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TitleLinking regional tectonic events with the stratigraphic succession and subsidence history of Orphan Basin, offshore Newfoundland, Canada
AuthorDafoe, L T; Keen, C E; Dickie, K; Williams, G L
Source4th Atlantic Conjugate Margins Conference; 2014 p. 108-109
Alt SeriesEarth Sciences Sector, Contribution Series 20140154
PublisherAtlantic Conjugate Margins
Meeting4th Atlantic Conjugate Margins Conference; St. John's; CA; August 20-22, 2014
Mediapaper; on-line; digital
File formatpdf
ProvinceNewfoundland and Labrador; Eastern offshore region
NTS1; 2
AreaOrphan Basin
Lat/Long WENS -53.0000 -41.0000 52.0000 46.0000
Subjectsstructural geology; stratigraphy; basin evolution; basins; unconformities; chronostratigraphy; rifting; tectonic history; tectonic evolution; subsidence; deposition; palynostratigraphy; seismic data; crustal thickness; Orphan Basin; Aptian-Albian event; Cretaceous; Jurassic
Illustrationsstratigraphic correlations; location maps
ProgramFrontier basin analysis, Geoscience for New Energy Supply (GNES)
AbstractOffshore Newfoundland, the Orphan Basin is a large rift basin bordering the Atlantic continental margin that formed during multiple rift phases. Extension in the Jurassic and Early Cretaceous resulted in faulting and thinning of the continental crust that ended in Aptian time. Subsequent extension, approximately perpendicular to the earlier rift phase, was focused east of Orphan Knoll and culminated in seafloor spreading in the Santonian (chron 33R). These regional tectonic events are recorded in the stratigraphic succession of Orphan Basin. We have integrated seismic and well data to develop a regional stratigraphic framework and identified basin-wide unconformities and syn-rift sedimentary packages. Combining the stratigraphy with analysis of the subsidence history allows us to make inferences on tectonic influence.

A top Jurassic unconformity is confined to the eastern portion of Orphan Basin where the earliest stages of rifting took place and thick Late Jurassic sediments accumulated. A more basin-wide, Aptian unconformity is present across the basin and is associated with greater degrees of erosion in the central part of the basin and atop basement highs. An overlying Santonian-aged unconformity also records similar erosion along basin margins and atop basement highs, although is less pronounced compared to the Aptian horizon. We propose that these major erosional unconformities in Orphan Basin are related to tectonic events that reflect the breakup of crust and/or lithospheric mantle at a regional scale outside of the basin. Associated isostatic rebound related to breakup events may explain the relative uplift and erosion at these times.
Following the end of rifting within Orphan Basin in the Aptian, there is an anomalous lack of thermal subsidence normally associated with post-rift deposition. Mid- to Upper Cretaceous deposits reflect shallow marine to shelfal (< 200 m) paleowater depths. The onset of subsidence does not begin until Late Campanian-Early Maastrichtian time when a significant transgression takes place across the basin. Major, basin-wide thermal subsidence is marked by development of the Base Tertiary horizon, a prominent seismic reflector recording development of bathyal water depths in the basin and a maximum flooding event. A mechanism is required to explain the delayed nature of post-rift subsidence in the basin and may include one of the following previously proposed models: 1) magmatic underplating; 2) a hot spot located in the vicinity of the rift; 3) removal of mantle lithosphere and replacement by hotter asthenosphere; or 4) flow of buoyant, depleted continental mantle below the rift basin. Based on an association to crustal/mantle breakup events and the nature of mechanisms explaining the subsidence history, it is clear that tectonic events played a major role in controlling the nature of the Mesozoic and earliest Cenozoic stratigraphy.
Summary(Plain Language Summary, not published)
Located offshore 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 deep-water Cenozoic sediments. 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.