Possible earthquakes recorded in stalagmites from a cave in south-central Indiana

The stalagmites collected from Donnehue’s Cave, south-central Indiana, may record seismic events near the Wabash Valley fault system located in the midwestern United States. Results of uranium–thorium disequilibrium dating of four stalagmites showing pronounced shifts in their central growth axes, episodes of growth initiation/cessation, and results of optically stimulated luminescence (OSL) dating of flood deposits within the cave reveal both the possibilities and problems associated with using stalagmites as indicators of seismic events. The first of a set of twin stalagmites, initiated about 300,000 yr B.P., recorded a major flood event (correlated with an OSL dated flood deposit) at about 246,000 yr B.P. as a central growth-axis shift and stopped growing at about 170,000 yr B.P. Other shifts present within this stalagmite contained embedded fine sediments associated with flooding. Its twin began growing at about 170,000 yr B.P., contained no shifts, and stopped growing at about 100,000 yr B.P. Both stalagmites resumed growing at about 6000 yr B.P. that overlaps in time, within sampling and analytical error, with an M_w 7.1–7.3 event recorded by liquefaction features dated, by others, at 6100 200 yr B.P. Another stalagmite began growing at about 55,000 yr B.P. and recorded multiple central growthaxis shifts showing dissolution and fine sediment layers associated with flood events within the cave. The third and youngest stalagmite contained no evidence of flooding and was initiated about 1800 yr B.P. (the same time, within error, as an M_w 6.2 seismic event recorded in the Wabash Valley sediments). This stalagmite had shifts in its central growth axis that occurred at the same time (within statistical error) as New Madrid seismic zone events at A.D. 660 and 900, and contained a shifted regrowth layer that may be coincident with either the A.D. 1811–1812 series or the A.D. 1895 event.