Abstract

Paleogeographic maps provide visual syntheses of complex ancient geologic settings. They also provide an easy-to-use tool for comparing and contrasting different geologic models. The paleogeographic maps presented here document the dynamic evolution of the Paradox Basin and adjacent Ancestral Rocky Mountains and contrast different views concerning their geologic history, geometric configuration, and tectonic sequences of events.

In Colorado, Utah, Arizona, and New Mexico, uplifts and basins of the Greater Ancestral Rocky Mountains (GARM) were built across the early and middle Paleozoic Transcontinental Arch, mostly at perpendicular to highly oblique angles. Isopach and facies maps document Early Pennsylvanian initiation of uplifts and basins with one phase of orogenic culmination in the Middle Pennsylvanian and a second, more aerially restricted event in the Early Permian. When viewed in detail with latest data concerning timing of tectonic motion on the various elements, it is apparent that elements display diachronous timing across the region. Superimposed on this complex tectonic pattern were numerous glacio-eustatic events related to late Paleozoic Gondwanan glaciation.

Paleogeographic maps document these events and the complex shifting facies patterns that resulted. Both marine highstand and lowstand maps are presented for most time slices covered in the paper; extreme changes in sea level accompanied by sharply contrasting shifts in depositional environments strongly stand out on the maps. During highstands, coarse detritus was trapped near shorelines and locally transported by turbidity and gravity process into deeper water. Mud was deposited in basin centers and at times in close proximity to adjacent uplifts. During lowstands, coarser material was transported across broadly exposed shelves; salinas developed in basin centers, and extensive evaporates were deposited there. Eolian sand was widely distributed and preserved during lowstand events.

Recent studies have suggested that a major portion of the Uncompahgre Uplift was inactive until the Early Permian. Therefore, the Paradox and Eagle basins may have been connected during the Pennsylvanian. Coarse alluvial clastics of the Early Permian Cutler Formation were formed coevally with salt flowage and deformation in the Paradox Basin. Although sharp uplifts of GARM were eroded and reduced rather quickly, some in several million years, the larger elements in Colorado persisted as epeirogenic highs well into the Mesozoic.