Stratal evolution and provenance of a precambrian delta in a tectonically active terrane: The lower Signal Hill Group, Avalon Zone, Newfoundland

Abstract

Sedimentologic and provenance studies of the syn-orogenic Ediacaran lower Signal Hill Group (Gibbett Hill and Quidi Vidi formations) in the Avalon Peninsula, Newfoundland, Canada, were conducted to test structural and depositional models related to the enigmatic late Ediacaran (ca. 575–550 Ma) Avalon orogenesis. Two facies associations corresponding to delta front and delta plain environments are identified from five stratigraphic sections. The presence of an unconformity between these facies near the location of a previously proposed thrust-related paleo-high and changes in sedimentary patterns reflecting shoreline regression support the inference of syn-sedimentary uplift and reveals coeval base level fall. Framework petrography, detrital geochronology, and detrital heavy mineral analysis indicate sediment sourcing from hinterlands of West Avalonian igneous and metamorphic basement. Changes in provenance between the delta front and delta plain facies coeval with regression of the Signal Hill delta suggest the thrusting of volcanic cover sequences over already exhumed plutonic sources and the exhumation of deeper/higher-grade metamorphic rocks in the hinterland. Detrital zircon U-Pb maximum depositional ages of the delta front and delta plain facies yield 557 ± 9 Ma and 556 ± 22 Ma, respectively, constraining this episode of West Avalonian hinterland exhumation, wedge-top foreland basin deformation, and forced regression to ca. 556 Ma. The regional significance of this late Ediacaran (ca. 565–538 Ma) foreland basin to tectonic models of West Avalonia’s transition from an arc setting to a Paleozoic rifted platform is not currently understood, but it may represent a retro-arc basin formed either as part of a coherent West Avalonian block overlying a subducted spreading ridge or on a subsidiary West Avalonian terrane prior to and during terrane collision preceding deposition of the Paleozoic overstep sequence.