Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Steven G. Driese

Committee Members

Claudia I. Mora, Kenneth R. Walker

Abstract

The York River Formation (Lower Devonian) of the Gaspé Peninsula, Quebec, Canada is part of a coarsening-upward siliciclastic succession reflecting a transition from shallow marine deposits of the Gaspe Limestones and York River Formation to overlying terrestrial deposits of the Battery Point and Malbaie Formations. The focus of this study is 164 meters of the Anse a Brillant section of the York River Formation, not previously studied in detail.

The Anse à Brillant section consists of two main facies associations: a Channel Sandstone Facies Association and a Fining-Upward Facies Association. The Channel Sandstone Facies Association is characterized by large-scale (up to 13 m thick), multistory channel sandstone bodies up to 13 meters thick. Immature fluvial detritus similar to the Battery Point Formation, large-scale unidirectional low-angle cross-beds, climbing ripples and a lack of bioturbation suggest that the Channel Sandstone Facies Association is representative of fluvially-influenced upper estuarine channels. The multistory nature of the channel sandstone bodies suggests fluctuations in sea-level, resulting in successive channel incision and fill.

The Channel Sandstone Facies Association is superimposed on the Fining- Upward Facies Association consisting of repetitious sheet-like deposits up to 3 meters thick of sandstone, siltstone and mudstone strata. The fining-upward sequences are interpreted to represent deeper middle estuarine deposits with a greater marine influence than the upper estuary channels. The Fining-Upward Facies Association is characterized by abundant bioturbation by a brackish-marine fauna, transported plant material (including Spongiophyton, Taeniocrada, Psilophyton and Lycopodia), small-scale, closely-spaced, symmetrical wave ripples and a 20 cm thick coal layer consisting dominantly of Spongiophyton mats. These features are indicative of a shallow-water nearshore depositional system. The fining-upward sequences of sandstone, siltstone and mudstone strata reflect deepening-upward sequences.

The repeated incision of the Channel Sandstone Facies Association into the Fining Upward Facies Association represents four discrete drops in sea-level. A Greenish-gray facies, identified by glauconite-rich strata and a brackish marine fauna, signifies the onset of a sea-level rise. The overall fining-upward nature of the entire Anse à Brillant section and the increase in marine-influenced facies up-section, indicate a transgressive system. Transgressions are necessary for estuarine conditions, as are both fluvial and marine sediment sources.

Although modem estuaries are well studied, recognition of estuarine sequences in the stratigraphic record has been limited due to the overlapping nature of estuaries and other nearshore clastic systems such as deltas, lagoons and tidal flats. Based on field observations, lithofacies analysis, identification of floral and faunal assemblages, petrographic examination and paleocurrent analysis, there is strong evidence that the Anse à Brillant section of the York River Formation is a wave- and fluvial-influenced barrier estuary. Therefore, this study provides a facies model for mixed wave and fluvial upper and middle estuary conditions and evidence for four discrete episodes of sea-level changes that enhances the understanding of ancient estuarine systems. Additionally, the Anse a Brillant section provides a greater understanding of the overlying Battery Point fluvial system and a means of identifying similar strata signifying marine incursions within the Battery Point Formation.

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