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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 66 (2018), No. 4. (December), Pages 725-751

Using Structure-From-Motion Photogrammetry to Recognize Lateral Versus Forward Accretion Bedforms in the Lower Cretaceous McMurray Formation, NE Alberta, Canada

Derek A. Hayes, Eric R. Timmer, Michael J. Ranger, Jeffrey L. Kavanaugh, Murray K. Gingras

Abstract

The juxtaposition of trough cross-bedded sand underlying inclined heterolithic stratification (IHS) is commonly interpreted to represent the growth of a fluvial or estuarine point-bar through time in the lower Cretaceous McMurray Formation. This paradigm has led to the development of a bias regarding the depositional architecture of McMurray Formation sediment, such that the majority of geobodies in the McMurray Formation are interpreted to represent point-bar deposition. This study addresses this bias by using an Unmanned Aerial Vehicle and Structure-from-Motion photogrammetry to generate three-dimensional outcrop models from which bedding architecture can be analyzed.

The purpose of this study is to recognize and discuss the stratigraphic significance of two types of facies architectures prevalent in outcrop exposures of the middle McMurray Formation: laterally-accreting point-bar deposits and forward-accreting compound-dune deposits. Previous HitBedNext Hit orientation data, when compared to sediment transport directions, show that outcrops along the Steepbank River are composed of stacked lateral accretion bar elements. At the Amphitheatre outcrop exposure along the MacKay River, master bedding surfaces are parallel to sediment transport direction, which suggests that the cross-bedded sand geobody is forward-accreting. Based on these distinct relationships, two dominant facies associations are recognized. The Steepbank #3 outcrops preserve a laterally accreting estuarine point-bar complex sharply overlying a fluvial dune succession, while sediments at the Amphitheatre outcrop are ascribed to a forward-accreting middle estuary compound dune complex that is truncated by an overlying IHS channel fill.

The recognition of compound dunes, in addition to well-recognized laterally accreted point-bars in the McMurray Formation, is important for the establishment of reservoir and stratigraphic models. In McMurray Formation subsurface studies, large-scale, middle estuary compound dune complexes are rarely recognized, despite their presence in outcrop exposures — this is an important theme that is explored in this paper. To this end, Previous HitbedNext Hit orientation data are combined with 3D photogrammetric outcrop models. Previous HitBedTop orientation data show two main facies associations: 1) laterally accreted bars which are bounded by bedding discontinuities and are characterized by IHS bedsets that thin, increase in mud content and increase in bioturbation intensity upwards; and 2) large-scale forward-accreting compound dunes which are characterized by low-angle planar tabular and trough cross-stratified medium-grained sand with current reversals and unevenly distributed bioturbation throughout.


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