cm 52.18–52.20 0.595 1.992 7.8
48
53
58
63
68
73
78
83
88
93
0 1 10 100 1000
Depth
(am
bsf)
d (10) d (50) d (90)
39
4.4. Carbon and LOI values, and water content
The sedimentary total carbon (TC), total organic carbon (TOC), total inorganic carbon
(TIC), and sulphur values determined by Expedition 347 Scientists (2014a) are illustrated
in Figure 27. TC values are relatively low and vary from 0.2 to 0.5 wt% in Units VI and
V. The sediments of Units VI and V are lean in TOC, with values of <5 wt%. TIC values
are also relatively low, varying around 0.1 wt% throughout the units. The TOC and TIC
values follow the TC trend, except for the TIC values at 50–58 ambsf. Generally, there
are low values of TC reaching only up to 5 wt% only in the uppermost part of Unit V.
The sulphur content is relatively flat-rated throughout the units, with the value settling
around 0.1 wt%.
Figure 26. Sulphur (S), total carbon (TC), total organic carbon (TOC) and total inorganic carbon (TIC) values
of Unit VI and V, between 48 and 91 ambsf. Data from Expedition 347 Scientists (2014a).
48
53
58
63
68
73
78
83
88
93
0 0,1 0,2 0,3 0,4 0,5 0,6
Depth
(am
bsf)
wt%
TC S TOC TIC
Unit V
Unit VI
40
The LOI and water content determination from 29 samples show that the values generally
increase from bottom to top throughout the sediment column (Figure 27). In general, the
LOI values measured range between 2.1wt% and 5.5wt% and the water content is
between 21wt% and 40.5%. In the lower part of Unit VI there is an increase of the values
around 85 ambsf. There is a decrease of the values at 79 ambsf, which is followed by a
short increase, and then a small decrease again at 75 ambsf. Between 74 and 69 ambsf the
values are relatively steady, and from there the values increase upwards. Both values
decrease at the bottom of Unit V at 53 ambsf, and then increase at the upper part of the
unit. The water content and LOI values follow the same trend throughout the column with
an exception at 63 ambsf.
Figure 27. Water content and LOI values of 29 samples from Units VI and V between 49 and 90 ambsf. Data
from this study's LOI and water content determination from 29 samples from Units VI and V.
2 2,5 3 3,5 4 4,5 5 5,5
49
54
59
64
69
74
79
84
89
20 25 30 35 40 45
wt%
Depth
(am
bsf)
wt%
water content LOI
Unit V
Unit VI
41
5. DISCUSSION
The physico-stratigraphic zonation of Units VI and V presented here is based on the
lithostratigraphy, physical properties and results from the grain size analysis from the
units. The reconstruction of the sedimentation environment is concluded from the
physico-stratigraphic zonation and previous knowledge of the Holocene glacial
environment of the BSB. Included are also relative age determination of the units and
correlation to different Holocene glacial sedimentation environments.
5.1. Sources of errors
In their reports, Andrén et al. (2015b) and Obrochta et al. (2017) discussed the difficulties
and challenges in the coring processes at Site M0063. Methane gas expansion caused
physical core disturbance, disturbing the between-sample accuracy of the paleomagnetic
record of the sediments recovered from the site. Coring disturbances and large nonlinear
sediment expansion were the cause of the hole-to-hole correlation remaining at a relative
approximate level of 0.5–1.0 m. At the top of each core, the physical property data had a
strong noise, which had to be cleaned. The lithologic information and seismic profiles
suggest the possibility of some type of gravity flows occurring in the area, which caused
the deforming of the sediment. There were many challenges in the correlation and there
are visible larger scale trends in all physical properties.
5.2. Physico-stratigraphic zonation of Units VI and V
The general trend in the clay-silt-sand ratio of Units VI and V is the upward increase of
clay content and decrease of silt content (Figure 17). In their study, Andrén et al. (2002)
stated that in the relation of grain size and colour, the only general factor is that the silt
content in brownish clay is higher than in grey clay. The upward decreasing silt and sand
42
content of Units VI and V is concordant to the colour change from brownish to grey.
According to Andrén et al. (2002), the change in colour can be caused by the change of
the sediment source area, the change in the input of coarser material, or the change of the
chemical and/or physical composition of the sediment. The upward fining of sediments
into weakly colour laminated clay can indicate increasing distal conditions and
continuous retreat of the ice sheet (Streuff et al. 2017a).
The sediments of Unit VI vary by colour from brownish/reddish grey clay at the
lowermost parts of the unit to brownish/greyish clay at the upper parts of the unit. This
colour change is also visible in the core images presented in Figures 8–12 and 21–24. The
volume distributions of the 76 samples are consistent with the variation of the grain size.
