C. Brenhin Keller

C. Brenhin Keller

Assistant Professor
of Earth Sciences
Dartmouth College

cbkeller at dartmouth . edu

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A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.

Pages

Posts

Looking for students

Published:

In March of 2019 I’ll be joining the Department of Earth Sciences at Dartmouth as an assistant professor, so will be looking for future grad students!

Plate tectonics and basalt geochemistry

Published:

New paper on basalt geochemistry with implications for the prevalence of plate tectonics and arc-style magmatism (hydrous flux melting) throughout the preserved continental rock record. Read all about it here!

fieldwork

Salient Platform, British Columbia

Published:

The reef core of the Ediacaran Salient Platform is spectacularly exposed atop the Interbedded Succession of the Upper Miette Group on the east face of Mount Machray as viewed from Salient Mountain, British Columbia.

Medicine Bow Mountains, Wyoming

Published:

Microbialitic metadolomite in the Paleoproterozoic (~2.05 Ga) Nash Fork formation, “valley of the stromatolites”, Medicine Bow Mountains, Wyoming.

The Great Unconformity

Published:

The Ignacio Quartzite (of contested age, though likely Cambrian) unconformably overlies the Mesoproterozoic (1.433 Ga) Eolus Granite in the Needle Mountains, Colorado.

Wernecke Mountains, Yukon Territory

Published:

The East Rackla River valley viewed from the north, looking towards Mount Mervyn. The Dawson Thrust runs parallel to the river valley.

Hell Creek, Montana

Published:

The K-Pg boundary claystone (lower pencil) just below the IrZ tonstein (upper pencil) within the IrZ coal at Herpejunk, Hell Creek, Montana

publications

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

C. Brenhin Keller and Blair Schoene.
Nature, 2012: https://doi.org/10.1038/nature11024
Preprint     Code and Data   

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.

Volcanic–plutonic parity and the differentiation of the continental crust

C. Brenhin Keller, Blair Schoene, Melanie Barboni, Kyle M. Samperton, and Jon M. Husson.
Nature, 2015: https://doi.org/10.1038/nature14584
Preprint     Code and Data   

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.

Temporal variation in relative zircon abundance throughout Earth history

C. Brenhin Keller, Patrick Boehnke, and Blair Schoene
Geochemical Perspectives Letters, 2017: https://doi.org/10.7185/geochemlet.1721
Preprint     PDF     Code and Data   

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.

Plate tectonics and continental basaltic geochemistry throughout Earth history

Brenhin Keller and Blair Schoene.
Earth and Planetary Science Letters, 2018: https://doi.org/10.1016/j.epsl.2017.10.031
Preprint     Code and Data   

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.

Neoproterozoic glacial origin of the Great Unconformity

C. Brenhin Keller, Jon M. Husson, Ross N. Mitchell, William F. Bottke, Thomas M. Gernon, Patrick Boehnke, Elizabeth A. Bell, Nicholas L. Swanson-Hysell, and Shanan E. Peters
Proceedings of the National Academy of Sciences, 2019: https://doi.org/10.1073/pnas.1804350116
Preprint     PDF     Code and Data   

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.

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

Alan Deino, Rene Dommain, C. Brenhin Keller, Richard Potts, Anna Behrensmeyer, Emily Beverly, John King, Clifford Heil, Mona Stockhecke, Erik Brown, Jessica Moerman, Peter de Menocal, and the Olorgesailie Drilling Project Scientific Team
Quaternary Science Reviews, 2019: https://doi.org/10.1016/j.quascirev.2019.05.009

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

C. Brenhin Keller, Patrick Boehnke, Blair Schoene, and T. Mark Harrison
Geochronology, 2019: https://doi.org/10.5194/gchron-1-85-2019
Preprint     PDF     Code and Data   

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.

Constraining crustal silica on ancient Earth

C. Brenhin Keller and T. Mark Harrison
Proceedings of the National Academy of Sciences, 2020: https://doi.org/10.1073/pnas.2009431117
Preprint     Code and Data   

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.

Increased ecological resource variability during a critical transition in hominin evolution

Richard Potts, René Dommain, Jessica W. Moerman1, Anna K. Behrensmeyer, Alan L. Deino, Simon Riedl, Emily J. Beverly, Erik T. Brown, Daniel Deocampo, Rahab Kinyanjui, Rachel Lupien, R. Bernhart Owen, Nathan Rabideaux, James M. Russell, Mona Stockhecke, Peter deMenocal, J. Tyler Faith, Yannick Garcin, Anders Noren, Jennifer J. Scott, David Western, Jordon Bright, Jennifer B. Clark, Andrew S. Cohen, C. Brenhin Keller, John King, Naomi E. Levin, Kristina Brady Shannon, Veronica Muiruri, Robin W. Renaut, Stephen M. Rucina and Kevin Uno
Science Advances, 2020: https://doi.org/10.1126/sciadv.abc8975

The composition and weathering of the continents over geologic time

Alex G. Lipp, Oliver Shorttle, Erik A. Sperling, Jochen J. Brocks, Devon Cole, Peter W. Crockford, Lucas Del Mouro, Keith Dewing, Stephen Q. Dornbos, Joseph F. Emmings, Una C. Farrell, Amber Jarrett, Benjamin W. Johnson, Pavel Kabanov, C. Brenhin Keller, Marcus Kunzmann, Austin J. Miller, N. Tanner Mills, Brennan O’Connell, Shanan E. Peters, Noah J. Planavsky, Samantha R. Ritzer, Shane D. Schoepfer, Philip R. Wilby, and Jianghai Yang
Geochemical Perspectives Letters, 2021: https://doi.org/10.7185/geochemlet.2109
PDF    

