Sunday, January 25, 2009

Sequence Stratigraphy and Industrial Mineral Exploration - Sequence and dynamic stratigraphic framework

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Please excuse some ad-hoc editing gone wild. Blogger refused to let me use a readable font-size so I had to find a work-around.

Please excuse my long break in posting the next contribution to this mini-series (Part 1 and Part 2). As you have read on my blog I was stuck in the field with lots of snow and other more urgent matters to attend to. Back home I was compiling my few preliminary results to present them.

In a note ahead I recommend reading the two articles referenced at the bottom for details. The topic is rather extensive and my post here is only a small glimps of the issue and far from a complete synthesis. Nevertheless I believe it will suffice to broaden my own and everybody's geological horizons.

Today I would like to discuss some concepts of the paper by Pawellek and Aigner called Dynamic stratigraphy as a tool in economic mineral exploration: ultra-pure limestones (Upper Jurassic, SW Germany) and it's implications for sequence stratigraphy and industrial minerals. Ultra-pure limestones are the resource for many industry uses in the manufacture of glass, paper and many other applications.

Sequence stratigraphy has long played an important role in predicting prospective regions or formations in the hydrocarbon industry, however, it can also be used for other, perhaps less known, approaches in the raw-material exploration.

Knowing the genesis of deposits greatly reduces the time and cost of exploration by focusing only on the most prospective areas. Pawellek and Aigner use concepts of "dynamic stratigraphy" for this, ranging from microfacies analysis, sequence to basin analyses to understand the occurences of ultrapure limestones. They are using reef and particle-rich limestones from the Upper Jurassic as an example.


Scheme of "Dynamic Stratigraphy"

Microfacies analysis is a good tool to determine depositional environments and the effects of diagenesis and thus also provides information on both the chemical composition and economic potential. For example low-energy carbonate rocks usually have a higher content of clay or other, unwanted matter and are less pure than high-energy rocks like grainstones.

Petrophysical and facies analysis focuses on the chemical-physical properties and is used in characterising the quality.

Architectural analysis allows the reconstruction of shape and volume of a deposit.Sequence analysis highlights the genetic framework and occurence within sedimentary sequences and cycles. Among other things this reveals the levels within the stratigraphic record where economic mineral concentrations could most likely be present.

Last but not least the analysis of stacking patterns and basin analysis allows us to determine regional concentrations and assess the basin-wide scale. A direct step to predicting the possible distribution of profitable facies.

In their paper Pawellek & Aigner examine two major facies of the Upper Jurassic. The so called "normal facies" and the "massive facies". The former consists mainly of well-bedded limestones and calcareous marls, the later has no or at least a very inconsistent bedding and is host of extensive reefs, mounds or bioherms.The two major facies are further divided into sub-categories based on their composition. Within the bedded limestones the particle-rich limestones composed mainly of intraclasts, peloids and ooids are the most pure. In the massive limestones the purest are the coral debris limestones and the stromatolites (+thrombolites). Both with an average CaCO3 content above 98% and reaching-up to 100%. These also have the highest witness index values.

As a sidenote: Due to the variable clay content these rocks have different levels of radioactivity with the purest limestones having the lowest activity and the clay-richest the most active. They show how this implies a correlation between gamma-ray count and facies types.


Gamma-ray signatures of facies groups

In sequence analysis facies belts can not only be recognised on a regional scale but also facies zones can be identified within outcrops, cores or logs. Shallowing and deepening would be present in vertical successions of regular cycles. This can be observed.Shallowing-upward and deepening-upward halfcycles show symmetrical facies successions. Considering a wide range of evidence like clay content, organism successions, matrix and ooids content and other evidence this can be attributed to changes in water-energy and waterdepth. As an example upward increases of ooids, size, roundness and sorting can be interpreted as an increase in depositional energy.

Cycles of meter-scale thickness (4 to 10m) can be regionally correlated in Southern Germany. These cycles are referred to as "genetic sequences" that record phases of shallowing followed by deepending. Seven of these have been identified in the Upper Jurassic of Southern Germany. Within these "genetic sequences" ultra-pure limestones are most abundant in zones of highest depositional energy. Clay and other impurities are prevented from settling in these high-energy environments. In general this results in the bioherms and particle-rich limestones to be the purest.


Sedimentological facies belts and genetic sequence

Several genetic sequences form a medium-scale sequence. These again form large-scale sequences of more than 100m thickness. The stacking-pattern in the cycles controls the distribution of ultra-pure limestones. Large-scale shallowing or deepening sequences are respondsible for the retreat or expansion of ultra-pure limestones and other facies belts.

To put this into a sequence stratigraphic framework:

When and where do bioherms and particle-rich limestones - reefs, stromatolites and peloid-ooid-pack- or grainstones form? As outlined we do need a high-energy depositional system with little clastic input and shallow waterdepth. When we think of the succession of depositional environments during sea-level rise and fall the above mentioned criteria are most usually met within the transgressive system tract at the shelf- or platform edge in the form of shoals or reefs. When sea-level rise continues we can expect the development of hardgrounds which are often concentrated along the maximum flooding surface. The production of large amounts of pure carbonate would cease.

