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73-31 GEOLOGICAL PAPER 73-31 SURVEY OF CANADA DEPARTMENT OF ENERGY. MINES AND RESOURCES SEDIMENT ARY HISTORY AND TECTONIC EVOLUTION OF THE SUSTUT AND SIFTON BASINS, NORTH-CENTRAL BRITISH COLUMBIA Map 14-1973 Sustut Basin, north-central British Columbia Pocket Figures, 1, 4, 5, 6, 7, 12, 13. Gerhard H. Eisbacher Price, $3.50 1974 GEOLOGICAL SURVEY OF CANADA CANADA PAPER 73-31 SEDIMENT ARY HISTORY AND TECTONIC EVOLUTION OF THE SUSTUT AND SIFTON BASINS, NORTH - CENTRAL BRITISH COLUMBIA Gerhard H. Eisbacher DEPARTMENT OF ENERGY, MINES AND RESOURCES ©Crown Copyrights reserved Available by mail from Information Canada, Ottawa from the Geological Survey of Canada 601 Booth St., Ottawa and Information Canada bookshops in HALIFAX - 1683 Barrington Street MONTREAL - 640 St. Catherine Street W. OTTAWA - 171 Slater Street TORONTO - 221 Yonge Street WINNIPEG - 393 Portage Avenue VANCOUVER - 800 Granville Street or through your bookseller A deposit copy of this publication is also available for reference in public libraries across Canada Price: $3. 50 Catalogue No. M44- 73-31 Price subject to change without notice Information Canada Ottawa 1974 CONTENTS Page Abstract v Introduction .................. ... ....... .... .. ....... ... .... 1 Acknowledgments . .. ............ ... .... .. ... .. ...... .. ... .... 1 History of geological exploration . .. ........ ..... ... ................. 1 Physiography and drainage evolution ......... ... .... ... .. ... .. .... 3 Regional geological setting ......................... ... ... .. ... .. 5 Proterozoic and Paleozoic miogeoclinal sedimentary rocks .. .. ....... 5 Stratigraphy ......... .. ........... .............................. 7 Sustut Group . ......... .. .... ..... ........... ..... .. ..... ... 8 Sifton Formation ................................................... 11 Paleocurrents ......................... ... ... ...... ........... .. 12 Provenance . ............................................... ........ 16 Sandstones . ............... ........................... .......... 16 Conglomerates ......... .. ............................. ... ... ..... 16 Sedimentologic interpretation .... ................... ... .............. 17 General considerations .... .. .. .. .... .............................. 17 Tango Creek Formation . ... ... ...................... ... .......... 22 Brothers Peak Formation ..... .. .... .... ........ .................. 27 Provenance of tuffs in the Brothers Peak Formation ......... .. ........ 29 Sifton Formation ................................................... 32 Structural geology ... ............... .. ........ .. .... ... ....... 37 Sustut Basin . .. .. ............ .......... ........... ......... 37 Sifton Basin ...... ......... ... .. ..... .. .. .... ..... ......... 43 Probable outliers of Sustut assemblage in north-central British Columbia .. 45 Uslika Formation ......... .... .. .. ....................... .. .. 45 Moricetown beds ... .. .. .. .... .. .. .... ........ ............... 48 Smithers "Fossil" beds ........... ... .. .. ........ .. ... .. ....... ... 49 Burns Lake beds ....................................... ........ 49 Tectonic evolution of the Sustut and Sifton basins 49 Economic potential .. ................. ....... .. .. ..... ....... ...... 50 References .... .. ...... .... .. ................... .................. 51 Illustrations Map 14-1973 Sustut Basin, north-central British Columbia ........... in pocket Figure 1. Index map of north-central British Columbia .. .............. in pocket 2. Late glacial erosional cirques in Brothers Peak Formation . 2 3. Present drainage of north-central British Columbia . 4 4. Generalized distribution of the principal lithological units within the inferred source area of the Sustut and Sifton basins ................ .. .... ........ ... .. .. .. ... in pocket 5. Measured stratigraphic sections of Tango Creek Formation ... in pocket 6. Measured stratigraphic sections of Brothers Peak Formation . in pocket 7. Paleocurrent rose diagrams for Tango Creek Formation, Brothers Peak Formation, and Sifton Formation . in pocket Page Figure 8. Generalized paleocurrents and maximum clast sizes of Tango Creek Formation . 13 9. Generalized paleocurrents and maximum clast sizes of Brothers Peak Formation . 14 10. Generalized paleocurrents and maximum clast sizes of Sifton Formation . 15 11. Modal composition of sandstones of Tango Creek Formation, Brothers Peak Formation, and Sifton Formation . 17 12. Relative abundance of clast types in conglomerates of Sustut Group and Sifton Formation . in pocket 13. Generalized distribution and composition of Sustut and Sifton conglomerates . in pocket 14. Change in the composition of conglomerate clasts with changing paleocurrents in the Sustut Group . 