Tien Hai Bang

B. Sc. Honours Thesis

Lacustrine Cyclic Sedimentation in the Lower Carboniferous Horton Bluff Formation at Rainy Cove, Nova Scotia

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The Lower Carboniferous Horton Bluff Formation at Rainy Cove in Nova Scotia is an excellent coastal cliff exposure of lacustrine strata. The freshwater depositional conditions are inferred from the presence in the strata of fish scales, ostracodes, plant materials and the absence of marine fossils.

The study area is a continuous cliff exposure on the east side of Rainy Cove which is approximately 800 metres north west of the town of Pembroke in Hants County. A 75 metres thick section of east west trending and overturned strata were examined. Two facies associations were identified. The first one is the nearshore lacustrine assemblage which represents deposition during low lake stand. As for the offshore lacustrine assemblage, deposition occurs in quiet and relatively deep water.

The lacustrine sediments at Rainy Cove display well developed cyclic sedimentation. The pattern of cyclicity is explained in terms of fluctuation of water level as a direct response to climatic change. With the rise and fall of water level, the physical and chemical characteristics of the lake are altered.

During low lake level, the lake was subjected to subaerial exposure as evidenced by desiccation cracks, rainprints and symmetrical “planed-off” ripples. The presence of evaporitic minerals and syneresis cracks point towards salinity increase in the environment presumably caused by climatic aridity. Appearance of carbonate concretions and abundance of iron-oxide also represent dryness in the depositional environment. Well developed symmetrical wave ripples indicates the nearshore environment. As the water level rose, sedimentation took place in a relatively deep and quiet environment. A reducing environment prevailed as indicated by the presence of medium dark grey shale and the absence of organic activity.

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Pages: 85
Supervisor: Martin Gibling