Upcoming Division Events
December 5th, 2019 - 12:00 - 1:00pm
Location: Province Rooms (2nd Floor), Schlumberger Canada 200, 125 - 9th Ave SE Calgary
*CSPG members can register for free and track their CPD hours!
The Effects of Mechanical Anisotropy on the Development of an Orogenic Wedge
Speaker: Malcolm A. Lamb, Geosciences Manager Shale Petroleum Ltd.
The development of an orogenic wedge is a complex process that reflects the interaction of many components and rates. One of these components, mechanical anisotropy, is present in all bedded sedimentary rocks, and understanding its influence on the development of the orogenic wedge is important due to its influence on failure geometry. By examining the structures at the leading edge of an orogenic wedge with respect to the orientation of the mechanical anisotropy relative to the principal stress directions, insight into the development of the wedge can be gained.
Field data (fracture orientations, bedding orientations, bedrock maps, and hammer seismic data), were combined with subsurface data (well log, seismic and aeromagnetic data) to interpret the anisotropy and structures at the leading edge of the orogenic wedge in the Southern Canadian Rocky Mountains. The data indicate that strength anisotropy influences the development and geometry at the leading edge of the orogenic wedge.
Malcolm has operated a private consulting practice in Calgary completing various projects locally and internationally and teaching field courses. He has also been Geoscience Manager for Shale Petroleum for the past 6 years. Before starting his consulting practice, he spent over 20 years at Schlumberger in a variety of technical roles. Malcolm holds PhD from University of Calgary.
Late Mesozoic Reactivation of the Snowbird Tectonic Zone and its Effects on Viking Formation Stratigraphic Architecture
Speaker: Sarah Schultz Geologist – Subsurface Geology & Geohazards, Alberta Geological Survey
The Paleoproterozoic Snowbird Tectonic Zone (STZ) is a basement structure that was reactivated during the evolution of the Western Canada Sedimentary Basin (WCSB). The STZ is a fault zone in the western Canadian Shield that trends southwest through central Alberta to the Cordilleran deformation front. Brittle faults associated that parallel this basement structure have propagated up into the overlying Paleozoic and Mesozoic sedimentary cover, affecting the distribution of sedimentary environments as well as resulting stratal architectures. In the late Albian, the convergence of terranes with the western margin of the North American craton led to the reactivation and subsequent differential subsidence within the STZ. During deposition of the Viking Formation, shorelines record significant along-strike variability in orientation as a result of this tectonic reactivation. Additionally, marked changes in the thickness at different intervals of the Viking point to local changes in accommodation space associated with the STZ, complicating the recognition and correlation of stratigraphic surfaces in the study area.
Two conspicuous sequence stratigraphic architectures have resulted due to this tectonic activity and concomitant differential subsidence. The first occurs along the lowstand paleoshoreline trend preserved between the Judy Creek and Joarcam fields. At these producing fields, the Viking Formation is 20 – 30 m thick and interpreted to have been deposited in a low accommodation setting. Between the fields (and lying within the STZ), however, an anomalously thick (45 – 60 m) deltaic unit is preserved, recording the creation of accommodation along depositional strike attributed to subtle differential subsidence of the underlying Paleozoic carbonates and Mesozoic siliciclastic units associated with basement reactivation. The timing of such readjustments are well expressed by the progressive distortion of stratigraphic datums internal within the Viking Fm. The second architecture occurs adjacent to the SE fault margin of the STZ. There, the Viking records the concurrent accumulation of transgressive and regressive sedimentary successions, manifest as lateral juxtaposition of stratal packages showing retrogradational and progradational stacking patterns, respectively. The resulting stratal architecture demonstrates marked diachroneity of the maximum flooding surface (MFS) separating the transgressive systems tract from the highstand systems tract.
Incorporating the effects that basement reactivation imposed on the Viking is integral to resolving the complex depositional geometries that are present across the STZ. The fact that convergence of allochthonous terranes along the western margin of the North American craton occurred throughout Mesozoic and Paleogene time suggests that other formations may have been similarly influenced. Results of this study underscore the importance of recognizing the relationships between basement tectonics and stratal evolution of sedimentary systems that is key to resolving complex stratigraphic architectures.
Co-Authors of the Paper: James A. MacEachern, H. Daniel Gibson, and Shahin E. Dashtgard, Simon Fraser University; Octavian Catuneanu, University of Alberta
Sarah Schultz currently works as a geologist for the Alberta Geological Survey and is focusing on the mapping of Triassic units in west-central Alberta.Sarah obtained her BSc Specialization Geology in 2014 from the University of Alberta. She is nearing completion of her PhD at Simon Fraser University, which focuses on creating a sequence stratigraphic framework for the Viking Formation in central Alberta. The results of her PhD thesis have been published in 2 journal articles and presented at 8 conferences.