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Single-grain detrital-muscovite ages from Lower Cretaceous sandstones, Scotian basin, and their implications for provenance

Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 3J4, preynold{at}dal.ca

Georgia Pe-Piper

Department of Geology Saint Mary’s University Halifax, NS B3H 3C3 gpiper{at}smu.ca

David J.W. Piper

Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, NS B2Y 4A2, dpiper{at}nrcan.gc.ca

A.M. Grist¹

Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 3J4, alexander.grist{at}bigpond.com

Lower Cretaceous deltaic sandstones in the Scotian basin form important gas reservoirs. This study uses single-grain geochronology of detrital muscovite to better understand the sources and dispersal patterns of sediment in the Early Cretaceous. One hundred muscovite grains were dated from a transect of wells near Sable Island and a further 17 grains were dated from the Naskapi N-30 well in the western part of the basin. Excluding a few old grains, the muscovite ranges in age from ca. 420 to 240 Ma. The lack of ages <240 Ma for muscovite and for rare detrital monazite suggests that ages were not reset by post-depositional alteration. The age distribution of muscovite from the wells near Sable Island suggests that the principal sources were rocks that had experienced resetting during Alleghenian deformation and Late Triassic– earliest Jurassic rifting. The distribution of ages, together with mass balance calculations, suggest that these sources mainly were Meguma metasedimentary rocks, especially phyllites, on the inner Scotian Shelf, although shear zones on land and the inner shelf also may have contributed. The age distribution at Naskapi N-30 is similar to that in the South Mountain batholith, except for some grains younger than 360 Ma that suggest an offshore source with Alleghenian resetting. On the inner Scotian Shelf, Upper Cretaceous and Tertiary rocks onlap across Appalachian basement and the eroded edge of Jurassic and Lower Cretaceous rocks, providing further evidence that the inner shelf was an erosional area during the Early Cretaceous.