02581nas a2200229 4500008004100000245014500041210006900186300001200255490000700267520187900274653001102153653001402164653002202178653001802200653001502218653001302233653001502246100001602261700002002277700001602297856003802313 2003 eng d00aFirst Middle Ordovician Biota from Southern New Brunswick: Stratigraphic and Tectonic Implications for the Evolution of the Avalon Continent0 aFirst Middle Ordovician Biota from Southern New Brunswick Strati a715-7300 v403 a

A limestone boulder in the Triassic Lepreau Formation near Saint John, New Brunswick, has yielded the first diverse marine fauna from the sub-Caradoc Ordovician of the western Avalon continent. This fauna includes the first Arenig conodonts recovered from Avalon and represents an unexposed interval in southern New Brunswick. Association of the conodonts Drepanoistodus and Baltoniodus and the trilobites Neseuretus, Nileus, and Stapeleyella emphasizes the faunal dissimilarity of Avalon and Laurentia through the late Middle Ordovician. Extension of the ranges of Neseuretus cf. Neseuretus parvifrons and Stapeleyella from Britain into New Brunswick further emphasizes that "eastern" and "western" Avalon were confluent parts of a unified, insular Avalon continent that originated in the latest Precambrian. This fauna correlates with the lower Amorphognathus (Lenodus) variabilis Zone (Kundan Stage) of Baltica and the terminal Arenig (upper Middle Ordovician; lower Darriwilian Stage) of Avalonian Britain. Available evidence suggests that an Arenig cover sequence with local shallow-water hematitic iron ore, quartz arenite, and rare limestone extended across the Avalonian marginal and inner platforms from eastern Newfoundland to the Boston, Massachusetts, region. This "western" Avalonian Arenig shows the greatest similarity with the Arenig of the Welsh Borderlands. Phosphatic fossils from the boulder have a thermal alteration index much lower than that of nearby lower Paleozoic outcrops and suggest derivation of the boulder from a weakly heated Avalonian succession brought into the Bay of Fundy region by post-Ordovician transcurrent faulting.

10aAvalon10aconodonts10aLepreau Formation10aNew Brunswick10aSaint John10aTriassic10atrilobites1 aLanding, E.1 aWestrop, S., R.1 aKim, D., H. uhttp://dx.doi.org/10.1139/e03-009