Three tectonic events affected the northern margin of Laurentia between Early Ordovician and Early Devonian time. Each tectonic cycle started with an unconformity followed by rapid subsidence and an influx of clastic material, then decreasing sediment accumulation rates. The first cycle extends from the Tremadoc to late Katian (480–448 Ma), the second from late Katian to Ludlow (448–426 Ma), and the third from Ludlow to Lochkovian (426–410 Ma).

A strong geodynamic link is interpreted between the first two sedimentary cycles and tectonic events on the composite Pearya terrane on northern Ellesmere Island, Nunavut, Canada. The first cycle is interpreted as a response to crustal thickening caused by the M’Clintock Orogeny on Pearya terrane and onset of subduction dipping under Laurentia. An extensive Middle Ordovician (Darriwillian) unconformity is not associated with a change in subsidence rate or a change of facies above and below, but is normally faulted. It is interpreted as a migrating forebulge or increase in crustal buoyancy due to breakoff of a subduction slab.

The second cycle is synchronous with a Late Ordovician minor faulting event on Pearya terrane and volcanic units in the deep water basin between Pearya terrane and the carbonate platform. A major platform margin stepback, along with a positive εNd shift are associated with the late Katian Irene Bay Formation. The event also introduced numerous organisms of Siberian affinity into northern Laurentia. The third cycle, starting in Ludlow time is related to the onset of deformation in the Boothia foldbelt and is not recorded as a deformational event on Pearya terrane.

The presence of aerially restricted intraplatform basins that are interpreted to be synchronous with, and caused by, tectonic events on Pearya terrane implies that it was close to its current location by Early Ordovician time.

You do not currently have access to this article.