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Fluvial-Facies Model for the Upper Devonian and Lower Mississippian (?) Kanayut Conglomerate, Brooks Range, Alaska
The allochthonous Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate is as thick as 3000 m and crops out along the crest of the Brooks Range in northern Alaska for a distance of almost 1000 km. The Kanayut Conglomerate was deposited by southwest-flowing streams that drained a mountainous region to the north and east. At least two major trunk streams carried clasts as large as 23 cm into the depositional basin. The largest clasts are present in the northeastern and north-central Brooks Range. The clasts consist of chert, quartz, and quartzite.
The Kanayut Conglomerate overlies and interfingers south-westward with shallow-marine deposits of the Noatak Sandstone that in turn overlie deeper marine shale and sandstone of the Hunt Fork Shale. The lowest member of the Kanayut Conglomerate is the lower shale member, which is as thick as 1160 m and is organised into fining-upward fluvial cycles. These cycles consist in ascending order of channeled basal conglomerate, trough cross-stratified sandstone, ripple-marked siltstone, and black to maroon shale, the latter thought to have been deposited on floodplains. The middle conglomerate member is as thick as 530 m and consists of fining-upward couplets of channeled conglomerate and parallel-stratified or cross-stratified sandstone. It contains the largest clasts, records the maximum progradation of the clastic wedge, and was probably deposited on a broad braidplain. The upper Stuver Member is as thick as 1300 m and is organised into fining-upward cycles that resemble those of the lower member. It grades upward into tidal and marginal-marine deposits of the lower sandstone member of the Kayak Shale.
The Kanayut Conglomerate records progradation and retreat of a large, coarse-grained, fluvial-dominated delta. The delta prograded southwestward during the Late Devonian and retreated during the Early Mississippian. Paleogeographic and palinspastic reconstructions are uncertain because of the present allochthonous distribution of the Kanayut Conglomerate deposits and the lack of well-defined and accepted plate tectonic reconstructions for the Arctic region.
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