Results of Smear-slide Analysis

N. Kukina

Description of the smear slides allow to indicate mineral associations and con-tents of terrigenous and biogenous components. The results of smear-slide es-timates in cores PS66/304, PS66/308, PS66/309, PS66/312, PS66/318, PS66/319, PS66/325, and PS66/333 are shown in Figures 9.21 to 9.28 (for lo-cation of cores see Fig. 9.1). In these figures, on one hand the abundances of quartz, feldspars, mica, terrigenous carbonate, volcanic glass, clay minerals, organic remains, Fe-hydroxides, and heavy minerals (summed up to 100%) are shown. On the other hand, the composition of heavy minerals (summed-up to 100%) is shown in separate graphs of the figures. Tables of the smear-slide data are listed in Chapter 12.4 (Annex).

Based on smear-slide analysis, the main minerals are quartz, feldspar, terri-genous carbonates, mica and clay minerals. The heavy minerals are presented by pyroxenes, amphiboles, epidote, garnets, Fe-oxides/hydroxides and black ores. Pyroxenes and amphiboles dominate, but in some intervals the Fe-oxides and hydroxides are enriched.

The study of the mineral composition and lithological description allowed to dis-tinguish the following types of sediments (units), ordered from core top to bot-tom:

The type 1 sediments are composed of dark brown and dark grayish brown soft silty clay. Clay minerals and quartz dominate in the mineralogical composition.

Amphiboles, Fe oxides/hydroxides and black ores increase, terrigenous car-bonates and organic remains decrease. The heavy minerals concentration changes from 10% (PS66/308) to 23% (PS66/309).

The type 2 sediments have very dark brown color, and oxidations, Fe-Mn nod-ules, sandy silt with gravel grain-size composition (“hard ground”) were found.

The mineral composition is characterized by much higher abundances of Fe ox-ides/hydroxides in these sediments. Terrigenous and biogenic carbonates are absent. Contents of pyroxenes and epidote increase from 20% to 35%.

The type 3 sediments are characterized by strong variability of lithological pa-rameters. The sediments are dark olive gray sandy silty clay. In the upper part of the unit elevated content of sand were observed. With increase of sand con-tent the heavy minerals concon-tent increase also. The terrigenous and biogenic carbonates were completely absent. Only rare amount of organic remains was found. The content of amphiboles and garnets increases.

Type 4 sediments, composed of very viscous gray or dark gray silty clay, are observed in cores PS66/308, -329, and -330. Quartz and feldspar are the main minerals, pyroxenes, epidotes and chlorites dominate in the heavy fraction.

The type 5 sediments (PS66/306, -309, -311, -313) are different from the other units due to high grad of compaction and fine to coarse grain-size. Color

The sediment is laminated. In the mineralogical composition, a relatively high content of volcanic glass and organic remains and a decrease of content of the heavy minerals were determined.

The type 6 sediments (Cores PS66/308 and 309) are of brown, olive gray and dark grayish brown colours and bioturbated, contain some lenses of olive gray sand and dropstones. The main minerals are quartz, feldspar and mica. Vol-canic glass and biogenic carbonates are absent.

Type 7 sediments are generally fine-grained and have gray and dark gray col-ours with black points. Description of smear slide showed increased abun-dances of sulphides and opaques. There are more amphiboles than pyroxenes.

The content of terrigenous and biogenic carbonates is increased (to 16-18% in cores PS66/318 and 319).

Future studies of mineral assemblages and grain-size composition have to be performed to describe the sediment type and to identify lithological units in more detail.

Fig. 9.21: Mineralogical composition of sediments of Core PS66/304, based on smear-slide es-timates.

Fig. 9.22: Mineralogical composition of sediments of Core PS66/308, based on smear-slide es-timates.

Fig. 9.23: Mineralogical composition of sediments of Core PS66/309, based on smear-slide es-timates.

Fig. 9.24: Mineralogical composition of sediments of Core PS66/312, based on smear-slide es-timates.

Fig. 9.25: Mineralogical composition of sediments of Core PS66/318, based on smear-slide es-timates.

Fig. 9.26: Mineralogical composition of sediments of Core PS66/319, based on smear-slide es-timates.

Fig. 9.27: Mineralogical composition of sediments of Core PS66/325, based on smear-slide es-timates.

Fig. 9.28: Mineralogical composition of sediments of Core PS66/333, based on smear-slide es-timates.

9.6.3 Results of Coarse Fraction Analysis J. Thiele, R. Saraswat

Foraminifers (unicellular, almost exclusively marine protists), have been used extensively for paleoclimatic reconstructions and are extremely helpful in provid-ing the chronology based on their oxygen and carbon isotopic composition.

Keeping the objective of reconstructing the past climatic variations and espe-cially the dating of megaslide events in view, a preliminary analysis of the coarse fraction was carried out onboard.

The longest Kastenlot core PS66/309-1 recovered during “Polarstern” Cruise ARK XX/3 was investigated in order to assess the coarse-fraction composition of different lithologies. This core was recovered from the north of Spitsbergen (see Figure 9.1 and annex for location details). Based on the differences in col-our and also to get an overview of the complete core, 24 samples were proc-essed for coarse fraction analysis as per prescribed procedures (freeze-drying followed by wet sieving over 63µm and 125µm sieves). A small representative fraction from the >125µm fraction was taken with the help of splitter, in order to count a minimum of 300 particles. A total of 15806 particles were counted. The particles were grouped into two categories, i.e., biogenic and abiogenic origin.

The abiogenic fraction constituted the larger part of the majority of samples (Fig 9.29). In the abiogenic fraction, quartz grains with angular to subangular edges were most abundant. In few samples, considerable numbers of pyritized worm tubes were also found. The biogenic fraction mainly consists of planktic fo-raminiferal tests with few benthic foraminifers and rare sponge spiculae. As re-ported earlier the planktonic foraminiferal assemblage was dominated by Neogloboquadrina pachyderma, the polar bear of planktonic foraminifers. The planktonic foraminiferal assemblage is almost monospecific. The benthic fo-raminiferal component is represented by few agglutinated specimens along with considerably large specimens of Pyrgo and few specimens of Cibicidoides.

From the intervals where sufficient planktonic foraminifers were available, specimens of N. pachyderma were picked for AMS dating (five in number) as well as stable isotopic analysis (24 in number).

The correlation of the major constituents at different intervals with the colour of the sediments shows that some of the brown coloured sediments are devoid of biogenic components while some of the gray coloured intervals are high in bio-genic components, mainly composed of planktonic foraminiferal tests. Out of the total of 24 samples analysed onboard, the maximum amount of biogenic components (approx. 92%), was reported in the very dark brown coloured silty clay sediments at 179 cm interval. One of the samples (249-252cm) taken from the sandy sediment layer that probably is the result of debris flow, is low in bio-genic components. Further analysis of sandy sediments showed the presence of few shallow water benthic foraminifers, probably indicating the transport of sediments from the shelf to the deeper regions from where the core has been recovered. This needs to be confirmed by detailed species identification and subsequent grouping into foraminiferal assemblages.

This preliminary onboard analysis provides an overview of the composition (biogenic and abiogenic) of the different lithologies. For detailed reconstruction of the past climatic events, closer spaced sample analysis has to be carried out.

Coarse Fraction Analysis

Fig 9.29: Down-core plot of abundance of biogenic and abiogenic components in 24 samples taken for preliminary onboard coarse fraction (>125µm) analysis. The figure shows the broad overview of the composition of different lithologies.

9.6.4 Main Lithologies and Preliminary Interpretation of ARK-XX/3