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The AAPG/Datapages Combined Publications Database
Jurassic sedimentary beds of the Morrison formation, which occur in the subsurface in about the western one-fifth of Kansas, range in thickness from a feather edge to 350 feet. The rocks consist primarily of shale, sandstone, and limestone with minor amounts of chert and anhydrite. Two lithologic units which are recognizable in the formation are persistent and traceable over large areas. The upper unit consists of sandy shale with limestone stringers; the lower unit consists of shale with chert and anhydrite. Present correlations suggest that the upper unit is equivalent to the Morrison as originally defined, and the lower unit is equivalent to the upper Sundance. The Morrison formation unconformably overlies Permian and Triassic(?) rocks and is unconformably overlain by retaceous rocks. Evidence suggests that the sediments are of fluvial and lacustrine origin, with the source of the sediments in Kansas probably from the southeast.
The northwestward tilting of the pre-Morrison surface into the Denver basin no longer reflected the structural development of the Hugoton embayment which had existed in the Paleozoic. The axis about which this tilting occurred is believed to be not too far distant from the present pinch-out of the Morrison. Because the present regional structure of the formation agrees closely with the regional structure of the Dakota, Carlile, and Niobrara formations, it is concluded that the sediments were folded in post-Niobrara time and that subsequently the area was tilted toward the east in post-Pliocene time.
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