Ca isotope constraints on the Neoproterozoic carbon cycle

Ca isotopes can help constrain the origin of heavy and light carbon isotope plateaus in the Neoproterozoic

Snowball Earth Geochronology

U-Pb zircon age constraints on the Sturtian Glaciation from northern Ethiopia

Thermochronological constraints on evolution of the Pilbara craton

U-Pb zircon and apatite ages provide insight into the structural and magmatic history of the craton

Recent Posts

This May 40 grad students, undergrads and faculty went for a weeklong trip through southern and central Scotland


We got a bit of coverage in the Science News section for our work in Ethiopia!


Selected Publications

In order to understand the onset of Snowball Earth events, precise geochronology and chemostratigraphy are needed on complete sections leading into the glaciations. While deposits associated with the Neoproterozoic Sturtian glaciation have been found on nearly every continent, time-calibrated stratigraphic sections that record paleoenvironmental conditions leading into the glaciation are exceedingly rare. Instead, the transition to glaciation is normally expressed as erosive contacts with overlying diamictites, and the best existing geochronological constraints come from volcanic successions with little paleoenvironmental information. We report new stratigraphic and geochronological data from the upper Tambien Group in northern Ethiopia, which indicates that the glacigenic diamictite at the top of the succession is Sturtian in age. U-Pb zircon dates obtained from two tuffaceous siltstones that are 74 and 84 m below the diamictite are 719.68 ± 0.46 Ma and 719.68 ± 0.56 Ma (2σ), respectively. We also report a U-Pb date of 735.25 ± 0.25 Ma from a crystal-rich tuff located 2 m above the nadir of a high-amplitude, basin-wide, negative δ13C excursion previously correlated with the Islay anomaly. This age for the anomaly agrees with Re-Os age constraints from Laurentia, suggesting that the δ13C signal is globally synchronous and preceded the Sturtian glaciation by ~18 m.y. The interval between the Islay anomaly and Sturtian glaciation is recorded in the Tambien Group as an ~600 m succession of predominantly shallow-water carbonates and siliciclastics with δ13C values recording a prolonged period at +5‰, followed by an interval of lower, but still positive, values lead- ing up to the glaciation. Our data are consistent with synchronous global onset of the Sturtian glaciation at ca. 717 Ma. Shallow-water carbonates in strata directly below the first diamictite suggest that glacial onset was rapid in terranes of the Arabian-Nubian Shield.
In Geology, 2018

The Makhonjwa Mountains, traditionally referred to as the Barberton Greenstone Belt, retain an iconic Paleoarchean archive against which numerical models of early earth geodynamics can be tested. We present new geologic and structural maps, geochemical plots, geo- and thermo-chronology, and geophysical data from seven silicic, mafic to ultramafic complexes separated by major shear systems across the southern Makhonjwa Mountains. All reveal signs of modern oceanic back-arc crust and subduction-related processes. We compare the rates of processes determined from this data and balance these against plate tectonic and plume related models. Robust rates of both horizontal and vertical tectonic processes derived from the Makhonjwa Mountain complexes are similar, well within an order of magnitude, to those encountered across modern oceanic and orogenic terrains flanking Western Pacific-like subduction zones. We conclude that plate tectonics and linked plate-boundary processes were well established by 3.2–3.6 Ga. Our work provides new constraints for modellers with rates of a ‘basket’ of processes against which to test Paleoarchean geodynamic models over a time period close to the length of the Phanerozoic.
In Geoscience Frontiers., 2018

Recent Publications

. The arc of the Snowball: U-Pb dates constrain the Islay anomaly and the initiation of the Sturtian glaciation. In Geology, 2018.

PDF Project

. Paleoarchean bedrock lithologies across the Makhonjwa Mountains of South Africa and Swaziland linked to geochemical, magnetic and tectonic data reveal early plate tectonic genes flanking subduction margins. In Geoscience Frontiers., 2018.


Curriculum Vitae


I have been a teaching assistant for two main classes listed below:

  • GEO103: Natural disasters- an entry level class aimed at getting non-majors acquainted with seismic and volcanic hazards, as well as climate change. We had a number of great physical analog demonstrations, one example was a jello volcano with relatively accurate dyke propagation!
  • GEO378: Mineralogy- Upper level class where we aim to teach the students symmetry, crystal structure and mineral identification in hand samples. This also involves geochemistry and some basic plate tectonic theory


Field Photos

Here are a selection of field photos: