Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil)

Daniele Maestrelli*, Vittorio Maselli, Benjamin Kneller, Domenico Chiarella, Nicola Scarselli, Paola Vannucchi, Luigi Jovane, David Iacopini

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

Circular to elliptical topographic depressions, isolated or organized in trails, have been observed on the modern seabed in different contexts and water depths. Such features have been alternatively interpreted as pockmarks generated by fluid flow, as sediment waves generated by turbidity currents, or as a combination of both processes. In the latter case, the dip of the slope has been hypothesized to control the formation of trails of downslope migrating pockmarks. In this study, we use high-quality 3D seismic data from the offshore Ceará Basin (Equatorial Brazil) to examine vertically stacked and upslope-migrating trails of depressions visible at the seabed and in the subsurface. Seismic reflection terminations and stratal architecture indicate that these features are formed by cyclic steps generated by turbidity currents, while internal amplitude anomalies point to the presence of fluid migration. Amplitude Versus Offset analysis (AVO) performed on partial stacks shows that the investigated anomalies do not represent hydrocarbon indicators. Previous studies have suggested that the accumulation of permeable and porous sediments in the troughs of vertically stacked cyclic steps may create vertical pathways for fluid migration, and we propose that this may have facilitated the upward migration of saline pore water due to fluid buoyancy. The results of this study highlight the importance of gravity-driven processes in shaping the morphology of the Ceará Basin slope and show how non-hydrocarbon fluids may interact with vertically stacked cyclic steps.

Original languageEnglish
Article number104291
Number of pages11
JournalMarine and Petroleum Geology
Volume115
Early online date10 Feb 2020
DOIs
Publication statusPublished - May 2020

Bibliographical note

Acknowledgments: We sincerely thank Petroleum Geo-Services (PGS), and specifically David Hajovsky and Opdyke (PGS) for releasing the 3D data (BMCE-2) used for the main interpretation analysis. CGG and C. Baron (CGG) are also thanked for furnishing their 3D full and partial stack data (BMCE 1&2) and allowed us to show these results. We kindly acknowledge the Associate Editor Daniel Praeg for his careful revision of the text and for the many useful comments that highly improved the quality of the manuscript. We thank three anonymous reviewers for their detailed and constructive reviews. We are grateful to M. Huuse and D. Duarte for their constructive comments on a previous draft, and to Bill Richards for the final review of the manuscript. D.M. was funded through the Tuscany PhD Regional program [grant POR ICO FSE 2014/2020-Asse C] and the Erasmus + exchange for his visit in Aberdeen. The seismic interpretation was performed at the SeisLab, Department of Geology and Petroleum Geology (University of Aberdeen).

Keywords

  • Brazil
  • Ceará basin
  • Cyclic steps
  • Sediment waves
  • Seismic geomorphology
  • Turbidity currents
  • Vertical fluid migration

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