Date of Award
Master of Science (MS)
Professor Roger G. Walker
The Tyrwhitt, Storelk and Tobermory Formations constitute the major part of a Pennsylvanian siliciclastic succession in the Southern Canadian Rocky Mountain. The eight defined facies composing the Tyrwhitt and Tobermory Formations are mutually exclusive from five of the six facies composing the Storelk Formation. The Storelk Formation, and part of the Tyrwhitt Formation, are further divisible into laterally persistent facies and facies assemblages (Intervals).
Major facies in the Tyrwhitt and Tobermory Formations, interpreted in the context of a storm dominated shallow marine shelf, are: (1) a fossiliferous thoroughly bioturbated structureless sandstone facies which dominates the sequences, and represents background conditions of sedimentation; (2) a medium scale trough crossbedded facies, with paleoflow directed offshore; (3) a small scale crosslaminated facies, and (4) a horizontal laminated facies, both of which are intimately vertically and laterally associated. Three carbonate facies and siltstone facies, deposited during periods of restricted sand supply, constitute a minor proportion of Formational thicknesses. Virtually all facies interbed with the structureless facies, and all were apparently deposited at or below storm wave base, where storm surge currents with weaker superimposed oscillatory flow are interpreted to be the primary depositional mechanisms. The strength of the storm surge currents, together with the grain size and rate of sediment supply, controlled the lithology of the facies and the type and preservability of the sedimentary structures.
Facies constituting the Storelk Formation, interpreted in an aeolian context, are: (1) a megaplanar facies, composed of planar sets 2 - 10 m thick; (2) a megatrough facies, composed of trough sets 2-6 m thick; (3) a large scale tough crossbedded facies, and (4) a large scale planar crossbedded facies, containing sets less than 2 m thick which interbed with (1) and (2); (5) the Storelk structureless facies, composed of structureless sandstone devoid of body or trace fossils, and which has a problematical origin; and (6) a thin fossiliferous carbonate facies, interpreted as the deposit of a brief marine transgression during Storelk time. The aeolian interpretation is based on the abundance of giant crossbedding, the moderate (10-25 degrees) foreset dip angles, the total absence of body or trace fossils (except for one facies), and the presence of widespread truncation surfaces. Each of these features is comparable to that of ancient or modern aeolian examples, and a shallow marine origin is improbable. Facies assemblages in the crossbedded Storelk Intervals appear to be correlative with specific types of wind regimes. The Storelk succession was deposited in a low latitude coastal desert under the influence of prevailing north-easterly tradewinds. Aeolian deposition commenced in this area possibly as a result of a glacioeustatic lowering of a sea level, and was terminated by a major marine transgression during Tobermory time.
Stewart, W. Douglas, "Pennsylvanian Shallow Marine and Aeolian Sediments, Tyrwhitt, Storelk and Tobermory Formations of Southeastern British Columbia" (1978). Open Access Dissertations and Theses. Paper 312.