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Mark Rowan presents
Overview of salt tectonics of the Norwegian Barents Sea Mark G. Rowan Rowan Consulting, Inc. Christopher A.-L. Jackson Imperial College Atle Rotevatn University of Bergen Overview Almost all published studies of the salt tectonics of the Barents Sea date from the mid-1990s The aim today is to summarize: existing ideas and models project goals and methodology implications for exploration Will first address the regional tectonic history and the relationship of salt to crustal rifting Will then address the geometries and evolution of salt structures Limited to publicly available data Barents Sea basins and salt domes Tectonic events Timaride Orogeny (Neoproterozoic) Caledonian Orogeny (Ordovician-Devonian) Uralide Orogeny (Late Carboniferous-Permian) Crustal extension culminating in margin breakup (DevonianCenozoic) Minor-moderate late inversion (Mesozoic? Cenozoic) Gernigon and Brönner, 2012 Timing and orientation of rifting, model 1 Henriksen et al., 2011 Age of crustal extension generally youngs from east to west Rift orientation gradually rotates counter-clockwise Evaporite deposition is ~ coeval Implication is that salt is prerift in west and syn- to postrift in east Note: Gudlaugsson et al. (1998) invoke initiation of rifting in the western basins as Carboniferous Faleide et al., 2008 Timing and orientation of rifting, model 2 Initial rifting everywhere due to post-Caledonian (DevonianCarboniferous) orogenic collapse Subsequently modified during Mesozoic extension, which triggered salt movement, and Cenozoic margin breakup Implication is that salt is synrift everywhere Gernigon et al., 2014 Nordkapp Basin Gabrielsen et al., 1990 Nordkapp Basin bound by major basement faults that switch polarity along strike Salt considered postrift, filling deep basin (e.g., Dengo and Røssland, 1992, Gabrielsen et al., 1992; Nilsen et al., 1995) Salt considered synrift, deposited during faulting (Bugge et al., 2002) NE Nordkapp Basin NPD-BA-11-106 modified from NPD website Base salt dips into major bounding fault Unconformity (blue) marks lower boundary of postrift strata Is all or only part of salt sequence younger than the unconformity? Regional line in formerly disputed area Mattingsdal et al., 2015 Different relationship in Tiddlybanken Basin Base salt is ~ parallel to presalt strata, which dip inward on both flanks Geometry suggests that salt is postrift Spatial & thickness distribution of the LES Questions what are the temporal relationships between crustal extension and evaporite deposition? i.e., is the salt prerift, synrift, postrift, or a combination? how does this vary spatially across the study area? how did this influence the composition, thickness, and hence source, reservoir, and seal potential of the LES? how did this influence the initiation and evolution of saltrelated deformation? Approach primarily seismic interpretation regional analysis of growth strata comparison of rift basins and rift shoulders (platforms) analogies with other salt basins Drives for salt-related deformation Extension Thick-skinned (tectonic) Thin-skinned (gravitational or tectonic) Contraction Thick-skinned (tectonic) Differential loading Depositional Erosional Sørvestnaget Basin Perez-Garcia et al., 2013 Invoke primarily extensional history: 1) extensional trigger; 2) passive diapirism; 3) extensional collapse; and 4) slight gravitydriven contraction Extension and diapir initiation/growth occurred during the Late Cretaceous to Eocene, when there was already a thick overburden Suggests there was an earlier history Nordkapp Basin Multi-stage evolution (Nilsen et al., 1995): Early Triassic – reactive diapirism during decoupled thick-skinned extension Middle Triassic – passive diapirism Middle-Late Triassic – welding of deep salt layer but continued passive rise driven by gravity gliding and consequent contraction Late Triassic – diapir burial Late Cretaceous – diapir rejuvenation driven by gravity gliding Middle Cenozoic – diapir rejuvenation driven by regional shortening In contrast, Dengo and Røssland (1992) invoked Triassic progradation and differential loading as the trigger for diapiric rise Nilsen et al., 1995 Tiddlybanken diapir Multi-stage evolution: Early Triassic – prekinematic section Middle Triassic – thinning and then erosional truncation Middle Triassic - Jurassic – salt evacuation and diapirism late inversion Note 3 halite-rich parts of LES Høy, 2013 Not extensional! Trigger was probably mid-Triassic contraction related to Uralide Orogeny Erosion of roof led to salt breakthrough and diapirism Coward and Stewart, 1995 Haapet Dome Høy, 2013 Post-Jurassic fold with salt in core Interestingly, width of structure is greater than width of salt basin Implies inversion of normal faults that are outside the edges of the salt basin Signalhorn Dome NPD1201-037 modified from NPD website Prekinematic below yellow horizon Thickening only above yellow on right side – due to evacuation into Tiddlybanken diapir after it broke through its roof Anticline formed late due to inversion tectonics Note deformation in LES, with two more mobile layers Veslekari Dome NPD-BA-11-117 modified from NPD website Similar to Signalhorn Dome, although with higher amplitude Although it appears to have been a high during the Triassic, it was only a monocline with expansion into the Nordkapp Basin Anticline formed only late due to inversion tectonics Note shifting depocenters in center of line Expulsion rollovers Ge et al., 1997 (modified in Hudec and Jackson, 2011) Progradation over salt creates basinward-shifting depocenters and distal salt inflation Inflation localised over a basement fault leads to diapir initiation Nordkapp Basin NPD-BA-11-106 modified from NPD website Most concentrated area of salt diapirs (along with Tromsø) A large majority are in the basin center, with only a few at the basin margins Instead, get faulted salt pillows at the margins NE Nordkapp Basin seismic image removed Key: cyan – top and base salt; red – carbonate buildups; pink – top Permian; salmon – top Halvert (intra Lower Triassic); blue – base Cretaceous Prominent unconformity and onlap surface at top Halvert NE Nordkapp Basin Simplified restorations carried out using Move™ on time data, without decompaction, and without isostatic correction top Halvert top Permian Salt deposited in half graben Upper Permian is prekinematic Salt movement triggered by progadational loading in earliest Triassic, generating expulsion rollover in proximal part of basin Displaced salt caused inflation on either side Erosion led to salt breakthrough and passive diapirism Diapirs buried prior to Cretaceous but rejuvenated by late shortening Initiation & evolution of salt structures Questions what is the spatial distribution of different types of salt structures? how was salt movement triggered and how did it evolve? how did this vary spatially across the study area? what was the relative importance of extension, contraction, and differential loading in the different basins? what were the relative roles of thick- and thin-skinned deformation? how did the different graben orientations impact early salt movement and late inversion? Approach seismic interpretation structural restorations analogies with other salt basins problem-specific analogue models (with University of Barcelona) Possible analog models progradation salt Landward-dipping step (done by Ge et al., 1997) Basinwardward-dipping step (is extension needed?) Rollover into landwarddipping step progradation salt progradation salt Practical applications Salt-related deformation impacts all aspects of the petroleum systems: trap, reservoir presence and quality, hydrocarbon maturation and migration, and seal – and not just around salt! A better understanding of the salt tectonics in the Norwegian Barents Sea is applicable to numerous possible plays: 1) presalt; 2) intrasalt; 3) simple salt-cored anticlines; 4) faulted salt pillows; and 5) three-way truncations against salt diapirs Requires a regional study of all aspects of evaporite deposition and stratigraphy, its relationship to crustal rifting and other tectonic events, and the initiation and evolution of salt structures Bottom line This will be a fantastic study (!) of poorly understood aspects of what is still a frontier petroleum province Your company really needs to participate… Thank you!