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

Akshay Mehra, C. Brenhin Keller, Tianran Zhang, Nicholas J. Tosca, Scott M. McLennan, Erik Sperling, Una Farrell, Jochen Brocks, Donald Canfield, Devon Cole, Peter Crockford, Huan Cui, Tais W. Dahl, Keith Dewing, Joe Emmings, Robert R Gaines, Tim Gibson, Geoffrey J. Gilleaudeau, Romain Guilbaud, Malcolm Hodgkiss, Amber Jarrett, Pavel Kabanov, Marcus Kunzmann, Chao Li, David K Loydell, Xinze Lu, Austin Miller, N. Tanner Mills, Lucas D. Mouro, Brennan O’Connell, Shanan E. Peters, Simon Poulton, Samantha R. Ritzer, Emmy Smith, Philip Wilby, Christina Woltz, Justin V. Strauss
GSA Today, 2021: https://doi.org/10.1130/GSATG484A.1
PDF    

The Sedimentary Geochemistry and Paleoenvironments Project

Úna C. Farrell, Rifaat Samawi, Savitha Anjanappa, Roman Klykov, Oyeleye O. Adeboye, Heda Agic, Anne-Sofie C. Ahm, Thomas H. Boag, Fred Bowyer, Jochen J. Brocks, Tessa N. Brunoir, Donald E. Canfield, Xiaoyan Chen, Meng Cheng, Matthew O. Clarkson, Devon B. Cole, David R. Cordie, Peter W. Crockford, Huan Cui, Tais W. Dahl, Lucas D. Mouro, Keith Dewing, Stephen Q. Dornbos, Nadja Drabon, Julie A. Dumoulin, Joseph F. Emmings, Cecilia R. Endriga, Tiffani A. Fraser, Robert R. Gaines, Richard M. Gaschnig, Timothy M. Gibson, Geoffrey J. Gilleaudeau, Benjamin C. Gill, Karin Goldberg, Romain Guilbaud, Galen P. Halverson, Emma U. Hammarlund, Kalev G. Hantsoo, Miles A. Henderson, Malcolm S.W. Hodgskiss, Tristan J. Horner, Jon M. Husson, Benjamin Johnson, Pavel Kabanov, C. Brenhin Keller, Julien Kimmig, Michael A. Kipp, Andrew H. Knoll, Timmu Kreitsmann, Marcus Kunzmann, Florian Kurzweil, Matthew A. LeRoy, Chao Li, Alex G. Lipp, David K. Loydell, Xinze Lu, Francis A. Macdonald, Joseph M. Magnall, Kaarel Mänd, Akshay Mehra, Michael J. Melchin, Austin J. Miller, N. Tanner Mills, Chiza N. Mwinde, Brennan O'Connell, Lawrence M. Och, Frantz Ossa Ossa, Anais Pagès, Kärt Paiste, Camille A. Partin, Shanan E. Peters, Peter Petrov, Tiffany L. Playter, Stephanie Plaza-Torres, Susannah M. Porter, Simon W. Poulton, Sara B. Pruss, Sylvain Richoz, Samantha R. Ritzer, Alan D. Rooney, Swapan K. Sahoo, Shane D. Schoepfer, Judith A. Sclafani, Yanan Shen, Oliver Shorttle, Sarah P. Slotznick, Emily F. Smith, Sam Spinks, Richard G. Stockey, Justin V. Strauss, Eva E. Stüeken, Sabrina Tecklenburg, Danielle Thomson, Nicholas J. Tosca, Gabriel J. Uhlein, Maoli N. Vizcaíno, Huajian Wang, Tristan White, Philip R. Wilby, Christina R. Woltz, Rachel A. Wood, Lei Xiang, Inessa A. Yurchenko, Tianran Zhang, Noah J. Planavsky, Kimberly V. Lau, David T. Johnston, and Erik A. Sperling
Geobiology, 2021: https://doi.org/10.1111/gbi.12462
PDF    

Thermochronologic constraints on the origin of the Great Unconformity

Kalin T. McDannell, C. Brenhin Keller, William R. Guenthner, Peter K. Zeitler, and David L. Shuster
Proceedings of the National Academy of Sciences, 2022: https://doi.org/10.1073/pnas.2118682119
Preprint     PDF     Code and Data   

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.

Continental flood basalts drive Phanerozoic extinctions

Theodore Green, Paul R. Renne, and C. Brenhin Keller
Proceedings of the National Academy of Sciences, 2022: https://doi.org/10.1073/pnas.2120441119
Code and Data   

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!

talks

teaching

EARS 80.03: Technical Computation in the Earth Sciences, Fall 2020

Undergraduate/Graduate Course, Dartmouth College, Department of Earth Sciences, 2020

Course overview:

Driven by increasing data availability, processing power, and model sophistication, scientific or technical computation has become increasingly central to basic research in the Earth Sciences. This course aims to provide Earth Science students with a working introduction to scientific computation including (1) hands-on experience applying common, widely applicable sampling and inversion algorithms to classic Earth Science problems; (2) an awareness of the factors limiting efficiency and scalability when working with large datasets; and (3) an introduction to some of the tools and best practices of software engineering used to produce more robust, maintainable software.

EARS 13: Introduction to Computational Methods in Earth Science, Winter 2021

Undergraduate Course, Dartmouth College, Department of Earth Sciences, 2021

Course overview:

This course aims to provide students with a hands-on introduction to the use and analysis of large, open datasets in the Earth Sciences. Along the way, we will introduce (in lab) some of the basic concepts of programming, as code literacy is increasingly obligator in Earth Science. Prior programming experience may be helpful, but is not required. After introducing some basic concepts and tools, each student will work with the instructor to find a real data analysis question that can be addressed (as a final project) using the techniques learned in class.