Mesozoic Stratigraphy, Sedimentology, and Paleogeography of Northern Yukon, Canada: ABSTRACT

Data derived from reconnaissance field work in 1962 and published data indicate that the Mesozoic succession is divided into 5 major cycles which reflect important events in the geologic history of the region: (1) Late Triassic transgression across a low shelf; (2) widespread Jurassic transgression and development of the Richardson trough; (3) earliest Cretaceous regression and basin filling that ended with local minor(?) uplift and erosion; (4) Albian transgression and development of the early Late Cretaceous regression; and (5) Late Cretaceous and early Tertiary nonmarine sedimentation in local tectonic basins. Within each of these major cycles several diastems and unconformities are present which increase in magnitude toward the basins' margins. During Jurassic and earliest Cretaceous times, the Richardson basin was filled with marine shale and bordered on the east by a landmass (probably mountainous) which shed sand westward. The sands now form a series of Lower, Middle, and Upper Jurassic and Lower Cretaceous nearshore sandstone bodies. During the earliest Cretaceous some sand in the Babbage River region was derived from the underlying Mesozoic and upper Paleozoic clastic sediments in the western Brooks Range geanticline. The earliest Cretaceous clastics filled the basin so that nonmarine conditions prevailed in the northernmost (Blow River) part. Moreover, slight uplift and erosion took place at that time. By the end of Aptian time, much of the eastern landmass had been peneplaned. The tectonic and sedimentary patterns changed drastically during Albian to early Tertiary times. Sediments were derived from a rising cordillera which formed the western and southern margins of the new foreland basin and developed across the previous eastern Jurassic and Lower Cretaceous landmass. A thick succession of largely silty Albian shale was deposited in this basin. The thin Upper Cretaceous sedimentary sequence consists of nonmarine strata (Eagle Plain Formation) and marine shale. Much of the deformation and uplift of the Richardson Mountains took place during middle Late Cretaceous time. During the late stages of the cordillera deformation on the south and southwest, several small, partly fault-bounded basins developed in which thick sequences of coarse clastic materials wer deposited. A similar but thicker Mesozoic succession appears to extend beneath the Mackenzie delta. One of the best prospective hydrocarbon zones is the sequence of well-sorted sandstones near the base of the Lower Cretaceous, if these sandstones do not grade to shale on the north. End_of_Article - Last_Page 2497------------