Abstract
In this study, data obtained from the Lower Cretaceous McMurray Formation in the central Athabasca Oil Sands, northeastern Alberta, Canada, are examined and used to establish the architecture of stacked fluvial and estuarine tidal bar deposits. A total of 13 distinguishable facies (F1–F7, F8a–F8b, and F9–F13) corresponding to stacked fluvial and estuarine deposits are recognized. These facies are then reassembled into four facies associations: fluvial deposits, tidal flat, tidal bar complex, and tidal bar cap. Of these, the lower fluvial deposits show a highly eroded channel lag and tidal influences in the cross-stratified sand and wavy interbeds. The fluvial deposits pass upwards into upper tidal-dominated tidal flats and a massive homogeneous tidal sand bar complex. Very thick tidal-influenced facies (F8a–F8b, up to 22 m) caused by semi-diurnal and semi-lunar cycles are also observed in tidal flats. Based on studies of the facies and facies associations, a three-dimensional (3-D) architecture model is finally established and used to analyze the internal distribution of the stacked fluvial and estuarine deposits. This is the first time that a 3-D model of the paleo-estuary tidal bar has been constructed. The results of this study will assist future research analyzing the architecture of stacked fluvial and estuarine deposits.
Highlights
IntroductionEstuarine tidal bars, which are called linear sand ridges or linear sandbanks, occur in the mouths of tide-dominated estuaries [1] or in mixed tide-and-wave dominated estuaries [2,3,4]
Estuarine tidal bars, which are called linear sand ridges or linear sandbanks, occur in the mouths of tide-dominated estuaries [1] or in mixed tide-and-wave dominated estuaries [2,3,4].Estuarine tidal bars show strong similarities with tidal bars found in tide-dominated deltas, as they can be elongated [1,5] or lobate [6], and are typically a few kilometers long, hundreds of meters wide, and between a few meters and tens of meters in height.To date, few studies have provided three-dimensional (3-D) architecture of the depositional environment of complex paleo estuarine sand bar stratigraphy
Outcrop observations and measurements from the Cretaceous McMurray Formation indicate that the paleo tidal sand bar was deposited on fluvial deposits and was approximately 7–15 km long, which is similar to that shown in 2-D architecture section and 3-D architecture model results (Figures 7 and 8)
Summary
Estuarine tidal bars, which are called linear sand ridges or linear sandbanks, occur in the mouths of tide-dominated estuaries [1] or in mixed tide-and-wave dominated estuaries [2,3,4]. Few studies have provided three-dimensional (3-D) architecture of the depositional environment of complex paleo estuarine sand bar stratigraphy. Sandbanks in the UK [7] and found that the that the strongest tidal currents and sand transport directions are primarily parallel to (and clockwise strongest tidal currents and sand transport directions are primarily parallel to (and clockwise around) around) the ridges, whereas, on the banks themselves, they turn progressively towards the crests in the ridges, whereas, on the banks themselves, they turn progressively towards the crests in shallower shallower water, thereby tending to maintain the banks. Bay, based on a finite element model called Telemac2D Their simulation results indicated that the northeastern side of the tidal sand bar called. The studyArea areaand is located in the central Athabasca oil sand area, in the Lower Cretaceous McMurray
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