Abstract

Growth of the salt anticlines of the Paradox basin, Colorado and Utah, began in Middle Pennsylvanian time shortly after deposition of the salt of the Paradox Member of the Hermosa Formation. Several of the salt structures developed adjacent to structurally high areas in pre-salt rocks that apparently were in existence prior to and during salt deposition. The NE. margin of the salt basin was bordered by the front of the ancestral Uncompahgre uplift, and arkosic debris derived from the crystalline core of the uplift was shed into the margin of the basin. A pulse of uplift on the ancestral Uncompahgre range, marked by the spread of arkosic debris into the basin, resulted in termination of conditions requisite for evaporite deposition. Initial gentle folding of the salt structures probably occurred at this time. During the remainder of Middle and Late Pennsylvanian time the basin continued to sink while receiving a cover of dominantly marine sediments, and the major salt structures in the basin increased their amplitudes by an amount that generally matched the thickness of beds deposited on their flanks. Arkosic debris derived from the Uncompahgre was shed several miles into the basin. Strong uplift on the ancestral Uncompahgre range, which occurred near the end of Pennsylvanian time, resulted in withdrawal of the seas and in the spread of arkosic debris across the basin. Thick sections of continental sediments were deposited adjacent to and between the salt structures in the deep-trough part of the basin, and by the end of Permian time the salt structures had amplitudes ranging from about 5000 to 9000 ft. By the end of Permian time, most of the salt may have been transferred from beneath the flanks of the salt structures into their cores, and the growth of the salt structures slowed considerably or ceased. Renewed pulses of uplift in the Uncompahgre, occurring from latest Permian through Middle Triassic time, were marked by corresponding renewed active growth of the salt structures. Uplift of the Uncompahgre largely ceased by Late Triassic time and the crystalline core of the uplift near the Uncompahgre front was buried by a veneer of Upper Triassic and younger sediments. The salt structures grew slowly during Late Triassic and Early and Middle Jurassic time, and probably most were buried in Late Jurassic time.

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