Abstract
Surficial sediments on the seafloor from passive continental margins can provide insight into recent Late Quaternary sedimentary dynamics acting over offshore sedimentary systems. This work focuses on the study of some particular ferruginous tubular structures resembling bioforms (FTB) located in the distal Galician Continental Margin (NW Iberian Margin) at water depths between ~ 1550 and ~ 2200 m. The characterisation of these structures made it possible to study in depth their formation environment and subsequent sedimentary evolution during the Late Pleistocene and Holocene. The FTB consist of goethite with a framboidal texture. They were interpreted as formed by an initial pyrite precipitation in reducing microenvironments conditioned by the activity of sediment-dwelling organisms during the early diagenesis. This is followed by the oxidation of pyrite by a combination of hydrothermal fluids and erosional processes, which triggers the formation of the framboidal oxyhydroxides. The data allowed obtaining a comprehensive understanding of the environmental context and the significance of these ferruginous tubules, as there are no previous studies in the scientific literature that describe these structures in a source-to-sink sedimentary system.
Highlights
The study of the surficial sediments and geological structures of the seafloor is an essential tool for characterising the most recent sedimentary and oceanographic dynamics of continental margins. This is the case of the West Galician Continental Margin, located northwest of the Iberian Continental Margin, which has been the focus of several sedimentary infill studies, especially after the sinking of the Prestige oil tanker (e.g. Murillas et al 1990; Ercilla et al 2006, 2008, 2011)
Despite the large number of works focused on the Galician Continental Margin, no previous work has focused on the attention and characterisation of the formation of ferruginous tubular bioforms (FTB)
FTB have been identified within rock fragment trails associated with comet marks that are aligned with the direction of the current behind the dropstones (Fig. 2c)
Summary
The study of the surficial sediments and geological structures of the seafloor is an essential tool for characterising the most recent sedimentary and oceanographic dynamics of continental margins. Despite the large number of works focused on the Galician Continental Margin, no previous work has focused on the attention and characterisation of the formation of ferruginous tubular bioforms (FTB). These materials were extracted and observed on the seafloor of the transitional zone (TZ) morphostructural province (Fig. 1), a geomorphological province defined by Vázquez et al (2008), which corresponds to a general elevation of the marginal platform of the margin (López-Pérez et al 2021a).
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