Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

The geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

Cretaceous and Cenozoic Basin Evolution Based on Decompacted Sediment Thickness from Petroleum Wells around New Zealand

<p>Decompacted sedimentary data from 33 New Zealand exploration wells is used to investigate basin evolution and tectonics from around New Zealand. This analysis is directed to both a comparison of basin behaviour and a search for common subsidence signatures. Common to almost all New Zealand basin subsidence curves is a sedimentary signature associated with rifting of the Gondwana super-continent (80-65 Ma). In the Great South Basin a second rifting event is inferred at 51 [plus or minus] 2 Ma, illustrated by a rapid increase in subsidence rates (with a maximum rate of 190 m.Myr-1 at Pakaha-1). Coinciding with the cessation of Tasman Sea rifting ([approximately] 53 Ma), and with the onset of rifting in the Emerald Basin ([approximately] 50 Ma), it is assumed that the event is related to the tectonic plate reorganization. An increase in sedimentation is noted at [approximately] 20 Ma in most South Island wells. Convergence on the Alpine Fault, leading to increased erosion is cited as a mechanism for this period of basin growth, consistent with the Cande and Stock (2004) model of plate motions. A second increase in sedimentation occurs at [approximately] 6 Ma in almost all wells around New Zealand. Climate-driven erosion resulting in isostatic uplift is thought to contribute to this event. Hiatuses in the sedimentary record for the Canterbury, Great South and Western Southland Basins during the late Oligocene are interpreted as the Marshall Paraconformity. It appears that the break in sedimentation located within a regional transgressional mega-sequence was caused by mid Oligocene glacio-eustatic fall and related oceanic current processes. Loading by the Northland Allochthon, in conjunction with paleobathymetry and subsidence data, is used to demonstrate the mechanical properties of the lithosphere. A lithospheric rigidity of 1.5 x [10 to the power of 22] Nm is estimated, with an elastic thickness of 12 km. Considerably lower than elastic thickness values previously calculated for the Plio-Pleistocene loading of the Taranaki Platform. It is noted that the Northland value represents a younger, hotter crust at the time of load emplacment. With the exception of the central Taranaki and Great South Basins, stretching factors ([Beta]) for the sedimentary basins surrounding New Zealand are below 2. This suggests crustal thickness prior to rifting was between 35 and 50 km, consistent with data from conjugate margins of Australia and Antarctica. An increase in water depth in the Taranaki Basin at 25 [plus or minus] 3 Ma is confirmed by this study. This coincides with a similar signature on the West Coast of the South Island at 26 [plus or minus] 2 Ma. It is suggested that a mantle flow caused by the initiation of the subduction zone at [approximately] 25 Ma extends over a broader region (>750 km) than previously thought.</p>

Cretaceous and Cenozoic Basin Evolution Based on Decompacted Sediment Thickness from Petroleum Wells around New Zealand

<p>Decompacted sedimentary data from 33 New Zealand exploration wells is used to investigate basin evolution and tectonics from around New Zealand. This analysis is directed to both a comparison of basin behaviour and a search for common subsidence signatures. Common to almost all New Zealand basin subsidence curves is a sedimentary signature associated with rifting of the Gondwana super-continent (80-65 Ma). In the Great South Basin a second rifting event is inferred at 51 [plus or minus] 2 Ma, illustrated by a rapid increase in subsidence rates (with a maximum rate of 190 m.Myr-1 at Pakaha-1). Coinciding with the cessation of Tasman Sea rifting ([approximately] 53 Ma), and with the onset of rifting in the Emerald Basin ([approximately] 50 Ma), it is assumed that the event is related to the tectonic plate reorganization. An increase in sedimentation is noted at [approximately] 20 Ma in most South Island wells. Convergence on the Alpine Fault, leading to increased erosion is cited as a mechanism for this period of basin growth, consistent with the Cande and Stock (2004) model of plate motions. A second increase in sedimentation occurs at [approximately] 6 Ma in almost all wells around New Zealand. Climate-driven erosion resulting in isostatic uplift is thought to contribute to this event. Hiatuses in the sedimentary record for the Canterbury, Great South and Western Southland Basins during the late Oligocene are interpreted as the Marshall Paraconformity. It appears that the break in sedimentation located within a regional transgressional mega-sequence was caused by mid Oligocene glacio-eustatic fall and related oceanic current processes. Loading by the Northland Allochthon, in conjunction with paleobathymetry and subsidence data, is used to demonstrate the mechanical properties of the lithosphere. A lithospheric rigidity of 1.5 x [10 to the power of 22] Nm is estimated, with an elastic thickness of 12 km. Considerably lower than elastic thickness values previously calculated for the Plio-Pleistocene loading of the Taranaki Platform. It is noted that the Northland value represents a younger, hotter crust at the time of load emplacment. With the exception of the central Taranaki and Great South Basins, stretching factors ([Beta]) for the sedimentary basins surrounding New Zealand are below 2. This suggests crustal thickness prior to rifting was between 35 and 50 km, consistent with data from conjugate margins of Australia and Antarctica. An increase in water depth in the Taranaki Basin at 25 [plus or minus] 3 Ma is confirmed by this study. This coincides with a similar signature on the West Coast of the South Island at 26 [plus or minus] 2 Ma. It is suggested that a mantle flow caused by the initiation of the subduction zone at [approximately] 25 Ma extends over a broader region (>750 km) than previously thought.</p>