Stratigraphy

 

The sedimentary record records the events of the Acadian orogeny in the form of flysch and molasse deposits, as well as revealing unconformities.

Large thrust sheets of Avalon collided with Laurentia, causing subsidence leading to the formation of a foreland basin. In addition, the transpression tectonic style caused strike-slip bound fault basins to sink rapidly and fill with flysch and molasse clastic sediments.

 

 

 

 

 

 

 

 

 

 

 

 

 

Weathering of the highlands created by the Acadian orogeny resulted in the creation of the Catskill Delta. The Catskill Delta began forming in southern New York in the Middle Devonian, expanding into eastern Pennsylvania in the Upper Devonian (Geology of Pennsylvania, 1999). More than 69,000 cubic miles of sediment were poured into the Catskill deltaic system from the Acadian highlands (based on the volume of preserved rocks) (Dott and Batten, 1976). In the more northern section of the Appalachians, in Quebec, sedimentation in the foreland basin produced the Seboomook/Littleton clastic wedge. The Seboomook formation can be extended to include the clastic wedges of southern New England and the Gaspe Peninsula of Canada.

 

Thick sequence of Catskill Delta strata, Genesse Gorge, near Rochester, western New York. (http://academic.emporia.edu/aberjame/struc_geo/appalach/appalach.htm)

 

Orogenesis along the eastern coast created subaqueousdeltas composed of upward-coarsening cycles that graded laterally northward and westward into siltstones, shales and limestones that filled the farther parts of the basin (Geology of Pennsylvania, 1999). Most of North America was covered by a shallow sea at this time.

Other sedimentary features associated with the Acadian orogeny include unconformities, such as the major unconformity at the end of the Silurian, aka the "Salinic disturbance" as well as patterns of subsidence and preservation that can be attributed to relaxation and isotasy after tectonic loading (Ebert and Matteson, 1993).

*Bold face words are defined in the glossary.