IRON AND SULFUR CONCENTRATIONS IN THE HUNTON GROUP, CENTRAL OKLAHOMA: ANALYZING THE RELATIONSHIP BETWEEN LITHOLOGY AND CHEMOSTRATIGRAPHY

The Hunton Group was deposited in a shallow epeiric sea that covered what is now parts of Oklahoma, the Texas Panhandle, and Kansas during the Late Ordovician, Silurian, and Early Devonian. A rich benthic fauna supports the interpretation that deposition of the Hunton Group occurred under oxic conditions. Understanding the Fe and S relationship provides additional insight into Hunton seawater geochemistry that was influenced by depositional setting and paleoproductivity. A continuous core that recovered more than 300 feet (>90%) of the Hunton Group from a single well in the Cleveland County, Oklahoma study area was analyzed with a portable X-ray fluorescence (XRF) instrument to determine the concentrations of selected elements. XRF elemental data, thin sections, and core slab photographs, in conjunction with wireline log curves, were used to establish the internal litho- and chemostratigraphy of the Hunton Group. While concentrations of redox-sensitive trace elements are very low across the entire section, different intervals of the Hunton Group have very different patterns of the abundance of sulfur and iron. These include concurrent increase and decrease in concentration of Fe and S, increased concentration of S while the concentration of Fe remains low, and increased Fe concentration while the concentration of S remains low. Patterns where Fe increases when S remain low could be the result of increasing iron-rich clay minerals such as chamosite (iron-rich chlorite) or iron-rich illite, whereas concurrent increasing Fe and S could be attributed to pyrite.