An experiment for 2021: Reviving the blog

Brian Romans wrote posts for his blog Clastic Detritus from 2005 to 2015 and, starting in 2021, he plans to reengage with this style of writing. Posts with this banner image will be used to signify a Clastic Detritus blog post and any viewpoints/opinions expressed are solely Brian Romans’ and not of students, post-docs, or collaborators of the VT Sedimentary Systems Research group or of his department or institution.

Remember blogs? Back in the 2000s and into the early 2010s, the ‘weblog’ venue for writing and sharing on the internet was quite popular, spawning various networks and grass-roots communities of people with shared interests. It was a whole thing. This was when I was in graduate school and the first few years after my Ph.D. and I found it to be both an enjoyable way to share and learn and also a vehicle for writing about science that wasn’t a technical paper/proposal but also not trying to be journalism or public outreach. I miss that outlet.

So, for 2021 I’m going to attempt to reengage with this style of writing as a way to ‘stretch those muscles’ a bit. I thought about doing this at the original site, but decided to make my life simpler by just using this research group website and identifying as a Clastic Detritus blog post with my ‘classic’ banner image and disclaimer at the top. I’m not going to be overly ambitious about it, I’m aiming for approximately one post per month. It’s an experiment, we’ll see how it goes! (I’m not going to have a comment thread as it would likely attract spam/trolls; you can find me on Twitter or reach out via email.)

A potential theme for some of the posts this year is exploring how geoscientists think about time. Over this recent holiday break, I reread the wonderful 2018 book Timefulness by Marcia Bjornerud and also read a fantastic new book by Vincent Ialenti called Deep Time Reckoning. Both books have similar subtitles: “How thinking like a geologist can help save the world” and “How future thinking can help Earth now”. Both of these works articulate one of the most valuable aspects of ‘deep time’ thinking common in geoscience — how studying longer timescales and reconstructing Earth history is critical for understanding our present and for thinking about our future. Not a new idea, to be sure, but these two books have refreshing takes on this notion in my opinion. Thus, I’ll likely write future posts about both of these.

As I’ve progressed in my own teaching, course development/design, and interaction with students, I’ve become increasingly interested in how we, as geoscientists, think about time. It’s not merely an appreciation for the vastness of Earth’s history or gaining knowledge about important processes that occur at very long timescales. Geoscientists also have the ability to consider a huge range of timescales, and can ‘zoom in’ and ‘zoom out’, temporally, with relative ease. We can intuitively identify and focus our thinking on a specific range of timescales for a certain question or problem. Indeed, these and similar are among the skills that Bjornerud has coined as timefulness. Deep time (long timescales and the distant past) is a key part of timefulness, but there’s more to it.

But, how do we generate this intuition? That is, how do students and novice geoscientists develop timefulness? And, how can I improve my teaching (and mentoring) to enhance that development? There’s a rich field of time-perception research as well as work by education researchers focused specifically on temporal reasoning to draw upon. For example, this GSA Special Paper from 2012 has several of insightful articles from geoscience education researchers about teaching and learning related to geologic time. My goal isn’t an exhaustive treatment of everything there is to know — I’m not an education researcher or cognitive psychologist and don’t pretend to be. My aim isn’t to write scholarly pieces suitable for journals — my goal is simply to share some aspects I found interesting in my own exploration and learning.

Again, getting back into this more stream-of-consciousness and ‘low stakes’ style of writing is an experiment. Maybe it gathers some momentum, maybe it fizzles, stay tuned. The first real post (in a few weeks time) will be about one, or maybe both, of the books mentioned above: Timefulness and Deep Time Reckoning.

Brian Romans mini-lecture about the Anthropocene (for Fall 2020 Sed-Strat course)

The final video ‘mini-lecture’ for my Sedimentology-Stratigraphy course includes some of my thoughts about how the ideas of the ‘Anthropocene’ intersect and connect with the concepts and skills associated with Sed-Strat. There was some broader interest in this so I decided to post the ~17-minute long video here for anyone to watch:

As I mention in the beginning, keep in mind a couple of things: (1) this is merely and entry point into these ideas, I provide some ideas for further reading and exploration at the end of the video, and (2) this was designed for juniors/seniors in our undergraduate (B.S. in Geosciences) program and in context of a particular course and not created with a broader audience in mind.

Technical note: The video that is embedded within our course management system includes close captioning, but I could not get that version to embed on this site. So, the video above does not have closed captioning, my apologies.

Drew Parent’s GSA 2020 presentation on U.S. Atlantic margin sedimentation during the Early Cretaceous

Sedimentary Systems Research group Ph.D. student Drew Parent gave a talk at the 2020 Geological Society of American (GSA) annual meeting about his work using detrital zircon geochronology to investigate passive-margin sedimentation on the U.S. mid-Atlantic during the Early Cretaceous.

