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TitleRegional stratigraphy and subsidence of Orphan Basin near the time of breakup and implications for rifting processes
AuthorDafoe, L T; Keen, C E; Dickie, K; Williams, G L
SourceBasin Research vol. 29, issue S1, 2015 p. 233-254,
Alt SeriesEarth Sciences Sector, Contribution Series 20140172
Mediapaper; on-line; digital
File formatpdf
ProvinceEastern offshore region
AreaOrphan Basin
Lat/Long WENS -52.0000 -46.0000 52.0000 48.0000
Subjectsstratigraphy; structural geology; geophysics; rifting; subsidence; stratigraphic correlations; stratigraphic analyses; structural basins; structural interpretations; structural features; unconformities; Aptian; Albian; Santonian; seismic surveys; seismic interpretations; seismic profiles; faults; Campanian; Maastrichtian; Jurassic; Cretaceous; Tertiary
Illustrationslocation maps; magnetic anomaly maps; seismic reflection profiles; stratigraphic correlations; graphs
ProgramBaffin Petroleum Systems, GEM2: Geo-mapping for Energy and Minerals
Released2015 09 18
AbstractThe stratigraphy, subsidence and structural history of Orphan Basin, offshore Newfoundland, is described from well data which has been tied to a regional seismic grid. This large (400 by 400 km) rifted basin is part of the non-volcanic rifted margin which experienced a long and complex rift history, spanning mid-Jurassic to Cretaceous time. It is underlain by variably thinned continental crust, locally thinned to less than 10 km. The work presented here shows the complex structural development, with major upper crustal faults terminating in the mid-crust, while lower crustal reflectivity suggests ductile flow, perhaps accommodating depth-dependent extension. This paper focusses on three major stratigraphic events connected to late-stage rifting and breakup. An Aptian-Albian unconformity appears to mark the end of upper crustal rifting in the Basin, while a second, more subdued unconformity was also noted atop basement highs and along the proximal margins of the basin in Santonian time. Between these two events there was only minor thermal subsidence, and the main phase of post-rift subsidence was delayed until Santonian-Campanian time, with rapid subsidence culminating in the development of a maximum flooding surface in base Tertiary time. Conventional models of rifting events predict significant basin thermal subsidence following cessation of extension. Recent work along some magma-poor passive margins world-wide has, however, identified examples in which subsidence is delayed even after the onset of seafloor spreading. The Orphan Basin is another example of this. The subsidence history suggests that depth-dependent extension, with more thinning of the lithospheric mantle than of the crust, may satisfy the observations. Thinning of lower lithospheric mantle appears to have persisted (25-30 Ma) longer than crustal deformation, which is consistent with recent quantitative models, predicting lower lithosphere counterflow toward the rift axis if the mantle is sufficiently buoyant. The Santonian event may coincide with the final breakup of continental lithosphere east of the Basin.
Summary(Plain Language Summary, not published)
Located offshore of Newfoundland, the Orphan Basin is a large frontier area which contains significant Jurassic oil reserves along its southeastern edge (Flemish Pass Basin). During opening of the North Atlantic Ocean, this region was subject to several phases of extension which resulted in a wide basin containing shallow marine Jurassic and Cretaceous sediments, and deepwater Cenozoics. In this study, we assess the significance of basin-wide marker horizons and their link to local and regional tectonic events associated with rifting and eventual formation of oceanic crust. In addition, we explain the delay in basin subsidence that is typically seen following the end of rifting within a basin. This has implications for the generation of mature petroleum source rocks and industry exploration in the area.