Earth Environment, Research School of Earth Sciences
The Australian National University
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The origins of sedimentary dolomite associated with coral reef depositional environments remained shrouded in mystery until my team discovered crustose coralline algae (CCA) were actively depositing significant amounts of dolomite on the reef flats of the Great Barrier Reef. Subsequently we have found dolomite is a common component within CCA globally. The dominant reef-building CCA, P. onkodes, is a critical component of coral reef architecture. This species of CCA is largely responsible for binding the disparate components of the reef together into a structure that can withstand the constant pounding the reef receives from ocean waves. In the 1960's W. G. H. Maxwell introduced the concept of immature, mature, and senile coral reefs. This observation is an important one, because CCA becomes more volumetrically important as a reef approaches senility. The longer a coral reef community is at sea level the better developed the CCA dominated algal facies. Caribbean reefs are immature relative to those growing in the Indo-Pacific and consequently the 'algal rim' facies on the reef flat are better developed. The efficient precipitation of dolomite from the global ocean into neritic carbonate systems can be directly associated with sea level stability. I will argue that the decline in sedimentary dolomite precipitation during the late Cenozoic is directly related to sea level dynamics and may explain the rapid increase in the Mg/Ca of sea water from the Oligocene through to the Holocene.