Richard Ash, Mike Evans, Vedran Lekić, Cecilia Sanders, and Nicholas Schmerr, University of Maryland
Faculty Lightning Talks
September 12, 2025 at 11:00 am (ESJ 0215)
Lightning-fast, 5-minute talks by 5 members of the Geology Faculty about their research.
Richard Ash — The UMD Plasma Lab and the Origin and Importance of Chondrites
Mike Evans — Common Era paleoclimate research emerging from a new database of databases
Ved Lekić — Topic TBD
Cecilia Sanders — The Geologic Record of Symbiosis and Community Resource Management (as told by A. Phosphorite)
Nick Schmerr — Planetary Geophysics: The Moon, Mars, and Beyond
Michael Kipp, Duke University
How precisely can we quantify oxygen levels in the ancient ocean?
September 19, 2025 at 11:00 am (ESJ 0215)
Reconstructing past changes in marine dissolved oxygen levels is critical for understanding Earth’s evolutionary history. It also allows us to use past events to guide our expectations for ocean chemistry under anthropogenic warming. In this talk, I will take a deep dive into the mechanics of what has rapidly become one of the most widely-used tools for estimating past ocean oxygen levels: the uranium isotopic composition of carbonate sediments. I will systematically review how this “paleo-redox proxy” works, moving from its calibration in the modern ocean to its quantitative underpinnings and finally to actual paleo-records from various archives. The talk will conclude with a preview of ongoing work to improve the rigor of statistical reconstructions from multi-proxy datasets.
Pupa Gilbert, University of Wisconsin, Madison
Biophysics of Biomineralization
September 26, 2025 at 11:00 am (ESJ 0215)
A cool human enamel evolution story, with fantastic images of enamel nanostructure, and how they changed dramatically with the introduction of meat 2 Ma and agriculture 12 Ka.
Matthew Jackson, University of California, Santa Barbara
A “Hotspot highway” that extends back into the Cretaceous Pacific… and into the Tonga Trench
October 10, 2025 at 11:00 am (ESJ 0215)
Samoa, Arago-Rurutu, and Rarotonga are three South Pacific Superswell hotspots that make up the “hotspot highway”, a suite of overlapping hotspot tracks in the Samoan and Cook-Austral region. Hotspot tracks emerging from the South Pacific Superswell—a region of unusually shallow bathymetry and high density of hotspots—can be traced back into the Cretaceous near the Mariana trench. We show that the Cretaceous portions of these hotspots are subducting into the Tonga trench, explaining the Mariana along-arc geochemical trends. Before subducting into the trench, two of the hotspots were overtopped by the Ontong-Java Plateau, which suppressed plume melting. Unfortunately, segments of all hotspot tracks remain unsampled and uncharacterized, particularly in the Cretaceous, leaving some uncertainty as to their long-term evolution. However, the 80-100 Ma sections of two of the hotspot highway hotspots, Arago-Rurutu and Samoa, allow us to redefine absolute plate motion models for the Cretaceous Pacific and show that the Louisville hotspot is linked to the eruption of the Ontong-Java Plateau.
Admin Husic, Virginia Tech
American Rivers are Transporting More Sediment in Less Time
October 17, 2025 at 11:00 am (ESJ 0215)
Rivers across the United States are increasingly event-driven, with both water and sediment transport often concentrated into short, intense periods of hydrologic activity. Using deep learning models trained on hydrometric, meteorological, and land-use data, we reconstructed multi-decadal records of event water fractions and suspended sediment dynamics at hundreds of sites nationwide. Results show that streamflow is increasingly dominated by ‘new’ water, with 34% of sites exhibiting significant increases in event water fraction, largely linked to deforestation, urbanization, and intensifying precipitation. Similarly, 33% of sites exhibited significant increases in sediment flux and the window of that transport has grown narrower – at most sites, half of the annual sediment load occurs in less than 2% of the time. Together, these findings reveal that U.S. rivers are exporting more sediment in increasingly compressed windows, reflecting the coupled impacts of climate change and human land use on watershed processes.
