Structural and sedimentary history of the Quaco Head area, southern New Brunswick

Abstract

Remapping of the Quaco Head area of southern New Brunswick has revealed a more complex structure than had been previously documented. The structure is dominated by two major thrust faults that dip to the south and southeast at between 35 and 45°. The lower (younger?) thrust emplaces Precambrian basalts and tuffaceous siltstones (Coldbrook Group) over alluvial sediments of the Boss Point and Tynemouth Creek formations (Westphalian A–B). Resting unconformably on the upper surface of the basalt is a thin layer (≤ 10 m) of marine, basal Windsor Group limestone, disconformably overlain by alluvial conglomerates of inferred Hopewell Group age. This sequence is truncated by an older, southeast-dipping thrust fault, to the southeast of which lie Hopewell conglomerates overturned towards the west and northwest. The latter sequence probably forms the lower limb of a large recumbent fold. Folding and thrusting in the Quaco Head area may have begun during Westphalian B times, although major movement was probably post-Westphalian C and occurred contemporaneously with dextral strike-slip movement on the Minas geofracture. Following this Alleghenian–Variscan deformation, the area underwent deep erosion prior to the deposition of a thick sequence of Triassic alluvial sediments. The more southerly reverse fault was reactivated as a normal fault during a phase of late Triassic or Jurassic faulting along the Bay of Fundy that was probably related to early Atlantic rifting.