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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 1. (January)

First Page: 115

Last Page: 115

Title: Structure of Precambrian Rocks of Medicine Bow Mountains and its Relationship to Post-Precambrian Structural Patterns: ABSTRACT

Author(s): Robert S. Houston

Article Type: Meeting abstract


A basement complex of gneisses and schists in the Medicine Bow Mountains has a northwestern trend that was established during early Precambrian time. On this, a series of sedimentary rocks, typical of a stable shelf tectono-environment and exceeding 30,000 feet in thickness, was deposited. In later Precambrian time all these rocks were deformed, and a northeastern to east-northeastern structural pattern was superimposed on the older trend. During or following this orogeny major northeast-trending faults and shear zones developed, the major one being the Mullen Creek-Nash Fork shear zone that separates the Medicine Bow Mountains into two major segments. During this second orogeny the Precambrian basement yielded by flexure and passive folding and the older northwestern tre d is preserved in one small area south of the Mullen Creek-Nash Fork shear zone and in a large block along the northwest slope of the mountains north of the shear zone. The original northwest basement trend did not affect the structural pattern established during the second orogeny. In contrast, structural patterns formed during post-Precambrian orogenies are influenced, in part, by both previously established trends.

Isopachs of Pennsylvanian strata show major north to northwest-trending zones of thinning and less well-developed northeastern zones of thinning, suggesting the two major Precambrian trends were reactivated during the development of the Ancestral Rockies. During the early part of the Laramide orogeny pronounced northeastern fold systems developed in the Laramie basin. These are considered to be basement-controlled. Later major north-south folds that developed in southeastern Wyoming do not appear related to basement structure, but segmentation of the Medicine Bow Mountain front during the final stage of the Laramide orogeny is clearly controlled by basement structure. On the northeast slope of the Medicine Bow Mountains the major thrusts developed during the last stage trend northwest and the cross-faults trend northeasterly, each paralleling one of the Precambrian structural patterns. Similarly, later faulting during Tertiary time is related to these two main basement trends.

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Copyright 1997 American Association of Petroleum Geologists