Provenance of Cape Spear Member conglomerates in the Ediacaran Cuckold Formation, Flatrock area, eastern Newfoundland: Implications for Avalonian paleogeography

English Abstract:

Attempts to constrain Avalonia’s position along the Gondwanan margin during the late Neoproterozoic have been a subject of intense debate since it was first recognized that the eastern flank of the Appalachian orogen is composed of exotic terranes. A consensus has been reached that Avalonia was one of several peri-Gondwanan terranes adjacent to the Amazonian or West African cratons, but its precise location is still controversial. To further test the paleoposition of Avalonia, we conducted new field and detrital zircon U-Pb provenance studies of red-bed fluvial strata within the Cape Spear Member of the Ediacaran Cuckold Formation in eastern Newfoundland. The main objective of the study is to identify Amazonian- or West African-derived detrital zircons in the Cape Spear Member in order to advance the long-standing debate about Avalonia’s position along the Gondwanan margin.

Fieldwork and detrital zircon sampling near the community of Flatrock, 20 km north of St. John’s, focused on a 5 m-thick conglomerate section of the Cape Spear Member with “exotic” clasts of pink quartzite, quartz-sericite schist, and other low-grade metamorphic rocks that have no known source. Clast counts were conducted at five separate stratigraphic levels in the conglomerate section (100 counts each). Locally derived volcanic and plutonic rock clasts comprise 95% of the unit, whereas the exotic clasts occur at a 5% level. Four detrital zircon samples were analyzed with laser ablation (LA-ICP-MS) techniques and include cobble-sized clasts of pink quartzite (85 analyses) and feldspathic sandstone (75 analyses) from the exotic section, a whole-rock conglomerate sample from the exotic section containing clasts and sand matrix (76 analyses), and a whole-rock sample of pebbly sandstone collected 10 m below the base of the exotic section (76 analyses). The new U-Pb results will be compared to published detrital zircon reference frames for the peri-Gondwanan terranes and the Amazonian and West African cratons to test sediment source regions and Avalonian paleogeography.