CHARACTERIZING PALEO ENVIRONMENTS AND DIAGENETIC PROCESSES IN THE OSAGE RIVER BASIN, USING GEOCHEMICAL DATA AND WELL LOGS

Paleo environment conditions and diagenetic processes alter and modify lithofacies in sedimentary environment. In this study well logs and geochemical data was analyzed to characterize the lithofacies in the center of the Osage River Basin located in western Vernon County, Missouri. Data was obtained from 10 wells that ranged in depth from 435 to 800 feet. The log data analyzed included Gamma ray (GR), Photoelectric (PE), density (RHOB), XRF and the XRD curves. The objective is to describe and characterize paleo environments and diagenetic process. Analysis shows that lithology consists of Sandstone, Limestone, Shale and thin interbedded Coal beds. Each lithological layer has its own unique value on the log curves that help us identify them. Using data values obtained from the logs and geochemical analysis, we are able to correlate key elemental content of formations and use the information to interpret the setting in which the rocks were deposited. For example, in Stoner well 14-6D traces of pyrite were found using the XRF analysis suggest the rocks were formed in an anoxic shallow marine environment due to the presence of reactive iron minerals which are believed to aid in the process of the formation of pyrite. Elevated pyrite content creates a large spike on the log where coal beds are identified, this can be an indicator of coalbeds in these settings. Although pyrite also occurs in formations where shale is present, it is not as elevated as in the coal layers. Elements such as iron, sulfur and phosphorus allow us to get a better understanding of the conditions under which they were deposited. A cross section correlation shows a cyclic pattern within the interval studied with repeating coal beds. This indicates an area where sea regression and transgression may have played a key role in the deposition of the layers. The presence of thin layers of coal suggest that the sea level remained the same for a period of time, allowing organic material to accumulate before the next transgression of the sea. Further interpretation of data from well logs and geochemical analysis can allow us to make assessments of the conditions that existed when the coal bed, shales, sandstones and carbonates were deposited during the middle of this Pennsylvanian time period.