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doi:10.2204/iodp.proc.347.111.2015

Biostratigraphy

Diatoms

At Site M0067, Holes M0067A and M0067B were both sampled at every fine-grained section top for siliceous microfossil analysis. Diatoms were identified to the species level, with the exception of Chaetoceros resting spores and vegetative cells, which were only identified to the genus level. A total of 77 diatom taxa were identified at Site M0067 (Tables T2, T3). Diatom taxa were assigned to salinity-based affinity groups based on the Baltic Sea intercalibration guides of Snoeijs et al. (1993–1998). In addition to diatoms, silicoflagellates and chrysophytes were noted. Chrysophytes were grouped into morphotypes. Diatoms were present at all analyzed levels to 3.48 mbsf in Hole M0067A. Diatoms were found to ~4.10 mbsf in Hole M0067B. Samples analyzed deeper than this depth were barren. In both holes, diatoms are considered to be well preserved, based on the preservation of fine structures and gracile diatom species. Quantitative preservational analysis will be undertaken during postcruise research, following Warnock et al. (2007).

All analyzed diatom-bearing samples represent a subrecent brackish-marine assemblage, typical of the Littorina/post-Littorina Sea stages of Baltic Sea history. This assemblage is typified by Chaetoceros resting spores, Cocconeis scutellum, Dimeregramma minor, Grammatophora oceanica, Paralia sulcata, Thalassionema nitzschioides, and Thalassiosira eccentrica. The presence of Pseudosolenia calcar-avis and Thalassiosira oestrupii in samples from the top of Section 347-M0067B-1H-1 indicates that modern sediment was not recovered, as these species are no longer present in the Baltic Sea (e.g., Snoeijs et al., 1993–1998; Andrén, 2000). The silicoflagellate Dictyocha speculum Ehrenberg was found in all samples containing the marine diatom assemblage recorded above. D. speculum has been described as requiring a salinity of >20 (Tappan, 1980) but has also been identified in the Black Sea with salinities as low as 10 (McCartney, 1993).

Foraminifers

Results are summarized from the samples taken offshore and onshore (i.e., samples taken from core catchers and regular sections). A total of 21 samples were processed from Holes M0067A and M0067B for the presence of foraminifers (Fig. F3; Table T4).

Site M0067 is located in Little Belt, in a more northwesterly location than Site M0059, and therefore may be expected to show a similar faunal assemblage. However, the recovered foraminiferal fauna is significantly different from that at Site M0059. The two sites also differ markedly in stratigraphy, as Site M0067 has only a ~4 m clay section before transitioning to sand and diamicton (see “Lithostratigraphy”), which contrasts markedly with the ~70 m clay section recovered at Site M0059, suggesting either a different depositional setting at the two sites or perhaps also that some erosion may have occurred at Site M0067.

Both agglutinated and calcareous foraminifers were present in Holes M0067A and M0067B. From 0 to ~3 mbsf, Eggerelloides scabrus is abundant and is the dominant species, composing 70%–100% of the fauna, with up to 100 specimens per ~20 cm³ sample. Increasing importance of the agglutinated foraminifer E. scabrus is generally associated with salinity >17 (Murray, 1991; Frenzel et al., 2005). Between 3 and 4 mbsf, abundance decreases before another maximum occurs in Sample 347-M0067B-2H-2, 12 cm (4.16 mbsf). This sample contains a diverse fauna of nine different species including Elphidium incertum, Ammonia beccarii, Elphidium williamsoni, Elphidium excavatum f. selseyensis, Haynesina sp., E. scabrus, Quinqueloculina sp., Elphidium albiumbilicatum, and Elphidium excavatum f. clavata (listed in order of abundance). Of the species present, E. incertum and A. beccarii are the most abundant, with 26% and 18% of the assemblage, respectively. This relatively diverse fauna with a significant contribution of E. incertum suggests bottom water salinity of at least 22 (Lutze, 1965; Kristensen et al., 2000).

Ostracods

A total of 21 samples (including 12 core catchers) from Holes M0067A and M0067B were examined for ostracods during the onshore phase of Expedition 347 at the Bremen Core Repository (Germany). Samples were studied in the >125 µm fraction. Ostracods were present in six samples (Fig. F4; Table T5).