Check out this recording of the talk:

Sediment recycling from strontium isotope ages of reworked fossils

Sedimentary Systems Research group alum Neal Auchter (Ph.D. 2016) has a new paper out in Geology based on one of his dissertation chapters.

In this study, we use strontium isotope stratigraphy on reworked fossil fragments from the Cretaceous Tres Pasos Formation (southern Chile) to document sediment recycling. Strontium isotope stratigraphy is an established method to determine numerical ages of primary calcium carbonate from the 87Sr/86Sr ratio. This works better in some periods of Earth history than others, and the Late Cretaceous is one of those periods. Check out this 2012 review by McArthur and co-authors to learn all about this method.

However, we apply strontium isotope stratigraphy in a different way. Instead of determining 87Sr/86Sr from shelly fossils found in situ (e.g., in growth position), we made this measurement on fossil fragments found in coarse-grained turbidite deposits. In other words, the fossils were eroded, transported, and deposited some time after they formed. The conceptual diagram below (Fig. 1 from the paper) puts into context our use of strontium isotope ages with commonly used zircon (U-Pb) dating methods. The important difference between detrital zircon and detrital strontium, however, is that the latter helps constrain recycling from within the marine basin.

Over the course of a few field seasons, Neal and others in the Chile Slope Systems team collected shell-fragment samples from across the ~100 km-long Tres Pasos outcrop belt. The figure below (Fig. 3B from the paper) summarizes the detrital strontium isotope stratigraphy data (n=94 ages). The samples are organized on the horizontal axis by sample sets (L1-L13), which represent stratigraphic units whose depositional age generally youngs southward (to the right). The gray rectangles are maximum depositional age ranges as defined by our published detrital zircon work. The strontium ages are color/symbol-coded by specimen type (inoceramid, oyster, gastropod, and bivalve).

The primary observation in the data plot above is that very few of the strontium ages are within the gray rectangles. In other words, most of the strontium ages are older than depositional age and, in some cases, >10 Myr older. We interpret these fossil fragments to have been recycled during Tres Pasos deposition. For example, downcutting by a submarine canyon could have tapped into the underlying older deposits that were then transported further into the basin via turbidity currents. Considering the tectonically active setting, even minor uplift along the basin margin, could have contributed to the exhumation of shallowly buried deposits then available to be reworked further into the basin.

Although there is uncertainty about the exact mechanism (or combination of mechanisms) that led to the recycling we emphasize that with this method we can (1) document that intrbasinal recycling is occurring and (2) constrain the residence time of shelly fossils between initial calcium carbonate precipitation and eventual deposition. The figure below (Fig. 4 from the paper) depicts the regional stratigraphy and our interpretation of how proportions of specimen type (namely, inoceramid versus oyster) represent intrabasinal source terranes. Check out the paper — it’s open access! — for all the details.

Congrats to Neal on getting this work out there! It can take a lot of effort to get a thesis/dissertation chapter refined, submitted, and eventually published after graduate school is officially done (for example, when life events and new opportunities become the priority).

Drone videos from Patagonia field work

Ph.D. candidate and Sedimentary Systems Research group member Sebastian Kaempfe created these two jaw-dropping drone videos of outcrops of the Cretaceous Magallanes Basin in southern Chile. (I recommend watching on a laptop or big monitor in ‘full screen’ view.)

The first video is from a locale known locally as El Chingue Bluff (the word ‘chingue’ means skunk in this part of Chile and is the name of the estancia). This turbiditic sandstone package forming the top of the bluff is interpreted as a partially ponded intra-slope system marking the transition from underlying Cerro Toro Formation to overlying Tres Pasos Formation.

This second video (below) is from the eastern end of a mountain range called Sierra del Toro and shows off strata that are interpreted as overbank (levee) deposits of the Cerro Toro Formation deep-marine channel system.

To see more of Sebastian’s photos and videos, please visit his Instagram page.

Presentations at AGU 2019

Three out of four of the members of Sedimentary Systems Research group will be attending the American Geophysical Union (AGU) Fall 2019 meeting in San Francisco next week. Here’s a rundown of our activities:

Monday (Dec 9) morning:

  • Ph.D. candidate Drew Parent is presenting a poster summarizing our flume experiment research testing the ‘sortable silt’ bottom-current proxy — Sorting of silt by bottom currents part II: Grain-size metrics and applicability to paleoceanography (PP11D-1415)
  • Also check out part I of this work, a companion poster in the same session led by our collaborator Kyle Strom from the Dept. of Civil & Environmental Engineering, which summarizes the flume design and details about the experiments — Sorting of silt by bottom currents part I: Laboratory experiments (PP11D-1412)

