The provenance of Jurassic and Lower Cretaceous clastic sediments offshore southwestern Nova Scotia

Abstract

Jurassic and Cretaceous sandstones in the Shelburne subbasin and Fundy Basin offshore Nova Scotia, are poorly known but are of current interest for petroleum exploration. The goal of this study is to determine the provenance of sandstones and shales, which will contribute to a better understanding of regional tectonics and paleogeography in the study area. Mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells, using scanning electron microscopy and an electron microprobe. Whole-rock geochemical composition of shales was used to test the hypotheses regarding provenance of Mesozoic clastic sedimentary rocks in the SW Scotian Basin. Lower Jurassic clastic sedimentary rocks in the Fundy Basin contain magnetite, biotite, and chlorite, suggesting local supply from the North Mountain Basalt and Meguma Terrane, whereas pyrope and anthophyllite suggest small supply from distant sources. In the SW Scotian Basin, detrital minerals, lithic clasts, and shale geochemistry from Middle Jurassic to Early Cretaceous indicate a predominant Meguma Terrane source and transport by local rivers. Rare spinel and garnet grains of meta-ultramafic rocks, only in the Middle Jurassic at the Mohawk B-93 well, suggest minor supply from the rising Labrador rift, via the same river that transported distant sediments to the Fundy Basin. Lower Cretaceous sandstones from the Mohican I-100 well contain minor garnet, spinel, and tourmaline from meta-ultramafic rocks, characteristic of sediment supplied to the central Scotian Basin at that time. The dominant Meguma Terrane provenance precludes thick deep-water sandstones in the eastern part of the Shelburne subbasin, but the evidence of Middle Jurassic distant river supply through the Fundy Basin is encouraging for deep-water reservoir quality in the western part.