We learned (and me, too): The most prospective areas for ultra-pure limestones are genetic sequences of shallowing-upward within the transgressive system tract that show distinct evidence of shallow, high-energy depositional environments close or on the shelf or platform edge.


References

  1. Thomas Pawellek and Thomas Aigner (2004): Dynamic Stratigraphy as a tool in economic mineral exploration: ultra-pure limestones (Upper Jurassic, SW Germany), Marine and Petroleum Geology, 21
  2. C. Robertsen Handford and Robert G. Loucks: Carbonate Depositional Sequences and System Tracts - Respondes of Carbonate Platforms to Relative sea-level change, in Loucks, R, G. and Sarg, Rick, eds., Carbonate sequence stratigraphy: Recent advances and applications: American Association of Petroleum Geologists Memoir 57

Saturday, January 24, 2009

Just a tiny addition

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You can now access my shared del.icio.us bookmarks via the small feature that I included a little bit downer on my sidebar. Not everything I find I can or want to turn into a post so I am hoping this to be a nice and easy way to share my digital endeavours of digging for geology related sites - and the occasional non-geology site of course.

Thursday, January 22, 2009

French rock face

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In a follow-up to my recent post on a rock face Bruno Granier from the University of Brest as sent me with kind permission to post the below image of a rock face from a road side near Saint-Ferreol-Trente-Pas, Drome, in SE France. He informed me that the carving is made in Albian glauconitic sandstone of the Marnes-Bleus-Formation.



A lot more artistic work seems to have gone into these example with inscriptions and numbers than into the exampe presented by me.

Tuesday, January 20, 2009

Fossil shark teeth stolen - Fossile Haifischzähne gestolen

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Via Steinkern.de - a German forum for fossil collectors and fans of palaeontology - I just came across the news that fossil shark teeth have been stolen from the Nierstein Museum in Germany in mid 2008. Descriptions in German, French, English and Dutch are available together with fotos of the specimens on the museum website. I took the liberty of re-posting the English text published by their director:

Fossil shark teeth stolen

In the middle of 2008 five rare and scientifically valuable shark teeth were stolen from a show case at the “Paläontologisches Museum Nierstein”.

The stolen teeth are two specimens of Woellsteinia oligocaena, and Isurolamna gracilis as well as one tooth of Alopias latidens.

The scientifically processed and published originals should be returned to their original depository where they should be made accessible to the public again. To facilitate their identification we are also going to publish some pictures on our website. You can see them at www.museumnierstein.de

There is evidence which indicates that meanwhile these shark teeth have ended up in collections in the Netherlands.

Herewith we would like to state that these teeth are still property of the “Paläontologisches Museum Nierstein”. The teeth have to be given back like stolen artwork, even if they should be found after years or decades. We have reported the theft to the police. The pictures displayed on this site have also been made available to the responsible authorities.

If you have one of these concise and clearly identifiable teeth in your collection or have seen it in another collection, we ask you for your help.

If you have acquired one of the teeth in good faith or traded one of them, we are interested in an amiable solution.

We are thankful for any piece of information (anonymous information also welcome), which could lead to the present whereabouts of the objects.

Harald Stapf (Director of the museum)

Sunday, January 18, 2009

Mineral Deposit Profiles of the British Columbia Geological Survey

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A great site about mineral deposits that I so far neglected to mention here is the collection of freely accessible Mineral Deposit Profiles of the British Columbia Geological Survey. More than 90 profiles of different mineral deposits are described in short and easy to understand summaries sorted by commodity, lithology or deposit group. It is a very valuable resource for anyone interested or working in the the wide field of mineral exploration. It covers different commodities from base metals, precious metals, industrial minerals and gemstones. Profiles include a short description, example deposits, features of host rocks and ore control, exploration aids and many other criteria. In total there are 156 profiles of which 91 may be freely accessed online. Additional profiles can be purchased from the BCGS.

Also I would like to recommend the Geoscience and Exploration websites of the BCGS that hold a lot of valuable information.

Scanning your samples

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Ever wondered how to document your samples and thin sections but didn't feel like spending hours taking fotos? Scan them! It works nicely with any kind of more or less planar surface. No need to grind or polish your sample. Just try to get a somewhat flat surface. In my mapping area one may find palaeokarst cavities in Jurassic limestones infilled with worthless (too small, Fe-concentration too low, too much cover and largely eroded) Eocene bean ore cemented by orange-brown carbonate. I used one to test the method and it works! Below you can see a scanned piece of bean ore.


Diameter roughly 3 to 4 cm.
Click to enlarge!


You can get good results for scanning samples with 600 dpi, however, 1200 will provide a clearer and bigger image and will generally be enough for any kind of sample. The above image has a resolution of 1200 dpi. If you want to scan thin sections 2400 dpi or more are recommendable. Unless you want do use the images only for illustrating the process of manufacture. My scanner can go up to 7200 dpi which delivers fantastic scans with great detail - if my computer doesn't crash under the load of truly huge images. So keep in mind to have a strong computer power behind your scanner.

That's it already! Scanning itself is done the same as for any other material. