http://metododirecto.pt/CM2010 ISBN: 978-989-96923-1-2 Volume V – p. 181 - 184
II CENTRAL & NORTH ATLANTIC CONJUGATE MARGINS CONFERENCE
Provenance of reservoir sandstones in the Flemish Pass and Orphan Basins (Canada): U-Pb dating of detrital zircons using the laser ablation method McDonough, M. (1); Sylvester, P. (2); Bruder, N. (1); Lo, J. (3); O’Sullivan, P.
(4)
(1) Statoil Canada Ltd., 2100, 635 8th Ave SW, Calgary, AB T2P 3M3.
[email protected],
[email protected] (2) Dept. of Earth Sciences, Memorial Univ., St. John’s, NL A1B 3X5.
[email protected] (3) Husky Energy, 707 8th Ave SW, Calgary, AB T2P 3G7.
[email protected] (4) Apatite to Zircon, Inc., 1521 Pine Cone Road, Moscow, ID 83843 USA.
[email protected]
ABSTRACT U-Pb age dating has been undertaken on detrital zircon populations from Tithonian, Berriasian and Aptian age sandstones from three Flemish Pass basin wells and one Orphan basin well. The U-Pb age data for Tithonian and Berriasian sandstones are indicative of distinct North American and Iberian provenance signatures, and provide a test of plate reconstruction models.
Introduction The Flemish Pass Basin is located in the northeastern Grand Banks of Atlantic Canada, approximately 250 km northeast of the Jeanne d’Arc Basin, and 100 km southeast of the Orphan Basin (FIG.1). Utilising the laser ablation U-Pb method, 207 Pb/206Pb ages have been determined for detrital zircons from Jurassic and Cretaceous reservoir sandstones from three wells in the northern Flemish Pass Basin, and one in the western Orphan Basin (Mizzen L-11, Mizzen O-16, Baccalieu I-78, and Blue H-28; Figure 1). U-Pb dating of detrital zircon has been undertaken to shed light on sandstone provenance in northern Grand Banks, as well as a test of palinspastic reconstructions of the North Atlantic.
FIG.1 - Location map of the exploratory wells in Flemish Pass and Orphan basins.
The Flemish Pass Basin is filled with Kimmeridgian through Albian rift sediments (Foster & Robinson, 1993), and comprises an elongate oblique slip extensional basin on the margin of the Flemish Cap. The main phases of rift-related sedimentation in Flemish Pass Basin occurred in Tithonian and Berriasian times. In essence, the basin forms a 181
displacement transfer system connecting late Jurassic to early Cretaceous rifting in the Jeanne d’Arc Basin to the south with extension in the Orphan Basin to the northeast (Aarseth et al., 2004; FIG.2).
O Nfld
O FC
Nfld
Iberia
FC
Iberia
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b)
FIG.2 - Deformed plate margin palinspastic reconstructions of the North Atlantic for Kimmeridigian (a) and Berriasian (b) times -factors; O, Orphan Basin; FC, Flemish Cap (from Aarseth et al., 2004).
Detrital Zircon Dating Results of the laser ablation U-Pb dating of detrital zircons from Flemish Pass and Orphan basins are very consistent from well to well. There are three primary detrital zircon 207Pb/206Pb age populations in Lower Cretaceous (Berriasian) and Upper Jurassic (Tithonian) sandstones, which are approximately: 1) 340-460 Ma; 2) 530-680 Ma; and 3) broadly Grenvillian ages in the range of 0.9-1.2 Ga. A secondary age population in late Jurassic sandstones ranges from 295-325 Ma (FIG.3 and 4). Detrital population (1) has multicyclic zircon grains with 340-460 Ma 207Pb/206Pb ages that are interpreted to be derived from the Central Meguma belt of the Appalachian orogen, with a probable derivation from the south and southwest. Detrital zircons of population (2) are also multicyclic, and have 530-680 Ma 207Pb/206Pb ages that are indicative of sandstone provenance from the Avalon Belt of eastern Newfoundland, or alternatively from pre-Variscan granites of Flemish Cap and Iberia, which were connected in Jurassic times (FIG.2). The Grenvillian 207Pb/206Pb ages of population (3) can arguably have been derived from North American and/or Iberian sources, and are not diagnostic in terms of provenance. The secondary population of detrital zircons with 300-325 Ma 207Pb/206Pb ages occurs in Jurassic sandstones from 3 wells. Intrusive rocks of this age range are not known as a provenance source within North America. These are equivalent in age to Variscan granites of the Iberian Peninsula (Montero et al., 2004), and are therefore interpreted to be indicative of Iberian sediment provenance.
