EXPLORING CLASTIC CAVE SEDIMENTATION IN AN OZARK CAVE USING PALEOMAGNETISM

Stable isotope and, more recently, magnetic susceptibility analyses of chemical and clastic sediments in caves provide robust, long-term (e.g., millions of years) proxy records for paleoclimate reconstructions. In the Ozarks of Arkansas and Missouri, caves commonly contain clastic sediments ranging from chert and limestone cobbles to fine-grained material, such as insoluble clays. Mineral magnetism techniques were applied to cave sediments to answer broad questions about the mineralogy, magnetic properties, and age of clastic sediments from Blowing Springs Cave in northwestern Arkansas, thereby contributing to mineral magnetism data in the Ozarks. The cave includes approximately 2,300 m of passage developed in Mississippian limestone and laminated clastic sediments can be found throughout the cave, with deposits ranging in thickness from <1 m to ~3 m. In 2013, three fully oriented U-channel sediment cores (1 to 1.5 m long) were collected from two sites in Blowing Springs Cave. The natural remanent magnetization of the sediment cores was measured at the University of Minnesota’s Institute for Rock Magnetism using a 2G Enterprises superconducting rock magnetometer, and several laboratory-induced magnetizations were imparted and demagnetized (ARM and IRM). Approximately 5-cm interval sub-samples were collected from the cores for hysteresis measurements and low-temperature magnetometry. No paleomagnetic reversals were found in the Blowing Spring Cave sediment, but inclination and declination of magnetic minerals (magnetite and goethite) varied with depth, providing evidence that the minerals have recorded geomagnetic secular variation. Future plans included analysis of stable isotopes of carbon, which will facilitate using radiocarbon dating to better constrain the age of the cores and enable construction of local and regional geomagnetic stratigraphy.