Grain size and description on gravity core samples from ANT-IV/2 expedition to the Bransfield Strait

From the above and the grafical results it can be concluded that cores in the research area are locally dominated by turbiditic sequences, which can be observed by a strong increase in coarser sediment (>35 µm). These coarser intercalations are lacking in the vicinity of basaltic seamounts, probably due to a shadowing effect of the seamounts. The infill of the King George Basin might be dominated by a north eastern current. Sedimentary structures as observed in the cores are often lacking or vague due to hydrothermal effects (Suess, L, 1986).

This report presents the results of a granulometric research on nine gravity cores from the King George Basin and a basin near Low Island in the Bransfield Strait. The cores were taken during the Antarktis IV /2 expedition November 1985 with the RV "Polarstern" of the Alfred Wegener Institute for Polar and Marine Research, Bremerhaven. The RGD was allowed by professor Dr. E. Suess of the School op Oceanographics of the Oregon State University in Corvallis to describe and subsample the cores. The results of the on board descriptions and grain size analyses will be briefly discussed.Core descriptions: the nine cores were mainly taken in the central part of the King George Basin. The core positions are indicated on the map (see further details). The centre of the King George Basin can be described as a sedimentary basin with a relatively flat bottom and a waterdepth of approximately 1950 m. Locally basaltic seamounts can be found in the area. The cored sediments are mainly glaciomarine hemipelagic and turbiditic deposits with several volcanic intercalations. The difference between the sediment types are often small, which can be ascribed to the generally high sedimentation rate (1 cm/yr) in the basin. The hemipelagic sequences consist mainly of olive gray clays, which are locally slightly silty. In zones intensively bioturbated and burrowed sedimentary structures often are absent. The turbiditic parts consist mainly of silty beds with a fining upward sequence. Hydrothermal alteration also occurs within the cores (Whiticar, M.J., et al., 1985). In core PS1327 at the base at 7.27 m a calcium carbonate hexahydrate crystal (CaCO3*6H20) was found, which occurence can be ascribed to hydrothermal alteration (Suess, E, et al., 1982). In two cores, PS1346-1 and PS1347-1 a petroliferous smell was observed. Often sedimentary structures were vague or absent and hydrothermal altered reddish brown clays were also found.Grain size analyses: the granulometric analyses were carried out by the Granulometric Laboratory of the Geological Survey of the Netherlands. The results, as presented in enclosure 3, are shown in two parts. The first part is a granulometric diagram in which four grain size classes are distinguished: 35 µm. These four classes are all normalized to 100 %. The second part of the granulometric analyses is a large table in which the values of i phi classes are given ranging from <2 µm to 2000 µm. The method used to analyse the sediment fractions 35 um were analysed by sieving.Interpretation of the results: A study of the grain size distributions in several cores (1357, PS1342, PS1341, PS1346 and PS1347) revealed a sharp boundary at which the coarse base of a turbidite can be localized. In the cores PS1341; PS1342 and PS1346 even two of such boundaries are present. Core PS1333 is most remote from the King George Basin and contains compared with the other cores no distinct turbiditic sequences. The same phenomenon was found in the cores PS1343 and PS1340.When all of the cores are positioned along the bottom profile it appears that the cores in which distinct turbiditic sequences are lacking (PS1333, PS1340 and PS1343) are very remote from the main sediment entrance of the King George Basin (PS1333) or are situated on the slope of a basalt hill (PS1340 and PS1343). In the cores PS1340 and PS1343 the classes PS1327). Therefore, an agreement exist to conclude that the sedimentary infill of the King George Basin is dominated from the northeast.

Identifier
DOI https://doi.org/10.1594/PANGAEA.738447
PID https://hdl.handle.net/10013/epic.35285.d001
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.738447
Provenance
Creator van Enst, J W; Laban, C
Publisher PANGAEA
Contributor Geological Survey of the Netherlands, Rijke Geologische Dienst
Publication Year 2010
Rights Creative Commons Attribution 3.0 Unported; https://creativecommons.org/licenses/by/3.0/
OpenAccess true
Representation
Resource Type Publication Series of Datasets; Collection
Format application/zip
Size 18 datasets
Discipline Earth System Research
Spatial Coverage (-61.650W, -63.233S, -57.433E, -62.223N); Bransfield Strait; King George Island, Antarctic Peninsula
Temporal Coverage Begin 1985-11-15T00:00:00Z
Temporal Coverage End 1985-11-27T00:00:00Z