Paradox Basin

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Coordinates: 37 ° 52 ′ 0 ″  N , 109 ° 10 ′ 0 ″  W.

Location of the Paradox Basin in the Colorado Plateau (outline in yellow) - recording altitude about 1500 km above ground

The Paradox Basin is an asymmetric foreland basin , predominantly in the southeast of the US state of Utah is located, but also in southwestern Colorado , northwestern New Mexico and the extreme northeast Arizona overlaps. This approximately 40,000 square kilometers large sedimentary basin was formed during the late Paleozoic Era ; the basin-forming processes were active from the Upper Carboniferous to the end of the Permian .

In contrast to the other sedimentary basins in the Rocky Mountains , the Paradox Basin is largely made up of evaporites . The sediments were deposited in alternating shallow water / deep water cycles. Because of the mighty salt sequences, salt tectonics ( rock salt is plastically deformable even at relatively low temperatures) plays a major role in the structural deformations that began after the Pennsylvania period .

stratigraphy

The Paradox Basin contains the following sedimentary sequence (from young to old):

The following rock units can be found in the subsurface of the actual Paradox Basin:

The Pinkerton Trail Formation, Paradox Formation and Honaker Trail Formation are combined to form the Hermosa Group .

Powers

The pre-carbonic deposits show a clear asymmetry in their thicknesses . In the southeast of the Paradox Basin they only reach 180 meters, in the northwest, however, up to 750 meters.

During the actual basin formation, over 6,700 meters of sediment accumulated from the Mississippian to the Lower Permian .

With a thickness of 1,800 to 2,100 meters, the Paradox Formation is undoubtedly the most significant. It is made up of 33 salt cycles - thick rock salt layers, which are interrupted by intermediate layers of anhydrites , silty dolomites and black, carbon-rich shale . The rock salt layers show thickness fluctuations from 7 to 270 meters and can contain sylvin .

The Triassic and Jurassic sediments together reach a maximum thickness of 1450 meters in the area of ​​the Book Cliffs , but only about 750 meters in the center of the basin.

From the later Tertiary ( Oligocene ), erosion prevailed in the basin area , and existing chalk and tertiary sediments were removed again. Preserved chalk sediments in neighboring sedimentation areas are up to 1850 meters thick, while early tertiary sediments and volcanic rocks there reach more than 750 meters. Given a comparable formation of the sediments in the Paradox Basin (which can be assumed), at least 2600 meters of erosion can be assumed.

Sedimentary development

With the onset of sedimentation of the Paradox Formation in the Upper Carboniferous before about 310 million years ago there was a very strong reduction of the Paradox Basin. Subsidence continued unabated during the deposition of the Cutler Formation, but slowed down after the end of the Lower Permian. Towards the end of the Permian all subsidence movements had come to a standstill. It transgredierten then Mesozoic cover layers over the basin of time. From the beginning of the Upper Cretaceous the surface layers were again subject to a strong subsidence, which lasted into the Maastrichtian (period 100-70 million years before today). For around 35 million years (Oligocene), the sedimentation area of ​​the Paradox Basin has undergone a steady uplift in connection with the Laramic mountain formation , the minimum amount of which is around 2000 meters.

structure

The Paradox Basin has a very asymmetrical cross-section; its deepest point is in the immediate vicinity of the Uncompahgre Plateau , a Precambrian basement block raised by steep, generally south-east-north-west trending thrusts . On the surface it has an elliptical shape, in its main direction of extent SE-NW it reaches 305 kilometers, in NE-SW direction only about 150 kilometers. The basin is girdled by various structural high areas: the previously mentioned, tectonically steeply pressed Uncompahgre Plateau in the northeast and the adjoining San Juan Dome in the southeast, as well as several relatively shallow basement bulges of laramic origin, such as the San Rafael Swell in the northwest, the Circle Cliffs Uplift in the west, Monument Upwarp in the southwest and the Defiance Uplift in the south. To the southeast, it goes over the high Four Corners Platform into the subsequent San Juan Basin . The transition to the Black Mesa Basin to the south is via the Tyende Saddle . In the north it borders directly on the Uinta basin . In the southwest, the White Canyon Slope provides the transition to the Henry Basin .

The Paradox Basin can be broken down as follows:

Furthermore, there are some structural areas that are no longer included in the actual Paradox basin:

The very deep basin area of ​​the Paradox Fold and Fault Belt is in the immediate vicinity of the Uncompahgre Uplift . It is crossed by four larger anticline trains in a SE-NW direction, two of these trains are underlain by "salt walls" of the Paradox formation. The blanding basin, on the other hand, is a much more undisturbed, shallow sub-basin. Most of the oil production comes from here.

Natural resources

Important mineral resources found in the Paradox Basin are petroleum , uranium , copper and potash salts .

Most of the oil production comes from porous carbonate accumulations in the Upper Carboniferous, such as algae mats. Additional oil reservoirs are tied to structural and stratigraphic oil traps (e.g. clumps raised by faults and discontinuous clastic layers). Main storage horizons are the Lower Carboniferous Leadville Limestone , the Upper Carboniferous Hermosa Group, and the Permian Cutler Formation .

In 2016 it became known that in the 1960s oil exploration drilling in the Paradox Basin had already encountered high- salt deep groundwater ( brine ) from which, according to analyzes at the time, up to 1700 mg / l of pure lithium could be obtained.

See also

Individual evidence

  1. ^ Stratigraphy of the Colorado River Basin
  2. ↑ Stratigraphy of the Hermosa Group ( Memento of the original from July 23, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , PDF file. @1@ 2Template: Webachiv / IABot / etd.lsu.edu
  3. ^ Stephan Bogner: Prima Diamond Corp. acquires the Green Energy project in Utah with historical lithium contents of 1700 mg / L. Rockstone Research, February 18, 2015 ( PDF )

swell

Baldridge, WS (2004) Geology of the American Southwest. Cambridge University Press. ISBN 0-521-01666-5

Web links