CHAPTER 1. AN INTRODUCTION TO THE DEVONIAN PERIOD, AND THE DEVONIAN IN NEW YORK STATE AND NORTH AMERICA

This chapter provides overviews of the Devonian Period globally, on Laurentia, eastern Laurentia, and in NY State. The Devonian encompasses 60 million years, 419.0 to 359.3 Ma. At that time, shallow seas covered large continental areas; global climate was warm, late in a global greenhouse episode. By the end Devonian, climate was shifting to a global icehouse. Life first fully colonized the land during the Devonian, led by primitive spore-bearing vegetation and small arthropods; by the Late Devonian, the first seeds and early tetrapods evolved. Decimeter-tall plants at the beginning of the period had evolved to tree-size forms by the Mid Devonian, ~30 million years later, when there were 400 days/year.

Devonian strata are widespread across North America. In the Devonian, Laurentia straddled the equator; NY lay north of 30^o south latitude. Shallow epicontinental seas were widespread. Mountain belts formed on the eastern, northern, and western margins of Laurentia, due to collisional tectonics. In the Early to Mid Devonian, eastern and western Laurentian seas were separated by an elevated transcontinental arch, and had distinctly different marine faunas. In the late Mid Devonian, sea level transgressed over the arch. This led to a more global Late Devonian fauna.

Eastern Laurentia was tectonically active throughout the Devonian, related to continent-continent collisions. Resulting uplift formed a mountain belt from east Greenland to Alabama. Orogenic processes in the Acadian Orogen included explosive eruptions of silicic volcanic ash, transported westward by winds. Crustal loading of the orogen led to subsidence and formation of an Acadian Foreland Basin. Initially filled with marine waters, it gradually overfilled from the east with massive volumes of synorogenic sediments, creating land.

Devonian geological and paleontological observation in NY by professional geologists of the early 19^th century were followed by the NY Geological Survey in 1836. The Devonian, nearly termed the “Erian Period” for NY’s Devonian strata, has long been the focus of extensive research in the state, which continues. The Devonian succession in NY includes strata from all seven stages of the period, with minor to ~major erosional gaps. A broad range of marine facies are accompanied by a large area of thick terrestrial strata.