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Models that reconcile the thicknesses of various Appalachian stratigraphic sequences in terms of subsidence associated with thrust loading are based on various assumptions about regional stratigraphy. Different assumptions, based on a different interpretation of Middle and Upper Ordovician stratigraphy, suggest that the geometry of lithospheric flexure due to Taconian thrust loading may have been different than predicted by existing models. Taconian flysch facies restricted to the eastern margin of the outcrop belt is the basis for identifying a thrust load‐induced foredeep. Coeval shallow marine facies were probably beyond the limit of thrust load influence. Stratigraphic thinning near the transition between the flysch and shallow marine facies is interpreted as a peripheral bulge and is located within the Valley and Ridge. Comparison is made with the Timor area north of Australia. Thrust load‐induced foredeeps and peripheral bulges predicted by this model are much narrower than predicted by previous models.

Two pronounced effects of the Taconic Orogeny were the creation of an eastern source area which influenced sedimentation through much of the Appalachian basin, and the early deformation of the eastern margin of the Appalachian basin. This field trip will investigate the stratigraphy of the Taconian (Upper Ordovician) and post-Taconian (Silurian) clastic strata in an attempt to illustrate the sedimentologic and structural effects of the Taconic Orogeny in the eastern portion of the Appalachian basin. The Taconian clastic sequence is an orogenic progradational sequence. The distal (western) facies of the clastic sequence were deposited between the carbonate shelf and the source area, in a deep basin which was created by tectonic downwarping of the eastern edge of the carbonate bank. During deposition of the Taconian clastics, there occurred a pronounced, probably glacio-eustatic lowering of sea level, which lasted until the beginning of the Silurian. The Silurian clastics are a series of post-orogenic quartz sandstones and mudrocks, the upper portion of which changes facies basinward to limestone. The sandstones comprise a number of tongues which are thickest near the basin margin, and thin to the west. The Silurian strata were deposited in relatively shallow water, implying that tectonic downwarping had ceased. The large-scale inter-tonguing of strata may have been caused by sea-level fluctuations.

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