Friday (Dec 13) morning:

  • Brian Romans is giving a talk in the session Multiproxy Approaches to Resolving Climatic and Tectonic Controls on Landscape Evolution about sediment recycling based on work from the Magallanes Basin — Effects of intrabasinal recycling on the preservation of tectonic and climate signal determined from provenance analysis (T52B-02) — this talk is at 10:35am in Moscone West 2004 L2

Friday (Dec 13) afternoon:

  • Ph.D. candidate Natalia Varela is presenting a poster in the session Southern Ocean Climate and Antarctic Ice Sheet Dynamics with some brand new results from IODP Exp 374 core samples analyzed over the past several months — A physical record of Antarctic Bottom Water (AABW) outflow in the Ross Sea from the late Pliocene (3.3 Ma) through present (PP53C-1456)

We are looking forward to sharing our latest work, hope to see you there!

Summer 2019 Update

It’s been an exciting several months since the last update. The Sedimentary Systems Research group and collaborators are busy working on a bunch of different projects.

First off, some papers that have been published so far in 2019:

We have a couple other papers currently in review and several others in the pipeline for 2020.

Here’s a brief update of what we’ve been up to so far in  2019 (this is just a sampling):

Sebastian Kaempfe (PhD student) had another successful field season in southern Chile in February-March, collecting loads of data for all three chapters of his PhD dissertation. He presented a poster at the AAPG Annual Meeting in San Antonio in May 2019 as well as presenting an update to the sponsors of the Chile Slope Systems program. The biggest highlight of the past several months for Sebastian is successfully passing his PhD preliminary examination, congrats SK!!

Natalia Varela (PhD student) had another busy spring semester, taking multiple classes and TAing our department’s “Resources” course for non-majors. During the semester and into this summer, she has been hard at work in our lab processing samples from IODP Exp 374 (West Antarctic Ice Sheet History, Ross Sea) and generating grain-size data. Natalia also attended the Antarctic Core Workshop in June 2019 organized by IODP and held at Texas A&M University.

Drew Parent (PhD student) is juggling multiple research projects this summer, making significant progress on finalizing the data set of terrigenous grain-size data from Newfoundland contourite drifts (IODP Exp 342), which we are using to reconstruct the history of deep-ocean circulation in the North Atlantic in response to the Eocene-Oligocene Transition. Additionally, he and Brian Romans visited the Maryland Geological Survey in May 2019 to sample cores of Early Cretaceous sandstones for detrital zircon work. Drew visited Danny Stockli’s (UT Austin) lab in August 2019 to generate U-Pb ages from detrital zircons from U.S. Atlantic continental margin sandstones.

Brian Romans (director of SSR) finished the second half of a speaking tour for the IODP Discovery Lecture Series in the early part of 2019 with visits to Scripps Institution of Oceanography, University of Cincinnati, Colorado School of Mines, University Texas Austin, University Nebraska-Lincoln, and University of Arkansas. In the spring semester, Brian led a graduate student seminar on deep-marine depositional systems where eleven students chose topics, readings, gave a presentation, and led a discussion. Thanks to the enthusiasm and efforts of the participating students we also ran a field trip to outcrops in the region to view sediment gravity flow deposits in Paleozoic strata.

Winter 2019 Update

It’s been quite a while since I provided an update on what the Virginia Tech Sedimentary Systems Research group is up to. Here’s a rundown of our activities over the past several months:

First, although it’s always sad to see a member of the group leave, I am also filled with joy to see them move on to the next stage. Former PhD student and post-doc of the group, Cody Mason, is now an Assistant Professor at the University of Western Georgia. Cody finished up his post-doc in summer 2018 and started at UWG that fall. We have some results from detrital zircon studies of the Amazon submarine fan we shared in this EarthArXiv pre-print, with the peer-reviewed paper (hopefully) coming very soon. I’m looking forward to collaborating with Professor Mason in the years to come!

Ph.D. student Natalia Varela has finished her first full year in the program and has hit the ground running. In summer 2018, Natalia attended the IODP Petrophysics Summer School in Leicester, UK and, later that summer, participated in the IODP Expedition 374 sampling party at the Gulf Coast Repository at Texas A&M University. Natalia’s dissertation research is focused on Miocene through Pleistocene continental slope deposits recovered during IODP Exp 374 in the Ross Sea, Antarctica (read the Exp 374 Preliminary Report). In addition to her research activities, Natalia has also been a teaching assistant for Sedimentology-Stratigraphy and Natural Resources courses.

Ph.D. student Sebastian Kaempfe is in southern Chile right now for his third field season. His dissertation research is part of the industry-funded Chile Slope Systems project, a multi-institution collaboration with colleagues and students at the University of Calgary and Colorado State University. Sebastian presented preliminary results of the first chapter of his dissertation work at the AAPG Annual Convention and Exhibition in May 2018 and also participated in the annual Chile Geological Congress in Concepcion, Chile in November 2018. Sebastian TA’d the Sedimentology-Stratigraphy course in fall 2018.

