NEOPROTEROZOIC ROCKS OF THE NEWFOUNDLAND AVALON ZONE

A ca. 15 km thick succession of volcanic and sedimentary Neoproterozoi c rocks are exposed within the Avalon Terrane of Newfoundland. Petrolo gic and geochemical study of volcanic suites and sedimentological anal yses indicate that most deposition took place in ensialic rift basins and associated continental are settings. On the Avalon Peninsula, over 7500 m of volcaniclastic strata include initial submarine fan and slo pe deposits, which pass upward into a prograded wedge of deltaic and f luvial deposits. This flysch-to-molasse transition, and associated fol ding and volcanism, mark the Neoproterozoic Avalonian Orogeny. Post-or ogenic erosion was followed by deposition of extensive Cambrian silici clastic deposits. Recent U-Pb zircon dating of many of the Neoproteroz oic volcanic units provides some constraints on both intra-Avalon and global correlations. More precise dates are needed to improve correlat ion and better constrain the geologic history of this region. Glacioge nic diamictites of the Gaskiers Formation exposed on the Avalon Penins ula may eventually also prove useful for global correlation. Biostrati graphic study of the latest Neoproterozoic-Lower Cambrian deposits has resulted in ratification of the Precambrian-Cambrian Boundary Stratot ype 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 chemostrati graphic, magnetostratigraphic or sequence stratigraphic work has been completed on the Neoproterozoic of the Newfoundland Avalon Terrane.