Integrated Ichnologic-Sedimentologic approach to reconstruct marginal to shallow marine paleoenvironments: The Lower Cretaceous Wabiskaw Member, Clearwater Formation, Alberta-Canada, Lower Permian Dandot Formation, and the Early Cambrian Khussak Formation, east-central Salt Range, Pakistan
Creators: Ahmad, Waqar
Publisher: name: University of Alberta Library
Year: 2024

<p>The interplay of independent variables (wave, river, and tidal input) in marginal and shallow-marine environments complicates identifying facies and interpreting paleoenvironments in the rock record. Therefore, predicting, correlating facies, determining facies thickness and distribution, and assessing the quality of shallow marine clastic reservoir facies remains challenging. This study integrates sedimentology and ichnology to characterize the depositional environments of the Lower Cretaceous Wabiskaw Member of the Clearwater Formation in north-east Alberta, Canada, the Lower Permian Dandot Formation of east-central Salt Range, Pakistan, and the Early Cambrian Khussak Formation of east-central Salt Range, Pakistan. The Wabiskaw Member (deltaic, strand plain shoreface-offshore deposits), the Dandot Formation (tide-dominated estuarine and deltaic deposits), and the Khussak Formation (tidal flat deposits) provide excellent case studies to evaluate the ichnological and sedimentological characteristics associated with laterally and vertically variable stresses in wave-tide, and river influenced nearshore settings. <br>
Ten sedimentary facies describe the Wabiskaw Member. The recurring facies are grouped into four facies associations representing both proximal and distal marginal marine environments, including 1) fluvial-influenced prodelta, 2) wave-storm influenced delta front to a mouth bar, 3) storm-influenced offshore, and 4) distal lower to middle shoreface. Characteristic sedimentological and ichnological signatures differentiate Wabiskaw Member deltaic (prodelta-delta front) deposits from related strand plains. The deltaic deposits exhibit soft-sediment deformation structures, fluid mud, syneresis cracks, and low-diversity and diminutive trace-fossil suites under comparable stress conditions. In contrast, fully marine strand plain shoreface-offshore complexes display comparatively robust trace fossils with high ichno-diversity and bioturbation intensities. To evaluate the reservoir quality of various reservoir facies (F-3, F-4, F-7, F-8) of the Wabiskaw Member, their reservoir characteristics (porosity, permeability, pore throat radii, flow-storage capacity, oil saturation, and thickness) are compared. Among the studied reservoir facies, F-4 has the highest quality and is the most productive (pore throat radius &gt;20 μm, 18% flow, and 4% storage capacity). Whereas F-3, with micro-porous characteristics (pore-throat radii ranging from 2 to 4 μm), has the lowest quality among the Wabiskaw Member reservoir facies, with 37% storage and ≤5% capacity flow.<br>
The Dandot Formation in northwest Pakistan is a 35-40 m thick succession of tide-dominated estuarine and deltaic deposits, which have been characterized using sedimentologic and ichnologic datasets. Thirteen sedimentary facies describe the lower Permian Dandot Formation (Salt range, north-west Pakistan). The recurring facies are grouped into eight facies associations representing both fluvial and marginal marine environments, including 1) Fluvial channel deposits, 2) Paleosol deposits, 3) Intertidal mud-flat to mixed-flat deposits, 4) Estuarine tidal bars, 5) Prodelta deposits, 6) Delta front deposits, 7) Proximal delta front-mouth bar, and 8) Tidally influenced channel deposits. The estuarine deposits show a fining-upward trend, are cleaner, and have better sorting than deltaic deposits, which form a coarsening-upward sequence. Additionally, trace fossils in deltaic deposits are more diverse and heterogeneously distributed than those in estuarine deposits, serving as a valuable criterion for distinguishing between the two settings.<br>
The Early Cambrian Khussak Formation of the east-central Salt Range, Pakistan, is studied to identify its ichnological and sedimentological characteristics. This integrated study resulted in identifying thirteen lithofacies and six recurring facies associations, including 1) Upper intertidal mud flat deposits, 2) Middle intertidal mixed flat deposits, 3) Lower intertidal sand flat deposits, 4) Inter-tidal creek point bar deposits, 5) Subtidal bar deposits and 6) Subtidal bay deposits. The Khussak Formation&#39;s tidal flat deposits exhibit a distinct trend in ichnofacies. The Cruziana Ichnofacies characterize the lower energy proximal deposits. In contrast, the Skolithos Ichnofacies represent high-energy distal deposits. The mud flat, mixed flat, sand flat, and sub-tidal deposits of the Khussak strata exhibit subtle and gradual ichnologic variation but are distinct enough to indicate facies.<br>
The work on the Wabiskaw Member in northeast Alberta (Township 95-98, Range 10-14), and the Lower Permian (Dandot Formation) and Lower Cambrian (Khussak Formation) strata of east-central Salt Range, Pakistan, is one of the first integrated sedimentologic-ichnologic studies of these units. Establishing a geological model for these units allows us to better understand the depositional process at the time of their formation. In addition, this study effectively addresses the gaps in our geological knowledge of the areas and contributes to the prediction and correlation of facies with greater confidence.</p>