07 November, 2015

Fossil roots in tuffites & bentonite deposits, Southern Germany

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Yesterday I joined #FossilFriday on Twitter. It made me realize how many images of fossil roots I actually have. I am not a palaeontologist, most of them will never make it into a publication. So, let's share here! All images were taken during my doctoral research in bentonite mines in Southern Germany. The Mid-Miocene bentonite deposits of the Upper Freshwater Molasse are often associated with so called "Harte Platte" (English: hard plate) - a descriptive term for hard clay of little economic value. The hard clays are usually composed of partially altered tuffites, silified bentonite or sandstone-like horizons, and are common in deposits of a thickness of roughly 3 meters and more. While the hard clays are economically useless, their reduced shrink-swell capacity and stiffer composition is probably the reason for an often excellent preservation of fossil root features! Unfortunately, I lack the in depth palaeobotanical expertise to identify the plants they are from. However, based on their large size they must once have been quite impressive trees or shrubs that, based on the literature on depositional settings, grew in wetland settings. I also have a number of thin-sections and SEM images of well-preserved root features that I use as side-notes in an upcoming publication. But if anyone knows if it is possible to use root morphology to do more than "tree" or "shrub" let me know! The upside is always at the top of each image.

This is the image I used for #FossilFriday depicted a loam-filled root mold. It is one of the largest root molds I found.

This down-ward branching examples is part of a finely bedded, almost laminated tuffite. The tiny circular objects are sectional views of more "roots". These examples were replaced by silica.

More branching root features. Filled with a mix of loam and carbonates.

Cross-section of silica-rich root trace with central root channel? Diameter ~ 1.5 cm.

Fe-Mn-stained roots about 1 cm in diameter.

Almost vertical loam-filled root features in an almost 4 m thick tuffite.

27 September, 2015

Old fieldwork pictures from Peru

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Things have been quiet here recently due to job hunting and working on my doctoral thesis and related publications. Going through my back-up files I came upon a number of fieldwork images from my ore exploration student internship in Peru. It ignited some nostalgia about those great times in the Andes! Here are some pictures...

Trujillo cathedral.
Trujillo city hall.
Desert and cactus.

We need to get up there!
Traveling off-road!

27 August, 2015

Online clay science resources

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When I began my doctoral research I was lacking a really good knowledge of clay rocks and clay minerals. So, during the years I have been looking for easy to understand resources on clay minerals and methods. Oddly enough I found the most useful resources now that I am closing in on finishing my project!

Anyways, I decided to share the best online resources. The first I found only last week. It is the YouTube channel of the Virtual Soil Science Learning Resources group initiated by Dr. Maja Krzic (UBC) in 2004. Their channel hosts dozens of short videos by soil experts on anything a starter might look for. I especially found the videos about methods, e.g. determining cation exchange capacity or salinity, the most useful.

22 August, 2015

Paper: Dolomite formation in non-marine bentonite deposits

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On August 6th the first of three publications that are a part of my doctoral research was finally published online in the Clay Minerals Journals at GSW (alternatively via ingentaconnect - abstract also available on RG). The study explores the role of authigenic carbonate formation during bentonitization. We used a combination of X-ray diffraction, micromorphology (based on thin-sections and SEM) and stable isotope analysis to investigate bentonite-assciated dolomite and calcite formation.

Bentonites in the Upper Freshwater Molasse formed from practically Ca- and Mg-free, calc-alkaline, rhyolitic air-fall tuffites. The presence of abundant authigenic dolomite (one deposit is capped by 1 m thick dolomite horizon) was a major surprise, and we extensively used XRD to confirm the mineralogical composition. By the combination of methods we were able to distinguish both dolomite-rich and calcite-rich pedogenic, palustrine and groundwater facies within deposits. The figures taken from the paper illustrate the carbonate microfabrics.

The carbon and oxygen stable isotope results (figure from paper shown below) were essential in resolving formational environments. The carbon isotope ratios imply a C3-plant-dominated carbon source with small additions from dissolved carbon from groundwater and atmospheric carbon in upper "soil horizons". However, a bi-modal distribution of carbon isotope results is consistent with carbonate formation in both water-logged and non-water-logged conditions and suggested repeated wetting and drying cycles. The oxygen isotope data then revealed evaporation processes and an at least a partially temperature controlled δ18OV-SMOW value of meteoric water of -7.0 to -4.8 per mil during carbonitization, and hence bentonite formation.
We concluded that dolomitization was a syngenetic to early diagenetic process - perhaps on the time-scale of soil formation. Both dolomite and bentonite formation occurred in non-saline, non-arid and repeatedly partially-oxygenated and reducing soil and groundwater environments. That actually comes as a small surprise because carbonates were so far dismissed as unrelated to bentonite formation. It also places bentonite formation into a soil and groundwater environment, and not later diagenesis. We, however, cannot rule out that smectite formation continued after blanketing of deposits with younger sediments.


M. H. Köster and H. A. Gilg (2015) Pedogenic, palustrine and groundwater dolomite formation in non-marine bentonites (Bavaria, Germany) Clay Minerals, June 2015, v. 50, p. 163-183, published online August 6, 2015, doi:10.1180/claymin.2015.050.2.0

19 August, 2015

Aesthetic calcite

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Regular readers will have noticed that I like posting pretty pictures. Today, I felt like posting the next one! This time it is a calcite crystals found in the voids of a carbonate nodule from the Bavarian bentonite deposits - as usually. The picture was made purely for aethetic enjoyment.

A wonderfully smooth calcite crystal.