28 May, 2015

Short anatomy of a bentonite deposit

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Bentonite deposits in Bavaria, Southern Germany, are located in a 10 by 40 km wide belt between Mainburg, Moosburg and Landshut, roughly northeast of Munich. Among non-geologists the region is more famous for its hop fields, and bentonite mines are scenically located between hop and gently rolling green hills. Underneath the hop, bentonites are hosted in fluviatile-lacustrine gravels of the Nördlicher Vollschotter (Northern Main Gravel) unit.

In the image you see one of the many small, lenticular bentonite deposits. This particular deposit was  part of my last Bachelor student's thesis in 2014 and the samples were a good test for a portable X-ray fluorescence unit a few months later. The pit nicely shows how a thin lenticular bentonite is hosted in micaceous footwall sands and hanging-wall fluviatile sand and gravels of the Nördliche Vollschotter. The region is blanketed by Quaternary loess of high agricultural value.

Bentonite in unconsolidated Miocene sediments. Bucket excavator and Bachelor student (left from center) for scale.

The sand and gravels are themselves a wonderful sedimentogical units with textbook-like depositional structures. Igneous, metamorphic and sedimentary clasts are derived from Mesozoic, Cenozoic and crystaline rocks of the Bavarian Forest, Swabian Alb, and from the Alps.

Cross-cutting sedimentary structures in fluviatile, sand-rich gravels. A sharp erosional contact separates loess and gravel.

In this deposit gray-greenish bentonite is sandwiched between thin floodplain marls and hanging-wall gravels. Upper contacts in bentonites are almost always erosional in nature. What is very unusual in Bavarian bentonite deposits is that they contain abundant authigenic dolomite. Two up-coming publications are dealing with those, and I can already reveal that dolomite and calcite formation are syn- to very early postgenetic to bentonitization. Using micromorphological, carbon and oxygen stable isotopes we can also show that bentonite-associated carbonates formed in pedogenic, palustrine and groundwater settings.

Bentonite, rather unspectacular, sandwiched between marl (part of the sand unit below) and gravel.

Last but not least a dolomite nodule from underneath the bentonite. Most of the sediments are rich in swelling clay minerals (smectites) and show typical shrink-swell features, such as slickesides. Carbonate precipitation is often related to these structures. The outer shapes of nodules often are perfect imprints of slickensides surfaces.

A medium-sized dolomite nodule from the marl bed. Macroscopically identical to those in bentonite.

17 May, 2015

Arizona impressions

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Early in 2014 I applied for a student research grant at the Clay Minerals Society. I asked for a boron isotope campaign to be partially funded. To my great pleasure the CMS granted enough support to fund a visit to the Arizona State University SIMS facility im Tempe, AZ. So in august 2014 I spent a week in the basement doing SIMS measurements. Besides wonderful data I also brought back home a suitcase full of pictoral landscape impressions that still feed my desire to return. 

First evening in Tempe, AZ. A lovely view from my appartment.
SIMS lab. Time spent: 7 days watching the screens.
After several days of countless boron isotope ratio measurements I sneaked out. Took a car and drove north!
On the interstate. Endless driving. A very meditating activity.
Grand Canyon South Rim! Worth every hour on the road! Note the perfect weather for monsoon season.
If you watch closely you will find the Colorado river in the lower left.
Making contact to the locals.


After spending a night in Williams, AZ, I took a long detour via Prescott to...
...see my first hectorite mine! The owner was so kind to meet-up with me. We spent an hour talking and filling  sample bags (Which almost got me arrested a few days later. But I will share that anecdote another time).

The mine owner recommend a country-side route away from the interstate to return to Phoenix. No other car for two full hours. Amazing!

The boron isotope data will be presented at the EuroClay2015 in Edinburgh, Scotland. 

The hectorite has since been XRDed, cut into thin-sections, and looked at by ESEM/EDX. 

Thanks for watching!

15 May, 2015

Returning to life

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This blog has been idle for eons.

The doctoral thesis and project is in its final year. My first publication has been accepted in early 2015 for publication in the Clay Minerals Journal. The 2nd publication is in the pipeline. Data for the 3rd is complete. Searching for a new job. Before christmas, I hope, I willl defend my thesis. Then move on to new adventures in geoscience - or should I say clay science?

I ought to change the blog name. No longer feeling lost!

Enough for today. Blog is alive again!


14 April, 2012

An award! :-)

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As hinted in my last post there was some big news in the pipeline. I wanted to wait until I had the official documents and confirmation. A few months ago I applied for the 2012 Graduate Student Fellowship of the Society of Economic Geologists (SEG).

Now I received the official confirmation that I have been awarded a Graduate Student Fellowship intended to support my graduate studies part of my recently started Ph.D. project! The award comes in the forms of a financial allowance for my research. Considering the still unsecure financing of my Ph.D this will allow me to produce some hands-on data for at least one publication. I am already having some ideas in terms of stable isotopes and SEM imaging. :)

30 March, 2012

More big news coming soon...

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A few days ago I have been giving the head-ups on some fantastic news related to my Ph.D. project. It's a bit too soon to reveal what it is until I received all the details. Let's just say I love economic geology and the open-minded people doing it. :-)