Vertical movements of the crust: Case histories from the northern Appalachian Basin

Abstract

Evidence of former deep burial of Ordovician to Devonian strata of the northern Appalachian Basin has been obtained from various techniques of study, including fluid-inclusion homogenization temperatures, δ 18 O, and vitrinite reflectance. Diagenetic minerals indicate paleotemperatures of 100–200 °C. Maximum depths of burial were calculated from the estimated paleotemperatures; a gradient of 26 °C/km was assumed. Silurian strata of the basin are interpreted to have reached maximum burial depths of 5.0 km; Devonian strata in the Catskill Mountains had former burial depths of ∼6.5 km; Lower Ordovician carbonate sequences were buried to >7 km; Middle Ordovician strata had paleodepths of ∼5 km; and Devonian carbonate strata had paleodepths from 4.5 to 5 km. If these strata were buried deeper than previously thought, unexpectedly large amounts of uplift and erosion, ranging from 4.3 to 7 km, must also have taken place to bring these strata to the present land surface. The occurrence of such large-scale vertical movements of the crust and lithosphere must be recognized in paleogeographic reconstructions. Such drastic changes represent isostatic unroofing, with widespread implications for paleogeography of a kind unrecognized at present.