COMPARATIVE ELEMENTAL GEOCHEMISTRY OF THE ARKANSAS NOVACULITE (DEVONIAN-LOWER MISSISSIPPIAN) AND BOONE CHERT (LOWER MISSISSIPPIAN), PALEOZOIC AREA, ARKANSAS

The Arkansas Novaculite (Devonian-Lower Mississippian) and Boone Formation penecontemporaneous chert (Lower Mississippian) are both undersaturated in REEs compared to igneous bodies. Generally low trace element concentrations and REEs likely reflect lack of a clay component for both lithologies. Most of the REEs present in siliceous deposits occur within silt and clay, while quartz REE concentrations are usually very low. Trace element and REE concentrations found in the Arkansas Novaculite compare favorably with volcanically sourced chert of the Nicoya Complex, Costa Rica (Hein et al., 1983). Average Nicoya Complex values: Co (3.38), La (15.8), Be (1.14), Cr (15.1), and Pb (8.1) are similar to those for the Arkansas Novaculite: Co (4.62), La (9.09), Be (3.08), Cr (16.26), and Pb (11.36).

Elevated levels of Al, and to a lesser extent Fe, Na and K, suggest that a source inherently rich in these elements produced the siliceous sediment comprising both novaculite and chert. Analysis of early chert diagenesis and chemical fractionation indicates that Al, Fe and REEs are immobile into or out of a crystalline silicate framework, so these two elements, as well as K, indicate a volcanic source (Murray, 1994; Hein et al.,1981).

Geochemistry of primary siliceous deposits preserved as the Arkansas Novaculite and Boone Formation indicates that the Novaculite is more enriched in trace elements and REEs. This enrichment suggests that a biologic contributor may have diluted trace element and REE concentrations preserved in the Boone chert. The ramp setting producing the Boone Formation would have had a much higher biologic contribution reflecting its proximity to the Burlington Shelf, in contrast to the sediment starved, pelagic setting of the Arkansas Novaculite. However, Al and K concentrations, indicators of a volcanic source, are aligned. General trends of the normalized data (consistent values across the suite of elements, except the relative enrichment in uranium and lead, and depletion of nickel relative to the other elements analyzed), are consistent for both formations. These relationships support the conclusion that the Arkansas Novaculite and the penecontemporaneous chert of the Boone Formation represent primary silica sedimentation from a similar volcanic source.