research

Our group is fascinated by the co-evolution of the crust, the ocean, climate, and life over Earth history. This work begins with geological mapping and sampling within measured stratigraphic sections. From this framework we use stable isotope geochemistry, U/Pb geochronology, paleomagnetics, and paleontology to build environmental records and tectonic histories.

Neoproterozoic-Cambrian Earth history

Neoproterozoic strata record the break up of the supercontinent Rodinia, multiple low-latitude glaciations, large-amplitude carbon and sulfur isotope excursions, the putative oxygenation of the deep oceans, and early animal evolution. To better understand the relationships between these events, we have pursued integrated litho-stratigraphic, chemo-stratigraphic, paleontological, paleomagnetic, and geochronological studies in Namibia, Mongolia, Alaska, and NW Canada. Future studies aim to address the age of the Cryogenian glaciations, the Neoproterozoic micropaleontological record, the evolution of the ocean redox state, the driver of large amplitude carbon-isotope anomalies, phosphogenesis, the origin and travels of microcontinental fragments, and the formation of continental crust in accretionary orogens.

Arctic Alaska

Neoproterozoic carbonates in Arctic Alaska were previously thought to be Tonian in age. During stratigraphic studies we identified two glacial horizons and produced carbon isotope profiles, which demonstrated that the Katakturuk Dolomite was deposited during the Cryogenian and Ediacaran. This refined age indicates that the Arctic Alaska-Chukotka Plate (AACP) is likely exotic to Laurentia. Future studies are necessary to correlate Pre-Mississipian strata throughout the AACP and better understand the Neoproterozoic and Paleozoic basin dynamics that accomodated these sediments.

Northwestern Canada

Although the Windermere Supergroup of northwestern Canada is one of the classic terminal Neoproterozoic successions, it is unknown exactly how units within the Windermere correlate both to the western margin of Laurentia and to other Ediacaran sequences globally. These correlations are significant because strata near the the Alaskan border hosts a diverse microfossil assemblage and many potentially datable volcanic horizons. In collaboration with Phoebe Cohen, Galen Halverson, Charlie Roots, David Johnston, and Mark Schmitz, I am using chemo- and litho-stratigraphy to better constrain the age of biologic, climatic, and geochemical change.

Mongolia

The Dzabkhan and Khubsugul Basins host two Neoproterozoic glacial diamictites, basal Ediacaran cap carbonates, phosphorite deposits, and thick Cambrian carbonates. With Dave Jones, J. C. Crevelling, David Johnston, and Sam Bowring, we are using integrated geochronology, paleontology, and chemo- and litho-stratigraphy to better understand and place age constraints on early Cryogenian glaciations, the Tayshir isotope anomaly, phosophogenesis, Early Cambrian isotopic variability, and early accretion in the Central Asian Orogenic Belt.

Namibia

In the Gariep Belt of southern Namibia, volcanic rocks of the Rosh Pinah Group are associated with the lower of two glacial diamictites. The Kaigas and Numees diamictites both display a rich and complex array of glacial sedimentary structures. The Numees is also overlain by a basal Ediacaran cap dolomite with many of the characteristic sedimentological and isotopic features. Further studies aim to refine age constraints on the Sturtian glaciation and better understand the origin of cap carbonates.

Tectonic Evolution of the Arctic & Asia

Understanding the tectonic history of the Arctic-Alaska Chukotka Plate (AACP) and Pearya is central to unravelling the development of the Arctic Basin. Similarly, the Dzabkhan and Khubsugul terranes occupy a central position in the Central Asian Orogenic Belt. Our group aims to better understand the origin and travels of these terranes through basin analysis and tectonic synthesis.

Impact Cratering in Australia

Through field studies at geophysical anomalies in the Outback of Australia we have identified shock metamorphic features associated with three new impact structures. Field mapping at these sites and others has helped constrain their age and define the structural form. We are currently working to archive much of Eugene Shoemaker's earlier, unpublished work on Australian impact structures and fallout. These studies have helped refine the cratering record in Australia, and to better understand the mechanics of impact cratering.

Yarrabubba

Shock effects including shatter cones, PDFs in quartz grains, impact melt rocks, and pseudotacylites were identified in deeply eroded granites in the Yilgarn Craton (119˚50’E, 27˚10’S). Geological and geophysical relationships suggest that the original structure was at least 30 km in diameter and was formed during the early Proterozoic.

Glikson

Glikson is an 18 km diameter impact structure located in the Little Sandy Desert of Western Australia (23˚59’S, 121˚34’E), that would not have been detected were it not for its extremely strong, ring-shaped aeromagnetic anomaly. Shoemaker visited the area in 1996, and he believed Glikson was an impact structure, but he was unable to find any definative shock features. While mapping the structure in 2002, we confirmed Shoemaker’s suspicions and discovered unequivocal shatter cones in Neoproterozoic sandstones. The source of the strong, aeromagnetic anomaly is likely the truncation of a flat-lying sill, and thus, the impact probably postdates the Cambrian mafic events of the Officer

Basin.

Amelia Creek

Amelia Creek is an asymmetrical, 20 X 12 km impact structure in the Davenport Ranges of the Northern Territory (20˚55’S, 134˚50’E). Evidence for an impact origin includes pervasive shatter-coning, planar microstructures in quartz grains, and the development of large autogenic breccias and clastic dikes. The impact occurred between Cambrian and Mesozoic times.