No abstract

Tree stumps of arborescent lycopods were discovered in situ at the contact of the Herrin (No. 6)

Longwall underground coal mining produces major changes in the hydraulic properties and groundwater levels of overlying shallow aquifers because of the fracturing associated with mine subsidence. Many aspects of these impacts remain unclear and unpredictable, particularly the variations in response between different sites. Our detailed, long-term studies of subsidence strains and hydraulic responses at sites in Illinois address this and other aspects of the conceptual model. At a study site in Saline County, inconsistent permeability changes and large rapid head drops, without significant recovery, were observed in a low transmissivity sandstone over an active longwall panel. Corresponding head changes in overlying glacial drift units reflected localized drainage from the drift to the bedrock. In comparison to our earlier study at a site in Jefferson County, Illinois, in which full recovery occurred in a moderately transmissive sandstone aquifer affected by longwall mining, the Saline site illustrates the importance of local hydrogeologic characteristics, particularly variations in transmisivity and continuity with recharge sources, in controlling site-specific responses to longwall mining.

Long coal ball formed on a single plant axis 13 Concentrated coal balls near the center of coal-ball area L 14 Exterior and cut faces of two transported coal balls I 15 Mixed coal ball from Old Ben Mine No. 27 1 Permineralized plant fragments in a clastic matrix 17 Concretion formed on channel-fill materials 18 Coal balls, coal-ball areas, and roof lithologies in the northern half of mapped area A 19 Coal balls, roof lithologies, and erosional channels in the southwest part of mapped area A 20 Coal balls, roof lithologies, and erosional channels in Old Ben Mine No. 27 21 Diagram of generalized coal-ball distribution within coal-ball areas 21 22 Adjustments made to the second longwall panel during mining 21 23 Relationship of type II coal balls to an erosional channel 24 Detail of several coal-ball zones from vertical section 3 within area L 25 Coal-ball area L and selected sample sites. Detail from mapped area A 26 Elements reported in this study and those of some potential environmental concern 27 Relationship between percentage of MgO and relative peak height of dolomite 28 Relationship between percent sulfur and relative peak height of pyrite 29 Relationship between pyrite and relative peak heights of dolomite 30 Frequency distribution of the La/Lu ratio for coal balls and associated materials 31 Stable carbon and oxygen isotope values for coal balls and associated units 32 Schematic block diagrams showing events leading to the formation of coal balls 33 Transitional roof areas near Franklin County 34 Distribution of coal balls in the Upper Foot and Gannister Coals in England 35 Coal-ball locations in Clarkson Mine 36 Bioturbation trace surrounded by coal from the top of the Herrin Coal