The agglutinated foraminifera content from the last 550ka record of the IMAGES core MD 97-2114 (Chatham Rise, New Zealand) was analysed in order to detect the possible linkage existing between the composition of the grains forming the agglutinated tests and the deposition of tephras. The studied core has been collected east of New Zealand, about 680 km far from the active Taupo Volcanic Zone (TVZ) located on the North Island. Therefore, the core contains numerous macro- and microscopic tephra layers regionally documented. Scanning Electron Microscopy and Energy Dispersive Spectroscopy analyses were carried out on entire agglutinated foraminifera as well as on sectioned specimens, sampled above, below, and within the tephra layers. The analyses show that the studied foraminifera built structurally complex tests, picking and selecting minerals and biogenic particles according to their availability and abundance in the substratum, as well as their composition, size and shape. In most of the studied species, the composition of the agglutinated grains does not change when the deposition of the tephra layer strongly enriched in volcanic glass shards the substratum. Only the species Karreriella novangliae changed significantly its grain composition, selecting volcanic glass fragments. Nevertheless, the tephra deposition seems to influence the wall microstructure of the agglutinated test. The textulariid specimens, coming from the volcanoclastic layers, show a thinner wall which was also characterised by less abundant calcareous matrix with respect to the specimens sampled under or upon the tephra layer. We hypothesise that the volcanic ash deposition probably interfered with the normal agglutinating process also favouring the development of more aggressive waters at the sea floor which, in turn, could have enhanced carbonate dissolution. Our data also suggest that the sediment type of the substratum is not the only one controlling factor on the construction of the agglutinated foraminifera test and grain selection, which appears primarily as species-dependent.

The agglutinated foraminifera from the SW Pacific bathyal sediments of the last 550 ka: relationship with the deposition of tephra layers

MANCIN, NICOLETTA;BASSO, ELENA;LUPI, CLAUDIA;COBIANCHI, MIRIAM;
2014-01-01

Abstract

The agglutinated foraminifera content from the last 550ka record of the IMAGES core MD 97-2114 (Chatham Rise, New Zealand) was analysed in order to detect the possible linkage existing between the composition of the grains forming the agglutinated tests and the deposition of tephras. The studied core has been collected east of New Zealand, about 680 km far from the active Taupo Volcanic Zone (TVZ) located on the North Island. Therefore, the core contains numerous macro- and microscopic tephra layers regionally documented. Scanning Electron Microscopy and Energy Dispersive Spectroscopy analyses were carried out on entire agglutinated foraminifera as well as on sectioned specimens, sampled above, below, and within the tephra layers. The analyses show that the studied foraminifera built structurally complex tests, picking and selecting minerals and biogenic particles according to their availability and abundance in the substratum, as well as their composition, size and shape. In most of the studied species, the composition of the agglutinated grains does not change when the deposition of the tephra layer strongly enriched in volcanic glass shards the substratum. Only the species Karreriella novangliae changed significantly its grain composition, selecting volcanic glass fragments. Nevertheless, the tephra deposition seems to influence the wall microstructure of the agglutinated test. The textulariid specimens, coming from the volcanoclastic layers, show a thinner wall which was also characterised by less abundant calcareous matrix with respect to the specimens sampled under or upon the tephra layer. We hypothesise that the volcanic ash deposition probably interfered with the normal agglutinating process also favouring the development of more aggressive waters at the sea floor which, in turn, could have enhanced carbonate dissolution. Our data also suggest that the sediment type of the substratum is not the only one controlling factor on the construction of the agglutinated foraminifera test and grain selection, which appears primarily as species-dependent.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/878234
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