ISGS Seminar Series: Characterization of Karst Terrain Using Remotely-Sensed Data in Jo Daviess County, Illinois
Approximately one-quarter of the bedrock surface area of Illinois is comprised of carbonate rock, and more than one-third of this amount is concentrated within the state’s five major karst regions, which includes the Driftless Area of northwestern Illinois. Characteristic features of karst terrain include sinkholes, caves, large springs, fluted rock outcrops, blind valleys, swallow holes, and solution-enlarged crevices. Because carbonate bedrock within the Driftless Area in Illinois mantled by unconsolidated deposits, direct observation of fractures and crevices has historically been limited to sparse occurrences of road cuts, quarries, and outcrops where bedrock is exposed at the ground surface.
An unforeseen outcome of the 2012 Midwest severe summer drought was that it provided a rare opportunity to indirectly examine the buried bedrock surface of the Driftless Area. Complex vegetated networks, referred to as “crop lines”, began to appear across the dry summer landscape of Jo Daviess County in northwestern Illinois. Primarily confined to alfalfa hay fields, the vegetated crop lines resulted from a combination of three factors: 1) persistent, extremely dry conditions; 2) a relatively thin soil zone and associated unconsolidated deposits 0.5 to 2 meters in thickness; overlying, 3) highly fractured and creviced carbonate bedrock comprised of Upper Ordovician (443–460 Ma) Galena Dolomite. Analysis of multidate aerial photography acquired over Jo Daviess County during the 2012 summer and early fall period identified nearly 18,000 vegetated crop lines. The crop line features were digitized, and a rose diagram created of the features reveals a dominant west–northwest orientation with an average azimuth of 275°. The azimuth of the subdominant trend is nearly north-south in orientation.
Past studies have determined that the bedrock fractures within Jo Daviess County are oriented west–northwest with an average azimuth of 275 degrees, and the subdominant fractures are oriented nearly north-south—consistent with the analysis of the vegetated crop lines. Overall these trends are consistent with bedrock fracture orientations observed in adjacent areas of Illinois, Indiana, and Wisconsin. Published field and laboratory results suggest that regional fracture systems form parallel to maximum compressive stress trajectories, making fracture orientations highly sensitive indicators of paleostress fields. We speculate that the dominant west-northwest fracture system formed in response to the late Paleozoic Alleghenian Orogeny. Origin of the subdominant north-south fractures is not entirely clear, but possibly could have formed in response to compressive stress associated with current rifting along the mid-Atlantic ridge.
Complementing the vegetated crop line data, LiDAR bare earth elevation data revealed alignments in areas of late 19th and early 20th century lead and zinc mine diggings, and within cover-collapse sinkholes developed in Silurian (412–443 Ma) dolomite which have very nearly the same dominant trends as the vegetated crop lines. The orientations of the crop lines, mine diggings and sinkhole alignments follow trends that are directly observed in solution-enlarged crevices exposed in outcrops, road cuts and quarries, and are convincing evidence that the vegetated crop lines can be used as surrogates for the known bedrock fractures of the Galena Dolomite within the Driftless Area.
Samuel Panno Education:Southern Illinois University, Geology, M.S., 1978. Sam is a Senior Geochemist and has been with the Illinois State Geological Survey since 1988. Currently, Mr. Panno is leading research on the geology, hydrogeology and groundwater quality of karst regions of Illinois, the location, significance and origins of saline springs throughout the Illinois Basin, the origin and evolution of Illinois Basin brines, and the use of speleothems in identifying paleoearthquakes in the Midwestern US.
Donald Luman Education:University of Illinois at Urbana-Champaign, Geography, Ph.D., 1978. Following a university teaching career of 20 years in Illinois, Don joined the Illinois Natural History Survey in 1993 and later the Illinois State Geological Survey in 1995. He retired earlier this year as a Principal Geologist. During his academic and Survey careers, Don’s primary teaching and research has been focused on the applications of remote sensing technology to natural resource applications.
Dennis Kolata Education: University of Illinois at Urbana-Champaign, Geology, Ph.D., 1973. Following a year of employment as a petroleum geologist with Texaco, Inc., Dennis joined the Illinois State Geological Survey in 1974. The primary focus of his work was on the stratigraphy and structural geology of Illinois. Following his retirement in 2004, he has been active as a geologic consultant to natural resource industries, and currently has been mapping the bedrock geology in Lee and Ogle Counties, Illinois as part of the USGS STATEMAP program.