Tide‐ and wave‐dominated inshore and shoreline sequences from the late Precambrian, Finnmark, North Norway
ABSTRACT The Late Precambrian Ekkerøy Formation of Finnmark, northern Norway represents a 40 m thick coarsening upward, prograding deltaic sequence. The upper 6 m of this formation consists of two small‐scale fining upward sequences representing two contrasting shoreline environments. These two sequ...
| Published in: | Sedimentology |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
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Wiley
1975
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| Online Access: | http://dx.doi.org/10.1111/j.1365-3091.1975.tb00283.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-3091.1975.tb00283.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3091.1975.tb00283.x |
| Summary: | ABSTRACT The Late Precambrian Ekkerøy Formation of Finnmark, northern Norway represents a 40 m thick coarsening upward, prograding deltaic sequence. The upper 6 m of this formation consists of two small‐scale fining upward sequences representing two contrasting shoreline environments. These two sequences have been the focus of a detailed facies analysis based on grain size, bed thickness and sedimentary structures. The study area comprises a series of horizontally bedded rocks which are continuously exposed for 3 km enabling individual facies and sedimentary structures be to traced‐out laterally. The lower sequence exhibits a wide variety of tidal features including directional bimodality of both large‐scale and small‐scale cross‐stratification, herringbone cross‐stratification, various sandstone‐mudstone alternations including lenticular and wavy bedding, and a general fining upward tendency. A detailed field analysis of the internal structures within the large‐scale cross‐stratified unit is presented and is interpreted as a sub‐tidal channel complex. The associated sandstone‐mudstone facies represents intertidal flats built up by tidal and storm‐generated currents. The upper sequence displays a wide variety of wave‐formed structures including wave‐ripples and swash‐lamination. Palaeocurrent data indicates a dominance of shoreward migrating megaripples and wave‐ripple crests oriented approximately parallel to the inferred shoreline with a distinct longshore component. The sequence is interpreted as a beach‐shoreface environment. In terms of sedimentary structures, palaeocurrent patterns and facies distributions, the sequence bears a remarkable similarity to the high‐energy, non‐barred shoreline of the modern Oregon coast U.S.A., described by Clifton, Hunter & Phillips (1971). |
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