30 April, 2009

Book recommendation: Microfacies of Carbonate Rocks

A while ago I recommended "Carbonate Sedimentology" by M. Tucker for all those interested in carbonate rocks. I would like to add another wonderful work on carbonate sedimentology. While "Carbonate Sedimentology" by Tucker is more focused on the macroscopic aspects of carbonate sediments Erik Flügel has written an all-encompassing work on any kind of carbonate microfacies. His probably well known book titled "Microfacies of Carbonate Rocks" is filled with more than 900 pages of very well researched knowledge combined with many useful microfotographs of many different kinds of carbonates under the microscope. Nineteen chapters will guide you from the introduction to carbonates through any aspect you may imagine. Methods and microfacies data are explained, diagenesis, porosity and classification discussed, the biological origin is highlighted and fossils in thin sections examplefied. Microfacies types are explained, you will learn how to interpret palaeoenvironment, depositional models and read about basin analysis. Also contrains and processes are reflected upon before a discussion of reservoir and host rocks of economic commodities. Last but not least even a link to archaeology is presented followed by an enormous list of references that is even expanded upon in the accompanying CD. Quite a good book - I just wish I had the time to actually read it for real!

Cover of the last edition (2004) of Microfacies of Carbonate Rocks

29 April, 2009

Karst Webpages

To re-start blogging after my unwanted hiatus I would like to share a few informative sources on karst and karstification with you. As you may be aware karst is an often re-occuring problem in soluble rocks. Usually found in carbonates (esp. pure limestones) it can also be observed in sulfates or evaporites. Besides influencing limestone resource quality and playing a role the formation of Mississippi-Valley-type deposits (hence my interest) it also is a very important aspect in hydrology and groundwater flow and is recognised as a potential geohazard in the form of sinkholes. Last but not least it can influence petroleum reservoirs.

Karst and the USGS


Karst Information Portal

Karst Home Page

Karst - A potential Geohazard and Reservoir

Introduction to carbonates

16 April, 2009

An online forum for Geology

An online forum for geology - does it exist? In the many years that I use the internet, email and discussion forums of various kinds I have failed to find any good and useful online discussion forum in english language on geology. That doesn't mean there aren't any but they are either of extremely low quality, specialised to a single expert topic, not used and half dead or share some or all of these negative points. There are a few good exception like the Geoversum which I frequent daily and find a great source of information - it is entirely German language. It's audience is limited to those capable of German; even though most people there also understand English. Nevertheless I love that place and met some, by now, real-life friends there. There is another forum specialised on carbonates in the form of the Carbonate Network which seems to be good on quality but is rather specialised and not very active.

Perhaps I missed the good one stop location in terms of geology forums, yet, I have I feeling I didn't. (If there is please point me to it)

There have been a couple of ideas going around in the geobloggosphere in the recent months. So perhaps it is time to add one more: To create a good quality and active online forum for geology. I could imagine such a place to be a great place for amateurs and those interested to ask question and find answer on geology, to meet like-minded people that don't want or don't have time to frequent the great variety of Geoblogs, also it might be a good place for us Earth Scientist (to also include geophysics, mineralogy, palaeontology, etc.) to talk and discuss ideas totally at ease or simply share anecdotes and information we don't feel like turning into a blog post.

There have been some ideas to expand on the Accretionary Wedge (sorry for not finding the appropiate links right now). Maybe it might be worth to include such a forum in there somehow?

I would be more than happy to share some thought with you on this issue. What are your opinions on this?

Geoblogs: Kreidefossilien and Nig-eosyncline

Today I discovered thanks to Lutz over at the Geoberg-Blog and to the latest version of Accretionary Wedge two Geoblogs or better said one geo-related site with a blog and one true Geoblog that are new to me.

One is a German site called kreidefossilien.de a website devoted to Cretaceous fossils and geology. It is very comprehensive and I found a new source of interesting and local geology information.

The other is Nig-eosyncline by Ikenna Okonkwo from Nigeria! I am very glad to have found especially the later one because Africa is so far a truly under-represented continent on the Geobloggosphere!

12 April, 2009

Happy Easter!

I would like to wish everyone a Happy Easter today and that you may pass a wonderful holiday!

11 April, 2009


After returning from fieldwork, partaking in a course on "Organic Petrology and Geochemistry of Petroleum Source Rocks" together with MapleLeaf and spending some days relaxing (finally!) I want to share with you a very nice example of some oncoids from the German Middle Jurassic that I found during my diploma mapping project in the Upper Rhine Graben. The image below is a neat cross-section through one of the many oncoids I found. It's not cut nor polished but simply splitt with a well aimed blow of the rock hammer.

