THE ATHOL SYNCLINE - TECTONIC EVOLUTION OF A WESTPHALIAN A-B DEPOCENTER IN THE MARITIMES BASIN, NOVA-SCOTIA

In the western Cumberland Basin, Nova Scotia, significant thickening o f Westphalian A-B strata towards the axis of the Athol Syncline sugges ts that development of the syncline coincided with that of the depocen tre. This contrasts with stratigraphic relations typical of the Late P aleozoic Maritimes Basin where thinning of Westphalian B strata indica tes regional, Late Carboniferous erosion or non-deposition. Post-depos itional structural complications within the Athol Syncline include tru ncation of its southern limb by a near-vertical, east-west zone of str ike-slip faulting. This zone, the Athol-Sand Cove Fault Zone (ASCFZ), has been correlated to the west with a complex zone of faulting expose d on the coast of Chignecto Bay where numerous normal, reverse and obl ique-slip displacements suggest predominantly brittle deformation and changes in the sense of strike slip. To the east, the ASCFZ splays nor th into the Springhill coalfield where it is responsible for complex p atterns of normal, reverse and strike-slip faulting within Westphalian A-B coal measures. Major Late Carboniferous strike-slip faults adjace nt to the Athol Syncline record dextral motion south of the Cumberland Basin (on the east-west Cobequid Fault) and possible sinistral motion along the basin's northwestern margin (on the northeast-southwest Har vey-Hopewell Fault). These faults are respectively interpreted to be s ynthetic and antithetic structures related to a regional dextral shear regime in which the east-northeast-west-southwest Athol Syncline and its associated depocentre formed in response to the direction of local compression during basin development. However, kinematic analyses ind icate that post-depositional motion on the ASCFZ was predominantly sin istral. Development of the Athol Syncline is therefore interpreted to have been controlled by dextral, syndepositional transpression during the Late Carboniferous, whereas later, post-depositional displacement across the ASCFZ reflects predominantly sinistral transtension and may be related to the opening of the Fundy Basin which reversed the sense of regional shear during the Middle Triassic.