Middle Paleozoic Mt. Building
Sea Level
Low at the end of the Ordovician (Glaciation). Transgression in the Silurian
accompanied by Silurian radiation of marine organisms.
Glaciation in the Devonian thought to be the result of widespread plant invasion of the
land (CO2 reduction in the atm.) causing a mass extinction event at the Fransian-Fammenian
Boundary (last 2 stages of the Devonian).
Silurian-Widespread Reef Development (Michigan Basin) Thornton Quarry-typical
stromatoporoid/coral-strome reef complex.
Many evaporite deposits points to a relatively warm earth at this time.
Second Mountain Building phase of the Appalachian Mts.= ACADIAN OROGENY
Foreland basin development over relatively shallow marine deposits deepening-black shale
deposition, then flysch and molasse (Old Red Sandstone, Catskill Delta).
Similar sequence of Limestones (Heldeberg Grp.), sands, silts, and shales deeper water flysch
(Hamilton Group) and Redbed Molasse Deposits (braided streams and alluvial fans)
Siccar Point-famous angular unconformity from James Hutton. Old Red Sandstone sitting on top
of Silurain Rocks. Formed from the highlands created during the Acadian Orogeny.
Acadian Orogeny. Larger land masses than in the Taconic Orogeny, suturing of terranes
Avalonia (N) and Carolina (S).
Western Margin of North America began to experience some orogenic events. Klamath
Terrance (volcanic arc) was situated offshore and was thrust onto the continent beginning in the
Devonian (Roberts Mt. Thrust) that pushed an ophiolite up onto the continent. This is termed the
ANTLER OROGENY.