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Analysis of paleocurrent trends, thickness variations, and lithologic intervals recorded to Cretaceous clastic sediments of the Methow-Pasayten graben indicates a dominantly eastern source through most of the Cretaceous, but with a Late Cretaceous interval of westerly derived sediments.
Neocomian black shales, volcanic sandstones, and conglomerates of Barksdale's Buck Mountain Formation and the Upper Jurassic Dewdney Creek Group of Coates were derived from the east. These sediments are overlain unconformably by arkosic Aptian sediments of Barksdale's Goat Creek, Panther Creek, and Harts Pass Formations, and Coates' Hauterivian to lower Albian Jackass Mountain Group, all apparently derived from the crystalline rocks of the Okanogan Highlands on the east. These Late Jurassic, Neocomian, and Aptian sequences of volcanic rocks, volcanic sediments, and arkosic sediments record the destruction of the volcanic cover and erosion into the Okanogan Highlands crystalline rocks. In sharp contrast, the unconformably overlying chert-grain sandstones and chert-pebble conglomerates f Barksdale's Upper Cretaceous Virginian Ridge Formation contain paleocurrent structures and variations in clast size and formation thickness which indicate derivation from a western source. The most probable source terrain is the Paleozoic Hozomeen Group of the Cascade core.
Unconformities and chert sandstones and conglomerates correlate with the mid-Cretaceous deformational episode of Misch in the North Cascades. These sediments could reflect tectonic uplift during thrusting or rapid isostatic rebound following mid-Cretaceous deformation and metamorphism.
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