GROWTH-RATES AND HOLOCENE DEVELOPMENT OF STROMATOLITES FROM SHARK BAY, WESTERN-AUSTRALIA

The growth rates and patterns of stromatolites are of interest in that fine-scale laminations in some Precambrian examples have been interpreted as daily growth layers whose orientations reflect the annual transit of the sun. By contrast, the modern and Holocene stromatolites at Shark Bay occur in a high-energy environment where accumulation and growth only marginally exceed erosion. Long-term vertical growth rates of ≤0.4 mm/year were determined by radiocarbon dating and supported by uranium-series methods. These rates are up to 250 times slower than those growth rates estimated from the laminae patterns of some Precambrian stromatolites. Thus, daily bands are not recognized and individual subtidal stromatolite columns from Shark Bay take up to 1000 years to reach their present heights of ˜350 mm. The earliest exposed stromatolites at Shark Bay grew during the interval 1250-1000 years ago and are now dead and stranded (in response to falling relative sea level) in terraces some 0.3 m above present high tide. © 1990, Taylor & Francis Group, LLC.