Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil). (May 2020)

• Record Type: Journal Article
• Authors: Maestrelli, Daniele; Maselli, Vittorio; Kneller, Benjamin; Chiarella, Domenico; Scarselli, Nicola; Vannucchi, Paola; Jovane, Luigi; Iacopini, David
• Is Part Of: Marine and petroleum geology. Volume 115(2020)
• Publication Date: 2020-05
• Subjects: Sediment waves -- Cyclic steps -- Vertical fluid migration -- Turbidity currents -- Seismic geomorphology -- Ceará basin -- Brazil; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2020.104291
• Languages: English
• ISSNs: 0264-8172

Abstract

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. Highlights: 3D seismic data are used to examine near-seafloor features offshore Ceará, NE Brazil. Depressions isolated or organized in trails are seen at and near seabed within a sediment succession recording downslope activity via canyons and channels. AVO analysis exclude that the depressions were created by hydrocarbon seepage. Depressions are interpreted as cyclic steps generated by gravity-driven flows. Cyclic steps formation provides pathways for passive fluid migration.