Wooster Geologists

Our group published a new paper today in Science Advances, which suggests that ice-flow models that predict future sea-level rise are missing an important process: Basal channels, which are “upside-down rivers” of buoyant water flowing along the undersides of ice shelves, have formed at the margins of some of Antarctica’s most important ice streams. For example, Pine Island Glacier, shown below in a 2007 NASA MODIS satellite image, has basal channels beneath both of its weak “shear-margins” (red dashed lines). We know warm water is flowing through these channels because they create open-water areas, called “polynyas,” at the ice-shelf edge. These channels are weakening the weakest areas of fast-flowing ice streams, making them more susceptible to ocean-driven break-up.

Check out Wooster’s press release here: https://news.wooster.edu/news/2019/10/wooster-professor-is-lead-author-in-new-study-on-antarctic-conditions-that-are-causing-sea-level-rise/

The full article is open-access and can be downloaded from Science Advances: https://advances.sciencemag.org/content/advances/5/10/eaax2215.full.pdf

I have long enjoyed exploring the Ordovician and Silurian rocks of Estonia with my Estonian friend Olev Vinn. We have done a lot of work together, and Estonia continues to provide fascinating fossils for our studies. Our circle of paleontologists has expanded continually over the years in Estonia, including other Estonians, Brits and Americans (along with many Wooster students — search “Estonia” in this blog).

This latest paper, Vinn et al. (2019), is from a project Olev, Ursula Toom, and I pursued with a single specimen from the Middle Ordovician (Darriwilian) of Estonia. It analyzes the unusual preservation of crustoid graptolite (rather rare in its own right) preserved inside the gloomy hollow of a nautiloid shell (its conch). Here is the abstract:

“A light grey nautiloid conch has a dark brown colony attached to its internal surface. This colonial fossil resembles hederellids and bryozoans, but is in fact a crustoid graptolite (Hormograptus? sp.). The colony has been lithoimmured inside this nautiloid conch by early cementation. Crustoid graptolites were a part of the encrusting communities in the Middle Ordovician of Baltica, but their abundance among encrusters of biogenic substrates reached a peak in the middle Sandbian. The cryptic mode of life appeared very early in the evolution of the crustoids. The discovery of this crustoid graptolite in a nautiloid conch indicates that the Baltic Middle Ordovician cryptic communities were taxonomically more diverse than was known previously. The nautiloid conch studied is sparsely encrusted with an encrustation density that is similar to those of other Middle Ordovician cryptic surfaces described from Estonia.”

From figure 2: Hormograptid graptolites from the Ordovician of Estonia. A–C. Hormograptus? sp., attached to the internal surface of a nautiloid conch; Harku Quarry, Kunda Regional Stage (lowermost Darriwilian) (GIT 494-41-1). [Image C is at the top of this post.]

The unusual taphonomic pathway of this specimen was through lithoimmuration, in which early calcite cement essentially entombed the crustoid graptolite colony against the internal nautiloid shell surface. That shell was made of aragonite which quickly dissolved, leaving the base of the graptolite exposed for us. That was enough to make the identification and show a bit of cryptic niche space occupied in the Middle Ordovician.

Reference:

Vinn, O., Wilson, M.A. & Toom, U., 2019. A crustoid graptolite lithoimmured inside a Middle Ordovician nautiloid conch from northern Estonia. Annales Societatis Geologorum Poloniae, 89: doi: https://doi.org/10.14241/asgp.2019.17

Phoenix, Arizona — It was a small group of Wooster Geologists at the annual meeting of the GSA held in Phoenix last week. The very early date (about a month earlier than usual) and the consequently earlier abstract deadline reduced attendance overall, especially for those geologists who needed the summer to collect data (most of our Independent Study students). Wooster had only one student at the conference: the happy Evan Shadbolt (’20) pictured above. Evan and I presented a poster on research by Team Jurassic Utah. Since we did the fieldwork in March 2019, we could get our abstract completed by the early deadline.

Dr. Greg Wiles gave an oral presentation on Holocene Alpine glaciation in southern coastal Alaska with a group of Wooster student and staff co-authors representing the Wooster Tree Ring Lab.

I was very proud to be part of a poster presentation on the Middle Jurassic of Israel by Yael Leshno Afriat, a graduate student at Hebrew University in Jerusalem. It was a delight to see Yael again, and her poster brought back great memories of fieldwork in the Negev.

The GSA annual meeting is where the Paleontological Society has its own annual meeting. This year long-time friend of Wooster Geology Dr. Paul Taylor was awarded a Fellowship of the society. Richly deserved. Search this blog for “Paul Taylor” and you’ll see how important he has been to us for decades.

