27 August, 2015

Online clay science resources

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


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-associated 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. The combination of methods enabled us to distinguish both dolomite-rich and calcite-rich pedogenic, palustrine and groundwater facies within bentonite deposits. The figures taken from the paper illustrates some of 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, the bi-modal distribution of carbon isotope results is consistent with carbonate formation in both water-logged and non-water-logged conditions, and suggests repeated wetting and drying cycles. The oxygen isotope data the impact of evaporation and temperature on δ18OV-SMOW values 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.

References:

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

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.

01 August, 2015

Mining machinery in action

During many visits to bentonite mines in Bavaria my doctoral supervisor, me, and our students usually had to arrange ourselves with active mining activity. This meant taking good care of communications with the mine manager, surveyor, and most importantly the machine operators. You do not want to get your head hit by the bucket of an excavator or run over by one of the trucks! Having a bulldozer and excavator around does of course have its benefits for taking samples and outcrop documentation. What a hand shovel will get done in 2 hours, the bucket excavator will get done in 5 minutes! So having good relationships with the mining folks will save you hours and days of tedious work! Anyways, over time, I managed to capture a lot of the machinery at work and I decided to put some of the better images online. Enjoy!

A track-driven scraper in action. Although slower they are more cost efficient in small-scale operations.

The bucket excavator was so kind to excavate the base of the bentonite deposit for us.

Same as above. Taking a break.

Hauling and loading of Volvo trucks with overburden.

Preparing the terrain and removing overburden with bulldozers and another bucket excavator.

Hauling and loading again with the aim of clearing a nice profile for us. View from the freshly excavated pit.