FORELAND BASIN RESPONSE AS A CONSTRAINT ON LAURENTIAN PALEOZOIC OROGENIES: INSIGHTS FROM SUBSIDENCE ANALYSIS AND FLEXURAL MODELING

The eastern margin of North America was subject to multiple Paleozoic orogenies, spanning Ordovician to Permian time. This complicated collisional history has oft resulted in uplift, erosion, and overprinting of earlier mountain building events, impeding direct observation of the tectonic history. In this study we present 30 geohistories and 10 2D flexural models to evaluate the timing and magnitude of flexure related to orogenic loads of the Appalachian, Variscan, Ouachita, and Marathon orogenic belts of North America and Europe.

We observe Taconic (ca. 465-445 Ma) subsidence throughout the U.S. Appalachians, with an earlier onset of subsidence in the Canadian Maritimes (ca. 485 Ma). The modeled orogenic load indicates up to 2.8 km of hinterland surface uplift, decreasing to the southwest.

The Salinic Orogeny (ca. 430-420 Ma) produced subsidence restricted to the central and northern U.S. Appalachians, with modeled hinterland surface uplift up to 1.5 km. We speculate that the southern terminus may represent the limit of the Avalonia microplate.

Acadian flexural subsidence (ca. 390-355 Ma) occurs throughout the U.S. Appalachian system; modeled hinterland surface uplift from flexural analysis is up to 3 km.

For the earliest portion of the Alleghanian Orogeny (ca. 325-300 Ma), there is not strong evidence for significant subsidence in the U.S. Strata from the latter portion (ca. 300-260 Ma) is mostly not preserved, limiting the analysis. However, we observe rapid subsidence from ca. 360-300 Ma along the Variscan front in the Anglo-Dutch Basin and in the Magdalen-Moncton successor basins of eastern Canada.

In contrast to published models, the Black Warrior, Arkoma, and Fort Worth forelands of the Ouachita system display synchronous flexural subsidence from ca. 320-305 Ma, while the Val Verde Basin (Marathon thrust belt) is significantly younger (ca. 305-285 Ma). These forelands have shorter wavelengths and higher amplitude than the Appalachian system, indicating weaker coupled lithosphere (consistent with estimates of current EET from tomography). The flexural modeling and geohistory analysis presented here provides complimentary input to the history of Paleozoic orogenies and highlights spatio-temporal variations in lithospheric strength, topographic uplift, and flexural load.