Regional distribution and geometry of salt diapirs and supra-Zechstein Group faults in the western and central North Sea
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Keywords:
Salt tectonics
Echelon formation
Horst and graben
Growth fault
Half-graben
Salt dome
The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip or as the locus of extension shifts towards the embryonic ocean spreading centre. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre-existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift-related depocentre located in the southern, most proximal part of the Santos Basin, Brazil along-strike of a failed spreading centre, the Abimael Ridge. The graben is defined by up to 3.5 km of base-salt relief along its basinward-bounding fault and internal base-salt horsts that are up to 1 km high. This compartmentalises deformation, producing intra-graben extensional and contraction salt structures, ramp-syncline basins, and expulsion rollovers, resulting in a remarkably different salt-tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyse the spatial and temporal evolution of salt-tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono-stratigraphic development of other salt-bearing rifted margins.
Salt tectonics
Diachronous
Salt dome
Syncline
Horst and graben
Half-graben
Echelon formation
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Salt tectonics
Half-graben
Syncline
Horst and graben
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Abstract. Basin-scale salt flow and the evolution of salt structures in rift basin is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward directed driver for salt tectonics. We designed a new experimental analog apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting and extension combined with tilting. Digital image correlation of top view stereoscopic images was applied to reveal the 3D displacement and strain patterns. Results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement, i.e. amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional fault developed, which resemble fault zones observed on basin flanks offset from the central graben zone.
Salt tectonics
Half-graben
Horst and graben
Overburden
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The Carboniferous Stoddart Group and Permian Belloy Formation record infill of a long-lived graben complex in the center of the Peace River Embayment. The Dawson Creek Graben Complex began down-dropping during deposition of the Rundle Group and Golata Formation and reached its maximum during Kiskatinaw time. The overlying Taylor Flat Formation shows graben filling and graben decay; whereas the flat Permian Belloy Formation beds within and beyond graben limits indicate tectonic stability. The complex comprised the larger Fort St. John Graben and satellite Hines Creek, Whitelaw, and Cindy grabens. The grabens consist of kilometer-scale horst and graben blocks bounded by normal faults. The internal blocks subsided at various rates, with differential subsidence occurring in the form of horsts subsiding slower than neighboring grabens. Syn- and post-depositional growth-type normal faults controlled formation and bed thickness, as did inter- and intra-formation unconformities. From these observations, a structural/stratigraphic model can be constructed that explains the complex stratigraphy and depositional interpretations. This model describes a basin dominated by tectonic controls rather than global sea-level events. Syn- and post-sedimentary growth-type block faulting, differential subsidence of fault blocks, sedimentary infill, and unconformity truncation were the major controls on the basin. The model provides an analog tomore » grabens and block-faulted basins of growth-faulted basins occurring elsewhere. The implications of the model to petroleum exploration are that all beds can be correlated by assuming that beds were essentially flat-lying prior to and during faulting. The combination of the block-faulted character and complex facies changes provides many structural and stratigraphic petroleum traps.« less
Horst and graben
Growth fault
Tectonic subsidence
Horst
Fault block
Half-graben
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Abstract. We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent inversion. An early stage of extension generated structural topography consisting of a series of en-échelon graben. Our salt analog filled these graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems, whereas deformation in suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults, forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was enhanced along and up the major relay or transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest, and salt had risen diapirically on the horst blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New pop-up structures also formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to natural examples such as those in the Moroccan High Atlas.
Salt tectonics
Horst and graben
Monocline
Half-graben
Doming
Echelon formation
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Horst
Horst and graben
Half-graben
Detachment fault
Growth fault
Anticline
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Abstract. We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent inversion. An early stage of extension generated structural topography consisting of a series of en-échelon graben. Our salt analog filled these graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems whereas deformation in suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults, forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was enhanced along and up the major relay/transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest and salt had risen diapirically on the horst blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New popup structures also formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to natural examples such as those in the Moroccan High Atlas.
Salt tectonics
Horst and graben
Monocline
Doming
Half-graben
Echelon formation
Salt dome
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Citations (1)
The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip or as the locus of extension shifts towards the embryonic ocean spreading centre. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre-existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift-related depocentre located in the southern, most proximal part of the Santos Basin, Brazil along-strike of a failed spreading centre, the Abimael Ridge. The graben is defined by up to 3.5 km of base-salt relief along its basinward-bounding fault and internal base-salt horsts that are up to 1 km high. This compartmentalises deformation, producing intra-graben extensional and contraction salt structures, ramp-syncline basins, and expulsion rollovers, resulting in a remarkably different salt-tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyse the spatial and temporal evolution of salt-tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono-stratigraphic development of other salt-bearing rifted margins.
Salt tectonics
Diachronous
Syncline
Salt dome
Horst and graben
Half-graben
Echelon formation
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Salt tectonics
Echelon formation
Horst and graben
Growth fault
Half-graben
Salt dome
Cite
Citations (25)
Abstract The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip, or as the locus of extension shifts toward the embryonic ocean spreading center. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre‐existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift‐related depocentre located in the southern, most proximal part of the Santos Basin, Brazil, along‐strike of a failed spreading center, the Abimael Ridge. The graben is defined by up to 3.5 km of base‐salt relief along its basinward‐bounding fault and internal base‐salt horsts that are up to 1 km high. This compartmentalizes deformation, producing intra‐graben extensional and contraction salt structures, ramp‐syncline basins, and expulsion rollovers, resulting in a remarkably different salt‐tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyze the spatial and temporal evolution of salt‐tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono‐stratigraphic development of other salt‐bearing rifted margins.
Salt tectonics
Diachronous
Syncline
Salt dome
Echelon formation
Horst and graben
Half-graben
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Citations (19)