Late Paleozoic to Cenozoic history of the offshore Sydney Basin, Atlantic Canada

The Sydney Basin covers a large offshore area south of Newfoundland, with a well-exposed outcrop belt on Cape Breton Island. The geological history of the poorly known offshore area is interpreted using an industry seismic gr id and Lithoprobe line 86-5, tied to outcrops and two wells. The mid-Devoni an to Upper Carboniferous - Permian basin fill is 6-7 km thick and represen ts three extensional phases with intervening and succeeding compressive pha ses. The mid-Devonian McAdams Lake Formation was deposited in a local half- graben during early post-Acadian extension. Following deformation, a suite of Early Carboniferous extensional basins filled mainly with Horton Group c onglomerates developed on northeast-trending and southeast-dipping master f aults. Some faults developed along Acadian terrane boundaries. The Windsor Group extends over the master faults to onlap basement as a result of therm al sag and Visean eustatic rise. Mid-Carboniferous deformation, linked to t he Alleghanian orogeny, reactivated faults and caused basin inversion and a basinwide unconformity. Upper Carboniferous to ?Permian coal measures and redbeds were subsequently deposited in a broad basin that developed over th e Early Carboniferous basins. Subsidence may reflect extension on major fau lts in the Cabot Strait coupled with thermal sag and (or) continued sag on an underlying mid-crustal detachment. After coalification, Acadian terrane boundaries and other lineaments were reactivated during a compressive tecto nic episode, probably during the Permian. The basin's polycyclic history, w ith repeated subsidence and inversion phases, has important implications fo r hydrocarbon systems.