Kansas Geological Survey, Open-file Report 1999-35
by
Nathan Allan Geier
KGS Open-file Report 1999-35
Submitted to the Department of Geology and the Faculty of the Graduate School of the University of Kansas in partial fulfillment of the requirements for the degree of Master of Science
The Humboldt Fault zone defines the eastern edge of the Nemaha uplift. The Humboldt Fault zone/Nemaha uplift system is the most structurally complex geologic feature of Kansas. This northeast-trending, regionally linear feature can be traced across the entire state. Seismic and drill data suggest a complex set of high-angle reverse and normal faults that posses over 600 m of cumulative displacement of the Precambrian granitic basement. In northeastern Kansas, the uplift separates the Salina basin-Forest City basin.
An integrated geophysical survey was conducted in northern Wabaunsee and southern Riley counties, Kansas to gain a better understanding of the structural nature and geological history of the Humboldt Fault zone/Nemaha uplift system. A high resolution seismic profile, a magnetic profile, and gravity profile traversed the uplifts and bounding fault zones.
Seismic data defined two major phases of faulting on the Humboldt Fault zone. A compressional stress regime resulted in high angle reverse faults with large offset (up to 300 m on a single fault) in Late Devonian-Early Pennsylvanian time. Smaller-scale <50 m) normal faulting occurred after deposition of the Shawnee group (Virgilian stage) requiring either a shift to an extensional stress regime or relaxation of the previous compressional stress environment. A reversal in fault movement from reverse in pre-Pennsylvanian sedimentary rocks to normal faulting in Pennsylvanian aged sedimentary rocks suggests most normal faults occurred along preexisting joints or small-scale reverse faults that formed during the compressional phase.
Eleven kilometers west of the Humboldt Fault zone and bounding the western edge of the Nemaha uplift is the newly interpreted Zeandale Fault zone. Cmnulative offset across this fault zone is in excess of 300 m. Two episodes of faulting are interpreted that appear to coincide with the two phases of faulting interpreted on the Humboldt Fault zone. All faulting in this fault zone is interpreted to be normal, however. Based on drill, seismic, magnetic, and gravity data, the Zeandale Fault zone is a localized feature roughly 15 km in total length and subparallel to the Humboldt Fault zone.
Kansas Geological Survey
Placed online May 30, 2019
Comments to webadmin@kgs.ku.edu
The URL for this page is http://www.kgs.ku.edu/Publications/OFR/1999/OFR99_35/index.html