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O-16 3340-3400
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FIG.3 - Relative age frequency distribution for detrital zircons from Tithonian sandstone in Mizzen O-16. pdf
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FIG.4 - Relative age frequency distribution for detrital zircons from Tithonian sandstone in Baccalieu I-78.
Reconstructions of the North Atlantic indicate that the continental basement of Flemish Cap and Iberia formed a continuous landmass prior to late Jurassic to early Cretaceous rifting (FIG.2). The Flemish Cap forms a steep borderland to the northern Flemish Pass Basin, and was exposed for much of the Jurassic, forming a proximal source for sediment derivation. It is underlain by ca. 697 Ma granodiorites (King et al., 1985), which likely contributed detritus to the Flemish Pass Basin in late Jurassic times. Berriasian and Tithonian sandstones from the Flemish Pass Basin also contain elongate, prismatic zircon grains with concordant 207Pb/206Pb ages that cluster at 141 Ma. Their morphology indicates that they are of volcanic origin, and they are therefore interpreted to be rift related. However, the prismatic zircons have ages that are younger than the Tithonian sandstones from which they were sampled. Therefore, they are interpreted to be derived from cavings in the wells from early Cretaceous tuffs that have elevated U and Th (FIG.5). The tuffaceous material is of very low shear strength and probably continuously sluffed material into the wellbore during ongoing drilling. The upper radiogenic interval in Figure 5 immediately underlies the Base Valanginian (140.2 Ma) Unconformity in the O-16 well. The age of volcanism is consistent with the ca. 146 Ma volcanics of the Bonavista C-99 well (Enachescu, 1992), located on the western margin of Orphan Basin.
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Spectral GR
BVU
FIG.5 - Spectral Gamma Ray log from Mizzen O-16 illustrating the potential tuff at 3,063 – 3,065 m MD; BVU= Base Valagnian Unconformity; pink curve= Th; light blue curve= U.
Conclusions The new detrital zircon data from Flemish Pass and Orphan basins demonstrate an Iberian connection for sediment provenance, and therefore provide an independent validation of the Kimmeridgian and Berriasian palinspastic reconstructions. However, the U-Pb data do not provide insight into the nature of Flemish Pass-Orphan extension. Future work will focus on dating of Jura-Cretaceous sands from Orphan basin to test the Flemish Cap escape model (Aarseth et al., 2004; Enachescu et al., 2005), as well as high resolution U-Pb dating of both the detrital and volcanic zircon populations from JuraCretaceous sandstones in Flemish Pass and Orphan basins. References Aarseth, E.S., Barnwell, A.C., Skogseid, J., Whittaker, R.C., Hunter, D., Stacey, E.C. and McDonough, M. 2004. A new palinspastic plate reconstruction for the southern North Atlantic, with implications for the development of the basins around the Grand Banks of Newfoundland. Canadian Society of Petroleum Geologists Abstracts with Program, http://www.geoconvention.org/archives/2004.cfm. Enachescu, M.E. 1992. Enigmatic basins offshore Newfoundland, Canadian Journal of Exploration Geophysics, v.28, p44-61. Enachescu, M.E., Kearsey, S., Hardy, V. Sibuet, J-C., Srivastava, S., Hogg, J., Smee, J. and Fagan, A. 2005. New Insights in the structural and tectonic evolution and petroleum potential of the Orphan basin, Atlantic Canada, AAPG Abstracts, Calgary, Alberta. Foster, D.G. and Robinson, A.G. 1993. Geological history of the Flemish Pass Basin, offshore Newfoundland. American Association of Petroleum Geologists Bulletin, v. 77, p. 588-609. King, L.H., Fader, G.B., Poole, W.H. and Wanless, R.K. 1985. Geological setting and age of the Flemish Cap granodiorite, east of the Grand Banks of Newfoundland. Canadian Journal of Earth Sciences, v. 22, p.1286-1298. Montero, P., Bea, F., Zinger, T.F., Scarrow, J.H., Molina, J.F. and Whitehouse, M. 2004. 55 million years of continuous anatexis in Central Iberia: single-zircon dating of the Peña Negra Complex. Journal of the Geological Society of London, v. 161, p.255-263.
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