Silt is dominant at depths between 67 and 90 ambsf, and finer clay is dominant upward
from ~67 ambsf. The d-values from the 76 samples also illustrated coarsening of the
material downward from ~67 ambsf (Figure 25).
Andrén et al. (2015b) state that peaks in NGR indicate variation and reduction of grain
size and the occurrence of meter-scale peaks throughout Unit VI indicate a
correspondence to intervals of reduced grain size. Figure 13 showed the upward
increasing NGR values which are concordant with the upward decreasing silt and sand
content illustrated in Figure 18. Density decreases upward in Units VI and V in relation
to the fining of the sediment (Figure 13 and 18). According to Harff et al. (2011) changes
in the depositional regime are reflected in the MS values. There are notable changes in
the MS values at certain depths throughout the sediment column.
Figure 27 illustrated that the water content and LOI values of the 29 samples from Units
VI and V follow the general trend of upward increasing values. Correlative shifts in LOI
values and the variation of grain size are related to sedimentary change. The LOI values
are relatively low throughout the sediment column and, according to MacLeod et al.
(2006), low LOI values represent the expected low levels of productivity in recently
deglaciated basin. The TOC and TIC values are also relatively low and in line with the
TC values throughout Units VI and V (Figure 26). Changes in ice sheet extent are thought
43
to be illustrated by the alternations between organic and non-organic sedimentation
regimes. (Smith 2003.)
Based on these differences in grain size variations and physical properties, the sediment
column of Units VI and V is divided into four subunits between certain depths. This
division is also illustrated in Figure 13.
5.2.1. Subunit VIa 87.5–93.3 ambsf
The frequent sand laminations and increased grain size, with pebble and sand grains,
between 87.5 and 93.9 ambsf indicate a proximal glaciolacustrine environment (Andrén
et al. 2015b). The massive brownish/reddish sandy diamict and pebbly sandstone between
90.8 and 93.3 ambsf (Figure 8a and 9a) are an indication of high-energy mechanism such
as ice-rafting. These lowermost parts of the subunit display a deposition environment of
an ice-proximal setting. Slightly disturbed interlaminations of grey and brown silt and
clay are also present at lowermost part of the subunit.
Unconsolidated sediments usually have lower density than lithified fragments, which is
why an increase of fragments and clasts could increase the density (MacLeod et al. 2006).
The density increases in the diamict and sandy sediment at the lowermost part between
92 and 93.3 ambsf (Figures 13 and 15). Because wet bulk density is sensitive to changes,
increased input of terrigenous sandy material can also cause an increase in density (Harff
et al. 2011). The increase in density is concordant with the increasing values of MS
illustrated in Figure 13. There occur larger excursions of MS at the lower part of the unit
(Figure 14), and according to MacLeod et al. (2006), the correlative shifts in MS values,
along with grain size variation, are related to sedimentary change. There also occurs slight
variation in velocity and NGR values. The TOC value increases and TIC value decreases
at 87 ambsf.
44
5.2.2. Subunit VIb 67.7–87.5 ambsf
The sediments are silt dominated and laminated by grain size and colour at 84–87.5,
71.0– 74.3 and 67.7–71 ambsf (Figures 9c, 10d and 11a). These sediments are most likely
formed by low-energy mechanism. The colour of the sediments varies from greyish
brown clay at the lower part between 74 and 87.5 ambsf to darker grey clay at 67.7– 74
ambsf. The intensified melting of the ice sheet leading to increasing sedimentation rate
can also be the cause for the colour change in the sediment (Andrén et al. 2002).
Sequences of darker clayey and lighter silty sediment couplets indicate winter and
summer seasons (e.g. Figure 8e and 10). Massive clay interbeds appear at 69.85–70.05
and 68.15–68.25 ambsf (Figure 8d and 11a). Andrén et al. (2011) write that varved clay
forms at ice-proximal areas and homogeneous clay deposits at ice-distal areas.
According to MacLeod et al. (2006) the decrease in MS is due to the increase of organic
and water content. A decrease in MS value is in relation to an increase in water content
and LOI, TIC, and TC values at approximately 85 ambsf (Figures 13, 26 and 27). A peak
in LOI values at 85 ambsf is possibly due to the formation of different precipitates.
Several alterations of water content and LOI values occur throughout the sediment
column. TOC values show an increase upward from 73 ambsf, and, according to Andrén
et al. (2002) increased organic production or enhanced preservation of organic carbon in
anoxic conditions can be the cause of increase in the content of organic carbon. The NGR
values are relatively constant, except for a few lower values. The velocity varies from
constant to frequent oscillations of the values.
5.2.3. Subunit VIc 54–67.7 ambsf
Common features are fine laminaes of varved clay, as well as mm-scale silt laminae and
slumping within thicker clay laminae. The variations in the concentration of the sediments
throughout the subunit might be related to changes in clay availability from the source
areas. There is also an increase of water content and LOI and carbon values upward from
67.7 ambsf. Homogeneous parts are present between 66 and 67 ambsf (Figure 11b) and
45
massive interbeds of homogeneous grey clay are present at 64.1–64.4 ambsf (Figure 11c).
