Microtextural signatures in quartz grains and foraminifera from tsunami deposits of the Portuguese shelf

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.

本研究呈现了葡萄牙南部陆架采集的两根沉积岩芯的分析结果，本研究的核心目标是阐明阿尔加维台地（葡萄牙南部）的沉积动力学特征，以及全新世（Holocene）高能事件留下的沉积印记。研究于近岸浅海区域获取上述沉积岩芯，其地层中发现了两处与海啸事件相关的沉积层——分别对应公元1755年海啸及距今约3400 cal BP（校准碳年）的古海啸事件。本研究重点量化了两处沉积层中石英颗粒与有孔虫（foraminifera）壳体的微结构印记，并基于这些颗粒表面的印记反演沉积物的搬运模式。

附录01：沉积物组成分析。本次分析仅针对250~500 μm粒级的沉积物开展，统计得到的组分被划分为生物碎屑（贝壳、软体动物、有孔虫及其他生物残体碎片）、石英、长石、不透明矿物及云母（白云母与黑云母）。统计得到的组分被划分为生物碎屑（贝壳、软体动物、有孔虫及其他生物残体碎片）、石英、长石、不透明矿物及云母（白云母与黑云母）。

附录02：石英颗粒微结构分析，以及岩芯GeoB23512-01的相关图表与统计数据。

附录03：石英颗粒微结构分析，以及岩芯GeoB23513-02的相关图表与统计数据。

附录04：有孔虫鉴定与埋藏学分类。本次分类依据有孔虫壳体的物理或化学蚀变程度开展，具体分级为：(0) 未蚀变，保存完好；(1) 轻微蚀变；(2) 中等蚀变；(3) 严重蚀变。

附录05：回流动力学概念模型：
A) 示意图展示了两根岩芯相对于波尔蒂芒峡谷（Portimão canyon）的大致位置。沿峡谷运移的回流流速随水深增加而升高。由于动能与流速呈正比，经波尔蒂芒峡谷约束的回流会在石英颗粒表面产生更多机械刻蚀印记，这一现象在岩芯GeoB23512-01的探测数据中得到验证。
B) a-b剖面示意图：回流可搬运高密度的近海外流，这一过程会加剧近海侵蚀与沉积物再搬运；(I) 侵蚀作用携带的高浓度沉积物易导致颗粒产生裂纹与撞击痕迹；(II) 水体中沉积物浓度较低时，颗粒间碰撞更为剧烈，会在颗粒表面形成新鲜断面。