Shallow seismic stratigraphy of the southwestern Algarve shelf (Portugal) and characteristics of offshore tsunami deposits

IF 2.2 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Marine Geology Pub Date : 2025-02-01 DOI:10.1016/j.margeo.2024.107463

Lisa Feist , Pedro J.M. Costa , Juan I. Santisteban , Stijn Albers , Piero Bellanova , Ivana Bosnic , Marc De Batist , João F. Duarte , Aurora Rodrigues , Klaus Reicherter

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Abstract

Understanding the sedimentary dynamics of continental shelves is crucial for decoding past high-energy events like tsunamis. Based on data from HSV FISÁLIA cruise of the Portuguese Navy, this study investigates the geomorphological features of the southwestern Algarve shelf and the seismo-stratigraphic characteristics of sedimentary units attributed to two tsunamis that occurred in 1755 CE (Lisbon earthquake) and ca. 3600 cal yr BP. Using high-resolution geoacoustic profiling in combination with sedimentological analyses and radiocarbon dating from prior studies, this study is the first to identify an Infralittoral Prograding Wedge on the shallow southwestern Algarve shelf. Furthermore, remnants of an older transgressive prograding wedge-shaped sediment body have been detected on the mid to outer shelf off Portimão. A crucial finding of this study is a high-amplitude reflector which has been associated with the ca. 3600 cal yr BP tsunami deposit. This reflector is particularly strong based on the corresponding deposit's stark compositional contrast with the surrounding sediment. In its distribution, this reflector is restricted to the base of the Infralittoral Prograding Wedge indicating this wedge as the most likely sediment source for the ca. 3600 cal yr BP deposit. On the other hand, the 1755 CE Lisbon tsunami deposit has no clear geophysical signature on the southwestern Algarve shelf due to its vestigial thicknesses and scarce compositional contrast with the surrounding sediment. This divergence raises significant questions about the different triggering mechanisms and transport processes that define both offshore tsunami deposits. Our findings highlight the significance of local bathymetric conditions, sediment sources, as well as triggering mechanisms and transport pathways in shaping offshore tsunami deposits.

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葡萄牙阿尔加维陆架西南部浅层地震地层与近海海啸沉积特征

了解大陆架的沉积动力学对于破解像海啸这样的高能量事件至关重要。本研究基于葡萄牙海军HSV FISÁLIA游轮的数据，研究了发生在1755年（里斯本地震）和大约3600 calyr BP的两次海啸的阿尔加维西南陆架的地貌特征和沉积单元的地震地层特征。利用高分辨率地球声学剖面，结合沉积学分析和放射性碳定年，这项研究首次在阿尔加维西南浅层大陆架上发现了一个沿海下推进楔。此外,一个年长的海侵推进式的残余楔形沉积物的身体已发现在中期Portimao外大陆架。本研究的一个重要发现是一个高振幅反射器，该反射器与距今约3600年的海啸沉积有关。根据相应沉积物与周围沉积物的鲜明成分对比，这种反射特别强烈。在其分布上，该反射体被限制在沿海下推进楔的底部，表明该楔最有可能是约3600 cal年BP矿床的沉积物来源。另一方面，1755 CE里斯本海啸沉积物在阿尔加维陆架西南部没有明显的地球物理特征，这是由于其残留的厚度和与周围沉积物缺乏成分对比。这一分歧提出了关于确定两种近海海啸沉积物的不同触发机制和运输过程的重要问题。我们的研究结果强调了当地水深条件、沉积物来源以及触发机制和运输途径在形成近海海啸沉积物中的重要性。

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来源期刊

Marine Geology 地学-地球科学综合

CiteScore

6.10

自引率

6.90%

发文量

175

审稿时长

21.9 weeks

期刊介绍： Marine Geology is the premier international journal on marine geological processes in the broadest sense. We seek papers that are comprehensive, interdisciplinary and synthetic that will be lasting contributions to the field. Although most papers are based on regional studies, they must demonstrate new findings of international significance. We accept papers on subjects as diverse as seafloor hydrothermal systems, beach dynamics, early diagenesis, microbiological studies in sediments, palaeoclimate studies and geophysical studies of the seabed. We encourage papers that address emerging new fields, for example the influence of anthropogenic processes on coastal/marine geology and coastal/marine geoarchaeology. We insist that the papers are concerned with the marine realm and that they deal with geology: with rocks, sediments, and physical and chemical processes affecting them. Papers should address scientific hypotheses: highly descriptive data compilations or papers that deal only with marine management and risk assessment should be submitted to other journals. Papers on laboratory or modelling studies must demonstrate direct relevance to marine processes or deposits. The primary criteria for acceptance of papers is that the science is of high quality, novel, significant, and of broad international interest.