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THE WnERSITY OF CALGARY An mte- geophysid investigation of basement conmls on Devonian carbonates in central Alberta, Canada Darran Jones Edwards A DISSERTATION SUBMllTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCïOR OF PHlLOSOPHY DEPARTMENT OF GEOLOGY AND GEOPHYSICS CALGARY,ALBERTA MAY, 1997 O Darran Jones Edwards 1997 National Libraiy 1+1 ofcmada Acquisitions and Acquisiins et Bibliographie Se~*ces seMces bibliographiques 395 Wellington Street 395, nwr Welhgton WwaON KlAOIYQ OttewaON KtAON4 CaMda Canada The author has granted a non- L'auteur a accordé une kence non exclusive licence ailowing the exclusive permettant a la National Lïbrary of Canada to Bibliothèque nationale du Canada de reproduce, loan, distriaute or seil reproduire, preter, disûiiuer ou copies of this thesis in microfonn, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/fh, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantkd extracts tiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract This study examines the role of basement stnrcture and lithology in the deposition of Middle and Upper Devonian carbonates in central Alberta and attempts to test various geophysical methods to help m detemiinmg tbis. This poorly understood aspect of Devonian carbonate sedimentation is assessed hugh a rnultidisciplinary approach incorporating seismic reflection, potentiai-field, and cidihole data The crystalline basement appears to be characte- by est- or southeast-dipping tbnist faults in east-central Alberta and West- to southwest-inclineci Iayering of possibie lithoIogicd origin to the west. Conventional and horizontal-gradient vector (HGV) potentid-field data seldom detect these proposed major basement contacts. However, a prominent northeast- to north-northeas-trending crusta1 discontinuity, the Snowbird Tectonic Zone, can be tracked throughout the study ares Basement surface morphology and the degee of sedimentary cover deformation varies across central Alberta Structurai, tithologicai and geomorphological processes probably shaped the topography of the basement surface. In places, basernent faults propagated directly into the sedimentary cover with a near-vertical attitude, Occasionally, dipping intrabasement seismic events may be projected to approxmiately coincide with low-relief irregulaïities on the basement surface. Basement structure can sometimes be indirectly transferred upsection through differential compaction or drape of sediments over such basement irregularities. This structural variation is similarly reflected in the different modes of basement interaction with Devorim carbonates. For example, kgRiver Formation paîch reefs melian- Givetian) werr initially mted direcrly on raidfault bIocks in north-central Alberta. To the south, channel development, an important influence on Swan Hills Formation (Givetian to Frasnian) pli-orrn morphology, may be tied to mctivated basement faulting. Elsewhere, drape over raised basement topography apparentiy provideci the loci for some Swan Hills and Leduc Formation (Frasnian) mfal buildups. Regionaiiy, very few potential-field lineaments coincide with knom carbonate buildups. Core data suggest that minor tectonic adjustments may have occurred synchronously with Keg River and Swan Hills reef .*. Ill growth, Post-Devonian movement on basement fdts may have enabIed hydroc~nsand doIomitizing fluids to ldyaccess these carbonates- The possible recognition of subtie geo10gical inhenentancebetween the basement and carbonate sedmienîary cover is of significauce in terms of future hydrocarbon exploration for Devonian carbonate reservoirs. Acknowbdgments A multidisciplinary project of this nature dksupon a variety of geophysical and geologicai datasets and personnel. 1owe a great deal of gratitude to a large nurnber of people. Firstly, 1 would like to thank my supervisor, Jim Brown, for giving me the opportunity to undertake research mto such a conmversial topic. His technical and moral support over the years are greatly appreciated. This dissertation has ptly benefited in many ways hm comrnents made by Gerry Ross, Don Lawton, Don Gend2;wii.I and Henry Lyatsky. Discussions with Fran Hein and Jim Didch aiso proved fruitful. The following companies and individuals are thanked for donating seismic data to this project: Compton Resources Ltd; Husky ûii Ltd (Michael Enachescu); International Colin Energy Co. @oug McLachlan); Mobil Oil Canada; Sigma Explorations Ltd (Barry Korchinski); Talisman Energy Ltd (Tom Andrews), and Unocal Canada Ltd (Ken Mitchell). The use of