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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 49 (1965)

Issue: 11. (November)

First Page: 1781

Last Page: 1800

Title: Geologic History of Rocky Mountain Region

Author(s): John D. Haun (2), Harry C. Kent (2)

Abstract:

During late Precambrian time, sedimentary rocks were deposited in a geosyncline in the Cordilleran region. Eastward extensions of this geosynclinal sea occupied parts of the Rocky Mountain region. After gentle deformation and erosion, the sea spread eastward during the Cambrian and Ordovician Periods. Discontinuous Ordovician, Silurian, and Early Devonian rocks indicate short intervals of marine invasion interrupted by periods of erosion. A major invasion of the sea over the craton is recorded by the onlap of Devonian and Mississippian carbonates and Devonian evaporites which rest on rocks ranging in age from Precambrian to Early Devonian.

The pattern of widespread shallow seas of the Mississippian Period was interrupted during the Pennsylvanian and Permian Periods by significant tectonic activity (Ancestral Rockies). Parts of the uplifts remained positive until Triassic or Jurassic time and supplied coarse clastic sediments to late Paleozoic basins in adjacent areas. At greater distances from land, sandstone, red shale and siltstone, evaporites, and carbonates accumulated. Marine Triassic sediments were deposited in southeastern Idaho and adjacent areas. Triassic and Early Jurassic continental deposits accumulated throughout much of the region.

A series of Jurassic marine invasions from the Arctic initiated another major sequence of events. The boreal sea extended southward into the northwestern and western parts of the region in Middle Jurassic time, and successive transgressions reached as far southeast as northern Colorado by Late Jurassic time. After withdrawal of the Jurassic sea, the pattern of overlap was continued by deposition of non-marine Jurassic and Cretaceous sediments. During the Early Cretaceous a sea again invaded from the north and in late Early Cretaceous time joined one from the south, forming a seaway which persisted throughout the remainder of the Period. During Early Cretaceous time, clastic sediments were derived from the craton on the east and from the Cordilleran region on the west. During Late Cret ceous time, the western source area predominated.

The present tectonic framework began to form during the Late Cretaceous and early Tertiary with the development of uplifts and intermontane basins (Laramide orogeny). Extensive thrust faulting occurred in the western part of the region. Lacustrine and fluviatile sediments, derived from surrounding uplifts, were deposited within intermontane basins.

Volcanic activity was moderately important on the west during the Cretaceous Period, but igneous intrusion and volcanic activity became widespread throughout the Rockies in the Tertiary. The present drainage system was largely developed as the intermontane basins filled. Subsequent stream erosion, accompanied by Pleistocene glaciation and regional uplift, shaped the present topography.

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