The thickness of the homogenous sediments varies which indicates nonconformities in
sedimentation. The sound velocity drops in homogeneous deposits, but the density
increases (Harff et al. 2011). There are notable declines in density between 64 and 67
ambsf and from 50 to 57 ambsf (Figure 13), which is related to the absence of coarser
sandy material (Figures 18 and 19). The MS values are relatively constant and low, but a
slight increase of NGR values occur at lower part, and velocity is constant in certain parts
of the subunit. The water content and LOI and carbon values show variations in the upper
part of the subunit.
5.2.4. Subunit Va 48–54 ambsf
The laminated clay between 48 and 54 ambsf is an indication of a possible depositional
environment (Andrén et al. 2015b). The internal structures show, in part, massive,
contorted silt laminated intervals with convolute bedding (Figures 12c and d) and
slumping features (Figures 8g and h). There are a few steeply inclined soft-sedimentary
microfaults at ~50 ambsf and bedding is strongly contorted and microfaulted at ~51
ambsf. The sediment also illustrates soft-sediment deformation. Due to compaction,
density decreases gradually in soft clay and silt (Harff et al. 2011). The decrease in density
between 48 and 50 ambsf (Figures 13 and 15) is related to the soft-sediment deformation
at the uppermost part of the unit. The very well sorted and distorted, convolute bedded
clay varies by colour from greyish brown to dark grey. The colour change from brownish
to grey can also be an indication of oxygen deficiency caused by an increase in the
sedimentation rate (Andrén et al. 2002).
Velocity decreases upward the subunit and more frequent variations of the values also
take place (Figure 16). The physical properties data from Expedition 347 Scientists
(2014b) suggests that the velocity drop is possibly due to the change of sediment type and
increase of organic material and water content. An increase of water content and LOI
values and, also the highest values of TC, TIC and TOC appear between 48 and 50 ambsf
(Figures 26 and 27). The MS and NGR values are relatively constant, except for the peak
of a lower NGR value at 52 ambsf.
46
5.3. Reconstruction of the sedimentation environment of Units VI and V
5.3.1. Relative age determination
The ice recession and the first drainage of the BIL are estimated to have taken place at
13.5– 13.0 ka (e.g. Andrén et al. 2011, Björck 1995). Proximal sediments of the
lowermost part of Unit VI are possibly deposited at the time of the first drainage of the
BIL and ice recession. The inferred age of the deglaciation of the Landsort Deep is ~13.5
ka (Obrochta et al. 2017). The reconstruction of the BIL by Vassiljev and Saarse (2013)
indicates that the Landsort Deep was deglaciated at 12.2 ka, and the water level at ice
margin was up to 140–150 m a.s.l.
Distinct pollen types at ~66 ambsf might imply a pre-Holocene age for that spectrum, and
it could also be related to the Bølling/Allerød interstadials (Andrén et al. 2015b). The
change in the sediment content in the lower part of subunit VIc (~66–67.7 ambsf)
substantiate warmer climate conditions. Previously dated pollen spectrum typical at 11.0–
10.5 ka was found at ~56.8 ambsf, suggesting a correlative age for the sediments (Andrén
et al. 2015b). According to Andrén et al. (1999), an ice-rafted debris (IRD) sequence
preceded the final drainage of the BIL. Dispersed intraclasts and sand grains in various
depths at 52.5–58 ambsf might reflect this IRD sequence of debris settling from melting
ice sheet and/or icebergs.
Sediments of the upper part of Unit V most likely represent the final drainage of the BIL
~11.7 ka ago (Andrén et al. 2015a), and the onset of the transition into the YS stage. The
silt content shows a slight increase upward Unit V which might have resulted from
intermixing of finer and coarser material and indicate reworking of sediments. Sharp
contacts of such sediments are interpreted as mass-transport deposits (Streuff et al.
2017a). The structure of Unit V also corresponds to an abrupt event such as the drainage
and lowering of the water level.
47
The Hole M0063C was analysed for siliceous microfossils for locating the 150-year
brackish phase of the YS stage by combining diatom stratigraphy with its stratigraphic
position, and a typical diatom assemblage of the YS stage was found at five levels in Hole
M0063C between 41 and 43 ambsf (Andrén et al. 2015b). According to Obrochta et al.
(2017) the brackish phase of YS is represented by the laminated grey clays with iron
sulphides that are overlying the thick sequence of varved glacial clays between 48 and 93
ambsf. Variations of the geochemistry in pore water from the Site M0063 reflects the
transition from the underlying glaciolacustrine sediments to Holocene brackish marine
deposits (Andrén et al. 2015b).
