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Abstract


Bulletin of Canadian Petroleum Geology
Vol. 45 (1997), No. 4. (December), Pages 415-433

Global Sequence Boundaries of the Triassic and Their Identification in the Western Canada Sedimentary Basin

Ashton F. Embry

ABSTRACT

Twelve second- and third-order T-R (transgressive-regressive) sequence boundaries have been delineated in the Triassic succession of the Sverdrup Basin, Arctic Canada. Sequence stratigraphic data from six other localities throughout the world, including Svalbard and Barents Sea, Germany, Italy, eastern Siberia, northern Himalayas and the southwestern U.S.A. indicate that these boundaries are global in extent. The ages and orders of these global sequence boundaries are: 1) near Permian-Triassic boundary (2nd order), 2) late Dienerian (3rd order), 3) late Smithian (3rd order), 4) near Early-Middle Triassic boundary (2nd order), 5) late Anisian (3rd order), 6) near Middle-Late Triassic boundary (2nd order), 7) early Carnian (3rd order), 8) mid-Carnian (3rd order), 9) near Carnian-Norian boundary (2nd order), 10) mid-Norian (3rd order), 11) near Norian-Rhaetian boundary (2nd order), and 12) near Triassic-Jurassic boundary (2nd order).

All twelve of these high-order boundaries are also readily recognizable in the Triassic succession of the Western Canada Sedimentary Basin. A widespread unconformity is associated with each boundary on the basin margin with a conformable transgressive surface forming the boundary farther basinward. Various potential stratigraphic traps are associated with each boundary.

At various localities, the global sequence boundaries commonly exhibit the effects of tectonic uplift and thus tectonics was a factor in the generation of these boundaries. To accommodate the combination of both tectonic and eustatic mechanisms in the generation of the global boundaries, it is proposed that they are a consequence of episodic, major plate tectonic reorganizations. During these episodes, changes in spreading rates and/or directions would induce changes in the horizontal stress regimes of the oceanic and continental portions of plates. This would in turn result in an initial eustatic fall and tectonic uplifts along basin margins. During the subsequent relaxation phase, eustatic rise and tectonic subsidence on basin margins would occur. These combined eustatic and tectonic movements would create sequence boundaries consisting of subaerial unconformities and conformable transgression surfaces as well as associated stratigraphic surfaces including ravinements, maximum flooding surfaces and regressive surfaces of marine erosion within stratigraphic successions in many areas throughout the world.

RESUME

Douze limites de deuxieme et de troisieme ordre de la sequence T-R (transgressive-regressive) ont ete delimitees dans la succession du Triassique du Bassin Sverdrup de l'Arctique canadien. Les donnees des sequences stratigraphiques de six autres emplacements a l'echelle mondiale y compris Svalbard et la mer de Barents, l'Allemagne, l'Italie, la Siberie orientale, les Himalayas du nord et le sud-ouest des Etats-Unis indiquent que ces limites sont d'etendue mondiale. Les ages et les ordres de ces limites de sequences a l'echelle mondiale sont: 1) limite Permien-Triassique proche (deuxieme ordre), 2) Dienerien tardif (troisieme ordre), 3) Smithien tardif (troisieme ordre), 4) limite du Triassique precoce-moyen proche (deuxieme ordre), 5) Anisien tardif (troisieme ordre), 6) limite du Triassique moyen-tardif proche (deuxieme ordre), 7) Carnien precoce (troisieme ordre), 8) medio-Carnien (troisieme ordre), 9) limite Carnien-Norien proche (deuxieme ordre), 10) medio-Norien (troisieme ordre), 11) pres de la limite Norien-Rhaetien (deuxieme ordre), 12) limite du Triassique-Jurassique proche (deuxieme ordre).

Ces douze limites d'ordre eleves sont facilement reconnaissables dans la succession du Triassique du Bassin sedimentaire de l'Ouest canadien. Une discordance etendue est relies a chaque limite sur la limite du bassin avec une surface transgressive conformable formant une limite plus eloignee dans le bassin. Divers pieges stratigraphiques possibles sont relies avec chaque limite.

1 Geological Survey of Canada Contribution No. 1997002

End_Page 415------------------------

Divers emplacements de limites globales affichent communement les effets du soulevement tectonique et par consequent la tectonique etait un facteur de la production de ces limites. Pour accomoder la combinaison des mecanismes tectonique et eustatique dans la generation de limites globales, il est suggere qu'ils sont la consequence de reorganisation episodique de plaques tectoniques importantes. Pendant ces episodes, les changements des taux de repartition ou des directions causeraient des changements des regimes de stress horizontaux des parties des plaques oceaniques et continentales. Ce qui produirait a son tour une chute eustatique initiale et des soulevements tectoniques le long des marges du bassin. Pendant la phase de relaxation subsequente, une croissance de l'activite eustatique et une baisse de l'activite tectonique se produiraient. Ces mouvements combines eustatiques et tectoniques causeraient des limites de sequences consistant de discordances subaeriennes et des surfaces de transgression conformables ainsi que des surfaces stratigraphiques associees incluant des ravinements, des surfaces d'inondation maximum et des surfaces regressives d'erosion marine avec successions stratigraphiques dans plusieurs regions du monde.

Traduit par Marie-Louise Tomas


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