ABSTRACT The St. Joe group (Lower Mississippian, Tournaisian) is petrographically and isotopically analyzed using δ 13 C and δ 18 O bulk sample stable isotopes in central, northeastern Oklahoma, and southwestern Missouri. Determined to be conformable in Oklahoma, this group represents deposition in the mid- to outer-ramp setting during one long-term depositional cycle and can be used as a reference section for geochemical chronostratigraphy. Minor diagenetic alteration did not overprint the initial isotope signal, and the resulting curve is similar to those from previous studies and is integrated with published conodont biostratigraphy. The resulting correlation indicates that the St. Joe group was deposited in the upper Tournaisian Stage.

Abstract The gamma-gamma density log measures formation electron density and, through tool calibration, converts the measurement to limestone bulk density. Lane-Wells Company marketed the first commercial density tool in the mid 1950s. The density log, originally developed to aid in surface gravity data interpretation, has evolved as an independent log analysis device which provides another indirect means to measure porosity. The second-generation tool employs a two-detector system that compensates for near-borehole problems, while the third-generation tool includes a measurement that aids in determining formation chemical composition or lithology and allows a better porosity determination from the bulk density measurement. The gamma-gamma density tool uses a chemical source to bombard the formation with gamma rays (Figure 8-1). A detector at a fixed distance from the source measures the remnant gamma-ray cloud. The interaction of gamma rays with the formation atoms can take one of three forms depending on the energy level of the incident gamma-ray photons. At low energy levels, below about 100 keV or 0.1 MeV, the gamma-ray photon, incident on an atom, will produce a photoelectron (Figure 8-2). The interaction depends on the number of electrons-atom or the atomic number (Z). The atomic number reflects the chemical composition of the atom and thus the photoelectron effect is a lithology indicator. At higher energy levels, from 0.075 to 2 MeV, the interaction is predominately by Compton scattering (Figure 8-3), the ejection of a Compton recoil electron and an “incident” gamma ray of slightly lower energy. Incident gamma-ray attrition