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Log Book for January 24, 2004
Geology Report
Sandy Musclow Reporting
Geologic Background of the Paradox Basin
The Mars Desert Research Station Hab sits within the Paradox Basin. The Paradox Basin is a late Paleozoic basin of Pennsylvanian and Early Permian age (~286MYA) which encompasses southeastern Utah and southwestern Colorado entirely within the Colorado Plateau. Over the last several million years, the Colorado Plateau has formed from regional uplift, and certain areas have experienced stream rejuvenation and downcutting. The region's rugged topography noted for its picturesque mesas, buttes, natural arches and deeply incised meandering river canyons has formed from the erosion of the Paleozoic and Mesozoic rock formations.
The Paradox basin is an elongate northwest- to southeast-oriented depression. During the Middle Pennsylvanian, the Paradox basin was an enclosed basin approximately 320km long and 160km wide. Tectonic activity in the Paradox basin was at a peak during this time, resulting in major uplift of the Uncompahgre region, which shed clastic debris into the northern and eastern portion of the subsiding Paradox basin. The deepest part of the basin is next to the Uncompahgre Uplift where a thick succession of alternating black, organic-rich shale and dolostone, evaporites, and quartz clastics were deposited. The basin shallows as a series of half grabens step up onto the more tectonically stable western and south-western carbonate shelf. Here, the periodically emergent shelf was marked by repetitive shoaling cycles of shallow marine carbonates, restricted marine carbonates and shales, and evaporites. Paleomagnetic and paleoclimatic data suggest that the Paradox basin was located approximately 15 to 20 degrees nort h latitude of the paleoequator during the Middle Pennsylvanian. This would infer that the Paradox basin would have been located in a subtropical, semi-arid to arid climatic belt.
As the Paradox basin subsided during Pennsylvanian time, sea level oscillated as a result of glaciation on the Gondwana supercontinent. Beginning in the early Permian, rapid subsidence of the basin ceased and marine waters withdrew to the west as continental shales and sands spread across the basin. Salt movement continued periodically into the Jurassic when major growth appears to have ceased. During Cretaceous time, the basin became a part of the Rocky Mountain geosyncline and was bordered on the west by uplifted and thrusted terrain in response to the Sevier Orogeny.
Much after the formation of the Paradox Basin, in mid- to late-Cretaceous time (~80MYA), North America was moving westward. This was a response to the opening of the Atlantic Ocean. This westward movement made the western continental margin a collisional margin. The orogenic belts along this margin were the sources of the siliciclastic sediments that were dropped eastward. Subsidence and the formation of many of the sedimentary basins throughout most of the western interior of North America occurred due to the loading of thrust sheets in the west.
At the same time, active spreading along the mid-Atlantic ridge displaced water out of the oceans. This water spilled onto the low-lying parts of the continents, including the North American western interior. These areas were flooded from the Arctic Ocean in the north, and the Gulf of Mexico in the south. Over time these waters mixed, forming a continuous seaway, the Western Interior seaway that covered the majority of the continental interior.
Regional uplift, volcanism, and erosion from Late Tertiary to the Present are responsible for the topography of the area.
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