Jurassic and lower cretaceous palaeogeography and depositional tectonics of Porcupine plateau and adjacent areas of northern Yukon and Mackenzie District, Northwest Territories
Authors: Jeletzky J A 
Published: March 2017

Jurasic and Lower Cretaceous paleogeography was characterized by the presence of a major northeast-trending marine intracratonic through (aulacogene) opening southward into the Mesozoic orogenic belt of the Canadian Cordillera. This Porcupine Plain - Richardson
Mountain Trough extended across the present Porcupine Plateau from the Yukon Coastal Plain to Selwyn Mountains, and covered most or all of the sites of the present Ogilvie and Wernecke Mountains. It separated an extensive, eastern, Peel Landmass from a western, Keele-Old Crow Landmass. The ancient
Peel Landmass extended at least from Tuktoyaktuk to Werneck Mountains, and was flanked on the west by a belt of arenaceous to argillaceous, marine to nonmarine Jurassic and Lower Cretaceous sediments derived from it. It became submerged in the earliest Albin stage of the Cretaceous. Keele-Old Crow
Landmass was flanked on its east side by Jurassic and Lower Cretaceous sediments derived from it and similar to those flanking Peel Landmass. The two belts of arenaceous and argillaceous rocks were separated by a belt of Jurassic and Lowe Cretaceous deep-water, predominantly argillaceous sediments,
40 to 120 miles wide, occupying the central part of the Porcupine Plain-Richardson Mountain Trough. This central argillaceous facies is unknown and probably absent in Ogilvie Mountains and in wells of Eagle Plain because of subsequent erosion; however, it occurs beneath the Aptian unconformity in
the Molar YTP-34 well. The prevalent quartzose to orthoquartizitic lithology of Jurassic to mid-Lower Cretaceous arenites of Keele Range and Nahoni Range suggests their derivation from early Carboniferous to Permotriassic quartzose elastics and mid-Paleozoic granitoids of Keele-Old Crow Range and
British-Barn Mountain areas in Yukon and adjacent areas of northeastern Alaska. The smallish present day plutons occuring in these areas apparently are the roots of much more extensive laccolith-to sheet-like plutons destroyed by Jurassic to mid-Early Cretaceous erosion. An abrupt regional
replacement of quartzose to orthoquartzitic arenites by chert-rich greywackes in the late Aptian supports this idea. The above-described facies and paleogeographical pattern of the trough was controlled by predominantly vertical, oscillatory, localized to interregional tectonic movements of the
principal tectonic elements of the report-area. The influence of eustatic fluctuations of sea level is discounted because of their insignificant amplitude (less than 500 feet) in comparison with that (2,000 to 4,000 feet) of the minimum short-term oscillatory vertical tectonic movements
characteristic of tectonically active belts. Within such belts, the effects of eustatic movements can be expected to be completely overprinted by those of the areally localized, contemporaty, oscillatory tectonic movements. Among the principal tectonic elements of the report-area, the
eastnortheast-trending Aklavik Arch was uplifted and flexed in late Early to early Middle Jurassic and again in Valanginian to mid-Hauterivian time. The north-trending Cache Creek Uplift (probably a northward offshoot of Aklavik Arch) and Canoe Depression apparently were active only in Valanginian
to mid-Hauterivian time. The oscillatory movements of these tectonic elements resulted in the emergence of short-lived and localized source areas and shallow-water areas within the Porcupine Plain-Richardson Mountain Trough. However, all these depositional-tectonic events were merely second and
third order complicating features happening on the longlasting background of a prevalent and strong subsidence and a rapid deposition of deep sea sediments within the well-defined, relatively narrow but deep, mid-basin zone of the trough. The partly decoupled vertical tectonic movements on the
flanks of the trough exhibit a Jurassic to early Valanginian phase of hinge-like movements around a centrally situated north-south-trending axis. In Early to Middle Jurassic time the eastern flank was moving up (relatively speaking) while the western flank was moving down. The direction of this
hinge-like movement was reversed in the Late Jurassic. One more reversal occurred in the early Early Cretaceous (Valanginian) when the eastern flank was again (as in Early to Middle Jurassic time) moving up while the western flank was moving down. The ensuing phase of regional oscillatory movements
started with the early to mid-Hauterivian uplift of both flanks coupled with the uplift of Aklavik Arch and Cache Creek Uplift inside the trough. This regional uplift was followed by a late Hauterivian to late Barremian subsidence which was followed, in turn, by a regional Aptian uplift. This uplift
culminated in the latest Aptian interregional orogeny which strongly uplifted the southern part of the trough and the southwestern part of Peel Landmass. This orogeny apparently caused an inversion and folding of most or ?all of the mid-basin zone of the trough south of Aklavik Arch and severed
permanently its longlasting depositional-tectonic connection with the Mesozoic orogenic belt of the Canadian Cordillera. The focal point of the latest Aptian tectonic pulse was situated south of the report-area. There was a gradual northward weakening of its effects resulting in the preservation of
a residual deep-water "furrow" in the westernmost part of the trough north of Aklavik Arch. This "furrow" continued to subside strongly while the adjacent part of the Keele-Old Crow Landmass continued to rise strongly. The resulting new type of hinge-like movement around a strongly asymmetrically
situated north-south-directed axis transformed this part of the trough into a foredeep of the latest Aptian Keele-Old Crow Landmass. This hinge-like movement dominated the entire studied length of the Porcupine Plain-Richardson Mountain Trough in the Early Albian. A mid- to Late Albian regional
uplift of the Porcupine Plateau concludes the Jurassic to Early Cretaceous tectonic history of the report-area. The Aklavik Arch has remained linear, contiguous and in its presentday geographical position at least since the early Paleozoic. The present claim of an en échelon arrangement of its
component uplifts is incorrect. Other major tectonic elements and source areas of northern Yukon retained their relative geographic positions at least since the earliest Jurassic. These data refute the alleged occurrence of post-Precambrian continental drift within northern Yukon, adjacent parts of
Northwest Territories, and northeastern and east-central Alaska. All of these regions formed part of an ancient North American craton which had been growing by accretion of adjacent orogenic belts at least since the early Paleozoic.