Austin Green, Virginia Tech
A Tale of Two Lithospheres: The Geodynamic Controls on the Habitability of Europa’s Subsurface Ocean
October 24, 2025 at 11:00 am (ESJ 0215)
Europa, the smallest of Jupiter’s four Galilean moons, harbors a 100-km deep ocean underneath its icy surface. Assessing the habitability (ability to support life) of this ocean is the overarching objective of NASA’s recently launched flagship mission Europa Clipper. Due to the ocean being entirely covered by ice, however, the hypothetical Europan biosphere cannot be supported by sunlight and by extension photosynthesis. Instead, chemotrophic life may be supported by the consistent delivery of nutrients into the ocean from both its overlying ice shell and underlying rocky/metallic mantle and core. These nutrients reside on Europa’s surface (oxidants) and within its mantle (reductants) and must be geodynamically conveyed through both icy and rocky lithospheres to the ocean by some means. In this talk, I will present my recent work on these geodynamic controls on ocean habitability in both the icy and the rocky layers of Europa’s interior. Salt infiltration may encourage weakening and densification of the surface ice lithosphere, causing it to collapse to the base of the shell, bringing these nutrients with it. The presence of volcanism on Europa’s seafloor will produce hydrothermal reductants to feed hydrothermal vent communities. Can the surface ice lithosphere overcome its rigidity and sink to the ocean? Can magma generated in Europa’s deep interior break through its rocky lithosphere to erupt on the seafloor?
David Williams, Arizona State University
Jupiter’s Volcanic Moon Io: Results from the Juno Mission and a Look toward Future Missions
October 31, 2025 at 11:00 am (ESJ 0215)
Jupiter’s moon Io is the most volcanically active object in the Solar System, where over 400 vents erupt effusive flows or explosive plumes rich in silicate, sulfur, or sulfur dioxide. Io’s geology is unique compared to other moons in the Solar System, and its tidally-induced activity is a model to investigate lava-rich exoplanets. While much was learned from the NASA Voyager flybys in 1979 and the NASA Galileo Jupiter orbiter from 1996-2001, and from additional spacecraft flybys and telescopic observations, new insights were provided by high-resolution observations obtained from the extended mission of NASA’s Juno Jupiter polar orbiter. In this talk we will review past results from earlier missions and take a look at results based on the new Juno data, as well as look ahead to possible future mission concepts such as the Io Volcano Observer and the Prometheus Io plume sample return.
Michelle Casey, Towson University
Surprises in the Feeding Ecology of Drilling Snails as Revealed by Stable Isotopic Analysis in the Field and Laboratory
November 14, 2025 at 11:00 am (ESJ 0215)
The stable isotopes of nitrogen and carbon are frequently used in modern ecological studies to estimate trophic position and diet of animals. Advantages of stable isotopic methods include their ability to capture complex trophic interactions and integrate multiple dietary sources spatially and temporally on timescales from days to months. Properly accounting for isotopic baseline requires the analysis of both trophic N and trophic C, for the most part restricting these methods to the soft tissues of extant invertebrates. However, even the best-studied organisms can yield surprising dietary preferences with macroevolutionary or macroecological implications. Drilling gastropods are marine predators of hard-shelled prey from two distantly related families, the Naticidae and the Muricidae. Drilling gastropods leave a distinct predation trace on the shells of their victims (in the form of drill-holes) that are frequently preserved in the fossil record and studied in detail as a means of quantifying ecological interactions in deep time. This study examines the stable isotopically derived diet and trophic position of the naticid Neverita duplicata in detail, both in the field and under laboratory conditions to evaluate the prevalence of cannibalism and omnivory in its diet. Results indicate a high prevalence of omnivory among N. duplicata from Long Island Sound. The ability of some drilling gastropods to supplement their diet with plant matter or detritus likely had wide-ranging implications for their structuring of subtidal ecosystems and response to environmental changes in the past.
