Allostratigraphy, Sedimentology and Paleogeography of the Cretaceous Upper Fort St. John Group (Upper Albian-Lower Cenomanian) in Northeastern British Columbia
Doctor of Philosophy
A. Guy Plint
The upper Albian to lower Cenomanian succession in northeastern British Columbia was deposited in the proximal foredeep and is greatly vertically expanded relative to the more eastern part of the basin. The study interval has a wedge-shaped geometry, and is ~780 m thick in the west and thins dramatically to ~280 metres over a distance of ~170 km. Rapid facies changes result in lithostratigraphic units being strongly diachronous. In order to determine depositional history, the present study subdivided the Upper Fort St. John Group into 16 genetically-related allomembers. The new allostratigraphic correlations established in this thesis combined with previous studies, permit the reconstruction of lateral facies changes from the western shoreline of the Western Interior Seaway in the proximal foredeep to the forebulge in central Alberta, over a distance of about 800 km. The Upper Viking, Westgate and Fish Scales alloformations collectively span approximately 2.7 Myr. The stratal geometry of the studied interval can be interpreted to be the result of two pulses of flexural subsidence (recorded by units VD and WA, and units WD, FA and FB) separated by a period of more subdued subsidence (units WB and FC). The stratigraphic surfaces in the studied interval are of regional extent, and can be correlated for between 300-1000 km. Almost all flooding surfaces can be traced throughout the study area (50 000 km2). The sedimentological and stratigraphic evidence indicates that the proximal foredeep was occupied by a shallow, low-gradient, storm-dominated ramp. The abundance of waveinfluenced structures (e.g. swaley and hummocky cross-stratification, wave and current ripples) suggests strong wave-reworking of sediment on a shallow marine ramp. The deposition on muddy portion of the shelf is interpreted to have been dependent on waveenhanced sediment gravity/geostrophic flows. Along-shelf transport was controlled by geostrophic flows towards the southeast. At least 16 major sequences were detectable on a regional scale; sequences have an average periodicity of 125-170 kyr. Facies successions and regional stratal geometry suggest relative sea-level fluctuations were of the order of 10-30 m which, on a time-scale of the order of 100 kyr, can only be explained by a glacio-eustatic mechanism.
Angiel, Piotr Jan, "Allostratigraphy, Sedimentology and Paleogeography of the Cretaceous Upper Fort St. John Group (Upper Albian-Lower Cenomanian) in Northeastern British Columbia" (2013). Electronic Thesis and Dissertation Repository. 1545.