An analysis has been made of the thickness of sediments accumulated in various parts of Arizona and adjoining areas during each of the periods of geologic history. From these and other sedimentary data, conclusions are drawn concerning the times and places of crustal movement in the region.

For the Paleozoic and Mesozoic eras, data have been compiled, period by period, in the form of isopach maps. For the Cenozoic era, information on thickness of sediments in individual basins is shown on a base map.

Five basic structures appear in Arizona on all of the Paleozoic maps. These consist of two positive areas (in the northeast and southwest respectively), the margins of two geosynclines (in the northwest and southeast), and a sag in central Arizona between the positive areas and connecting the two geosynclines. Prongs or submarine ridges extending basinward from the positive areas, and areas of more rapid sinking between them, appear to have shifted position from period to period.

Four major changes in isopach pattern are as follows: (1) The Uncompahgre-San Luis highlands of Colorado were formed and north central New Mexico became an area of more active and extensive sedimentation starting with the Pennsylvanian. (2) Central and southern Arizona became a high area contributing sediments to the north during Triassic time. (3) Northern Arizona received no sediments in Lower Cretaceous time, but in southern Arizona an uplift was followed by development of a deep, northwestward-trending trough from Mexico. (4) Deposits of Upper Cretaceous age were accumulated across northern Arizona in and near a sea that expanded westward from the Rocky Mountain trough.

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