In central Borneo there is this huge cave, I mean like the second biggest in the world and, in my, opinion the smelliest one. As you walk in, there are long, narrow shelf like structures, attached to the side of a cave, suitable as steps for a leprechaun. They are not impressive and I looked at them for about a nano second. Part of these steps are living organisms and form stromatolites.
A stromatolite is built when photosynthesizing bacteria (cyanobacteria) produce minerals in a process called biomineralization. This is not so strange when you consider our teeth and bones are made biologically and shells and corals are also formed by a similar process. However, instead of using calcium from the calcium carbonate in the cave, these critters use phosphorous from the bat guano!
In the cave, millions of bats hang around during the day producing guano. This guano mixes with water and drips down onto the “shelves” providing a rich mixture of phosphorus for the cynobacteria to convert into a hard substance.
The entrance to the cave, I like to think of it as a cavern, allows sunlight to infiltrate deep into the recesses where the stromatolites form. They only need a bit of light to grow and live in the dimmest part of the cave. Therefore one has the perfect ingredients: sunlight, fertilizer from the bat guano and water from a hole in the roof. These three combinations, plus a warm temperature come together to form the perfect conditions. In fact, this is the only place in the world where they appear in freshwater conditions and on the wall of a cave.
Well, not exactly on the wall. No cave has a smooth surface. There are always places where indentations occur especially in Deer Cave where rainwater runs down the walls. The water erodes unstable parts of the rock forming ledges. It is on these ledges the stromatolites form and build upward and outward forming the ledges or steps.
When you cut a chunk of stromatolite in half there are alternating dark and light bands. They seem to be evenly separated. The researchers think they may be are caused by the different amounts of rainfall. Although there is rain usually every day, the amount increases or decreases with the seasonal monsoons. Each layer, therefore, should provide an accurate record of the amount of rain over an extended period of time. Unfortunately, rainfall records for comparison are scant and altogether missing for the war years.
All things bright and beautiful, all creatures great and small, all things wise and wonderful, the Lord God made them all.
The article was adapted from:
Lundberg, Joyce and McFarlane Donald Subaerial freshwater phosphatic stromaolites in Deer Cave, Sarawak-A unique geobilogical cave formation in Geomorphology 128 (2011) 57-72 and
Presentation by the authors 18 July 2011 Sarawak Museum, Kuching, Sarawak.