Interactions between deep-water gravity flows and active salt tectonics

Abstract

Behavior of sediment gravity flows can be influenced by seafloor topography associated with salt structures; this can modify the depositional architecture of deep-water sedimentary systems. Typically, salt-influenced deep-water successions are poorly imaged in seismic reflection data, and exhumed systems are rare, hence the detailed sedimentology and stratigraphic architecture of these systems remains poorly understood. The exhumed Triassic (Keuper) Bakio and Guernica salt bodies in the Basque–Cantabrian Basin, Spain, were active during deep-water sedimentation. The salt diapirs grew reactively, then passively, during the Aptian–Albian, and are flanked by deep-water carbonate (Aptian–earliest Albian Urgonian Group) and siliciclastic (middle Albian–Cenomanian Black Flysch Group) successions. The study compares the depositional systems in two salt-influenced minibasins, confined (Sollube basin) and partially confined (Jata basin) by actively growing salt diapirs, comparable to salt-influenced minibasins in the subsurface. The presence of a well-exposed halokinetic sequence, with progressive rotation of bedding, beds that pinch out towards topography, soft-sediment deformation, variable paleocurrents, and intercalated debrites indicate that salt grew during deposition. Overall, the Black Flysch Group coarsens and thickens upwards in response to regional axial progradation, which is modulated by laterally derived debrites from halokinetic slopes. The variation in type and number of debrites in the Sollube and Jata basins indicates that the basins had different tectonostratigraphic histories despite their proximity. In the Sollube basin, the routing systems were confined between the two salt structures, eventually depositing amalgamated sandstones in the basin axis. Different facies and architectures are observed in the Jata basin due to partial confinement. Exposed minibasins are individualized, and facies vary both spatially and temporally in agreement with observations from subsurface salt-influenced basins. Salt-related, active topography and the degree of confinement are shown to be important modifiers of depositional systems, resulting in facies variability, remobilization of deposits, and channelization of flows. The findings are directly applicable to the exploration and development of subsurface energy reservoirs in salt basins globally, enabling better prediction of depositional architecture in areas where seismic imaging is challenging.

Forward Modelling for Structural Stratigraphic Analysis, Offshore Sureste Basin, Mexico

“…The Onlapse-2D model shows packages of sediment gravity flows that thicken into the basin-axis of Minibasin-4 from Well-A in Zone 2, and thin onto and eventually onlap onto High-1. The stratal geometry here is consistent with the observations of subsurface (Mayall, et al, 2010;Doughty-Jones, et al, 2017), outcrop (Cumberpatch, et al, 2021), and numerical modelling (Sylvester, et al, 2015) of deepwater sediment gravity flows in confined tectonically active basins. These thicker sediment gravity flows could represent the sand-rich lobe axis of a confined lobe complex which progressively became unconfined through time as sediment input outpaced growth of structural accommodation.…”

The Role of Salt Tectonics in the Energy Transition: An Overview and Future Challenges

“…Overall, the focus of most recent literature on reservoir development in salt basins has been on deepwater clastic systems, driven by deepwater hydrocarbon exploration (e.g. Mayall et al, 2010;Giles and Rowan, 2012;Oluboyo et al, 2014;Cumberpatch et al, 2021). However, the economics of CO2 storage favours short CO2 transport distances, shifting the focus to present-day shallow water and onshore areas, where the reservoir targets for CO2 storage may be shallow marine and continental rather than deep water deposits.…”

“…Mello et al, 1995); ii) mobile, such that salt-related deformation generates a myriad of trapping locations and styles within salt basins, whereas the structural deformation modifies topography and bathymetry and therefore influences the distribution of syn-deformational reservoirs (e.g. Seni and Jackson, 1983;Hodgson et al, 1992;Rowan and Weimer, 1998;Gee et al, 2006;Winker and Booth, 2000;Cumberpatch et al, 2021); and iii) self-healing and crystalline meaning it is in most cases impermeable to pore water, hydrocarbons, and gases, and thus typically forms an ideal seal, to such an extent that 14 of the world's 25 largest oil fields are sealed by salt (Warren, 2006) (Fig. 1).…”

Bottom Current Modification of Turbidite Lobe Complexes

“…Individual turbidite beds form lobes with predictable facies distributions; lobes then combine to build larger lobe complexes (Figure 1A) (Piper and Normark, 1983;Deptuck et al, 2008;Jegou et al, 2008;Prélat et al, 2009;Grundvåg et al, 2014;Marini et al, 2015;Kane et al, 2017;Spychala et al, 2017;Ferguson et al, 2020). Topography on continental slopes and basin floors can influence individual gravity flows, which in turn affects the ultimate geometry of their deposits (Figure 1B) (Kneller et al, 1991;Kneller and McCaffrey, 1999;Sinclair and Tomasso, 2002;Al Ja'Aidi et al, 2004;Prélat et al, 2010;Bakke et al, 2013;Patacci et al, 2014;Salles et al, 2014;Doughty-Jones et al, 2017;Soutter et al, 2019;Howlett et al, 2019;Cumberpatch et al, 2021).…”