5.3.2. Sediments, processes and deposition environment
The stratification of the glacial lake controls the resulting processes of sedimentation that
may occur through processes such as the deposition from meltwater flows, direct
deposition from the glacier front, settling from suspension, re-sedimentation by gravity
flows, current reworking and rain-out from icebergs (Bennett and Glasser 2009). The
depth and extent of ice-marginal lake, such as the BIL and its sedimentation are controlled
by different factors e.g. location of the ice sheet margin, volume of sediment supply and
differential isostatic rebound (Teller 2013).
The poorly sorted massive sandy diamict of subunit VIa were presumably deposited
directly at the ice sheet margin. The diamict with silt interlaminas appearing in an upward-
fining succession suggests depositional environment with initially higher energy but
increasingly lower depositional energy. According to Björck and Möller (1987), this kind
of subglacial melt-out sediment is deposited by slow melt-out release of basal debris from
stagnant ice. Thick sequences of proximal sediments possibly depict very slow retreat of
the ice margin (Streuff et al. 2017b). The ice-distal sediments overlaying the ice-proximal
sediments of subunit VIa possibly indicate that the retreat of the ice sheet was relatively
continuous. The interlaminas of more sorted sediment are synsedimentary and melt-out
deposits, and they are deposited in cavities at the ice sheet sole/bed boundary or in
englacial cavities produced by running water (Björck and Möller 1987).
48
Varved glacial clay is present between 71 and 90 ambsf with varying thickness
(Expedition 347 Scientists 2015). Varves form during the melting of the ice sheet, runoff
and proglacial sedimentation and demonstrate the pace of deglaciation, and they generally
reflect regular, most likely seasonal variations in sediment and meltwater supply. The
varves are very compact and disturbed in the lowermost part of Unit VI (Expedition 347
Scientists 2015). Differences in varve thickness are generally caused by changes in
sediment input by meltwater, slight oscillations of the ice margin and local iceberg
activity. The varve thickness between 81 and 87 ambsf is 10–20 mm, and some layers are
a little darker (Expedition 347 Scientists 2015). At 77.5–81 ambsf, the varve thickness is
1–5 mm, and there are no changes between darker and lighter layers (Expedition 347
Scientists 2015) which reflects seasonal invariability.
The input of water and sediment is highly seasonal, and thin finer clayey layers form in
the winter, while thicker and coarser silty and sandy layers form during the summer. The
varve thickness is 10 mm and grain size does not change between lighter and darker layers
between 71 and 77.5 ambsf (Expedition 347 Scientists 2015). At ~74 ambsf, the content
is generally all clay and there is no change in grain size between winter and summer layers
(Expedition 347 Scientists 2015). This might be due to generally cooler conditions and
glacier re-advance which can lead to decrease of meltwater and sediment availability and
be related to a lack of turbidites. The formation of varves is related to the forming of
freshwater basin at the changing ice sheet margin (Stroeven et al. 2015a). According to
Andrén et al. (2015b), varved internal grading of rhythmically banded clays indicate lake
deposits. Continuous varved clay that are overlain by silt and sand layers were formed
during the regression of the BIL (Björck and Möller 1987).
Sediment changes to dark grey clay with sandy and silty interlaminas upward from 71
ambsf (Expedition 347 Scientists 2015). The exposed till after deglaciation offers an
ample source of clay (MacLeod et al. 2006). The upward decreasing grain size indicates
a low-energy and depositional environment, and sediments were most likely deposited by
suspension rainout from meltwater or from the water column in ice-distal setting. Thicker
sand laminae occurring at ~69 ambsf might be due to larger-scale event, such as ice sheet
outwash. Increased sediment supply can result in rapid sediment accumulation which
49
increases the clay content (Andrén et al. 2002). This change in sediment content in subunit
VIb possibly indicates enhanced meltwater and material input caused by warmer climate
and deglaciation. Massive interbed at ~68 ambsf and homogeneous parts between 66 and
67.7 ambsf indicate rapid deposition possibly through meltwater flows. A rapid warming
event occurred at 11.5 ka (Borzenkova et al. 2015). The fast retreat of the SIS and the
relative sea level changes caused a rapid regression in the recently deglaciated regions,
which led to increasing sedimentation rate (Andrén et al. 2011). The sedimentation rate
was ~0.4–0.55 mm year–1 at 11.0 ka and decreased to ~0.4 mm year–1 at 10.0 ka (Obrochta
et al. 2017).
According to Harff et al. (2011), homogeneous sediments replaced by laminated
sequences is an indication of the transition from freshwater to brackish-marine
environment. According to Andrén et al. (2015b), convolute bedding indicates that the
clay deposits were possibly remobilized in a slump event. The accumulation of contorted
layers can relate to gravitational slump events which reworked and redeposited the
sediments down-slope (e.g. Forsberg et al. 1999, Streuff et al. 2017b). Folded and faulted
clays and silts might be a result of icebergs settling into the soft bottom mud during the
declining of the lake level, and icebergs can supply detritus of all size and add it to the
sediments on the lake floor, deforming the pre-existing laminaes (Teller 2013). The
sediment between 48 and 50 ambsf is grey clay with intraclasts, which can be formed by
debris flows.
