Geomorphology and paleontology of Riverbluff Cave, Springfield, Missouri

Riverbluff Cave developed near the southern margin of the Springfield Plateau as a single passage between James River and its tributary, Ward Branch. Portions of the cave preserve a general fining-upward sediment sequence, but with highly fossiliferous gravel beds near the middle. These gravel beds include fragments of various vertebrates, including mammoth and horse. Trackways and claw marks are also preserved atop the sediment in numerous locations. Cosmogenic isotope data provide burial dates for some of the sediment layers and fossil remains. The earliest sediment (reverse magnetic polarity) entered the cave at approximately 1.1 Ma, while the fossiliferous gravel bed is dated at approximately 0.74 Ma. The overlying laminated silts and clays have normal polarity with a burial date of approximately 0.65 Ma at the base. Thus, the sediment sequence spans the Matuyama/Brunhes paleomagnetic datum, and records at least 450 ka of sedimentation within the cave.