REPLY TO DISCUSSION of C.W. Langenberg, F.J. Hein, D. Lawton and J. Cunningham: Seismic modeling of fluvial-estuarine deposits in the Athabasca oil sands using ray-tracing techniques, Steepbank River area, northeastern Alberta

Abstract

We appreciate the discussion of our paper (Langenberg et al., 2002) by Michael Ranger and Murray Gingras. Their elicited strong reaction to our work shows clearly the importance of this topic for understanding the oil sands in the Athabasca deposit, the complex nature of the stratigraphy and sedimentology of the deposit, and the wide range of views and opinions concerning interpretations of the oil sands. Ranger and Gingras (this issue) have two main critiques of our work: 1) the definition of channel complexes and the criteria used to distinguish them, and 2) the stratigraphic nomenclature and subdivision as applied to the McMurray Formation. Because this critique concerns sedimentology and stratigraphy of the oil sand deposit only and not the seismic modeling, we changed the order and number of responding authors. Ranger and Gingras (this issue) express the opinion that our definition of channel complexes is “simplistic, ill-defined, and of questionable validity;” and that “their channel complex model from the Steepbank River outcrops and surrounding wells is based on questionable criteria and is likely incorrect.” In our original paper, we stated, “individual channel complexes were identified in the heterolithic valley-fill units of the upper McMurray Formation. Channel complexes generally contain a basal scour surface overlain by Inclined Heterolithic Stratification (IHS) with consistent paleoflow directional indicators” (Langenberg et al., 2002, p. 188). This text was accompanied by further written description and measured stratigraphic sections from outcrops 3, 4, 7 and 9 on the Steepbank River (our Figs. 6⇓–9) and two core descriptions with wireline logs (our Figs. 10, 11). As written, with the accompanying diagrams, we thought it was apparent that a channel complex is a lithofacies package, defined by major bounding surfaces (generally a basal scour surface), with genetically related facies (in this case channel, point bar lateral …