Cool-Water Carbonate Accumulation Rates,
New Zealand, Ireland, Croatia, and Estonia
 
plant stems

 

 

Holocene cheilostome bryozoan 
(Celleporina grandis) from the 
Otago Shelf of New Zealand.

Marcus M. Key - Dept. of Geology, Dickinson College, U.S.A.
Abigail M. Smith - Dept. of Marine Science, University of Otago, New Zealand
Patrick N. Wyse Jackson - Dept. of Geology, Trinity College, Ireland Maja Maja Novosel – Dept. of Biology, University of Zagreb, Croatia
Andrej Ernst - Institute of Earth Sciences, Kiel University, Germany

Linda Hints - Institute of Geology, Tallinn University of Technology, Estonia
Students: Catherine Jamet ('99), Dustin Moore ('04), Timothy Samson ('05), Kristen Miller ('06)

       The goal of this project is to quantify the growth rates of cool-water, shallow marine fossil bryozoan colonies in order to estimate the gross carbonate production rate of cool-water, shallow marine, bryozoan-rich limestones.  Much is known of shallow marine, tropical, biogenic carbonate production rates as a result of numerous studies on growth rates of tropical, carbonate-producing organisms (e.g., corals).  Much less is known about cool-water carbonate production ratesdue to the relative lack of understanding of the growth rates of cool-water, carbonate-producing organisms (e.g., bryozoans).  As bryozoans are a dominant skeletal contributor in cool-water, shallow marine, carbonate environments, their colony growth rates can be used as a proxy for gross carbonate production in bryozoan-rich limestones.  Carbonate production will be measured in terms of skeletal volume as determined from serial transverse sections parallel to and at increasing distances from the growing surface of the colonies.  Time will be determined from seasonal oxygen isotope profiles along longitudinal sections perpendicular to the growing surface. The methodology has been developed on extant bryozoans from Doubtful Sound, New Zealand and the Adriatic Sea, Croatia.  The key to this project is the preservation of a seasonal water temperature signal in the oxygen isotopes of the fossilized bryozoan skeletons.  Low Mg-calcite trepostome bryozoans will be chosen due to their diagenetic stability.  Mid paleolatitude, shallow marine, carbonate paleoenvironments will be chosen due to their strongly seasonal water temperatures.  The best candidates for this study are the trepostome bryozoan faunas of the Ordovician of Ireland and Estonia.  This study will contribute to our knowledge of the accumulation rates of cool-water, shallow marine limestones which are increasingly being recognized as important petroleum reservoirs and groundwater aquifers in many areas.