The stratigraphy and depositional environment of the Lower Ordovician Bell Island and Wabana Groups, Conception Bay, Newfoundland

Ranger, Michael Joseph (1978) The stratigraphy and depositional environment of the Lower Ordovician Bell Island and Wabana Groups, Conception Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The stratigraphy of the Lower Ordovician Bell Island and Wabana Groups was studied in order to determine their depositional environments. A proposed depositional model was then used to study the environment of formation of the Wabana ironstones. -- Accessible stratigraphic sections were measured in detail and the data compared to documented examples of modern and ancient environments of a generally similar nature. -- On the basis of this study a modified geological subdivision is proposed. The division of the succession into two groups is retained and their subdivision into nine formations is suggested. -- It appears that sedimentation in the Bell Island and Wabana Groups was controlled by tidal processes. Two major environments are represented in the strata: interbedded sandstones, siltstones and shales interpreted to be a tidal flat complex, and massive sandstones interpreted to be an offshore barrier or tidal bar. Three subenvironments of the tidal flat complex were recognized: the subtidal, intertidal and supratidal. -- Coarsening- and shoaling-upwards sequences at two locations may be prograding delta cycles, suggesting that the over all environmental control may have been that of a high-destructive, tide-dominated delta system. Paleocurrent directions support these interpretations. -- Provenance studies indicate that the source terrain was Precambrian volcanic, plutonic and probably sedimentary rocks that are exposed nearby on the Avalon Peninsula. Detrital garnet, muscovite and metamorphic rock fragments may have been derived from a presently unexposed crystalline basement. -- The chamosite oolites apparently formed as primary precipitates in shallow lagoons and accumulated on tidal bars and tidal flats where they were oxidized, possibly to goethite, forming hematite on diagenesis. The periodic occurrence of ironstones in the strata may be the result of migrating delta distributaries. -- A general correlation of the Wabana iron ores with similar Lower Ordovician deposits of Nova Scotia, North Africa and Europe is known. The sedimentology of the host rocks, where studied, appears to be strikingly similar to that of the Bell Island and Wabana Groups.

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