Publications

A Bayesian inversion for emissions and export productivity across the end-Cretaceous boundary

Editor’s summary: The end-Cretaceous mass extinction, which included the elimination of all nonavian dinosaurs, occurred after the impact of a meteorite and during a stretch of large-scale volcanism. Although it is known that the impact is temporally linked to the extinction, the relative roles are hard to disentangle. Cox and Keller used an inversion scheme that is agnostic about what occurred geologically but provides best guesses for a number of variables, including carbon and sulfur dioxide release. These gases cause environmental changes, and the results may argue for a two-stage extinction related to the volcanism. This approach should be useful for disentangling other complex events in Earth systems and elsewhere. —Brent Grocholski

A Bayesian framework for subsidence modeling in sedimentary basins: A case study of the Tonian Akademikerbreen Group of Svalbard, Norway

A Bayesian formulation for estimating the composition of Earth’s crust

The composition of the continental crust is important for understanding Earth's evolution on global and regional scales. We build on previous work estimating Earth's composition with a new approach using Bayesian statistics, where prior information from rocks sampled at Earth's surface is combined with information from seismic properties to estimate Earth's crustal composition at depth. To connect seismic properties and compositions, we model the seismic properties of rock compositions. Our approach provides rigorous uncertainty estimates for crust composition at depth. By quantifying the sources of this uncertainty, we are able to propose a path forward for future work to further improve compositional estimates for Earth's crust at depth.

Reply to Henehan and Witts: Continental flood basalts drive extinctions after the mid-Mesozoic

Pb-loss-aware Eruption/Deposition Age Estimation

Thermochron.jl: Open-source time-Temperature inversion of thermochronometric data

Prolonged Slip on the South Tibetan Detachment Constrains Tectonic Models for Synorogenic Extension in the Central Himalaya

Continental flood basalts drive Phanerozoic extinctions

Although the causes of the five largest mass extinctions remain controversial, geochronological improvements have revealed an apparent correlation between large igneous provinces (LIPs) and periods of Phanerozoic faunal turnover. This paper establishes that this relationship is unlikely to occur by chance and defines an eruptive rate threshold, above which known continental LIPs correlate with large extinctions. Continental LIPs also have an approximately linear relationship between their eruptive rate and extinction magnitude. It is difficult to attribute the causality of any one extreme event like an extinction with certainty, but there is an overall correlation between continental LIPs and extinction events that warrants consideration.

See also the Dartmouth News story by Harini Barath!

Cryogenian glacial erosion of the central Canadian Shield: The “late” Great Unconformity on thin ice

Possibly the best-resolved Cryogenian exhumation signal yet!

Onset of long-lived silicic and alkaline magmatism in eastern North America preceded Central Atlantic Magmatic Province emplacement

Reply to Flowers et. al.: Existing thermochronologic data constrain Snowball glacial erosion below the Great Unconformity

Volcano-pluton connections at the Lake City magmatic center (Colorado, USA)

Timescales for pluton growth, magma-chamber formation and super-eruptions

Thermochronologic constraints on the origin of the Great Unconformity

The Great Unconformity involves a common gap of hundreds of millions to billions of years in the geologic record. The cause of this missing time has long eluded explanation, but recently two opposing hypotheses claim either a glacial or a plate tectonic origin in the Neoproterozoic. We provide thermochronologic evidence of rock cooling and multiple kilometers of exhumation in the Cryogenian Period in support of a glacial origin for erosion contributing to the composite basement nonconformity found across the North American interior. The broad synchronicity of this cooling signal at the continental scale can only be readily explained by glacial denudation.

Metasediment-derived Melts in Subduction-zone Magmas and their Influence on Crustal Evolution

The Sedimentary Geochemistry and Paleoenvironments Project

Igneous rock area and age in continental crust

Zircon U-Pb Geochronology Constrains Continental Expression of Great Meteor Hotspot Magmatism

The paleogeography of Laurentia in its early years: new constraints from the Paleoproterozoic East-Central Minnesota batholith

An evaluation of Deccan Traps eruption rates using geochronologic data

Curation and Analysis of Global Sedimentary Geochemical Data to Inform Earth History

The composition and weathering of the continents over geologic time

Heterogeneous Hadean crust with ambient mantle affinity recorded in detrital zircons of the Green Sandstone Bed, South Africa

Increased ecological resource variability during a critical transition in hominin evolution

Constraining crustal silica on ancient Earth

On geologic timescales, Earth’s habitable climate is maintained by a negative feedback process wherein atmospheric CO₂ is consumed by reaction with silicate rocks during erosion and weathering. However, relative to modern continental crust, many models propose an ancient crust that was thinner, denser, and significantly lower in silica for the first 1 to 2 billion years of Earth history. Like modern oceanic crust, such mafic crust would likely be poorly exposed to the atmosphere, resulting in a less climatically stable early Earth. We find that two geologic processes (mantle cooling and atmospheric oxidation) significantly compromise some previous methods for estimating ancient crustal composition. Accounting for these factors results in estimates much closer to the composition of modern continental crust.

Stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis of microfractured Hadean zircon

The oldest known minerals on Earth are Hadean (> 4.0 Ga) zircons from the Jack Hills, Australia. We present the first application to such Hadean zircons of stepwise chemical abrasion isotope dilution thermal ionization mass spectrometry with trace element analysis (stepwise CA-ID-TIMS-TEA). We examine the evolution in U-Pb age and trace element chemistry of zircon domains accessed by successive chemical abrasion steps in the context of the geologic history of the Jack Hills zircons.

