karst

karst 1, a photo by hallucygenia on Flickr.

A little light relief from our Guizhou fieldwork. We were driving downhill from Balang Village, after a visit to a possible Cambrian stratotype and one of the localities of the Kaili Biota (for the non-geologists reading this, some very important and serious rocks, which we looked at with due solemnity and reverence). We spotted this exposed in the side of the road and had to stop.

The white rock is limestone of Cambrian age (perhaps 500 million years old), and the red mud is filling in fissures created when the limestone became the land surface much more recently. To cut a long story short, if you rain on limestone, it dissolves and large fissures form. This would not have been a safe place to walk! I can't find any good information on when this dissolution would have happened, but it's probably within the last million years, thus falling into the realm of geography rather than geology.

The red mud filling in the fissures contained small bits of bone, but nothing recognisable.