Multi-proxy isotope investigation of palaeo-environmental conditions of the Precambrian-Cambrian transition
The evolution of Earth and life are closely connected. The changing character of Earth's surface environments helped to drive modification of the genetic and molecular systems that constitute life, while biochemical processes in turn modified the composition of the atmosphere and oceans. The profound changes at the Ediacaran to Cambrian transition record these interactions, along with hallmark climatic and biospheric events, and are preserved in stratigraphic archives on the Yangtze Platform in South China and adjacent microcontinents. These provide unique access to widely undisturbed marine carbonates deposited on a large palaeogeographic scale and under atmospheric-oceanic conditions of that time.
The objective of our research program is to reconstruct and quantify weathering conditions, oceanic pH and atmospheric CO2 of the Ediacaran to Early Cambrian period using non-traditional stable B and Ca isotope measurements on marine carbonate rocks. To provide a multi-faceted constrain on the environmental conditions, we aim to combine our data with conventional stable, radiogenic and other non-traditional stable isotopes (subprojects 2 and 4) and integrate them with palaeo-biological (subproject 3 & 6) and stratigraphic-sedimentary (subproject 1) information. Such a multi-proxy approach provides a powerful means of cross-checking the reproducibility of isotopic trends and validity of reconstructed environmental conditions.
We plan to sample a shallow-marine to deep-basin continental-margin transect of paleontologically well-characterized marine carbonates that preserves an exemplary geochemical record of Ediacaran to Early Cambrian time. Thus we are able to validate our hypothesis that changing ocean-atmospheric conditions have catalysed the advent and radiation of metazoa.
A detailed study on Neoproterozoic carbonates from Namibia demonstrated that robust estimates of seawater pH, weathering rate variations and palaeo-pCO2 levels can be obtained from Neoproterozoic marine carbonates using B- and Ca-isotopes. This shows that we can collect and identify lithologically homogeneous carbonate samples from ancient rocks in which primary isotope patterns, even for boron, are still retained. Recent data verified the reproducibility of the isotope pattern in stratigraphic sections recording different water depths and palaeo-environments and determined the lateral scale and regional significance of such variations.