Acritarch biostratigraphy and taxonomy of the Winterhouse Formation (Upper Ordovician), Port au Port Peninsula, Newfoundland

Gillespie, Helen (1998) Acritarch biostratigraphy and taxonomy of the Winterhouse Formation (Upper Ordovician), Port au Port Peninsula, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Upper Ordovician Winterhouse Formation (Long Point Group) is exposed only along the northwestern coast of Long Point on the Port au Port Peninsula, southwest Newfoundland. Detailed acritarch study of this formation has identified 74 palynomorph species assigned to 31 genera. One new combination, Ammonidium parvipinnatum (Uutela and Tynni), is proposed here. Fossils are extremely well preserved. An average Acritarch Alteration Index of 1.6±0.3 in transmitted light corresponding with clear and colourless to pale yellow and white to bright yellow in flourescence, indicates that these acritarchs have undergone very little thermal maturation. These rocks sit at or above the oil window. Co-occurrence of Villosacapsula setosapellicula, Multiplicisphaeridium irregulare, Ordovicidium heteromorphicum, Petaloferidium stigii, Cheleutochroa diaphorasa, Dicommopalla macadamii, Actinotodissus crassus, Poikilofusa spinata, and Excultibrachium concinnum confirm the middle to late Caradoc age assignment of Quinn et al. (in prep). -- In distribution, a minimum of three acritarch assemblage zones are defined from palynomorph counts and statistical analysis. These may be used locally to correlate the Winterhouse Formation in the subsurface of the Port au Port and Gulf of St. Lawrence region. The Veryhachium Assemblage Zone (VA Zone), found at the base of the Winterhouse Formation is defined by peak abundances of Gloeocapsomorpha sp., Veryhachium trispinosum, Villosacapsula setosapellicula, and Micrhystridium fragile. The Micrhystridium Assemblage Zone (MA Zone), in the middle of the Winterhouse Formation, is marked by peak abundances of Micrhystridium sp. C, Micrhystridium equispinosum, Veryhachium oklahomense, Multiplicisphaeridium sp. B, Micrhystridium aremoricanum, Comasphaeridium varispinosum, Multiplicisphaeridium martae, Polygonium sp. C and a significant decrease in the abundance of Villosacapsula setosapellicula and Veryhachium trispinosum. The Polygonium Assemblage Zone (PA Zone) found at the top of the Winterhouse Formation, near the transition with the Misty Point Formation, is defined by peak abundances of Polygonium gracile, Veryhachium valiente, Lophosphaeridium aequicuspidatum, Villosacapsula entrichos, Moyeria cabottii, Lophosphaeridium endense, Lophosphaeridium papillatum. Polygonium sp. A, and the first appearance of Cryptospore sp. B and Petaloferidium stigii. Each of the three zones represent different aspects of Caradoc offshore shelf dominated environments. Differences in the assemblages of fossils correlate with changes in the depositional environments as the shelf evolved from a shallow water carbonate rich environment (the VA Zone), through a deeper water transition zone of mixed siliciclastic/carbonates (the MA Zone), and back to a shallow water environment that was carbonate poor (the PA Zone).

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