NORTHERN APPALACHIAN BASIN SEDIMENTATION AND THE TIMING OF ACADIAN OROGENIC EVENTS

Changes in foreland basin sedimentation through time and space sometimes reflect orogenic events and processes active in an adjacent mountain belt. These may be recorded as distinctive variations of sediment type (carbonate versus siliciclastic), facies, distribution, geometry, and composition through time and space. Soft-sediment deformation may record seismic events in the orogen. And preserved volcanic airfall tephras (tuffs, K-bentonites) provide some indication of the timing and distribution of explosive volcanism in the orogen.

The timing of a number of Acadian-related events and processes in western New England recorded in northern Appalachian foreland basin sediments is reasonably well-constrained. Dated volcanic tephras (tuffs, K-bentonites) provide geochronologic ages for Acadian volcanism and other events in adjacent strata. The timing of other events is relative but, through biostratigraphy, sea level cyclicity and other methods, can be clearly pinned to intervals within international Silurian and Devonian stages.

Sedimentary data from uppermost Silurian and Devonian strata in New York may variously pinpoint the timing of Acadian-related events and processes in western New England (+/- beyond), including: uplift and loading events (marked by stratigraphic patterns indicative of subsidence and other flexural processes in the foreland); uplift-related influx of orogen-derived sediments (carbonates overlain by orogen-derived siliciclastic sediments); and changes in exposure and unroofing in western New England (shifts in conglomerate and sandstone composition). In addition, soft-sediment deformation of strata may sometimes record seismic events in the orogenic belt. Finally, data from around the entire Appalachian basin provides a larger picture of the timing and possible distribution of volcanism (preserved airfall tephra beds) during the Acadian orogen. Major Acadian uplift events, possibly associated with greater explosive volcanic activity, appear to occur around 418 Ma (ca. Silurian-Devonian boundary), 408 Ma, 390 Ma, and roughly ca. 382 Ma.