Jurassic and lower cretaceous paleogeography and depositional tectonics of porcupine plateau, adjacent areas of northern Yukon and those Mackenzie District
Authors: Jeletzky J A 
Published: March 2016

Jurassic and Lower Cretaceous paleogeography was characterized by the presence of a major northeast trending marine intracratonic trough (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 Wernecke Mountains, and was flanked on the west by a belt of arenaceous to argillaceous, marine to non-marine Jurassic and Lower Cretaceous sediments derived from it. It became submerged in the earliest Albian 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 Lower 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 YT P-34 well. The prevalent quartzose to orthoquartzitic 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 occurring 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, OOO to 4, OOO 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, contemporary, oscillatory tectonic movements Among the principal tectonic elements of the report- area, the
east-northeast-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
hingelike 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 long lasting 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 fore deep 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.