Microtextural signatures in quartz grains and foraminifera from tsunami deposits of the Portuguese shelf
Description
This study presents results from two sediment cores collected on the southern Portuguese shelf, the main objective of this work is to understand the sediment dynamics and imprints of high-energy Holocene events on the Algarve platform (southern Portugal). The sediment cores were retrieved in the shallow offshore area and revealed the present of two deposits associated with tsunami events (CE 1755 and app. 3400 cal BP). The work presented here focus on the quantification of microtextural imprints in quartz grains and foraminifera tests on those deposits and in the sediment transport modes inferred from these imprints in the surface of these particles Appendix 01: Compositional analysis of the sediments. The compositional analysis of the sediments was carried out only on the 250-500 μm fraction. The counted elements were grouped in bioclasts (fragments of shells, mollusks, foraminifera and other organisms), quartz, feldspar, opaques and micas (muscovite and biotite). The elements were grouped in bioclasts (fragments of shells, mollusks, foraminifera and other organisms), quartz, feldspar, opaques and micas (muscovite and biotite). Appendix 02: microtextural analysis of quartz grains, graphs and statistics of core GeoB23512-01. Appendix 03: microtextural analysis of quartz grains, graphs and statistics of core GeoB23513-02; Appendix 04: Identification and taphonomic classification of foraminifera. The individuals were classified according to the degree of physical or chemical alteration. Was considered: (0) when the shells were unaltered, being considered well-preserved; (1) slightly altered; (2) moderately altered and (3) very altered. Appendix 05: Conceptual model of backwash dynamics: A) Diagram illustrating approximately the position of the cores in relation to the Portimao canyon. The backwash flow concentrated in the canyon reaches higher velocities as the depth increases. As the energy is proportional to the velocity, the flow channeled by the Portimão canyon promotes more generation of mechanical marks on the quartz grains, which is observed in the GeoB23512-01 sounding. B) Schematic profile a-b, backwash transports high density offshore flows this can lead to more offshore erosion and reinsertion; (I) High concentration of sediments carried by erosion favors the formation of fractures and percussion marks. (II) The low concentration of sediment in the water column generates more energetic collisions and fresh surfaces in the grains.