The Precambrian-Cambrian Ecosphere (R)evolution: Insights from Chinese microcontinents
The DFG Forschergruppe 736 is the German side of a multidisciplinary binational project and has its administrative center at the Institut für Geologische Wissenschaften of the Freie Universität Berlin. However, group member also come from other institutions in Berlin, Germany and one international location:
Institut für Angewandte Geowissenschaften of the TU Berlin, Museum für Naturkunde of the Humboldt Universität zu Berlin, Geowissenschaftliches Zentrum of the Universität Göttingen, Universität Bonn, University College London
Seven projects make up the FG 736. They range from geochemistry over sedimentology, paleontology and taphnonomy, to mineralogy and geochronology. The German groups are matched with Chinese groups of approximately equal size.
Because new molecular data tend to support the classic “explosion” model (the notion of a very rapid evolutionary phase at the beginning of the Phanerozoic) , we need to initiate a better-focused search for the underlying and still enigmatic causes of the late Proterozoic to early Phanerozoic “evolutionary inventiveness”.
Several theoretical approaches have listed possible causes, acting at different levels of the Earth system:
- Neoproterozoic plate tectonics may have served as a principal agent, providing rapidly changing environments during the late Precambrian (breakup of the supercontinent Rodinia followed by assembly of Gondwana).
- Modified oceanic circulation patterns and changing ocean chemistry in the aftermath of the late Proterozoic Icehouse may have caused or contributed to climatic instability.
- Kirschvink and Raub (2003) suggested that rapid “global warming” may have been caused by unprecedented true polar wander and resulting mass exhalation of high-latitude gas hydrates (but see Torsvik et al., 1998, for a representative dissenting view).
- Late Precambrian (ca. 700-545 Ma) oxygenation events, during which a lack of oceanic overturn increased oxygen availability to marine shallow-water environments, possibly assisted the evolution of heterotrophic organisms in Ediacaran shelf habitats. An improved nutrient supply in Ediacaran oceans, especially of the biologically limiting phosphorous and nitrogen supply, may have been a consequence of the improved oxygenation.
Hypotheses and Strategy
In the Forschergruppe, we are testing the hypotheses and their predictions resulting from the new molecular-systematic theoretical framework with paleontological, biostratigraphic, sedimentological, geochemical and geochronological techniques. Examples of our work include the isotopic study of the past oceanic and atmospheric CO2- content, the mobility of redox-sensitive elements, the temporal and facies evolution of mobility and predation, the change in physical properties of sedimentary bedding, and the variable availability of key nutrients to evolving metazoans. The sedimentary archives of the Ediacaran - basal Cambrian interval preserve ample evidence of the unique ecological events, such as voluminous phosphorite, chert and black shale deposits occurring in shallow- and deep-water facies (“oceanic anoxic events”).
Understanding the evolutionary processes in the late Precambrian-early Cambrian biosphere and distinguishing causes and environmental and ecological consequences of these events requires a multidisciplinary approach and constitutes one of the recognized frontiers of current international research. Our research will test numerous hypotheses relating to the increasingly well-documented bioradiative events during the Ediacaran and basal Cambrian and explore their connections to the still poorly understood environmental changes at that time.
The Forschergruppe builds up and expands on a successful DFG-Bündelprojekt (2001-2004) which had a similar structure:
From "Snowball Earth" to the Cambrian bioradiation: Stratigraphic and sedimentary analysis of the Yangtze Platform in the latest Neoproterozoic
Christoph Heubeck, Bernd Weber, Elodie Vernhet
The time interval following the planet's most severe glaciation records numerous exciting ecologic, climatic, and tectonic events that affected the evolutionary development of lifeforms. Our stratigraphic work along the southern margin of the Yangtze Platform attempts to understand the sedimentary systems that formed the backdrop and base to the diversification of lifeforms culminating in the Cambrian explosion.