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The Middle Devonian formations to be studied in this paper are the Jeffersonville and North Vernon Limestones. Together these formations make up the Muscatatuck Group in the Illinois Basin portion of Indiana. In the area of study, the Jeffersonville Limestone consists from the base upwards of the Geneva Dolomite Member, Vernon Fork Member, and Paraspirifer acuminatus Zone. The North Vernon Limestone consists of the Speed Member overlain by the Beechwood Member.In the study area, the subsurface Muscatatuck Group dips to the southwest at a rate of 20 to 50 feet per mile. These rocks thicken to the southwest, and range in thickness from 136 to 170 feet. Closed-structural highs are present on the top of the Muscatatuck Group over Silurian pinnacle-like reefs.Resistivity log - sonic log cross plots were constructed to analyze the subsurface carbonate facies in the study area. A total of 13 cross plots were constructed with over 1,490 points plotted.From this study five conclusions can be drawn about the application and usefulness of the cross plot method in analyzing the the surface distribution of carbonate facies. As explained in the text, these conclusions remain valid only when applied to the area of study.The conclusions are as follows:1. The positioning of the point groups on the cross plots is controlled by the amount and type of porosity present in the rocks.2. Due to the diagenetic alteration of the primary porosity in the rocks, the point groups can not be divided into depositional textures or facies.3. In this case, because of the uncomplex nature of the stratigraphy and the ease of correlation of the lithologic units on the logs, the cross plots were not useful in analyzing the subsurface distribution of the carbonate facies in the area.4. The cross plots were useful in checking the accuracy of the log correlations.5. The cross plots may be used to infer lateral porosity changes in the rock units, and possibly variations in the diagenetic alteration within these units.

M.Sc. / The Lower Devonian Bokkeveld Group is the Middle unit of the tripartite Cape Supergroup, which outcrops along the western, southern and eastern coastline of South Africa. A well-established sedimentary and stratigraphic understanding of the Bokkeveld Group allowed for geochemical and geochronological investigation in order to gain insight into the provenance characteristics, as well as the paleotectonic environment of the provenance areas. In order to observe any changes within the Bokkeveld Basin, complete profiles for geochemical investigation were sampled in the western, southern and eastern parts of the basin, and compared. Major and trace element patterns suggest that the western part of the basin received detrital input from felsic, magmatically evolved, and possibly alkaline sources, and that the sediment was highly recycled before deposition. Furthermore, the geochemistry suggests that the western part of the basin experienced “passive margin” type sedimentation. The geochemistry of the southern basin, in contrast, suggests input from less evolved, non-alkaline sources, and predicts sedimentation under “active margin” conditions for the lower part of the group. The eastern basin is geochemically intermediate between the western and southern basins. Zircon populations for the three parts of the basin further suggest that sources of different ages fed the three parts of the basin. The zircon population of the western basin suggests that the Namaqua Natal Belt (Mesoproterozoic) and Neoproterozoic cover successions were the major source of detritus, with only minor input from Paleozoic sources. The eastern basin also appears to have sourced mainly Namaquan aged material as well as Neoproterozoic material, with no Paleozoic input. The southern basin has a remarkably different zircon population, with the majority of grains being Paleozoic in age, and only a few Neoproterozoic and Mesoproterozoic grains. Furthermore, many of the grains are younger than any known source-rocks on the Kalahari Craton, and thus allude to input from an extra-Kalahari source into the southern part of the basin. The youngest grain from the southern basin overlaps with the established depositional age of the Bokkeveld Group, suggesting some syn-depositional or briefly pre-depositional magmatic activity in the source area(s) of the southern basin, as predicted by the geochemistry. The complete lack of zircon ages older than the Namaqua Natal Belt (Mesoproterozoic), would suggest that the Archean to Paleoproterozoic inner part of the Kalahari Craton, the Kaapvaal Craton, was not sourced by the Bokkeveld Group. This is most likely due to the Namaqua Natal Belt having served as a large east-west trending morphological divide during Bokkeveld deposition, preventing transport of detritus from the craton interior. Remarkably, this would suggest that the Namaqua Natal Mountain Range must have survived erosion and persisted as a morphological boundary for ca. 600 Ma to serve as the major source of detritus for the Bokkeveld Group. Even an extensive, craton-fringing sedimentary cover-succession such as the Bokkeveld Group, may thus not provide a “detrital fingerprint” of the craton interior, and paleogeographical implications must be taken into consideration during provenance studies. Paleocurrent directions for the Bokkeveld Group indicate a west to east transport direction in the southern part of the basin, and as such, a western, extra-Kalahari source, most likely the Rio de La Plata Craton and surrounds, is expected to have been the source of both the young Paleozoic zircons, as well as undifferentiated material as revealed in the geochemistry.

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