2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 2
Presentation Time: 1:50 PM

The Eve of Biomineralization: Seawater and Climate Controls on Skeletal Mineralogy


ABSTRACT WITHDRAWN

, Rachel.Wood@ed.ac.uk

A quantitative compilation of inorganic and biominerals from the onset of biomineralization (Late Ediacaran (~550 Ma) to the Middle Ordovician (~460 Ma)) infers a correspondence between sea water chemistry and the first adopted mineralogy of skeletal clades. Ediacaran to Tommotian skeletons and inorganic precipitates were composed exclusively of aragonite or high-Mg calcite, but these were replaced by low-Mg calcite mineralogies during the early Atdabanian, inferring the onset of a ‘calcite' sea. This transition is empirically constrained by fluid inclusion data. Late Atbadanian to Botoman inorganic precipitates revert to aragonite, with High-Mg calcite echinoderms and solitary tabulaconids, and aragonitic massive tabulaconids originating during this interval. Mid-Cambrian to Ordovician inorganic precipitates are low-Mg calcite, and the Ordovician radiation in its skeletal expression is due mostly to groups with low-Mg calcite mineralogies. These short-lived transitions can be most parsimoniously explained by either minor oscillations of mMg:Ca around ~2 during this interval, or the progressive onset of greenhouse conditions during the mid-late Cambrian.