Title:Understanding Earth’s paleoenvironmental evolution (on long timescales)

Abstract: Animals originated and evolved during one of the most unique times in Earth history—the Neoproterozoic Era—and early animal evolution has long been causally linked to environmental change during this interval. However, geochemical patterns of change are often noisy, and no stratigraphic section covers the entirety of Earth history; global database studies are required. Here, data from the Sedimentary Geochemistry and Paleoenvironments Project (SGP) will be used to demonstrate how machine learning methods and increased emphasis on accounting for sampling bias can yield a more resolved pattern of environmental change in deep time. The talk will also discuss the prospects and pitfalls of ‘team science’ approaches in the geological sciences. The results suggest that early animals evolved in a Neoproterozoic world that had lower oxygen levels and lower primary productivity than the Paleozoic, although the magnitude of oxygen change at the dawn of the Phanerozoic was likely less than commonly hypothesized. Finally, ecosystems along modern natural gradients of oxygen and primary productivity will be used to conceptualize Neoproterozoic ecosystems and deduce the possible role of environmental change in the Cambrian ‘explosion’ of animal life. 

*Please note that this lecture will not be recorded or posted after. 

Title: The life and times of a ferruginous lake

Abstract: Permanently stratified lakes that are also ferruginous (i.e. abundant dissolved iron) are biogeochemical hot spots for (microbial) redox transformations of major and trace elements. Across such an interesting set of gradients (light, oxygen, temperature, salinity, nutrients, etc.), there is really something to interest every flavor of biogeochemist. In this talk I will discuss one modest little lake in northern Minnesota that has given us some real insights into how ferruginous aquatic conditions function and the geochemical records they might leave behind. This is of particular interest to geoscientists who want to better understand how biogeochemical cycles operated in the Archean and Proterozoic oceans. Lakes aren’t oceans, though, and so I will address both the applications and limits of this analogy.

*Please note that this lecture will not be recorded or posted after. 

Title: Why do Great Continental Earthquakes Nucleate on Branch Faults?

Watch the lecture here.

Title:Uranium Isotopes as Tracers of Seafloor Weathering

Abstract:The oceanic crust and marine sediments are exposed to pure and chemically altered seawater. Fluid-rock interactions between these reservoirs provoke a wide variety of chemical reactions that modify the physical and chemical properties of both the fluids and the solids involved, with implications for the global cycles of water, carbon dioxide, and fluid-mobile elements in Earth’s surface and interior. Uranium is a powerful tracer of weathering reactions at the seafloor because it is highly soluble in its oxidized form in seawater, and undergoes two flavors of isotopic fractionation: one during water-rock interaction, and one during redox transitions between U(VI) and U(IV). In this talk, we show how uranium isotopes can be used to fingerprint weathering dynamics in serpentinites and in marine sediments. We use our results to show that low-temperature weathering of oceanic serpentinites by chemically evolved seawater is pervasive at the seafloor, and that continental serpentinites host unique uranium isotope signatures driven by the grain size of U hosting minerals. We investigate the role of iron oxides as mineralogical hosts for uranium in seafloor serpentinites and discuss possible implications for the whole-earth uranium isotope cycle

Title:"Road Trip! Jay Quade, Field Geology, Geochemistry" Presented by Thure Cerling

Title: Ontogenies of Orogenies and Erodibilities of Landscapes

Abstract:Understanding how erosion rates are influenced by tectonics, climate, and lithology is crucial for interpreting the evolution of Earth’s topography. The rate of rock uplift is one of the primary controls on erosion rate. Mountain ranges adjust to changes in uplift rate by adjusting their steepness so that erosion rates balance the rates of rock uplift. The amount that a landscape needs to steepen to achieve an erosion rate that balances the rate of rock uplift depends on multiple factors that control the efficiency of erosion, such as rock erodibility. Previous research has investigated the influence of erodibility on the relationship between erosion rates and landscape steepness by analyzing erosion rates and steepness values across catchments with varying fracture densities. These studies have shown that catchments with higher fracture densities exhibit greater erodibility and require less channel steepness to achieve a given erosion rate compared to catchments with lower fracture densities. However, the possibility of erodibility variations across different stages of mountain building (ontogeny) on a continental scale has yet to be directly investigated. In this talk, I will present results from ongoing research on the relationship between erosion rates derived from ¹⁰Be cosmogenic nuclides and channel steepness across orogens of different ages in the conterminous United States. Rock erodibility is expected to have a relationship with orogen age following from the general observation that during orogenesis, cooler, upper crustal rocks experience greater amounts of brittle strain than warmer, more ductile rocks at depth, creating a ‘fracture stratigraphy’. This fracturing process is expected to reduce the erodibility of the upper crust in young and tectonically active orogens. In contrast, areas that have not recently experienced intense deformation (i.e., tectonically quiescent), should have lower fracture densities.