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Fare thee well, Wilrich and Falher. Enter the Elmworth

May 31, 2018

 

As my Clastic Sedimentology professor, “Cactus” Jack Lerbekmo, would stress to our class, “Geology is a descriptive science.”  To be useful, your terminology must be clear.  Imprecise or outdated nomenclature should be revised or abandoned.  Such is the case with the Upper Mannville in the Deep Basin.  Put another way, obsolete terminology does not just exasperate, it exacerbates challenges in advancing understanding (TF, if you're out there and reading this, you'll smile. -AF).  Take for example the Spirit River and its Members; the Notikewin, Falher and Wilrich.  These terms are generally used to describe the Upper Mannville of the Deep Basin notwithstanding that the type sections for these intervals lie well updip of the Deep Basin edge.

 

As Enlighten has progressed with the development of our Upper Mannville stratigraphic model, it has become apparent that the Notikewin/Falher/Wilrich nomenclature is getting in the way of clarity.  While the Notikewin as a lowstand sequence unconformably overlying the “Falher” remains viable, the Falher/Wilrich terminology needs to be addressed. Recent work (e.g. Newitt, 2017) has begun to stress that, in a sequence stratigraphic sense, each unit in the lower Upper Mannville continues from the predominately continental Falher to the shoreline and marine Wilrich. 

Schematic stratigraphic cross-section of the Upper Mannville (Newitt, 2017)

 

This stratigraphic model maintains the Falher designation whether for the marine or continental part of the section.  Retaining the Falher designation, however, might create a mental block and prevent people from fully utilizing the sequence stratigraphic framework.

 

For this reason, we started using the term “Lower Upper Mannville” (or LUM) for the Falher/Wilrich succession.  This term is more than a bit clunky and we decided to discard the LUM in favour of something that flows off the tongue a bit more fluidly.

 

Hence, we propose, and are using, the Elmworth Member to refer to what was formerly the Falher/Wilrich interval using the 100/10-01-070-11W6/00 well as the proposed type section.  Using the original well from Smith et al., 1984 allows for the continuity with other work in the Spirit River while using a well with most of the relevant parasequences present.  This designation has the following advantages:

  • Encourages the adoption of a sequence stratigraphic model for the lower portion of the Spirit River Formation

  • Ties the stratigraphy more closely to the most economically significant play in this formation

 

Elmworth member type log

 

References

 

Newitt, D., 2017.  Integrated sedimentology, sequence stratigraphy, and reservoir characterization of the basal Spirit River Formation, west-central Alberta. M. Sc. Thesis, University of Calgary, Calgary, AB, Canada

Smith et al., in AAPG Memoir 38, Elmworth: Case Study of a Deep Basin Gas Field, 1984.  Masters, J. A., ed.  American Association of Petroleum Geologists, Tulsa, OK, USA.

 

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