18 15. Alluvial fan depositional model . 20 16. Braided stream depositional model . 21 17. Meandering stream depositional model . 23 18. Exhumed pediment underneath Sustut Group, east of Lawyer's Pass . 23 19. Large scale crossbedding in basal conglomerates of Niven member . 24 20. Sandstone-mudstone sequences in Niven Member . 24 21. Massive sandstones of Tango Creek Formation . 26 22. Massive Tatlatui sandstone channels interbedded with mudstones and siltstones south of Thutade Lake 27 23 . Laslui conglomerate member of the Brothers Peak Formation 28 24. Partial sections through basal Laslui 'Conglomerate' member . 30 25. Composite ash-fall tuff in Brothers Peak Formation . 31 26. Ash-fall tuff overlying conglomerate bed west of Birdflat Creek . 32 27. Sole marks on alluvial fan conglomerate beds of Laslui member . 33 28. Pebbly sandstones of Spatsizi member . 34 29. Probable source region of Brothers Peak tuffs . 35 30. Massive granite-quartzite boulder conglomerate on Prairie Mountain . 36 31. Limestone-quartzite debris-flow conglomerate near Estella Lakes . 36 32. Regional structural setting of the Sustut Basin . 37 33. Kitchener monocline . 39 34. Folded Niven member . 39 35. Angular unconformity between Tango Creek Formation and Bowser Assemblage . 40 36. Influence of plunge on closure of folded structures . 41 37. Angular discordance between Tango Creek and Brothers Peak formations . 44 38. Schematic diagram for the structural evolution of the Sifton Basin . 44 39. Uslika Formation on Conglomerate Mountain . 45 40. Sketch map of the area near Uslika Lake . 46 41. Tectonic setting of Sustut and Sifton basins . 47 ABSTRACT The Sustu and Sifton basins of Late Cretaceous - early Tertiary age contain continental sedimentary rocks that were deposited during the uplift of the Columbian and Pacific orogens. The present valley system of northern British Columbia seems to have been inherited largely from southeasterly-trending Eocene valleys although vigorous Pliocene to Recent stream capture has caused much of the drainage to be deflected towards the Pacific Ocean. Within Sustut Basin the Sustut Group has been divided into two formations: the Tango Creek Formation (containing Cenomanian - Paleocene fossil leaves and palynomorphs) and the Brothers Peak Formation (containing Paleocene fossil leaves and radiometrically dated Eocene ash-fall tuffs). Thickness of the Sustut Group ranges from about 300 metres (1, OOO feet) to 2300 metres (7, OOO feet). Paleocurrents maximum clast-size trends, and clast composition suggest an easterly to northerly provenance for the Tango Creek Formation most of which was laid down by meander ing rivers. The Brothers Peak Formation had a westerly to northerly provenance and was deposited in an alluvial fan environment which supplied debris to a southeasterly-flowing river system. The ash-fall tuffs of the Brothers Peak Formation are probably the airborne products of explosive volcanism in the Sloko volcanic province of northwestern British Columbia. Tectonic deformation in the western part of Sustut Basin proceeded during deposition of the Sustut Group and is reflected by changing paleocurrent patterns and tectonic overprinting along dif ferent structural trends. Sifton Basin is in and near the northern Rocky Mountain Trench and is occupied by the Sifton Formation containing Late Cretaceous - Paleogene fossil leaves and palynomorphs. Paleocurrents and composition suggest local provenance and southerly-flowing rivers. Late-orogenic deformation disrupted the basin fill along northwesterly- trending fault zones. Sustut and Sifton basins contain part of the Cordilleran 'molasse facies' and were separated from each other by a metamorphic culmination within the Omineca Crystalline Belt. The Sustut Basin has potential for epigenetic uranium and fossil placer-gold occurrences. REsUME Les bassins Sustut et Sifton du Cretace superieur- de but de l' ere tertiaire renferment des roches sedimentaires continentales qui ont ete deposees lors du soulevement des orogenes colombienne et pacifique. Le systeme actuel de vallees du nord de la Colombie-Britannique semble en grande partie !'heritage de vallees eocenes a orientation sud-est, bien que la capture energique de cours d'eau entre le Pliocene et le Recent a eu pour effet de detourner en grande partie le drainage vers le Pacifique. A l'interieur du bassin Sustut, le groupe de Sustut a ete divise en deux formations: la formation de Tango Creek (renfermant des feuilles et des palyno morphes cenomaneens-paleocenes fossiles) et la formation de Brothers Peak (renfer mant des feuilles paleocenes fossiles et des tufs, dus aux retombees d e cendres eocenes, dates par radiometrie). La largeur du groupe de Sustut varie entre 300 metres (1, OOO pieds) environ et 2, 300