The annual Wooster alumni gathering was, like every other event at this meeting, unusually under-populated. Nevertheless it was a great group, and there were alumni there we hadn’t seen at this meeting before. The photograph is of those present at our traditional 8:00 pm Monday picture time. There were several other Wooster geologists at the meeting who could not make it to the event at this time.

Next year in Montréal! This meeting will have more reasonable dates: October 25-28, 2020.

Four new studies from the Wooster Tree Ring Lab have recently appeared in Ecology, Journal of Geophysical Research – Biosciences, The Holocene and Chemosphere.

Brian Buma lead the study published in Ecology that described the results of revisiting a classic ecological succession site in Glacier Bay National Park and Preserve. The article is titled: 100 years of primary succession highlights stochasticity and competition driving community establishment and stability. We blogged about some of the fieldwork for this study a few years ago here.

Abstract: The study of community succession is one of the oldest pursuits in ecology. Challenges remain in terms of evaluating the predictability of succession and the reliability of the chronosequence methods typically used to study community development. The research of William S. Cooper in Glacier Bay National Park is an early and well‐known example of successional ecology that provides a long‐term observational dataset to test hypotheses derived from space‐for‐time substitutions. It also provides a unique opportunity to explore the importance of historical contingencies and as an example of a revitalized historical study system. We test the textbook successional trajectory in Glacier Bay and evaluate long‐term plant community development via primary succession through extensive fieldwork, remote sensing, dendrochronological methods, and newly discovered data that fills in data gaps (1940’s to late 1980’s) in continuous measurement over 100+ years. To date, Cooper’s quadrats do not support the classic facilitation model of succession in which a sequence of species interacts to form predictable successional trajectories. Rather, stochastic early community assembly and subsequent inhibition have dominated; most species arrived shortly after deglaciation and have remained stable for 50+ years. Chronosequence studies assuming prior composition are thus questionable, as no predictable species sequence or timeline was observed. This underscores the significance of assumptions about early conditions in chronosequences and the need to defend such assumptions. Furthermore, this work brings a classic study system in ecology up to date via a plot size expansion, new baseline biogeochemical data, and spatial mapping for future researchers for its second century of observation.

Photo taken in the West Arm of Glacier Bay close to where the Cooper plots were “rediscovered”.

Dr. Ben Gaglioti (University of Alaska – Fairbanks)  just lead another innovative study. This time Ben has assembled a time series of traumatic resin ducts (TRDs) in mountain hemlock that  is a record of past winter conditions and the strength of the Aleutian Low. The article appeared in the Journal of Geophysical Research: Biogeosciences.

The study included tree-ring records from four wild outer coast sites along the the Gulf of Alaska. This is the first work to use these TRD features in tree-rings as a proxy for winter storminess.

a – The clearly-stressed trees used in this study. b – Careful observations and measurements from increment cores were taken to work out the timing of maximum wind stress and storminess. c, d –  Examples of Traumatic Resin Ducts in the tree rings.

Once assembled, the decadal variability of the winter time record was clearly related to the Pacific Decadal Oscillation (see below). This new record is the first of its kind and gives us a new record of wintertime variability from the North Pacific.

Rob Wilson (University of St. Andrews) lead a study from the Yukon. He used blue intensity tree-ring records from white spruce to improve dendroclimatic temperature reconstructions from the southern Yukon.

The study is titled: Improved dendroclimatic calibration using blue intensity in the southern Yukon. and the abstract reads like this: In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June–July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43–51% of May–August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.

The Figure above shows the location of the Yukon study site and includes various other sites the Wooster lab has worked on in Alaska. Rob has been a great help in the efforts at the Wooster Tree Ring Lab facilitating our lab’s ability to perform these analyses.

Mary Garvin (Biology, Oberlin College) lead the study using tree-rings and chemical analyses entitled: A survey of trace metal burdens in increment cores from eastern cottonwood (Populus deltoides) across a childhood cancer cluster, Sandusky County, OH, USA.  

Abstract: A dendrochemical study of cottonwood trees (Populus deltoides) was conducted across a childhood cancer cluster in eastern Sandusky County (Ohio, USA). The justification for this study was that no satisfactory explanation has yet been put forward, despite extensive local surveys of aerosols, groundwater, and soil. Concentrations of eight trace metals were measured by ICP-MS in microwave-digested 5-year sections of increment cores, collected during 2012 and 2013. To determine whether the onset of the first cancer cases could be connected to an emergence of any of these contaminants, cores spanning the period 1970–2009 were taken from 51 trees of similar age, inside the cluster and in a control area to the west. The abundance of metals in cottonwood tree annual rings served as a proxy for their long-term, low-level accumulation from the same sources whereby exposure of the children may have occurred. A spatial analysis of cumulative metal burdens (lifetime accumulation in the tree) was performed to search for significant ‘hotspots’, employing a scan statistic with a mask of variable radius and center. For Cd, Cr, and Ni, circular hotspots were found that nearly coincide with the cancer cluster and are similar in size. No hotspots were found for Co, Cu, and Pb, while As and V were largely below method detection limits. Whereas our results do not implicate exposure to metals as a causative factor, we conclude that, after 1970, cottonwood trees have accumulated more Cd, Cr, and Ni, inside the childhood cancer cluster than elsewhere in Sandusky County.

