Abstract: Inversion During the Early Stages of Seafloor Spreading: Seismic and Field Evidence from the Bay of Fundy, Canada

Paul E. Olsen, Martha Oliver Withjack

Seismic, well, and field data show that the Fundy basin of southeastern Canada experienced two distinct episodes of early Mesozoic deformation. The first episode, during the Middle Triassic to Early Jurassic, was extensional. Rifting associated with NW-SE extension reactivated NE-trending Paleozoic thrust faults as normal faults, forming the northwestern boundary faults of the Fundy basin. Rifting also reactivated E-trending Paleozoic compressional structures as oblique-slip faults with normal and sinistral strike-slip components, forming the northern boundary faults of the Fundy basin. Up to several kilometers of sediments and lava flows filled the Fundy basin during rifting.

The second episode, during the Early to Middle Jurassic, was compressional and synchronous with the onset of seafloor spreading in the Central Atlantic Ocean. Inversion associated with NW-SE shortening occurred along the faulted margins of the Fundy basin. The northwestern boundary faults became reverse faults with up to several kilometers of displacement, broad anticlines developed within their hanging walls, and the Fundy basin acquired its synclinal form. The northern boundary faults became oblique-slip faults with reverse and dextral strike-slip components. Gentle synclines, tight anticlines, and reverse faults deformed the synrift strata near the northern margin of the Fundy basin. Neither collision nor subduction can explain the inversion in the Fundy basin during the Early to M ddle Jurassic. Hence, we believe that the seafloor-spreading process, itself, produced the inversion during the transition from rifting to drifting.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994