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<br /> <br />2.04.6(2)(a) <br />marine shales and siltstones thin to the west where they are <br />' replaced by several littoral marine barrier-beach type <br />sandstones. The Rollins in the Ldorth Fork area is this type <br />' of sandstone, marking the start of a regressive cycle which <br />followed the "Afancos transgression." The deposition of this <br />sandstone probably resulted from a progradation of sediments <br />from the west, causing an eastward retreat or regression of <br />the sea. Stratigraphic evidence indicates that the strike <br />t of the strandline was approximately north-south during <br />deposition of the PSesaverde sediments. <br />' At the time of deposition of the coals in the L3orth Fork area, <br />' it appears that tk~e paleo environments consisted mainly of <br />deltas plus barrier-beach systems along the coastal plain <br />which provided suitable areas for peat swamp conditions to <br />develop. During the lower coal member cycle, one of the <br />depositional centers of the delta system is thought to have <br />been situated southeast of the area of the Rear Mine. Peat <br />accumulated behind a north-south trending barrier-beach which <br />' extended northward from this delta. Evidence for this is the <br />greater consistency and thickness of the lower member coals <br />' in the immediate vicinity of the Pear :dine. The A, B and <br />C seams show more variation in thickness and correlations <br />' are less certain in the south. The sandstone lithologies <br />replacing the coals of the lower member support the presence <br />of a major deltaic distributary in that area. The thickness <br />t of the B seam represents a long period of near equilibrium <br />conditions, while the A and C seams were probably deposited <br />' under brief stable periods during tl~e transition from marine <br />to maximum-coal-forming and back to marine environments. <br />1 <br />' 36 <br /> <br />