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One of the most important events in the Phanerozoic biosphere occurred during the Ordovician where family-level diversity tripled and new ecological niches were filled by a diversifying biosphere. Commonly referred to as the Great Ordovician Biodiversification Event (GOBE), this event has been long studied, yet the causes remain poorly understood. Geologists have speculated that the causes could be due to environmental changes such as cooling, upwelling of nutrients, oxygenation, or even meteorite impacts! Others have argued that the causes were due to biological forces where competition of resources and ecospace forced animals to adapt new lifestyles (predation and avoidance of predation) and spread out geographically, ultimately evolving new species. Each of these hypotheses are supported with good evidence, but the question remains what was the relative timing of these events compared to diversification and if a confluence of several processes contributed to diversification.
Current research projects (excellent potential for undergraduate research!
1) Causes of Ordovician and extinction
2) Stable and radiogenic isotope stratigraphy – Carbon, oxygen, sulfur, strontium, and neodymium
Isotope geochemical data are highly useful in helping to unravel how environmental change were important during key intervals in Earth history. Stable isotopes like carbon (δ13C), oxygen (δ18O), and sulfur (δ34S) are used for chemostratigraphic purposes – correlation of strata using isotopic data and trends – as well as providing information about paleoclimate and redox changes of ancient oceans. High-resolution sampling of well-preserved fossils and bulk rock improve correlations of stratigraphic successions where key geologic information may be missing in some sections (e.g. poor biostratigraphic age control). Radiogenic isotopes like strontium (87Sr/86Sr) and neodymium (143Nd/144Nd) can be used in the same way and add an independent measure to calibrate correlations because these isotope systems have significantly different residence times in the ocean.
3) Investigating the causes of the end Devonian (Frasnian–Famennian) mass extinction
Not only do we geologists and paleontologists have a hard time understanding the causes for long-term biodiversification, we can also have a hard time explaining the causes for mass extinctions. The end Devonian mass extinction is one of the “big five” mass extinctions and arguably one of the least understood. Hypotheses for the causes of this major biotic event range from:
- Expansion of anoxic waters in shallow environments,
- Global cooling due to the expansion of terrestrial forests made up of plant matter that was resistant to microbial breakdown and drew down atmospheric CO2, thus reducing the greenhouse effect
- Higher weathering rates (possibly due to the expansion of terrestrial forests) that ‘polluted’ carbonate platform environments and increased silicate weathering rates (also a CO2 sink)
- Collapse and deterioration of carbonate reefs that had detrimental impacts on the marine ecosystem and ultimately global biodiversity.
Geochemistry and isotopes can provide answers to these hypotheses and potentially offer several opportunities for student research. The anoxia hypothesis, for example, is based on several positive carbon isotope excursions thought to be driven by organic burial under anoxic conditions. However, the global nature of this phenomenon has yet to be clearly demonstrated, as well as be recorded in other redox-sensitive geochemical systems (δ34S, I/Ca, [Mn], Mo/TOC, etc.).
Potential projects for undergraduate research:
- Controls on Sr concentrations and isotopes in conodonts and brachiopods through time
- Oxygen isotopes of brachiopod calcite using Secondary Ion Mass Spectrometry (SIMS): is ocean temperature and/or seasonality preserved in brachiopod calcite?
- Sedimentology, facies patterns, and chemostratigraphy of the lower Paleozoic in the southern Appalachians
- Lower Paleozoic Strontium isotope (87Sr/86Sr) stratigraphy of the Great Basin region, USA
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