Effects of X-ray computed tomography (CT) on the ichnologic interpretation of the Mira River estuary sediment core, SW Portugal

Abstract

Computed tomography (CT) is a relatively new technique in ichnofossil analysis, which permits superior identification of individual trace fossils, their morphology, infill, tiering relationships, and preservation potential, thus providing better environmental interpretations. It also allows non-professional ichnologists to interpret trace fossils in 3D slices with ease, especially in relatively homogeneous and mud-rich sediments. Herein, CT imagery results have been compared with conventional core logging results based on two push core samples from a muddy tidal flat of the Mira River estuary, Portugal. CT images provide a significantly more accurate description of cores and their environmental interpretation due to enhanced visibility of physical and biogenic sedimentary structures. They also reveal complex tiering relationships between burrows with preferential preservation of deeper tiers. The appearance of stacked Scalichnus-like and other siphonichnidal burrows made by infaunal bivalves indicates discontinuous deposition on a tidal flat likely caused by seasonally related fluctuations in an estuarine environment.

Keywords:

• CT scanning
• tiering
• equilibrichnia
• paleoenvironmental analysis
• estuary

Acknowledgements

This work is devoted to Dr. George S. Pemberton, who was the leading author’s Ph.D. supervisor, mentor, and “ichnological father”. Drs. Francisco Fatela and Conceição Freitas from the University of Lisbon are thanked for their valuable help in the organization of fieldwork and obtention of the push cores.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 under the project “UIDP/50019/2020 – Financiamento Plurianual de Unidades de I&D 2020-2023 – IDL” and co-funded by European funds (POCI), Regional Operational Programmes (COMPETE) and national funds (FCT) under the project “European Multidisciplinary Seafloor and Water Column Observatory (Portugal) - EMSO-PT (PINFRA/22157/2016)” in the scope of “Portuguese Roadmap of Research Infrastructures”. Jacqueline Santos received financial support through grant IPMA-2020-011-BI (under the project EMSOPT) and Ana Alberto through PhD grant UIBD/151497/2021 (IDL).