Speaker: Christopher Connors of Washington and Lee University/USGS
Abstract: It is generally accepted that in Arctic Alaska and the adjacent offshore Paleozoic contractional deformation ceased by the end of the Devonian, with a transition to rifting and passive margin development in the Carboniferous. Interpretations of newly available 3D, and recently reprocessed 2D, time-migrated seismic reflection data show that, while pre-Mississippian contractional deformation was ubiquitous in the Franklinian megasequence, shortening continued in places for much of the late Paleozoic. Seismic observations in the Ellesmerian sequence reveal the presence of growth strata and distinct, though subtle, unconformities. Both stratal relationships are tied to biostratigraphic data from many North Slope wells and document the timing of additional contractional episodes in the early to middle Mississippian, and a separate one likely in the late Pennsylvanian to Permian. Using principles of fault-related folding, trends of Paleozoic fold-and-thrust belts are determined to be generally east-west, with both north and south vergence. Timing relationships, overlapping locations, and distinctive structural styles indicate that pre-Mississippian contractional fabrics influenced the subsequent reactivation of many structures in the late Paleozoic. These observations suggest a more complex late Paleozoic tectonic history than was previously recognized for the region, and merit further study to determine their broader implications for the tectonic evolution and petroleum systems of Arctic Alaska and the adjacent offshore.