Subsurface geometry and petrography of rock units between the Beech Creek ('Barlow') limestone (Pope Group) and the Springfield coal (Carbondale Formation) across part of the La Salle anticlinorium, Lawrence County, Illinois

The subsurface geometry and petrography of rock units between the Beech Creek ("Barlow") Limestone (Pope Group) and the Springfield Coal (Carbondale Formation) were studied within a 168 mi{dollar}sp2{dollar} (273 km{dollar}sp2){dollar} area of Lawrence County, Illinois in order to determine the effect of structural movements of part of the north-northwest trending La Salle anticlinorium upon the deposition, distribution, and deformation of Carboniferous rock units.; Geophysical logs from 720 oil and gas wells were used to construct a grid of 28 preliminary cross sections having a mean borehole spacing of 2,138 feet (652 m). A series of detailed cross sections having a mean borehole spacing of 1,232 feet (375 m) was also constructed to correlate and determine the shape of discontinuous and variably thick sandstone bodies. Both sets of cross sections were used to produce isopach maps of the thicker sandstones within the Caseyville and Tradewater Formations.; Drill cuttings from 30 boreholes representing more than 12,300 feet (3,649 m) of stratigraphic section were described by binocular microscope to determine the mineralogy, grain size, and other petrographic aspects of sandstones and shales represented on geophysical logs. Point counts of three sandstone samples were obtained to determine the sandstone mineralogy. Statistical tests were conducted to determine possible associations between color, the presence or absence of carbonaceous matter, mica (muscovite), and fissility of shales.; Detailed cross sections indicate that four sandstone units between the Glen Dean Limestone (Pope Group) and the Colchester Coal (Carbondale Formation) have a unique distribution and thickness pattern that record distinct episodes of uplift and erosion of the La Salle Anticlinorium and its asymmetric western limb, the Charleston monocline. The initial uplift of the northeastern part of the study area began after deposition of the Glen Dean Limestone and prior to or during deposition of "sandstone A," a conglomeratic sandstone unit that unconformably overlies the Glen Dean Limestone. Sandstone A can be interpreted as either the basal part of the Caseyville Formation or the laterally equivalent Tar Springs Sandstone (Pope Group). Subsequent differential erosion and faulting along the margins of the uplifted area governed depositional patterns of Caseyville and Tradewater strata.