Chronostratigraphy of the Baringo-Tugen-Barsemoi (HSPDP-BTB13-1A) core – 40Ar/39Ar dating, magnetostratigraphy, tephrostratigraphy, sequence stratigraphy and Bayesian age modeling

Coupled stratigraphic and U-Pb zircon age constraints on the late Paleozoic icehouse-to-greenhouse turnover in south-central Gondwana

Chronostratigraphic model of a high-resolution drill core record of the past million years from the Koora Basin, south Kenya Rift: Overcoming the difficulties of variable sedimentation rate and hiatuses

U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction

See also Perspective by Seth Burgess

Neoproterozoic glacial origin of the Great Unconformity

It has long been observed that the sequence of sedimentary rocks deposited in the past half-billion years often sharply overlies older igneous or metamorphic basement at an erosional surface known as the Great Unconformity. We provide evidence that this unconformity may record rapid erosion during Neoproterozoic “snowball Earth” glaciations. We show that the extent of Phanerozoic sedimentation in shallow continental seas can be accurately reproduced by modeling the accommodation space produced by the proposed glacial erosion, underlining the importance of glaciation as a means for lowering erosional base level. These results provide constraints on the sedimentary and geochemical environment in which the first multicellular animals evolved and diversified in the “Cambrian explosion” following the unconformity.

Chron.jl: A Bayesian framework for integrated eruption age and age-depth modelling

A model framework for the interpretation of mineral age spectra in stratigraphic context

A Stochastic Sampling Approach to Zircon Eruption Age Interpretation

“Weighted Means Considered Harmful” – try the alternative here!

New measurement of the 238U decay constant with inductively coupled plasma mass spectrometry

A New Workflow to Assess Emplacement Duration and Melt Residence Time of Compositionally Diverse Magmas Emplaced in a Sub-volcanic Reservoir

Potassic, high-silica Hadean crust

A record of deep-ocean dissolved O2 from the oxidation state of iron in submarine basalts

UC Berkeley press release

Plate tectonics and continental basaltic geochemistry throughout Earth history

In this longer-format paper we examine in detail the record of basaltic rocks preserved in the continental crust, building on the weighted bootstrap resampling procedure of Keller and Schoene, 2012. A range of rapid trace element variations in the basaltic record can be explained as a result of mantle melting systematics (changing partition coefficients as a result of Grt and Cpx-out). Both trace element signatures of slab fluid input and major element signatures of calc-alkaline vs tholeiitic differentiation are remarkably stable and consistently arc-like, strongly suggesting the occurence of subduction and plate tectonics throughout the preserved rock record (back to at least 3.85 Ga). While some non-plate tectonic models may produce some flux melting, a virtually constant proportion of flux to decompression melting in the preserved continental record is a tall order for any non-plate model for Archean tectonics.

Zircon age-temperature-compositional spectra in plutonic rocks

Complementary crystal accumulation and rhyolite melt segregation in a late Miocene Andean pluton

Temporal variation in relative zircon abundance throughout Earth history

Here we investigated the variation in the amount of zircon expected to saturate from magmas of different ages throughout Earth history by running full MELTS simulations along with trace element partitioning calculations (on a local Princeton University cluster) for each of the ~70,000 samples in the Keller & Schoene (2012) dataset. We found that older magmas crystallize substantially less zircon per unit mass due to the geochemical consequences of secular mantle cooling – suggesting that a larger volume of felsic magmatism is required to explain the Archean (and perhaps the Hadean) zircon record than previously considered. We note also that anorthosite flotation crust is largely zircon free and thus invisible to zircon-based crustal growth models, with implications explored in the supplement.

Early formation of the Moon 4.51 billion years ago

Geochemical Evolution of Earth’s Continental Crust

Ph.D. Dissertation. Advisor: Blair Schoene

Zircon record of the plutonic-volcanic connection and protracted rhyolite melt evolution

Magma emplacement, differentiation and cooling in the middle crust: Integrated zircon geochronological–geochemical constraints from the Bergell Intrusion, Central Alps

Volcanic–plutonic parity and the differentiation of the continental crust

Here we used the weighted bootstrap resampling approach from our 2012 paper to address the longstanding question of volcanic-plutonic parity. The results indicate that felsic plutons are not (on average) significantly more cumulate than felsic volcanics, favor fractional crystallization as the predominant mechanism of geochemical differentiation, and suggest the influence of magmatic water content on magma stalling and intrusion. This paper was my first foray into high-performance computing, running ~1.3 million pMELTS simulations to invert for P-T paths and water contents that produce differentiation trends similar to the those observed in the natural dataset.

Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5 Gyr ago

My first significant computational work - originally a side project to work on as a grad student while waiting for Blair's clean lab to be built. We were surprised by the strength and consistency of the geochemical trends we observed on Gyr timescales. The simplest signals directly reflect secular mantle cooling, but others hint at a change in crustal evolution that appears to coincide temporally with oxidation of the surface Earth in the Great Oxygenation Event.

Chemical Constraints on the Origin of the Frailes Volcanic Complex in the Central Andean Altiplano Plateau, Bolivia

B.S. Thesis. Advisor: Suzanne Mahlburg Kay