RESTLESS KANSAS: EVIDENCE OF STRUCTURAL DEVELOPMENT IN THE FLATLANDS

The structural development of Kansas is recorded by stratigraphic and sedimentological evidence. A major change in the structural regimen of Kansas took place in the late Paleozoic as a result of events in adjacent areas. The structural development was mainly by vertical differential movement of rigid Precambrian basement blocks along faults as they adjusted to the stress. These movements are recorded in the changes of sediment thickness on and off plains-type folds (small anticlines formed by draping and compaction of younger sediments over the fault blocks). Concurrently, as the basement blocks adjusted, seismites were formed by paleoearthquakes; by mapping their occurrence vertically and laterally, some conclusions can be made on their intensity and frequency. The paleoquakes seemingly occur less frequently with time, but this may be a function of suitable conditions for their formation and preservation. Some sedimentary convolute structures and small intraformational faults occur in the Cretaceous. Paleoliquefaction features also have been reported in Holocene sediments in Edwards, Wabaunsee, and Woodson counties, Kansas. Historical earthquakes and microseisms are evidence that the structural movement is continuing today. The major disturbances, for the most part, occur along the Nemaha Anticline and east-bounding Humboldt Fault Zone. From the evidence then, it is inferred that the structural development of Kansas is not and was not spectacular, but was continuous and intermittent.