LITHOPROBEseismic data was kuidly made available by Gerry Ross and Emie Kanasewich. Drillhole data were provideci by Digitecb Infoxmation SeNices Ltd and CD Pubco Inc. Gridded magnetic and Bouguer gravity &ta were available thugh the Geological Survey of Canada. Commmwedth Geophysical Geophysical Development Co. (Sudhir Jain) provideci access to additional magnetic data in north-central Alberta. Without these various types of data, this research would not have been possible. Within the Department of Geology and Geophysics, tecbnïcai support at different stages of this smdy by members of the LITHOPROBESeismic Rocessing Facility (LSPF) and CREWES groups is appreciated. In particular, 1 would like to acknowledge Kns Vasudevan, Rolf Maier, Hugh Geiger, Arie van der Velden, Darren Foltinek and Henry Bland for their assistance. Jeff Thurston is thanked for sbaring his knowledge of the horizontal-gradient vector (HGV)algorithm. The various stafi of the Gallagher Library and main office were also helpfui during my time there, particularly Regina Shedd, Marvel Nash and Marg Westbrook. Financial support for this project was provideci by an Amoco Canada Graduate Feliowship, an Alberta Minister of Advanced Education Intemational Education Award, LiTHOPROBE Supporthg Geoscience Awards and an NSERC Operathg Grant (to Jim Brown), together with graduate teaching and rtsearch assistantships administered by the Department of Geology and Geophysics. Over the years, a great number of fiends have successfully manageci to distract me m many ways hmlong &ys and nights spent working on this dissertation. Sunice it to Say, late night discussions wirh fellow students mevitably seemed to involve ferrnented beverages and a pool table. Away hmthe university, the proximity of the mountains made for many memorabIe moments and experiences. Fmaliy, but by no means least, 1 would like to thank my parents, Lewis and Valmai Edwards, for their constant support and encouragement over the years, and for frequently askuig "have you nearly finkhed?". 1fiope that thïs dissertation will inspire Merstudy in the years to corne. .. Approval page .................................................. n Abstract ....................................................... in... Acknowledgments ................................................ v Table of contents ................................................ vii List of tables .................................................... x List of figures .................................................. .xi Chapter 1: Introduction .......................................... 001 1.1 Background .......................................... 001 1.2 Dissertation objectives ................................... 005 1.3 Methodology ......................................... 006 1.4 Dissertation outlke ..................................... 013 Chapter 2: The potential-field horizontal-gradient vector (HGV)method ..........015 2.1 Utïlïty of magnetic and gravity data in central Alberta ............... 016 2.2 The horizontal gradient of potential-field data .................... 021 2.3 The horizontal-gradient vector method .........................023 2.4 Synthetic 3-D modelling of potential-field HGV data ............... 036 2.4.1 Prism mode1 ..................................... 037 2.4.2 Dome mode1 ..................................... 049 2.4.3 Dipping-layer mode1 ............................... -049 2.5 Geological comboraticm of HGV interpretation: an example fiom the Wopmay Orogen .................................... 056 2.6 Sumxmy ............................................ 063 Chapter 3: Regional basement structure of centrai Alberta. ...................065 3.1 A heterogeneous basement: regional domains of central Aibe rta. ....... -066 3.2 Crustal-scde seismic data and basernent structure ................. 078 3.3 Basement stmcture and the sedimentary cover of central Alberta ........091 vii Chapter 4: Conmls of modern recf development .........................0% 4.1 Thecarbonatefactory ....................................096 4.2 The modeni carbonate growth wmdow: the requisite environment ...... 097 4.3 General conmls on carbonate buiidups ....................... -10 4.3.1 Antecedent topography ............................... 100 4.3.2 Tectanism ....................................... 103 4-33 Eustatic sea-level changes ............................. 104 4.4 Artificial reefs ......................................... 106 45 Discussion ........................................... 106 Chapter 5: Basement influences on the Keg River Formation of north-cenûd Alberta .