Abstract

Fammenian to Tournaisian rocks of the Moncton Basin are currently included in two unconformity bounded groups: the Horton Group, which includes the petroleum system of the Albert Formation; and the overlying Sussex Group. At the southern margin of the basin, these rocks are involved in a fold-thrust belt along the northern contact with pre-Carboniferous crystalline basement of the Caledonia Highlands, along a contact that is the trace of the Caledonia Fault. This structure trends ENE, but in the Albert Mines area the trace turns southward, whilst a major splay, the St-Joseph Fault, runs to the ENE. In the Peck Creek section, west of Albert Mines, panels of rocks of the Sussex Group are bounded by thrusts that are splays of the Caledonia Fault. Thrusts are associated with hanging-wall anticline-syncline pairs and chevron folds with broken hinges produced by progressive deformation originating in bedding-parallel high strain zones.

Three units of the Sussex Group are involved in the deformation: the Round Hill, Gautreau, and Weldon formations. In the general area of Peck Creek, the group lies unconformably on pre-Carboniferous crystalline basement, cutting out the lower Horton Group. Folds and faults affecting the Sussex Group are truncated by the unconformity at the base of the Hillsborough Formation, dating the deformation as end-Tournaisian. Many of the characteristics of the Sussex Group folds and deformed vein arrays indicate thrusting occurred before these sediments were fully dewatered. Geometry of folds, bedding-parallel high strain zones and slickenside lineations define an oblique sidewall ramp in the Peck Creek section deflecting the Caledonia Fault around a topographic high in the pre-Carboniferous Caledonia basement. This feature is coincident with Sussex Group overstep onto basement, locally cutting out the petroleum system of the underlying Horton Group in the area from east of Peck Creek, westward ten kilometres to Rosevale.