Detrital zircons as provenance indicators in the Lower Cretaceous sedimentary rocks of the Scotian Basin, eastern Canada: a SEM-CL study of textures

In this project, detrital zircons from the Lower Cretaceous sandstones form the Scotian basin were studied. The backscattered electron and cathodoluminescent characteristics of detrital zircons were used as provenance indicators to help provide evidence for or against the paleogeographic models proposed by Pe-Piper and MacKay (2006 and Pe-Piper et al. (2007). A second objective was to complete a regional study of zircons from the on-land Chaswood Formation (Noftall, 2007). The zircon grains came from sandstone samples collected from conventional cores from the wells Alma K-85, Thebaud C-74, Glenelg N-49, Venture 1 and 4, Peskowesk A-99 and Dauntless D-35, and heavy mineral separates of cutting samples from the Fox I-22 and Crow F-52 wells. A sample from the upper part of the Chaswood Formation from Diogenes Brook, western Cape Breton Island, was also studied to complete a regional study of the on-land Chaswood Formation. The zircons were classified in three distinct groups: igneous first cycle, metamorphic first cycle, and polycyclic zircons. The igneous first cycle grains were further subdivided into six different subgroups based on a series of criteria. The Alma K-85, Thebaud C-74, Glenelg N-49 and Venture 1 and 4 wells cover geographically the central part of the basin. The western (Alma K-85 and Glenelg N-49) wells, and the eastern (Venture 1 and 4) wells have different zircon assemblages and were therefore supplied by two different sediment types, resulting in the differences in the zircon populations observed. The Lower Missisauga zircon population of the Thebaud C-74 well is dominated by polycyclic zircons and this is a unique feature for the central part of the Scotian Basin. Zircons from Peskowesk A-99 show minor stratigraphic differences, but have persistent differences from the same stratigraphic level in the central part of the basin, indicating variability in sediment sources. Fresh igneous zircons dominate in the Missisauga Formation of the Dauntless D-35 well, and the participation of polycyclic and metamorphic zircons is small. The differences between the Upper Missisauga Formation in Dauntless D-35 and Peskowesk A-99 are sufficiently large to suggest a different sediment source. For Diogenes Brook, fresh igneous zircons dominate in the upper part of the Chawood Formation and the participation of polycyclic zircons is small. This is consistent with other Chaswood Formation localities, arguing for progressive unroofing of crystalline basement. Such a study is particularly useful for assessing the role of polycyclic sediment supply and a useful precursor to more expensive single grain zircon dating.