PALEOSOL EVIDENCE FOR EDIACARAN GLACIATIONS NEAR BOSTON, MASSACHUSETTS, USA

Fossil ice wedges of periglacial paleosols in the upper Squantum and upper Brookline Members of the Roxbury Conglomerate, and other intervening paleosols of humid temperate paleoclimate, now indicate two separate post-Cryogenian glacial episodes near Boston, Massachusetts, which had an Ediacaran paleolatitude of 50^o. Two episodes and several glacial stages are also revealed by extensive chemical analyses for Ba/Sr ratios and chemical index of alteration of sediments within both the Roxbury Conglomerate and the Cambridge Argillite. One glacial episode predates a local tuff dated by ²⁰⁷Pb/²⁰⁶Pb at 567 ± 1.7 Ma, and the second glacial episode of 4 distinct glacial stages postdates that tuff and predates early Cambrian sandstones. Both glaciations are Ediacaran because they postdate well dated local basement rocks: Lynn-Mattapan Volcanics at 596-602 Ma and Dedham Granite at 606-610 Ma. Age models and international correlations suggest early Ediacaran (ca. 582 Ga) and late Ediacaran (ca. 550 Ga) ages for these glacial episodes, as for Gaskiers and Baykonur Glaciations of Newfoundland and Siberia, respectively. In the South Australian Ediacaran stratotype, these two glacial episodes are represented by dropstones in the Bunyeroo Formation and diamictites in the Billy Springs Formation. Both glacial episodes are represented by ice wedges near Boston, which today are evidence of maritime glacial climate like that of coastal Greenland and Arctic Canada, unlike continental glaciation and sand wedges of inland Antarctica and the Cryogenian Elatina Glaciation of South Australia. Simple discoidal vendobiont fossils (Aspidella terranovica) in the Dorchester Member of the Roxbury Formation (newly discovered) and in the Cambridge Argillite are in heterolithic shale-siltstone facies interpreted as intertidal to shallow marine, as for Aspidella-bearing shales of the Fermeuse Formation of Newfoundland. These were sessile benthic organisms with filamentous internal microstructure.