Seismic, structural and stratigraphic evolution of the cretaceous sequences of the orphan basin, offshore Newfoundland and Labrador

Hardy, Victoria E. (2008) Seismic, structural and stratigraphic evolution of the cretaceous sequences of the orphan basin, offshore Newfoundland and Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

The continental margin of Newfoundland is made up of a series of interconnected, deep, Mesozoic sedimentary basins. Between the Cumberland Belt Transform Zone and the Charlie Gibbs Transform Zone the Avalon terrane is dissected into a 450 km wide track of extensional ridges and grabens collectively known as the Orphan Basin. From both a tectonic and a petroleum potential point of view the basin can be divided into an older (Late Triassic - Early Jurassic) sub-basin known as the East Orphan Basin and a younger (Cretaceous) sub-basin known as the West Orphan Basin. The Orphan Basin is an underexplored area and few studies have been completed on the structural, tectonic and stratigraphic framework of the area. -- Seismic stratigraphic analysis of the basin identified six major sequence boundaries ranging in age from pre-Mesozoic (Seismic Basement) to present (Water Bottom) and four Cretaceous sequences were identified, mapped and described. Four fault families were defined within the study area on the basis of their regionality, timing and duration of movement and depths of detachment: the Basin Bounding Fault Family, the Basement Involved Fault Family, the Sedimentary Fault Family and the Transfer Fault Family. -- Based on the mapping of the Cretaceous sequences and the orientations of major faults seen in the study area, the Orphan Basin can be divided into three distinct tectonostratigraphic regions. From west to east they are Areas A, B, and C. Areas B and C were affected by the Late Triassic - Early Jurassic Tethys Rift and the Late Jurassic - Early Cretaceous Atlantic Rift. Area B was reactivated for a third time with the Aptian - Albian Labrador rift that caused uplift and inversion of large structures in this area. Area A was predominantly affected by the Aptian - Albian Labrador rift and has Early and Late Cretaceous basin fill. The orientation of the major basement involved and basin bounding faults in the basin show a counterclockwise rotation from east to west as the rift propagated landward. The oldest faults (located in Area C) have a NE-SW orientation in line with the Tethys rift while those faults in the younger Area A have an approximate N- S to NNW-SSE orientation in line with the Labrador rift. -- A proven petroleum system has not been identified in the Orphan basin; however, due to the timing of rifting, two different petroleum systems are proposed for the East Orphan and the West Orphan basins. Considering all the elements and processes required for a working hydrocarbon system, the most likely plays within the East Orphan Basin are: an oil prone source rock equivalent to the Egret Member of the Rankin Formation; reservoirs of Early Cretaceous stacked sandstones, a seal of Late Cretaceous and Tertiary shales; large structural traps in the form of drape over horst blocks, extensional anticlines and rotated fault blocks of Late Jurassic - Early Cretaceous age. The petroleum system for the East Orphan Basin is likely analogous to that of the Jeanne d'Arc Basin. In the West Orphan Basin the most likely plays are: Late Cretaceous and early Tertiary organic rich shales equivalent to the Bjarni and Markland Formations in the Labrador basins; reservoirs made up of Late Cretaceous and early Tertiary sands; seals of thick Nautilus or Banquereau equivalent shales; structural, stratigraphic and combination traps, most likely basin margin fans pinched out updip or draped over some form of structure. The petroleum system for the West Orphan Basin is likely analogous to that of the Labrador basins.

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