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#           Late Oligocene to present contractional structure in and around the Susitna basin, Alaska—Geophysical evidence and geological implications      

      October 1, 2016    

The Cenozoic Susitna basin lies within an enigmatic lowland surrounded by the Central Alaska Range, Western Alaska Range (including the Tordrillo Mountains), and Talkeetna Mountains in south-central Alaska. Some previous interpretations show normal faults as the defining structures of the basin (e.g., Kirschner, 1994). However, analysis of new and existing geophysical data shows predominantly (Late Oligocene to present) thrust and reverse fault geometries in the region, as previously proposed by Hackett (1978). A key example is the Beluga Mountain fault where a 50-mGal gravity gradient, caused by the density transition from the igneous bedrock of Beluga Mountain to the >4-km-thick Cenozoic sedimentary section of Susitna basin, spans a horizontal distance of ∼40 km and straddles the topographic front. The location and shape of the gravity gradient preclude a normal fault geometry; instead, it is best explained by a southwest-dipping thrust fault, with its leading edge located several kilometers to the northeast of the mountain front, concealed beneath the shallow glacial and fluvial cover deposits. Similar contractional fault relationships are observed for other basin-bounding and regional faults as well. Contractional structures are consistent with a regional shortening strain field inferred from differential offsets on the Denali and Castle Mountain right-lateral strike-slip fault systems.

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#### Richard G Stanley

##### Scientist Emeritus

Geology, Minerals, Energy, and Geophysics Science Center

rstanley@usgs.gov

650-329-4918

#### Peter J Haeussler, Ph.D.

##### Research Geologist

Alaska Science Center

pheuslr@usgs.gov

907-786-7447

#### Jamey Jones

##### Acting Earth MRI Coordinator and Associate Center Director for Geology

Alaska Science Center

jvjones@usgs.gov

907-786-7442

####             Chris Potter (Former Employee)          

##### Research Geologist

Central Energy Resources Science Center

#### Kristen Lewis, PhD

##### Supervisory Geophysicist/USGS Geomagnetism Program Group Leader

Geomagnetism Program

klewis@usgs.gov

303-273-8471

## Related Content

#### Richard G Stanley

##### Scientist Emeritus

Geology, Minerals, Energy, and Geophysics Science Center

rstanley@usgs.gov

650-329-4918

#### Peter J Haeussler, Ph.D.

##### Research Geologist

Alaska Science Center

pheuslr@usgs.gov

907-786-7447

#### Jamey Jones

##### Acting Earth MRI Coordinator and Associate Center Director for Geology

Alaska Science Center

jvjones@usgs.gov

907-786-7442

####             Chris Potter (Former Employee)          

##### Research Geologist

Central Energy Resources Science Center

#### Kristen Lewis, PhD

##### Supervisory Geophysicist/USGS Geomagnetism Program Group Leader

Geomagnetism Program

klewis@usgs.gov

303-273-8471

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