Flexural Modeling of Paleozoic Foreland Basin Subsidence, Offshore Western Newfoundland: Evidence for Substantial Post-Taconian Thrust Transport

Abstract

Multichannel seismic reflection data gathered by the petroleum industry, offshore of western Newfoundland, constrain the absolute thicknesses of the Middle Ordovician and post-Middle Ordovician portions of the Anticosti foreland basin immediately adjacent to the Appalachian structural front. These seismic lines, which include 1970s-vintage data in the public domain, and recently acquired proprietary data, indicate that the Middle Ordovician ("Taconian") portion of the foreland basin is more than an order of magnitude thinner than the preserved post-Middle Ordovician ("Salinian-Acadian") portion. The mechanical lithospheric coupling of foreland basins and their adjacent overthrust belts is a well-understood phenomenon. A thin Taconian foreland succession and a thick Salinian-Acadian succession imply that the overthrust loads responsible for flexural depression of the Anticosti basin were much more distant and/or much smaller during the Middle Ordovician Taconian orogeny than they are today. We quantify this qualitative conclusion to first-order using a two-dimensional, nonuniform, thin elastic plate formulation to model lithospheric flexure. Our approach constrains ( 1 ) the position of Taconian overthrust loads at the end of the Taconian orogeny, and (2) the palinspastic location of the Cambro-Ordovician passive margin hinge line. Acceptable solutions require development of a significant (~300 m-high) peripheral bulge in early Late Ordovician time and suggest that the toe of the Taconian overthrust wedge was many tens to perhaps 100 km or more from its present position at the end of the Taconian orogeny.