Sarawak Museum is inviting our members and friends to attend a public talk on Freshwater stromatolites in Deer Cave, Sarawak - a unique geobiological cave formation.
Speaker: Prof. Joyce Lundberg, Department of Geography and Environmental Studies,
Carleton University, Ottawa, K1S 5B6, Canada
With: Prof. Donald A. McFarlane, Claremont Colleges, Claremont, CA 91711.
Date: July 18th, 2011 (Monday)
Venue: Niah Lecture Room, Dewan Tun Abdul Razak Hall, Sarawak Museum, Kuching.
Driving to venue: Please come in by driving through Jalan P. Ramlee, the RTM road.
All are welcomed, free entrance.
Prof. Lundberg in field work.
Stromatolites are laminated usually mounded sedimentary fossil formed from layers of cyanobacteria, calcium carbonate, and trapped sediment. A suite of distinctive freshwater subaerial phosphatic stromatolites is developed close to the northeastern entrance of Deer Cave in Gunung Mulu National Park, Sarawak, Borneo. Deer Cave is already famous for its huge passages and vast bat population. In the zone of low light close to the northern entrance, we have found freshwater, sub-aerial, phosphatic stromatolites, the first of their kind reported in the world. Here we describe another special feature of the cave, this time on a small scale. They grow in a series of narrow shelves up a part of the cave wall that is exposed to low light, underneath a guano-laden shelf, and washed by fresh water from a shower head above. These stromatolites are not particulate; they are composed of alternating layers of more and less porous, amorphous hydroxylapatite with enrichment in metal ions formed through the process of biomineralisation. Their micro-morphology reveals dense networks of cyanobacterial fossils (both coccoid and filamentous forms). The stromatolites are emergent from the rock face by several cm. The stromatolites are present as horizontal shelves arranged in series on a steep rock face that is vertically under a guano-laden shelf. The rock face undergoes active dissolution from acidic guano drainage water and from aggressive rainwater from an overhead discharge. The rock face is corroded by the running water, except for the parts protected by the stromatolites, creating a form like tiny pillars or hoodoos. The stromatolites grow upwards in annual laminae but are at the same time destroyed from underneath by biological corrosion and laterally by mechanical breakage. A dynamic equilibrium is established between upward accretion of the fresh surface and destruction at the base such that the base of the stromatolite moves over time. Thus, over time they climb up the wall!
The stromatolites (grey) emergent from the corroded bedrock face (white) with guano-organic slime coatings (black) (the brown leaf is ~12 cm wide). The examplemarked by the leaf is one of the few that has developed a depression in the stromatoliteagainst the back-wall and shallow undercut in the rock at the base of the back wall.
|Freshwater stromatolites in Deer Cave, Sarawak - a unique geobiological cave formation|