LATE ORDOVICIAN NEARSHORE FAUNAS AND DEPOSITIONAL-ENVIRONMENTS, NORTHWESTERN MAINE

The Little East Lake Formation represents a spectrum of Late Ordovicia n (Ashgill) nearshore environments. These physical environments are ch aracterized by a variety of quartz- and feldspar-rich sandstone and sl ate. Depositional environments include neritic nearshore, beach, tidal flat, and alluvial(?). The beach and neritic nearshore environments c ontain a variety of fossil invertebrates. The majority of the brachiop od fauna is confined to two taxa: Eodinobolus rotundus Harper, 1984, a nd Dalmanella testudinaria ripae Mitchell, 1978 (in Cocks, 1978). Some of the specimens have been broken and abraded suggesting transport wi thin the beach swash zone. Gastropods include Lophospira cf. L. miller i (Hall), Lophospira(?), Trochonemella cf. T. notabilis (Ulrich and Sc ofield), and Daidia cerithioides (Salter). Tidal-flat environment cont ains the trace fossils Palaeophycus and Planolites. The Late Ordovicia n (Caradoc and Ashgill) sedimentary basins developed subsequent to the collisional Taconian orogeny, wherein an arc accreted to the eastern Laurentian margin. Prior paleomagnetic reconstructions place the south eastern continental margin of Laurentia at approximately 25-degrees so uth latitude during the Late Ordovician. Using these reconstructions, the siliciclastic Ashgill rocks discussed here would have been deposit ed in an elongated, northeast-trending basin on the southeastern Laure ntian margin. The fauna developed along this margin, but in contrast t o possibly adjacent Irish and Scottish assemblages, was located in muc h shallower water.