5.3.3. Correlation
In their climate models Rinterknecht et al. (2006) suggest that changes in the North
Atlantic climate affected the mass balance of the SIS, due to its location downwind of the
North Atlantic Ocean. Temperature fluctuations of only ±1°C, and increases in total
precipitation can lead to significant changes in ice sheet evolution (Patton et al. 2016).
Between 14.5 and 10.0 ka, the SIS melt-out contributed ~8m to global sea-level rise
(Cuzzone et al. 2016). The final drainage of the BIL led to rapid release of fresh water
into the North Atlantic, which possibly caused a minor temporary disturbance in its
circulation (Andrén et al. 2002). The geographical location of the BSB serves as a link to
50
North Atlantic marine records and Greenland ice cores and, also between the north-
western European and the Eurasian terrestrial records (Expedition 347 Scientists 2014d).
The comparison of the climatic information from the Greenland ice core to the retreat
rates of the ice sheet display a general correspondence between climatic forcing and
retreat rate (Stroeven et al. 2015b). The variability between iceberg-dominated and
meltwater-dominated glacimarine sedimentation might not only be related to glaciology
and climate, but the sedimentation can also be dependent on local factors such as seafloor
topography, glacier size and distance to the ice margin (e.g. Ó Cofaigh et al. 2001, Streuff
et al. 2017b). Glacimarine sediments of fjords deposited during the deglaciation of the
Svalbard-Barents Sea Ice Sheet (Streuff et al. 2017a) show similar principal sedimentary
processes as during the deglaciation of the SIS. Sandy turbidites formed by gravitational
mass flows in ice-proximal setting and weakly stratified mud deposited in ice-distal areas
by suspension settling from meltwater (Streuff et al. 2017a).
Varved clays deposited during the deglaciation in the BIL were connected to the existing
chronology of ice recession and depositional environment of southern Sweden. The
coastal area and valley below the highest shoreline were dominated by varved clays,
littoral sand and glaciofluvial gravel. Above the highest shoreline, areas of transverse and
hummocky moraine were formed from Late Weichselian glaciofluvial sediments. During
the retreat of the ice sheet, the areas above the highest shoreline were drained by large
glacial river systems. The river systems carried clay and silt into the BIL, and these annual
deposits of varved clay draped the bedrock, till and subaqueous glaciofluvial deposits
(Wohlfarth et al. 1994.).
Sedimentary sequences from the Sokli basin In Finnish Lapland represents the variations
of the interglacial/glacial cycle (Helmens et al. 2000). In comparison to Units VI and V,
the sediment sequences from the Sokli basin show also the upward fining of the sediments
overlaying diamict deposits. These finer sediment sequences from the Sokli basin are
interpreted as deglaciation sequences (Helmens et al. 2000).
51
According to Ignatius et al. (1981), the ice sheet had retreated far north at the end of the
YS stage, and today's BSB was mostly deglaciated, except the Bothnian Bay. Therefore,
varved glacial clay deposit are found in the Bothnian Bay, and postglacial sedimentation
occurs in the southern and central parts of the basin (Ignatius et al. 1981).
Postglacial deposits from Otokomi Lake in Montana have similar features like the
deposits from the Landsort Deep. The trend of LOI values might be due to coarser
sediment, and the parallel trends of LOI and water content could indicate initial
postglacial warming, which was interrupted by cooling and followed by warming shortly
after (MacLeod et al. 2006). A relatively shallow thermocline might had been a significant
distribution mechanism pending long-term periods of ice cover (MacLeod et al. 2006).
6. CONCLUSIONS
Grain size analysis enables the interpretation of depositional conditions, sediment
provenance and transport history, and sediment grain size is a common proxy of climatic
changes in studies. The determination of the stratigraphic characteristics of the sediments
from Units VI and V from the Landsort Deep enabled the interpretation of the late and
postglacial stage of the BSB. The relative age determination of the sediments connects
them to the BIL stage and the onset of the transition into the brackish YS stage, roughly
approximated between 13.5 and 11.5 ka.
The sedimentation of the Landsort Deep is characterized by low- and high-energy
transport and distribution mechanisms. High-energy mechanism, such as ice rafting and
mass movements, has led to coarser sand and clast deposits. Clay and silt deposits are
likely formed by low-energy mechanisms. The lower ice-rafted part of Unit V
demonstrates a deposition environment of an ice-proximal setting, and the upper part
displays ice-distal facies types. The coarser ice-proximal varved sediments are changed
at ice-distal areas into thinner varved clays and eventually into clayey and silty sediments.