Bored oncoid with shell nucleus

On top of the Middle Hauptrogenstein is a layer called Mumienbank (Mummy Bed) that consist almost entirely of oncoids of up to 6 cm in diameter. The first geologists to work on this coined the term because this layer is unusually rich in gastropod shells (Nerinea sp. most commonly) as nucleus of the oncoids. The below sample is a wonderful example of the nucleus forming gastropods picked from another location within my mapping area.

Oncoids with gastropod shells as nucleus

There is one really cool outcrop of the Mumienbank in the southern half of my mapping area that should get even the most reluctant to utter some equivalent of "cool" or "wow". It is even better when standing right in front of it of course. The lower layer is one of the usual Oo-Pack-/Grainstones that are so abundant in my mapping area. In the middle is a layer of smaller oncoids of up to 2 cm diameter. In the upper layer oncoids are 2 to 5 cm in diameter.

Outcrop of the Mumienbank with upward increasing oncoid size

So what's an oncoid? How do we recognise one in the field and why does it matter?

An oncoid is in the most basic sense nothing but nodular coated grain. A nucleus that can be of diverse origin is encursted by microbes, algae or other encrusting organisms, i.e. foraminifera. They are unattached, rounded and up to several cm in size. There are both calcerous and non-calcerous nodules of more or less concentric nature and with partially overlapping laminae around a bio- or lithoclast as nucleus. In America the term pisoid is also still in use for oncoid. They are most common in limestones and marls. Best way to recognise them is size and the irregular, concentric and partially overlapping laminae around a nucleus.

So why does it matter? It matters because they are in contrast to most other carbonate grains very good indicators of palaeoenvironment, sea-level changes and depositional settings. They appear from tropical to arctic environments, depending on the encrusting organisms. Even though they can be found even in basinal deposits most fossil oncoids appear in shallow environments and peritidal carbonates. Beware - they are not exclusively marine and can be found in freshwater and saline waters in lacustrine and fluvial environments from the Precambrian until today.

So why does that matter to me when I map potential lime resources? Two reasons: First, they are very easy to recognise in the field without any special equipment. The oncolite horizons form excellent stratigraphic orientation marks in the field, indicating the very top of a several 10s of meters thick and very pure limestone succession. Second, while mapping I noticed marly clay inbetween the oncoids at least in some areas. That's undesirable considering your resource requirements and has to be considered.

There exist a wide range of oncoids that I don't have the time to detailledly explain here. I recommend taking a look into Carbonate Sedimentology by Maurice E. Tucker and V. Paul Wright (take a look at my post about Wright's Revised Classification of Limestones) or Microfacies of Carbonate Rocks by Erik Flügel. If you are more a fan of the internet take a look into the USC Sequence Stratigraphy Web.

02 April, 2009

(Almost) Done!

The last few days were pretty intense. I was in the last steps of completing my self-set mapping programm and drafting the new geological map of the region. Quite amazing that I managed to map 16 square kilometers in 6 weeks. Especially considering the partially awful weather and unfavourable terrain. Yesterday's field tour with my supervisor and the good results in my supervisor's opinion were (and are) a great relief. Today I quickly mapped two minor areas that deserved another look. So now I am done with fieldwork - and ready for some vacations actually. Before I return homewards there will be another short visit to the office in Freiburg to return some of the equipment I had borrowed. Then, on saturday, it's finally time to go home! I will take a short rest there before I start to compile the actual map that I will be delivered to the geological survey. Also I need to write my diploma mapping report for university. So I will have plenty to do for the next two months! But before that I will be attending an - I hope interesting - short course (6th to 9th of April) on Coal Geology and Organic Geochemistry of Petroleum Deposits held at my local university by Professor Kalkreuth who is an expert working at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil.

01 April, 2009

1200 degrees Celsius

Today was an important day. Field tour with my diploma mapping supervisor and the future geologist respondsible for compiling the mineral resource map of the region. The supervisor was very satisfied with the map and me very relieved about that. In the 2nd half of the day we drove north to visit a limestone quarry. A cool visit - especially the view into the fires of hell of the oven in which the limestone is burnt. 1200 degrees Celsius viewed with the bare eye after the seal and window was opened for us. A cool view - and very warm!

1200 degrees Celsius!