Interactions between deep-water gravity flows and active salt tectonics

Zoë A Cumberpatch,Yohann Poprawski,Ben A Kilhams,David M Hodgson,Christopher A-L Jackson,Euan L Soutter,Ian A Kane

doi:10.2110/jsr.2020.047

Abstract

ABSTRACTBehavior 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.

Highlights

The sedimentology and stratigraphic architecture of deep-water systems deposited in unconfined basins (e.g., Johnson et al 2001; Baas 2004; Hodgson 2009; Prelat et al 2009; Hodgson et al 2011; Spychala et al 2017), or in basins with static or relatively static topography (e.g., Kneller et al 1991; Haughton 1994; McCaffrey and Kneller 2001; Sinclair and Tomasso 2002; Amy et al 2004; Soutter et al 2019), are reasonably well established compared to those in basins influenced by active topography (e.g., Hodgson and Haughton 2004; Cullen et al 2019)
Seafloor topography is generated by a variety of geological processes, including relief above mass-transport deposits (MTDs)
Sparse biostratigraphic data (Agirrezabala and Lopez-Horgue 2017) hinders correlation across the structures; we refer to the Lower (LBF) and Upper (UBF) Black Flysch group only, to avoid further subdivisions based on geographic location (e.g., Robles et al 1988; Vincente-Bravo and Robles 1991a, 1991b, 1995; Poprawski et al 2014)

Summary

Introduction

The sedimentology and stratigraphic architecture of deep-water systems deposited in unconfined basins (e.g., Johnson et al 2001; Baas 2004; Hodgson 2009; Prelat et al 2009; Hodgson et al 2011; Spychala et al 2017), or in basins with static or relatively static topography (e.g., Kneller et al 1991; Haughton 1994; McCaffrey and Kneller 2001; Sinclair and Tomasso 2002; Amy et al 2004; Soutter et al 2019), are reasonably well established compared to those in basins influenced by active topography (e.g., Hodgson and Haughton 2004; Cullen et al 2019).Seafloor topography is generated by a variety of geological processes, including relief above mass-transport deposits (MTDs) (e.g., Ortiz-Karpf et al. 2015, 2016; Soutter et al 2018; Cumberpatch et al 2021), syndepositional tectonic deformation (e.g., Hodgson and Haughton 2004; Kane et al 2010) and salt diapirism (Fig. 1; e.g., Hodgson et al 1992; Kane et al 2012; Prather et al 2012; Oluboyo et al 2014). Seafloor topography is generated by a variety of geological processes, including relief above mass-transport deposits (MTDs) Salt-tectonic deformation influences over 120 basins globally (Hudec and Jackson 2007), including some of the world’s largest petroleum-producing provinces (e.g., Booth et al 2003; Oluboyo et al 2014; Charles and Ryzhikov 2015; Rodriguez et al 2018, in press; Grant et al 2019, 2020a, 2020b; Pichel et al 2020). Subsurface studies have shown that salt structures deforming the seafloor can exert substantial control on the location, pathway, and architecture of lobe, channel-fill, levee, and mass-transport deposits (Fig. 1; e.g., Mayall et al 2006, 2010; Jones et al 2012; Wu et al 2020; Howlett et al, in press). Note the complex and sinuous paths taken by slope channels around salt structures (Modified from Mayall et al 2010)

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