Ostracods were found in the interval between 0.21 and 4.17 mbsf (Holes M0067A and M0067B). Abundance of ostracod valves per sediment volume is relatively low (<20 valves/20 cm³ sample) for most of the samples. At ~3.2–3.5 mbsf (Hole M0067A), an abundance peak reaching 50–130 valves/20 cm³ is observed. A total of seven taxa were identified for this site: Robertsonites tuberculatus, Cytheropteron latissimum, Elofsonella concinna, Sarsicytheridea bradii, Sarsicytheridea punctillata, Acanthocythereis dunelmensis, and Finmarchinella sp. A relatively low ratio of juvenile valves (30%) suggests that either it was an assemblage living in a high-energy environment or that some of the valves are allochthonous (Whatley, 1983). Based on the lithologic description (see “Lithostratigraphy”), the interval with high ostracod abundance most likely represents a high-energy environment where some redeposition was taking place. The sediments shallower than 3.3 mbsf have high organic matter content, and ostracods are probably dissolved. All of the taxa are shallow-water marine and today are commonly found on Arctic shelves (e.g., Stepanova et al., 2007; Frenzel et al., 2010).

Palynological results

Site M0067 is situated in Little Belt in the southwestern part of the Baltic Sea. The vegetation of the borderlands in that region belongs to the temperate forest zone. Palynological analyses for this site focused on Hole M0067A.

Only two samples from core catchers from Hole M0067A have been analyzed because experience gained from sediments from other sites indicated that only Core 347-M0067A-1H was likely to contain well-preserved in situ palynomorphs. As expected, the core catcher sample from Core 1H contained pollen and other palynomorphs in good preservation and high concentration (~190,000 pollen grains/cm³; Fig. F5; see PalyM0067.xls in PALYNOLOGY in “Supplementary material”), whereas the core catcher sample from Core 2H was virtually barren of palynomorphs.

The only detailed pollen spectrum from Hole M0067A is dominated by pollen of broad-leaved trees and Corylus avellana. The highest percentages were noted for Quercus (25%), Alnus glutinosa type (20.5%), and C. avellana (22%) (Fig. F5, No. 1). Moreover, pollen of other more thermophile trees is present in relatively high amounts: Tilia cordata type (Fig. F5, No. 2) and Fraxinus (both 3%), as well as Ulmus (4.5%) (Fig. F5, No. 3). Fairly low amounts were noted for Pinus sylvestris type and Betula alba type pollen, at 11.5% and 6%, respectively (Fig. F6). Because of the distinct similarity of this spectrum to the depth interval between 21.86 and 31.95 mbsf in the pollen diagram from Hole M0059A and considering neighboring terrestrial pollen profiles (e.g., Dörfler et al., 2012), the pollen spectrum from the core catcher of Core 347-M0067A-1H may provisionally be correlated with the late Atlanticum/Subboreal periods (~5000 cal. y BP). The age apparently cannot be younger than 2500–3000 cal. y BP, as no Fagus pollen has been noted, which around this time is one of the dominating broad-leaved trees in the region (e.g., Dörfler et al., 2012, compare to results for Site M0059). Several remains of aquatic insects are present, most noteworthy an insect jaw that can be ascribed to the chironomid genus Cryptochironomus (Fig. F5, No. 6).

The marine palynomorph assemblage in the sample from Core 347-M0067A-1H is similar to that encountered in some samples from Hole M0059A. Almost 30 organic-walled dinocyst specimens have been identified, of which ~56% belong to the genus Operculodinium/Protoceratium. Lingulodinium is also present (~22%), with relatively short process lengths averaging 8.5 µm that probably indicate low surface water salinity. The third frequent dinocyst type belongs to the genus Spiniferites (~15%) (Fig. F5, No. 4). Cysts of Gymnodinium (probably predominantly Gymnodinium nolleri) are very frequent and may indicate an age of ~4000 y or younger. Combined with the findings from pollen analyses (e.g., absent Fagus), the sample age is probably between 4000 and 2500 y BP. Gymnodinium cysts were excluded from the dinoflagellate percentage calculations because of their extraordinary high occurrences: they compose >75% of the total dinocyst assemblage. Foraminiferal test linings are also present in the sample (Fig. F5, No. 5). Combined, the palynological proxies indicate some marine influence, similar to that encountered in the comparable interval from Site M0059, but based on the low dinocyst (excluding Gymnodinium) to nonsaccate pollen ratio (value = 0.21) and the presence of aquatic insect larvae and freshwater algae, the terrestrial influence was strong.

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