KINEMATIC SIGNIFICANCE OF SEDIMENT-FILLED FISSURES IN THE NORTH MOUNTAIN BASALT, FUNDY RIFT BASIN, NOVA-SCOTIA, CANADA

Numerous sediment-filled fissures are present near the upper surface of the North Mountain Basalt (similar to 202 Ma) of the Fundy basin, which formed during Triassic-Jurassic rifting. The fissures are infilled with the same clastic material comprising the basal parts of the overlying earliest Jurassic-age sedimentary formations, which accumulated less than 200 k y after the cooling of the basalt. Nearly all of the 1368 fissures measured in this study are planar to sub-planar and are sub-vertical (after correcting the basalt flows to paleo-horizontal). The fissures typically formed along preexisting columnar joints within the basalt. Northeast-striking fissures generally define a preferred orientation and commonly are wider than other fissures. The sediment-filled fissures therefore indicate earliest Jurassic-age NW-SE extension. This extension direction is consistent with that indicated by the NE-striking Shelburne diabase dike, the attitude of mesoscopic faults, and the geometry of the Fundy rift basin. Thus, sediment-filled fissures by themselves can serve as useful kinematic indicators and place tight constraints on the relative timing of extension.