Figure – shows the extent of the cancer cluster that coincides with more accumulated Cd, Cr and Ni in the tree-rings.

The class stands in front of one of the unconformities in Wooster Memorial Park (aka Spangler). There was some discussion if this is a disconformity (yes) or a nonconformity (maybe yes). The lodgment till at the base is overlain by a fluvial gravel. The high relief of the contact is due to high mineralization – iron, manganese and other oxides; interestingly, many of the clasts were coated with over a centimeter-thick rind.

Two class members (in the distance) work on the fluvial sediments sitting on top of the Mississippian bedrock. This is the Great Unconformity in the Spangler Gorge. The Fluvial sediments are capped with mill pond (legacy) sediments. Others drill in stainless steel erosion pins into the bedrock channel. Morgan in the foreground points one of the pins out.

Evan examines a debris flow that moved into the fluvial point bars sediments. He found organics in the flow and we have sampled and sent wood samples out for radiocarbon analysis. Results are pending, but they will give us information on the geologic evolution of the gorge.

The Schmidt Hammer is being used to measure  rock strength. Several measurements of the bedrock will be taken to “map out” the relative rock strength of the gorge floor (bedrock stream).

It was a delightful August day in northeastern Ohio with pleasant temperatures and thunderstorms that obligingly went around us. Nick Wiesenberg, our geology technician, and I were invited by Dr. Nigel Brush (Ashland University) and friends to examine an outcrop of the Cuyahoga Formation (Lower Carboniferous) near Jeromesville, about a 25 minute drive west of Wooster. Nigel has been investigating a strange limestone in a thick shale sequence that doesn’t seem to fit into our known stratigraphy for the region. I’m always up for a new limestone to look at! As a bonus, the shales here have excellent fossils, especially in concretionary beds. The outcrop, with Nick for scale, is about ten meters high. It is on land owned by the Bricker family, who are geology enthusiasts with beautiful rock and fossil collections.

The shale cliff is steep and has been cut rapidly by the stream (Quaker Springs Run). assisted by occasional dredging of the channel for gravel. The limestone in question is about a meter over our heads here. That’s me, Nigel Brush, and Jeff Dilyard. Photo by Nick.

The shale beds contain siderite concretionary beds loaded with fossils. The most common are spiriferid and spiriferinid brachiopods preserved as internal and external molds and occasionally their original calcite. The taxonomy of these brachiopods is well known, but their paleoecology is still to be determined. (Future Independent Study projects!)

Here is a piece of that limestone eroded from the cliff into the stream. You can immediately see how different it is from the surrounding muddy shales. It is cross-bedded, coarse-grained, and loaded with shale intraclasts (the gray chips), which are mud flakes that were incorporated into the rock while it was being deposited. It looks very much like a storm deposit, possibly associated with a sudden drop in sea level (and rise again).

We took a piece of the above limestone and cut it with a rock saw to begin assessing its composition and fabric. The round grains you see are almost entirely crinoid fragments, mostly stem and arm fragments. The gray chips are the shale intraclasts. Clearly this rock has a story to tell! We will now make acetate peels of this limestone for microscopic study.

One primary question we must address is just where this unit fits in the local stratigraphy. We know it is the Cuyahoga Formation, but which member? It could be the Wooster Shale, Armstrong, or Meadville Shale. One clue would be the conodonts present in the rock. Conodonts are phosphatic dental elements of long-extinct swimming animals. They have considerable biostratigraphic value and so can be used to place units in a stratigraphic column. Since they are phosphatic, they can be collected from limestones by dissolving the carbonate matrix with formic acid and sifting through the remaining insoluble residue. I did this for my dissertation many years ago, and most recently Dean Thomas (’17) dissolved Ordovician limestones for these little critters. I started the process this evening in the paleo lab. Above you see two basins which contain limestone fragments in a 10% solution of formic acid. They are bubbling furiously as the carbonate dissolves. In a few days I’ll sieve the residues and see if we have any conodonts. You’ll be the first to know.

Thank you, Nigel Brush, for the invitation and all your expert fieldwork. It was a fun day as the summer wanes and our first classes of the fall rush towards us.