Hidden Cretaceous basins in Nova Scotia

Abstract

Early Cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of Nova Scotia are preserved in narrow half-grabens obscured by glacial drift. The Chaswood Formation sediments can be subdivided into three members; upper and lower members dominated by cyclical sand–mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin. Ferruginous oxisols are common in the fine-grained facies of the upper and lower members. Seismic data indicate that Chaswood Formation strata in the Elmsvale Basin are deformed into steeply dipping faults and fault-related folds (Rutherford Road fault zone). An Aptian–Albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the Late Cretaceous and Tertiary that truncates the Chaswood Formation. Exhumation of a thick cover of Mesozoic sediment (1–2 km) is needed to account for the preservation of Chaswood Formation outliers after ~80 Ma of erosion. The half-grabens that host the Chaswood Formation were formed in the Mesozoic and were antecedent to the present-day structurally controlled lowlands.