Speleothems (stalagmites, stalactites, and other cave deposits) represent an exciting but previously under-utilised palaeoclimate proxy. Not only are mean annual temperature, rainfall, and surface vegetation data recorded in successive layers of actively growing speleothems, often with annual to seasonal resolution, but they also reside below the Earth’s surface, within a stable environment, and so may remain remarkably well-preserved for many millions of years. In the past few years, we have developed methodologies for the chronology of speleothems using the U-Pb decay scheme which now extends their utility as palaeoclimate archives back beyond the range of U-series analysis, into deep Earth history. These techniques open up a wealth of new possibilities and have much to contribute to studies of global climate change, biodiversity and human evolution

see, for example:

Woodhead, J., Reisz, R., Fox, D., Drysdale, R., Hellstrom, J., Maas, R., Cheng, H & Edwards, R.L. (2010) Speleothem climate records from deep time? Exploring the potential with an example from the Permian. Geology, 38, 455-458. Free download: http://geology.geoscienceworld.org/cgi/content/full/38/5/455?ijkey=8pB/327zNyXIk&keytype=ref&siteid=gsgeology

Dirks, P.H.G.M., Kibii, J.M., Kuhn, B.F., Steininger, C., Churchill, S.E., Kramers, J.D., Pickering, R., Farber, D.L., Meriaux, A-S., Herries, A.I.R., King, G.C.P. & Berger, L.R. (2010) Geological setting and age of Australopithecus sediba from Southern Africa. Science 328, 205-208.