--> Abstract: Eustatic, Tectonic, and Oceanographic Controls on the Birth, Life, and Death of a Late Ordovician Carbonate Ramp, Newfoundland Appalachians, by Kelly L. Batten and George R. Dix; #90039 (2005)

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Eustatic, Tectonic, and Oceanographic Controls on the Birth, Life, and Death of a Late Ordovician Carbonate Ramp, Newfoundland Appalachians

Kelly L. Batten and George R. Dix
Carleton University, Ottawa, ON

The Lourdes Formation outcrops along an 18-km, continuous strike section on the Port au Port Peninsula, western Newfoundland. It contains the history of re-establishment of carbonate platform sedimentation, then its demise, in the northern Appalachians following Taconic orogenesis. Unconformities bound the formation and its three members and record eustatic, tectonic, and oceanographic controls on base level. Microtopography along the base of the lower Shore Point Member reveals a non-conformable contact with an underlying thrust sheet. Transgression allowed peritidal siliciclastic and carbonate sedimentation, and appears coincident with Caradocian eustatic sea level rise. Renewed transgression following brief emergence of the platform led to deeper subtidal, but local shoal, facies of the Black Duck Member, including variably argillaceous, nodular wackestones and packstones, crinoidal grainstones, and coral patch reefs. A prominent disconformity caps the member; evidence for differential erosion and seaward transport of siliciclastic detritus suggests tectonic influence on base level. Subtidal carbonate sedimentation resumed; the upper Beach Point Member contains a greater input of silt and clay. However, hardgrounds and possible shallowing-upward cycles capped by oncolite-intraclast grainstones may indicate a higher-order rhythmic pattern of sedimentation during the latest stage of Lourdes deposition. The Lourdes Formation is overlain by the mostly siliciclastic Winterhouse Formation. The contact is a marine hardground with local lag deposits of pyrite-coated and bored Lourdes clasts. As there is no evidence for a significant rise in sea level, the boundary may signify oceanographic controls, with change in circulation and siliciclastic input marking a new stage of basin development.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005