52
The sediments from the upper part of Unit V have probably deposited during the final
drainage of the BIL at ~11.7 ka and the beginning of the transition into the YS stage.
Timing and chronology of the SIS retreat and the different stages of the BSB vary and are
debated due to different dating methods. Different glaciological and climatic settings
affect the glacimarine sedimentary processes, and their variability is also caused by local
controls e.g. the topography of the seafloor and the distance to the ice margin. The wide
range of the deposited sediments of the BSB is due to variations in the water exchange
between the BSB and the world ocean, the prevailing climatic conditions and the
proximity of the retreating ice sheet.
53
REFERENCES
Andrén, T., Björck, J., and Johnsen, S. 1999. Correlation of Swedish glacial varves with the
Greenland (GRIP) oxygen isotope record. Journal of Quaternary Science, 14, 4, 361–371.
Andrén, E., Andrén, T., and Kunzendorf, H. 2000a. Holocene history of the Baltic Sea as a background for assessing records of human impact in the sediments of the Gotland Basin. The
Holocene, 10, 687–702.
Andrén, E., Andrén, T., and Sohlenius, G. 2000b. The Holocene history of the southwestern Baltic Sea as reflected in a sediment core from the Bornholm Basin. Boreas, 29, 233–250.
Andrén, T., Lindeberg, G., and Andrén, E. 2002. Evidence of the final drainage of the Baltic Ice
Lake and the Brackish phase of the Yoldia Sea in glacial varves from the Baltic Sea. Boreas, Vol. 31, 226–238.
Andrén, T., Björck, S., Andrén, E., Conley, D., Zillén, L., and Anjar, J. 2011. The Development
of the Baltic Sea During the Last 130 ka. In: Harff, J., Björck, S., Hoth, P. (eds.). The Baltic
Sea Basin. Springer, Berlin, 75–97. Andrén, T., Jørgensen, B.B., Cotterill, C., Green, S., and the IODP expedition 347 scientific party.
2015a. IODP expedition 347: Baltic Sea basin paleoenvironment and biosphere. Scientific
Drilling, 20, 1–12. Andrén, T., Jørgensen, B.B., Cotterill, C., Green, S., Andrén, E., Ash, J., Bauersachs, T., Cragg,
B., Fanget, A.-S., Fehr, A., Granoszewski, W., Groeneveld, J., Hardisty, D., Herrero-Bervera,
E., Hyttinen, O., Jensen, J.B., Johnson, S., Kenzler, M., Kotilainen, A., Kotthoff, U., Marshall,
I.P.G., Martin, E., Obrochta, S., Passchier, S., Quintana Krupinski, N., Riedinger, N., Slomp, C., Snowball, I., Stepanova, A., Strano, S., Torti, A., Warnock, J., Xiao, N. and R. Zhang.
2015b. Site M0063. In: Andrén, T., Jørgensen, B.B., Cotteril, C., Green, S., and the Expedition
347 Scientists. Proceedings of the Integrated Ocean Drilling Program, Volume 347. Bennett, M. R., and Glasser, N. F. 2009. Glacial geology, ice sheets and landforms. Wiley-
Blackwell, UK, p. 385.
Bergsten, H., and Nordberg, K. 1992. Late Weichselian marine stratigraphy of the southern Kattegat, Scandinavia: evidence for drainage of the Baltic Ice Lake between 12,700 and 10,300
years BP. Boreas, 21, 223–252.
Berndmeyer, C., Thiel, V., Schmale, O., Wasmund, N., and Blumenberg, M. 2014. Biomarkers
in the stratified water column of the Landsort Deep (Baltic Sea). Biogeosciences, 11, 7009– 7023.
Björck, S., and Möller, P. 1987. Late Weichselian Environmental History in Southeastern Sweden
during the Deglaciation of the Scandinavian Ice Sheet. Quaternary Research, 28, 1–37. Björck, S. 1995. A Review of the History of the Baltic Sea, 13.0–8.0 ka BP. Quaternary
International, 27, 19–40.
Blott, S.J. and Pye, K. 2001. GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments. Earth Surface Processes and Landforms, 26,
1237– 1248.
Borzenkova, I., Zorita, E., Borisova, O., Kalniņa, L., Kisielienė, D., Koff, T., Kuznetsov, D.,
Lemdahl, G., Sapelko, T., Stančikaite, M., and Subetto, D. 2015. Climate Change During the Holocene (Past 12,000 Years). In: The BACC II Author Team (eds.), Second Assessment of
Climate Change for the Baltic Sea Basin. Regional Climate Studies. Springer, Cham, p.
