Stratigraphy of the middle ordovician long point group western newfoundland canada

Stait, B.A.; Barnes, C.R.

Geological Survey of Canada Paper (90-9): 235-244


Accession: 007822610

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The Long Point Group is the only fossiliferous Ordovician sequence in Newfoundland that postdates the deposition of synorogenic flysch and possibly also the emplacement of the allochthons. Thus, understanding the biostratigraphy and depositional history of this sequence is a critical element in any tectonic model for the Appalachian Orogen. The Long Point Group consists of the lower, 75 m thick Lourdes Formation and the upper, 300 m thick Winterhourse Formation. Although the Lourdes Formation deepens up-sequence, it consists of three shallowing-upward sequences, each formally established as new members. The boundaries between the lower two members are unusual "planed-off" surfaces, whereas the top of the formation is transitional to the deeper Winterhouse Formation. The lowest Shore Point Member begins with a green sandstone: probably reworked flysch or Humber Arm rocks. The remainder of the member is massive sandstone and interbedded sandstone and intertidal carbonate. The Black Duck Member is characterized by the presence of in situ coral heads. At the base, these are isolated heads, but in the upper six meters they form wall-like "reefs". These upper six meters contain a very diverse fauna, including trilobites, nautiloids, ostracodes, stromatoporoids, bryozoans, and gastropods. The uppermost Beach Point Member represents a deeper water environment and contains rolled and worn corals and other fossils in the upper subunit. The Winterhouse Formation is interpreted as a deeper water, possibly slope, deposit. As the Long Point Group has been considered traditionally to immediately overlie the allochthonous Humber Arm Group, it provides a minimum age for the emplacement of the Taconic allochthons in western Newfoundland. Recent reinterpretations suggest that the present location of the allochthons was a result of the Acadian Orogeny. Resampling for conodonts has confirmed a predominantly Prioniodus gerdae Subzone age (Blackriveran to mid-Kirkfieldian) for most of the Lourdes Formation.