A note on the discovery of Miaolingian acritarchs in the Flagg Cove Formation, Grand Manan Island, New Brunswick, Canada: implications for the stratigraphy of the Castalia Group.

Pre-Mesozoic rocks on Grand Manan Island are divided into two groups; an older Grand Manan Group of early Ediacaran or older age, and a younger Castalia Group, considered to be latest Ediacaran to earliest Cambrian. The Castalia Group as it is currently defined comprises a basal sequence of clastic marine sedimentary rocks assigned to the Great Duck Island and Flagg Cove formations and an upper sequence of mainly mafic volcanic and volcaniclastic rocks assigned to the Ross Island, North Head, Priest Cove and Long Pond Bay formations. A maximum age for the Castalia Group is ca. 600 Ma, based on the presence of volcanic clasts in conglomerate of the Great Duck Island Formation that are derived from the underlying Ingalls Head Formation (ca. 618 Ma). Additional age constraints include a U-Pb age of 539 ± 3 Ma for felsic tuff from the Priest Cove Formation and a minimum age of earliest Cambrian based on an assumed intrusive relationship between the ca. 535 Ma Stanley Brook Granite and the Flagg Cove Formation. However, stratigraphic relationships are generally poorly known due to intense deformation and thrusting, and most contacts are faulted. The Flagg Cove Formation consists of quartzose sandstone and green to dark grey silty shale, previously reported to contain rare trace fossils (Planolites) in strata along Flagg Cove. A sequence of sandstone and silty shale containing abundant morphologically simple trace fossils, including Planolites, at the south end of Stanley Beach in Flagg Cove recently yielded organic walled microfossils (Micrhystridium sp.) of a type also found in the King Square Formation in the Saint John area. This suggests a much younger (Miaolingian) age for the Flagg Cove Formation, indicating that its relationship with the Stanley Brook Granite and inclusion in the Castalia Group need to be re-evaluated. [ABSTRACT FROM AUTHOR]