Reflection Seismic Mapping Efforts Along the Scotian Margin: New Results, Challenges, and Enduring Questions

Abstract

With >290000 km² of sparse to dense digital reflection seismic coverage in offshore areas extending from Georges Bank to the Burin Platform, including 23500 km² of 3D seismic, >156000 line km of 2D seismic, and ∼180 exploration wells, the continental shelf and slope off Nova Scotia are truly data-rich. Over the past eight years these data-sets have been used to map the distribution of key geological elements within and above crystalline basement, providing insight into the structural and stratigraphic development of the Scotian margin before, during and after rifting. Widespread salt deposition took place mainly during the late synrift, and improved mapping of the top of basement and synrift strata below the salt, along with correlation of salt feeders rooted into the primary salt layer, helps place a perimeter around the primary salt basin. Its seaward limit coincides with a significant basement step that parallels the outer part of the East Coast Magnetic Anomaly (ECMA). The transition between continental and oceanic crust across the ECMA remains equivocal, but a simple four-part seismic facies classification scheme shows clear patterns in the reflection seismic response of ‘basement’ seaward of the primary salt basin. The change from seaward dipping reflections (SDRs) in the southwest to crust with a less diagnostic reflection seismic character to the northeast appears to takes place sharply along a 60 km dextral offset in the primary salt basin, across an interpreted transform margin. Widespread postrift mobilization of salt played an important role in the younger structural and stratigraphic development of the margin. In the west, most of the expelled salt still lies immediately above the primary salt basin; in the east, expelled salt largely escaped the primary salt basin and now lies within younger stratigraphic successions above oceanic or transitional crust. Recent mapping efforts have substantially improved our understanding of the timing and distribution of different postrift salt tectonic styles, but despite improvements several uncertainties remain. Correlation confidence of pre-Cretaceous strata from the well-calibrated shelf onto the poorly-calibrated slope remains low, and seismic imaging below areas of complex salt bodies, as well as areas covered only by older surveys, remains poor. This talk aims to highlight key learnings about the margin over the last number of years, but equally to highlight important questions that remain unanswered.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016