Abstract The Chouteau Limestone is late Kinderhookian in age in Illinois and late Kinderhookian to Valmeyeran in Indiana (Rexroad and Scott, 1964). The Chouteau conformably overlies the Kinderhookian Hannibal Shale of the New Albany Group (Figures 7-1 and 2-12), except in southwestern Illinois where the Hannibal is absent and it overlies Devonian and older strata (Willman et al., 1975). In places, the lower part of the Chouteau grades laterally into upper beds of the Hannibal. The Chouteau is widespread in the basin and is generally less than 20 ft (6 m) thick. It is a carbonate mudstone and wackestone that is dolomitic and cherty in places and commonly wavy-bedded. The depositional extent of the Chouteau (Figure 8-9) coincides with the shelf-margin, slope and basin areas (Figure 8-5) of the New Albany deposition (Cluff et al., 1981). It coincides with the area of the overlying Borden delta and with the fringes of the Burlington-Keokuk carbonate bank. The Chouteau was probably deposited at a time when siliciclastic influx was minimal. With a minor unconformity, the Chouteau is overlain by a variety of lithofacies in the lower Valmeyeran Series, including Borden Siltstone in central and eastern Illinois and adjacent parts of Indiana, Burlington Limestone in western Illinois, Meppen or Fern Glen formations in southwestern Illinois, Springville Shale in southeastern Illinois, and New Providence Shale in Kentucky (Figure 9-1).

Configuration of the buried part of the Teays Valley system across western Ohio, Indiana, and eastern Illinois suggests that the Teays is not a preglacial system, but rather, that it was formed marginal to a major glacier earlier than that which created the Ohio River, probably in similar fashion by consolidating and diverting fragments of older drainages. Pertinent criteria include (1) the relatively straight gorge that (2) crosses at least three regionally high areas with (3) few tributaries that join at grade. Also significant are (4) the depth of the gorge across a broad limestone plateau that has (5) relatively shallow karst development. These features imply a youthful valley system that was destroyed by burial before reaching a mature stage. Although thousands of drillholes and seismic datum points in Indiana alone detail the bedrock surface and the nature of the unconsolidated deposits that overlie it, many questions remain regarding the evolution of that surface. Fluvial and lacustrine deposits associated with the earliest presently known till in Indiana (>0.8 Ma) fill eastern parts of the Teays gorge. Are there tills of pre-Teays age, and is any part of a pre-Teays valley system identifiable? What stratigraphic criteria distinguish those parts of the Teays that have been reoccupied and incorporated into younger, but now also buried, valley systems? The Blue River Strath of southern Indiana shares many characteristics with the type Teays and the ancestral Kentucky River valley and may be coeval with them; are there other such features? A regional approach to these and related questions should yield results.

Abstract: While coalbed methane (CBM) is a significant source of natural gas production globally, uncertainties regarding the proportions of biogenic and thermogenic natural gas in CBM reservoirs still remain. We integrate major gases, hydrocarbon composition, hydrocarbon stable isotopes and noble gases in fluids from 20 producing CBM wells to more accurately constrain the genetic source of natural gases in the eastern Illinois Basin, USA. Previous studies have indicated primarily biogenic production of methane (>99.6%) with negligible contributions from thermogenic natural gases. However, by integrating noble gases, we identify quantifiable (up to 19.2%) contributions of exogenous thermogenic gas in produced gases from the Seelyville and Springfield coal seams. Thermogenic gases are distinguished by a positive relationship between methane, ethane and helium-4, lower C 1 /C 2 +, heavier δ 13 C-CH 4 , more radiogenic noble gases ( 4 He, 21 Ne*, 40 Ar*), and lower abundances of atmospherically derived gases ( 20 Ne, 36 Ar). Biogenic gases displayed lighter δ 13 C-CH 4 , higher C 1 /C 2 +, higher levels of atmospheric gases and lower abundances of radiogenic noble gases. Our data suggest that natural gases from a deeper, exogenous thermogenic source likely migrated to the Pennsylvanian-aged coals at an unknown time and later mixed with biogenic methane diluting the geochemical signature of the thermogenic methane within the Springfield and Seelyville coal seams.

The Escuintla and La Democracia debris avalanches are the two largest debris avalanches so far identified in Guatemala, with respective volumes of 9–15 km 3 and 2.4–5 km 3 . Based upon their geographic locations on the Guatemalan coastal plain, both deposits have several possible source volcanoes. The Escuintla debris avalanche could have originated at either the Fuego or Acatenango volcanic complexes, or Agua volcano. Farther to the west, the La Democracia debris avalanche could only have come from the Fuego or Acatenango volcanic complexes. An apparent collapse scar on the east face of the Meseta edifice (the northernmost vent of the Fuego volcanic complex) has been attributed to the formation of the Escuintla debris avalanche. A mostly obscured summit collapse scar on Acatenango and an erosional remnant of a debris avalanche deposit near the base of the cone have been linked to the La Democracia debris avalanche. Petrographic and geochemical analyses of lava blocks collected from the Escuintla debris avalanche suggest that a substantial volume of amphibole-bearing dacitic lavas were present at its source volcano. Examination of rocks from the possible source volcanoes indicate that no dacitic lavas or tephras are known to have erupted from the Fuego volcanic complex and that the rocks exposed in the Meseta scarp bear little resemblance to the Escuintla debris avalanche samples. A few dacitic lavas and tephras are known from the Agua volcano, and several dacitic tephras have erupted from Acatenango. Geochemical comparisons of lavas and tephras from these volcanoes with rocks from the Escuintla debris avalanche showed greater similarities than those from Fuego and Meseta. Even though Acatenango is not known to have erupted dacitic lavas, its geochemistry is the most consistent with that of the Escuintla debris avalanche. Lava blocks from the La Democracia debris avalanche are mostly basaltic, although one andesitic sample contains phenocrystic amphibole. Geochemical analyses of Fuego and Meseta lavas overlap with the La Democracia debris avalanche samples; however, no amphibole-bearing rocks are known from Meseta, and Fuego is presumed to be younger than the La Democracia debris avalanche. Compared to the Acatenango rocks, the geochemistry and mineralogy of the La Democracia debris avalanche are quite similar. Furthermore, rocks from the debris avalanche deposit on the flank of Acatenango are also consistent with the chemistry of the La Democracia debris avalanche. Thus, Acatenango produced at least one debris avalanche, the La Democracia debris avalanche, and possibly also generated the Escuintla debris avalanche.