Ph.D. student Andrew Parent has been quite busy both leading and contributing to various different projects. A lot of progress was made in generating a late Eocene-mid Oligocene terrigenous grain-size record from IODP Site U1406 (Newfoundland Ridge drifts) to complement former SSR student Kristin Chilton’s record from Site U1411. Drew presented a poster with these new data at the AGU Fall Meeting in Washington, D.C. in December 2018. Drew and I have also been collaborating with researchers in the Civil & Environmental Engineering department on an American Chemical Society-funded grant on ‘sortable silt’ flume experiments. CEE master’s student Jeff Culp presented a poster of our preliminary results at AGU. Finally, Drew worked with collaborators in the Mining Engineering department to help with seismic stratigraphic characterization of the South Carolina Trough for a Dept. of Energy-funded project to characterize offshore carbon storage potential.

As for me, I’ve been traveling around the U.S. as one of the IODP distinguished lecturers for the 2018-2019 academic year. I’m honored to be among the six lecturers for this year and have been having tons of fun sharing our IODP science. My talk summarizes our work on the Newfoundland drifts (Exp 342) and previews the research to come from the Ross Sea (Exp 374). Here’s a 4-minute video that science communicator Kim Kenney produced as both a summary and advertisement of the talk:

Welcome new Ph.D. student Natalia Varela

I’m very happy to welcome Natalia Varela to the VT Sedimentary Systems Research group. Natalia arrived in January 2018 as a Ph.D. student.

Natalia is from Santiago, Chile, and received a Bachelor’s in Geology at the Universidad de Concepción in 2009 and earned her professional degree in 2015. She has participated in several stratigraphy-related projects in central Chile, Patagonia, and Antarctica, studying the organic portion of Cretaceous formations and their correlation with the depositional environment. Natalia also has experience working as a geologist for energy, mining, and environmental companies.

Natalia will be working on IODP Expedition 374 (Ross Sea West Antarctic Ice Sheet History) samples and data for her dissertation research. Specifically, Natalia will use the occurrence and character of thin-bedded, overbank turbidites recovered from a core drilled on a continental rise canyon-channel system to investigate the Antarctic Bottom Water (AABW) production history in the Pliocene-Pleistocene. For another project, Natalia will use downhole logs from a continental shelf site in the Ross Sea to characterize ice-sheet-proximal lithofacies and examine ice sheet advance/retreat history over the past ~17 million years.

We are excited to have her on board. ¡Bienvenida Natalia!

New paper on catchment-fan system erosion rates during Pleistocene climate change

We have a new paper out in Earth and Planetary Science Letters led by former Sedimentary Systems Research group Ph.D. student and current post-doc Cody Mason.

Sediment supply has long been considered an important factor in observed depositional patterns and facies in sedimentary basins. Indeed, accommodation and supply are commonly invoked as the two fundamental controls on stratigraphy. However, directly measuring paleo-sediment supply from the stratigraphic record is a significant challenge. In most cases, sediment supply is estimated in a relative sense. Thus, the aim of this study was to calculate sediment supply, in an absolute sense, from outcropping Pleistocene alluvial and lacustrine deposits using cosmogenic radionuclides. We applied the catchment-integrated denudation (erosion) rate methodology that is typically used for modern river sediments to a succession of now-exhumed catchment-outlet deposits in Panamint Valley, California. This approach allowed us to generate a time series of paleo-erosion rates (which we use as a proxy for sediment supply).

The figure below (Fig. 6 from the paper) is a summary of our results. In order to calculate paleo-denudation rate we needed some constraint on depositional age, which we got using 10Be/26Al burial dating techniques. The ~180 m thick succession we studied ranges from ~1.2 Ma to ~0.3 Ma old (part D of the figure below). 

The resultant denudation rates (part E of figure above) show that the sediment supply out of the catchment varied from as low as ~24 mm/kyr to as high as ~54 mm/kyr with a long-term mean rate of ~36 mm/kyr. In the paper, we discuss the potential controls of glacial-interglacial climatic variability and Mid-Pleistocene Transition on source-to-sink dynamics. Additionally, we present an end-member mixing model to explore how sediment storage and/or landslide processes in the upper catchment may have influenced our paleoerosion rate calculations.

If you cannot access the EPSL version, you can get a freely available version on EarthArXiv (or feel free to email us and we can send you a copy).

Additional thanks to Ron Schott for joining us out in the field area during one our trips to take some beautiful GigaPan images of the outcrop (see the images called ‘Ballarat Delta’).