Neoproterozoic rocks of the Newfoundland Avalon Zone

Abstract

A ca. 15 km thick succession of volcanic and sedimentary Neoproterozoic rocks are exposed within the Avalon Terrane of Newfoundland. Petrologic and geochemical study of volcanic suites and sedimentological analyses indicate that most deposition took place in ensialic rift basins and associated continental arc settings. On the Avalon Peninsula, over 7500 m of volcaniclastic strata include initial submarine fan and slope deposits, which pass upward into a prograded wedge of deltaic and fluvial deposits. This flysch-to-molasse transition, and associated folding and volcanism, mark the Neoproterozoic Avalonian Orogeny. Post-orogenic erosion was followed by deposition of extensive Cambrian siliciclastic deposits. Recent U Pb zircon dating of many of the Neoproterozoic volcanic units provides some constraints on both intra-Avalon and global correlations. More precise dates are needed to improve correlation and better constrain the geologic history of this region. Glaciogenic diamictites of the Gaskiers Formation exposed on the Avalon Peninsula may eventually also prove useful for global correlation. Biostratigraphic study of the latest Neoproterozoic-Lower Cambrian deposits has resulted in ratification of the Precambrian-Cambrian Boundary Stratotype in an exposure on the Burin Peninsula. Older Neoproterozoic rocks contain well-preserved Ediacara-type fossils and a low-diversity suite of microfossils including acritarchs and carbonaceous filaments, the latter of which have little biostratigraphic utility. Aside from work on the Precambrian-Cambrian boundary section, little or no chemostratigraphic, magnetostratigraphic or sequence stratigraphic work has been completed on the Neoproterozoic of the Newfoundland Avalon Terrane.