25– 49. Brunnberg, L. 1988. Diatoms in glacial clay in the Södertörn area, Stockholm region. In: Miller,
U. and Robertsson, A.-M. (eds.), Proceedings of Nordic Diatomist Meeting. University of
Stockholm, Department of Quaternary Research Report, 12, 7–9.
Böttcher, M.E., and Lepland, A. 2000. Biogeochemistry of sulphur in a sediment core from the west-central Baltic Sea: Evidence from stable isotopes and pyrite textures. Journal of Marine
Systems, 25, 299–312.
Cuzzone, J.K., Clark, P.U., Carlson, A.E., Ullman, D.J., Rinterknecht, V.R., Milne, G.A., Lunkka, J-P., Wohlfarth, B., Marcott, S.A., and Caffee, M. 2016. Final deglaciation of the Scandinavian
54
Ice Sheet and implications for the Holocene global sea-level budget. Earth and Planetary
Science Letters 448, 34–41. Expedition 347 Scientists. 2014a. Carbon and sulphur content (raw data) of IODP Hole
347- M0063C. https://doi.org/10.1594/PANGAEA.839492.
Expedition 347 Scientists. 2014b. Visual core description and core images IODP Hole 347- M0063C. https://doi.org/10.1594/PANGAEA.837860.
Expedition 347 Scientists. 2014c. Physical properties of IODP Hole 347-M0063C.
https://doi.org/10.1594/PANGAEA.838479.
Expedition 347 Scientists. 2014d. Paleoenvironmental evolution of the Baltic Sea Basin through the last glacial cycle. Integrated Ocean Drilling Program.
https://doi:10.2204/iodp.pr.347.2014.
Expedition 347 Scientists. 2015. Description of lithologic section units of IODP Hole 347- M0063. https://doi.org/10.1594/PANGAEA.843039.
Forsberg, C. F., Solheim, A., Elverhøi, A., Jansen, E., Channell, J.E.T., and Andersen, E.S. 1999.
The Depositional environment of the western Svalbard margin during the Late Pliocene and the Pleistocene: Sedimentary facies changes at Site 986. In: Raymo, M.E., Jansen, E., Blum,
P., and Herbert, T.D. (Eds.). Proceedings of the Ocean Drilling Program, Scientific Results,
Vol. 162.
Harff, J., Endler, R., Emelyanov, E., Kotov, S., Leipe, T., Moros, M., Olea, R., Tomczak, M., and Witkowski, A. 2011. Late Quaternary Climate variations Reflected in Baltic Sea Sediments.
In: Harff, J., Björck, S., Hoth, P. (eds.). The Baltic Sea Basin. Springer, Berlin; 99–132.
Heinsalu, Atko., Veski, Siim., Vassiljev, J. 2000. Palaeoenvironment and shoreline displacement on Suursaari Island, the Gulf of Finland. Bulletin of the Geological Society of Finland. 72, 1–
2, 21–46.
Heiri, O., André, F.L., and Lemcke, G. 2001. Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results. Journal of
Paleolimnology, 25, 101–110.
Helmens, K.F., Räsänen, M.E., Johansson, P.W., Junger, H., and Korjonen, K. 2000. The Last
Interglacial-Glacial cycle in NE Fennoscandia: a nearly continuous record from Sokli (Finnish Lapland). Quaternary Science Reviews, 19, 1605–1623.
Houmark-Nielsen, M., and Kjær, K.H. 2003. Southwest Scandinavia, 40–15 ka BP:
palaeogeography and environmental change. Journal of Quaternary Science, 18, 769–786. Hughes, A.L.C., Gyllencreutz, R., Lohne, Ø.S., Mangerud, J., and Svendsen, J.I. 2015. The last
Eurasian ice sheets – a chronological database and time-slice reconstruction, DATED-1.
Boreas, 45, 1–45.
Hyttinen, O., Kotilainen, A., Salonen, V-P. 2011. Acoustic evidence of a Baltic Ice Lake drainage debrite in the Northern Baltic Sea. Marine Geology, 284, 139–148.
Ignatius, H., Axberg, S., Niemistö, L., and Winterhalter, B. 1981. Quaternary geology of the
Baltic Sea. In: Voipio, A. (ed.). The Baltic Sea. Elsevier Scientific Publishing Company, the Netherlands, 418 p.
Kaskela, A.M., Kotilainen, A.T., Al-Hamdani, Z., Leth, J.O., Reker, J. 2012. Seabed geomorphic
features in a glaciated shelf of the Baltic Sea. Estuarine, Coastal and Shelf Science, 100, 150– 161.
Lambeck, K., Smither, C., Johnston, P. 1998. Sea-level change, glacial rebound and mantle
viscosity for northern Europe. Geophysical Journal International, 134, 102–144.
Lambeck, K., Purcell, A., Zhao, J., and Svensson, N-O. 2010. The Scandinavian Ice Sheet: from MIS 4 to the end of the Last Glacial Maximum. Boreas, 39, 410–435.
