The Kap Ekholm section – the molluscs’ tale

TY - ABST

T1 - The Kap Ekholm section – the molluscs’ tale

AU - Funder, Svend Visby

PY - 2011

Y1 - 2011

N2 - The Kap Ekholm section shows three marine pre-Holocene periods bounded by glacial sediments (Mangerud & Svendsen 1992=MS). In 1993 the mollusc faunas were investigated by on-site analyses and collection of bulk samples. The results are discussed here in connection with the revised stratigraphy of Jensen et al. (in prep.)=MJ. The lowest marine beds (Unit B according to MS/ units 2-3 according to MJ.) are characterised by low-diverse assemblages dominated by Macoma calcarea but also with old thick-shelled and deeply burrowed Mya truncata. Animals, which were crushed by cobbles dropped on them, and frequent escape tracks from burrowers testify to an unstable environment with frequent slumping. The only indication of a fairly warm climate was the occurrence of Mytilus edulis, which however was both sparse and represented only by small thin-shelled individuals - probably washed down from the littoral zone. Mytilus probably were brought in as larvae from more pleasant areas, indicating that such areas did exist elsewhere on Svalbard at the time. In the upper part it is replaced by Astarte borealis, indicating a deterioration of the environment. Although local events may have overruled the regional signal, this scenario has always been difficult to fit into the concept of a warm Eemian interglacial, as discussed by MS. The fauna-signal agrees much better with the new interpretation of this unit as a glaciomarine diamicton dating to an earlier ice-free period. In the overlying Phantomodden interstadial fauna (Units D/8-9) there are only species, which are also present in unit B, but fewer. The simplest interpretation here is that unit D is a continuation of the deterioration seen in unit B – and that the Phantomodden interstadial therefore is not a distinct interstadial, and the separating “till” reflects a local high sedimentation event. This is underlined by the difference to the much richer and more diverse assemblages from the overlying Kap Ekholm interstadial (unit F/11), which without any doubt represent an entirely different type of marine environment. The fauna results therefore agree with the new sedimentological interpretation. However, there is one disagreement: The new sediment-interpretation of Units B, C, and D evokes a glacier-proximal environment. Although the mollusc faunas also indicate unstable conditions with intermittent periods of slumping they do not indicate proximity (< c. 2 km) to a glacier front. This kind of environment is usually characterised by burrowing sediment eaters which can cope with constantly high sedimentation-rates and large inflow of fresh water, notably Portlandia arctica. These species are absent or rare, while such a suspension feeder as Mya trunacata has managed to live to old age. This would suggest that the slumping events were on a decadal rather than annual scale, and therefore not very close to a glacier. References Mangerud, J. and Svendsen, J.I. (1992). The last interglacial-glacial period on Spitsbergen, Svalbard. Quaternary Science Reviews, 11, 633-664 Jensen, M.A., Håkansson, L., Hormes, A. & Preusser, F. In prep: A revised stratigraphy from the Kapp Ekholm section, Billefjorden, Svalbard: implications for late Quaternary glaciation history

AB - The Kap Ekholm section shows three marine pre-Holocene periods bounded by glacial sediments (Mangerud & Svendsen 1992=MS). In 1993 the mollusc faunas were investigated by on-site analyses and collection of bulk samples. The results are discussed here in connection with the revised stratigraphy of Jensen et al. (in prep.)=MJ. The lowest marine beds (Unit B according to MS/ units 2-3 according to MJ.) are characterised by low-diverse assemblages dominated by Macoma calcarea but also with old thick-shelled and deeply burrowed Mya truncata. Animals, which were crushed by cobbles dropped on them, and frequent escape tracks from burrowers testify to an unstable environment with frequent slumping. The only indication of a fairly warm climate was the occurrence of Mytilus edulis, which however was both sparse and represented only by small thin-shelled individuals - probably washed down from the littoral zone. Mytilus probably were brought in as larvae from more pleasant areas, indicating that such areas did exist elsewhere on Svalbard at the time. In the upper part it is replaced by Astarte borealis, indicating a deterioration of the environment. Although local events may have overruled the regional signal, this scenario has always been difficult to fit into the concept of a warm Eemian interglacial, as discussed by MS. The fauna-signal agrees much better with the new interpretation of this unit as a glaciomarine diamicton dating to an earlier ice-free period. In the overlying Phantomodden interstadial fauna (Units D/8-9) there are only species, which are also present in unit B, but fewer. The simplest interpretation here is that unit D is a continuation of the deterioration seen in unit B – and that the Phantomodden interstadial therefore is not a distinct interstadial, and the separating “till” reflects a local high sedimentation event. This is underlined by the difference to the much richer and more diverse assemblages from the overlying Kap Ekholm interstadial (unit F/11), which without any doubt represent an entirely different type of marine environment. The fauna results therefore agree with the new sedimentological interpretation. However, there is one disagreement: The new sediment-interpretation of Units B, C, and D evokes a glacier-proximal environment. Although the mollusc faunas also indicate unstable conditions with intermittent periods of slumping they do not indicate proximity (< c. 2 km) to a glacier front. This kind of environment is usually characterised by burrowing sediment eaters which can cope with constantly high sedimentation-rates and large inflow of fresh water, notably Portlandia arctica. These species are absent or rare, while such a suspension feeder as Mya trunacata has managed to live to old age. This would suggest that the slumping events were on a decadal rather than annual scale, and therefore not very close to a glacier. References Mangerud, J. and Svendsen, J.I. (1992). The last interglacial-glacial period on Spitsbergen, Svalbard. Quaternary Science Reviews, 11, 633-664 Jensen, M.A., Håkansson, L., Hormes, A. & Preusser, F. In prep: A revised stratigraphy from the Kapp Ekholm section, Billefjorden, Svalbard: implications for late Quaternary glaciation history

M3 - Conference abstract for conference

T2 - APEX Fifth International Conference and Workshop, Quaternary Glacial and Climate Extremes.

Y2 - 1 June 2011 through 4 June 2011

ER -