GSA Connects 2021 in Portland, Oregon

Paper No. 202-6
Presentation Time: 9:30 AM


PEACE, Alexander, McMaster University, 1280 Main St W, Hamilton, ON L8S 4L8, CANADA, SCHIFFER, Christian, Department of Earth Sciences, Uppsala University, Villav├Ągen 16, Uppsala, 752 36, Sweden, JESS, Scott, University of CalgaryGeoscience, 2500 University Drive NW, Calgary, AB T2N 1N4, CANADA and PHETHEAN, Jordan, School of Environmental Sciences, University of Derby, Derby, DE22 1GB, United Kingdom

Inversion of rift-related faults on passive margins through reactivation is documented globally. These highly variable inverted structures form an integral part of many petroleum systems, provide constraints on the kinematic and structural evolution of rifts and passive margins, and in some cases, can be used as global or regional markers of far-field stresses. Despite the importance of inverted normal faults, the controls on their kinematic evolution, as well as existence, extent, and interactions within fault populations are often poorly constrained. As such, there is a need for detailed investigations of inversion, including its relationship with halokinesis. We present structural interpretation of an inverted relay ramp structure imaged on the Penobscot 3D seismic reflection survey, offshore Nova Scotia, Canada, down to ~3.5 s TWTT and constrained by two exploration wells. The relay ramp comprises two dominant faults that dip ~S and are associated with smaller antithetic and synthetic faults. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both N and S. The two major normal faults display evidence for inversion in their lower portions (below ~2.5 s TWTT) manifesting as low amplitude folding and reverse offset, though retain a normal offset in upper sections. The smaller faults tend to only affect the uppermost strata and do not show evidence of inversion. Through our structural analysis, and the previous regional interpretation of widespread salt, we determine that the documented inversion is likely caused by halokinesis. We constrain the movement of this salt to have occurred later than the upper Cretaceous, however, placing an upper age limit on this is problematic. The oldest strata affected by inversion varies across the Penobscot 3D study area. The timing of salt movement broadly corresponds to documented times of kinematic reorganisation on many Atlantic margins, and thus salt movement may have been in response to reorganisation. The kinematic dichotomy with depth is important as inversion such as this may go unrecognised if the full depth of a structure is not imaged, implying that inversion may be more widespread than previously thought. In addition, the localisation of inversion onto larger structures is an also important observation, with implications for interpretation of inverted structures elsewhere. Interpretation of salt at an important contributor to kinematic inversion of faults is crucial as it likely provides a mechanism to explain inversion at other locations globally.