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Brief Report for Fluorspar Area fault complex, Lusk Creek fault zone (Class A) No. 1028e
Partial Report ||Complete Report
Compiled in cooperation with the Illinois State Geological Survey
citation for this record: Nelson, W.John, and Nelson, W.John, compilers, 1999, Fault number 1028e, Fluorspar Area fault complex, Lusk Creek fault zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/regional/qfaults, accessed 11/24/2009 05:58 AM.
| Synopsis | General: In most of the area of the Fluorspar Area fault complex, thin and patchy Quaternary sediments overlie Paleozoic bedrock, and the time of faulting is known only to be post-Pennsylvanian. Younger movement comes to light where the faults pass southwestward into thicker Cretaceous, Tertiary, and Quaternary deposits of the Mississippi Embayment. Mapping in southernmost Illinois, Ross (1963 #3893; 1964 #3894) interpreted Tertiary and possible Quaternary displacements on some faults of the complex. However, Kolata and others (1981 #3886), reviewing the evidence, concluded that no post-Cretaceous tectonism could be demonstrated. Tertiary and Quaternary activity in the Fluorspar Area fault complex finally was documented through detailed geologic mapping combined with test drilling, high-resolution seismic surveys, and trenching (Nelson and others, 1997 #3888; 1999 #3889; 1999 #3918). In Kentucky, geologic quadrangle maps depict faults of the Fluorspar Area fault complex displacing the Mounds Gravel, which is of late Miocene to early Pleistocene age (Amos and Wolfe, 1966 #3882; Amos, 1967 #3880; 1974 #3881). Together, these studies reveal multiple episodes of post-Cretaceous tectonic activity in the Fluorspar Area fault complex. Narrow NE- to NNE-trending grabens that contain Tertiary and Pleistocene (Illinoian and older) sediments are characteristic. Several grabens show more than 30 m of dip-slip offset on Pleistocene units; in one case the throw may exceed 150 m. Deformation of Wisconsinan sediments is localized and small, less than 3 m. No Holocene movement has been detected.
Nelson and others (1999 #3889) demonstrated Quaternary faulting at seven sites on six fault sections within this fault complex. The lengths of Quaternary ruptures are unknown. Average strikes are given for each section, where available. The sections described here are parallel, independent faults, instead of adjoining sections of the single, contiguous fault. Sections: This fault has 6 sections. |
| County(s) and State(s) | |
| AMS sheet(s) | Paducah |
| Physiographic province(s) | |
| Length (km) | This section is 0 km of a total fault length of 0 km. |
| Average strike | (for section) versus (for whole fault) |
| Sense of movement | Normal |
| Dip Direction | SE; NW |
| Historic earthquake | |
| Most recent prehistoric deformation | Middle and late Quaternary (<750 ka) |
| Slip-rate category | Less than 0.2 mm/yr |
| Date and Compiler(s) | 1999 W. John Nelson, Illinois State Geological Survey |