Freya Morris, Hamilton College
Snowballs in the Desert: The Deglaciation of the Marinoan Snowball Earth in the Naukluft Mountains, Namibia
November 21, 2025 at 11:00 am (ESJ 0215)
The termination of the Marinoan Snowball Earth glacial epoch was one of the most extreme climate events in Earth history. Yet, the transition from global glaciation to an ice-free warmer climate is still poorly constrained. The Naukluft Nappe Complex of south-central Namibia contains several stratigraphic formations that record the environmental and tectonic transitions of the Neoproterozoic, including glaciogenic deposits and basal-Ediacaran cap carbonate of the Marinoan Snowball Earth. This stratigraphic record has the potential to provide a critical record of the climate, sea-level history, ocean chemistry, and time frames across the climate transition of the Marinoan Snowball deglaciation.
We first show a detailed study of the sedimentology and stratigraphy of the upper Blässkranz Formation and Tsabisis Formation cap carbonate to develop an environmental and sequence stratigraphic history spanning and following the deglaciation. In downdip areas Marinoan diamictite transitions upward into dolostone intermixed with sandstone and extrabasinal clasts that is gradually overlain by fine grained laminated dolostone. Updip localities show the diamictite is overlain by intercalated sandstones, gravels, and shales before an abrupt change to laminated dolostone of the cap carbonate. A succession of stromatolites, which become strongly elongate upward, prograde into the laminated dolostone in the updip localities. The stromatolites are overlain by laminated dolostone that grades upward into rhythmite with intercalations of shale. Near the top of the cap, rhythmites may be reworked into tabular intraclast conglomerate, locally intercalated with hummocky cross stratified sandstone, which passes upward into the shale and limestone members of the Tsabisis Formation. The lateral and vertical distribution of facies indicate a retreat of the shoreline and glacially sourced siliciclastics near the base of the cap carbonate, a shallowing succession to fair-weather wave base at the top of the stromatolite facies, and a second shallowing succession to storm wave base near the top of the cap carbonate. Maximum flooding occurred soon after the initiation of carbonate deposition and two sequence boundaries mark higher stratigraphic levels within the cap carbonate. With a sea-level history and chronological framework inferred from the sequence stratigraphy we can consider different mechanisms of sea-level change, which may reflect the timescale and synchronicity of deglaciation.
Next, we consider the structural and stratigraphic relationships between the Neoproterozoic units of the Naukluft Mountains to define and contextualize the extent of the terminal Marinoan geologic record. We show that the Northern Pavian Nappe, which includes the Marinoan-associated Blässkranz and Tsabisis formations, is stratigraphically succeeded by the dolostone dominated Kudu Nappe and is not correlated or genetically related to the nearby Southern Pavian Nappe. Additionally, the modified stratigraphic and structural relationships allow for a simplified nappe emplacement history that reduces the magnitude of shortening associated with convergence along the Damara Orogen.
Finally, we use sea-level modeling of the Naukluft Marinoan record to constrain the duration of global deglaciation. Using a range of reconstructed synchronous and continuous deglaciation models, we evaluate if the observed sea-level patterns of the Naukluft can be fully explained by glacial isostatic mechanisms driven by the deglaciation. Short Snowball deglaciation durations, on the order of ~2 kyr, result in exclusive sea-level rise, or sea-level rise followed by sea-level fall, but cannot drive two distinct phases of sea-level fall. However, for longer duration snowball deglaciations, of ~10-30 kyr, we can drive two distinct intervals of sea-level rise and fall across much of the width of a continental margin, consistent with the stratal patterns observed in Naukluft Mountains cap carbonate succession. Our spatially varying sea-level predictions resulting from longer duration deglaciations may be applicable in interpreting stratal patterns of other cap carbonate successions. Furthermore, this work underlines the need for better constraints on the areal distribution and volume of Marinoan ice sheets, including improved understanding of plausible deglacial durations using updated global climate models.
Vasilije Dobrosavljevic, Carnegie Science Earth & Planets Laboratory (EPL)
March 27, 2026 at 11:00 am (ESJ 0215)
Barbara Romanowicz - Helz Lecturer, University of California, Berkeley
April 3, 2026 at 11:00 am (ESJ 0215)
Cole Nypaver, Smithsonian Institution Center for Earth and Planetary Studies, National Air and Space Museum
April 10, 2026 at 11:00 am (ESJ 0215)
The coordinator for the Colloquium Series is Dr. Cecilia Sanders.