research principally focuses on understanding the interactions between life,
tectonic, biogeochemical and climatic processes, on a range of time scales. To
better understand these interactions, I use radiogenic isotope geochemistry in
particular, the rhenium-osmium (Re-Os) geochronometer and Os and Sr isotopes.
The Re-Os geochronometer system differs from other geochemical techniques in
its ability to provide precise depositional ages for sedimentary rocks and holds
exceptional promise in our efforts to understand the mechanisms driving
geological phenomena throughout Earth history. During my PhD, I was trained as
a geochronologist and geochemist, but in the past four years I have been
complementing these techniques with more field-based skills such as geological
mapping, sedimentology, and paleontological analysis.
My research interests are centered on four main areas: 1) refining Proterozoic Earth history, especially Neoproterozoic (1000 – 541 Ma) glaciations, eukaryotic diversification and large-scale tectonic reorganizations, 2) combining geochemical proxies with microfossil and sedimentological analyses from modern-day glaciated regions to better understand the external and internal forces acting on ocean-ice sheet dynamics throughout the Quaternary, 3) understanding hydrocarbon systems through the use of geochronology and organic geochemistry, and 4) integrating the Re-Os geochronometer into the EARTHTIME organization and leading an international effort for interlaboratory standardization.
1) Proterozoic Earth HistoryDuring my PhD and post-doctoral appointments I generated new Re-Os ages and chemostratigraphy profiles for fossiliferous Mesoproterozoic strata from the West African and Siberian cratons (Rooney et al., 2010; Sperling et al., 2014). These data helped demonstrate that early eukaryotes evolved and diversified in heterogeneous ocean redox conditions rather than in response to a discrete rise in atmospheric oxygen (Sperling et al., 2014). Data from the Neoproterozoic–Cambrian Dalradian Supergroup of Scotland yielded much-needed age constraints and simultaneously indicated that the Re-Os geochronometer is robust in samples that have experienced greenschist facies metamorphism (Rooney et al., 2011). Two of my most recent publications yielded Re-Os age constraints from multiple paleocontinents indicating that the Sturtian glaciation lasted >55 Myr and that deglaciation was globally synchronous. Osmium isotope data further supported the hypothesis that global cooling was initiated by the weathering of extensive sub-aerial flood basalt provinces, emplaced near the equator prior to the onset of glaciation (Rooney et al., 2014; 2015). Furthermore, new data from strata hosting Neoproterozoic vase-shaped microfossils document the ability of Re-Os geochronology to provide global calibrations of sedimentary, paleontological, and geochemical records in a time period that suffers from a paucity of biostratigraphically useful fossils (Strauss et al., 2014).
2) Quaternary Climate Science
Recently, I have begun using Os isotope geochemistry, benthic foraminifera and sedimentological analyses to evaluate the relationship between weathering rates, ice sheet dynamics and ocean circulation patterns during the Quaternary. This work aims to answer fundamental questions about the interactions between ice sheet fluctuations and ocean currents. Particularly, what are the major internal and/or external forces controlling feedbacks between the Greenland and Antarctic ice sheets and ocean currents? My work on the Disko Bugt region of West Greenland used Os isotope stratigraphy on recovered core material to provide a high-resolution chemostratigraphic record from the Jakobshavn Isbrae over a ~10 kyr interval indicating that the retreat of this ice-stream was more intricate than first appeared from cosmogenic and fossil records alone (Rooney et al., 2012a; Rooney et al., submitted). Potential new projects will focus on reconstructing former ice sheets in terms of their extent, flow dynamics and the nature of retreat using chemostratigraphy and bedrock studies. Results from these projects would generate much-needed empirical constraints to help refine numerical models of the Greenland and Antarctic ice sheets and their contribution to future sea level change.
3) Organic and hydrocarbon geochemistryUnderstanding the timing of petroleum generation remains one of the major sources of risk in hydrocarbon exploration. Application of the Re-Os geochronometer in hydrocarbon systems has yielded age constraints interpreted to reflect the timing of oil generation or migration. To better understand and evaluate the response of the Re-Os geochronometer to hydrocarbon generation I used hydrous pyrolysis experiments on suites of source rocks. The results indicate that Os isotopes can be used to fingerprint petroleum deposits to specific source rocks (Rooney et al., 2012b).
Possible future research projects (in collaboration with the hydrocarbon industry and the USGS) would employ Re-Os geochronology, Os isotopes and other platinum group elements to track variations of these elements in hydrocarbons and their source rocks and help reduce risk in hydrocarbon exploration. These and future studies will help to further reveal the maturation and migration history in sedimentary basins.
4) Re-Os systematics and tracer solutionsCurrently, many Re-Os laboratories use their own tracer solutions for geochronology and geochemistry and, as a result, the uncertainties inherent in each tracer solution renders inter-laboratory comparisons problematic and can limit the accuracy and precision of age determinations. To increase precision and accuracy and to support the homogenization of data reduction techniques in the Re-Os community I am leading an effort to improve the traceability of Re-Os geochronology data through the development and distribution of gravimetrically calibrated tracer and synthetic reference solutions. This work will come under the auspices of the EARTHTIME initiative and will involve collaborations between the U-Pb and Re-Os communities.
Re-Os EarthTime initiative