Lepland, A., and Stevens, R.L. 1998. Manganese authigenesis in the Landsort Deep, Baltic Sea.
Marine Geology, 151, 1–25. MacLeod, D.M., Osborn, G., and Spooner, I. 2006. A record of post-glacial moraine deposition
and tephra stratigraphy from Otokomi Lake, Rose Basin, Glacier National Park, Montana.
Canadian Journal of Earth Sciences, 43, 447–460. Myrberg, K., Leppäranta, M., and Kuosa, H. 2006. Itämeren fysiikka, tila ja tulevaisuus.
University Press, Helsinki, 202 p.
55
Obrochta, S.P., Andrén, T., Fazekas, S.Z., Lougheed, B.C., Snowball, I., Yokoyama, Y., Miyairi,
Y., Kondo, R., Kotilainen, A.T., Hyttinen, O., and Fehr, A. 2017. The undatables: Quantifying uncertainty in a highly expanded Late Glacial-Holocene sediment sequence recovered from
the deepest Baltic Sea basin—IODP Site M0063. Geochemistry Geophysics Geosystems, 18,
3, 858–871. Ó Cofaigh, C., Dowdeswell, J.A., Grobe, H. 2001. Holocene glacimarine sedimentation, inner
Scoresby Sund, East Greenland: the influence of fast-flowing ice-sheet outlet glaciers. Marine
Geology, 175, 1–4, 103–129.
Patton, H., Hubbard, A., Andreassen, K., Winsborrow, M., Stroeven A.P. 2016. The build-up, configuration, and dynamical sensitivity of the Eurasian ice-sheet complex to Late
Weichselian climatic and oceanic forcing. Quaternary Science Reviews, 153, 97–121.
Patton, H., Hubbard, A., Andreassen, K., Auriac, A., Whitehouse, P.L., Stroeven, A.P., Shackleton, C., Winsborrow, M., Heyman, J., Hall, A.M. 2017. Deglaciation of the Eurasian
ice sheet complex. Quaternary Science Reviews 169, 148–172.
Rinterknecht, V.R., Clark, P.U., Raisbeck, G.M., Yiou, F., Bitinas, A., Brook, E.J., Marks, L., Zelčs, V., Lunkka, J-P., Pavlovskaya, I.E., Piotrowski, J.A., and Raukas, A. 2006. The Last
Deglaciation of the Southeastern Sector of the Scandinavian Ice Sheet. Science, 311,
1449– 1452.
Smith, J. 2003. Aspects of the loss-on-ignition (LOI) technique in the context of clay-rich, glaciolacustrine sediments. Geogr. Ann, 85 A (1), 91–97.
Streuff, K., Cofaigh, C.Ó., Noormets, R., and Lloyd, J.M. 2017a. Submarine landforms and
glacimarine sedimentary processes in Lomfjorden, East Spitsbergen. Marien Geology, 390, 51–71.
Streuff, K., Cofaigh, C.Ó., Hogan, K., Jennings, A., Lloyd, J.M., Noormets, R., Nielsen, T.,
Kuijpers, A., Dowdeswell, J.A., Weinrebe, W. 2017b. Seafloor geomorphology and glacimarine sedimentation associated with fast-flowing ice sheet outlet glaciers in Disko Bay,
West Greenland. Quaternary Science Reviews, 169, 206–230.
Stroeven, A.P., Heyman, J., Fabel, D., Björck, S., Caffee, M.W., Fredin, O., and Harbor, J.M.
2015a. A new Scandinavian reference 10Be production rate. Quaternary Geochronology 29, 104–115.
Stroeven, A.P., Hättestrand, C., Kleman, J., Heyman, J., Fabel, D., Fredin, O., Goodfellow, B.W.,
Harbor, J.M., Jansen, J.D., Olsen, L., Caffee, M.W., Fink, D., Lundqvist, J., Rosqvist, G.C., Strömberg, B., and Jansson, K.N. 2015b. Deglaciation of Fennoscandia. Quaternary Science
Reviews, 147, 91–121.
Teller, J.T. 2013. Subaquatic Landsystems: Large Proglacial Lakes. In Evans, D.J.A. (edit.)
Glacial Landsystems. Routledge, New York, 532 p. Vassiljev, J., and Saarse, L. 2013. Timing of the Baltic Ice Lake in the eastern Baltic. Bulletin of
the Geological Society of Finland, 85, 9–18.
Winterhalter, B. 1992. Late-Quaternary Stratigraphy of Baltic sea Basins – a review. Bull. Geol. Soc. Finland 64, Part 2, 189–194.
Wohlfarth, B., Björck, S., Holmqvist, B., Lemdahl, G., and Ising, J. 1994. Ice recession and
depositional environment in the Blekinge archipelago of the Baltic Ice Lake. GFF, 116:1, 3– 12.
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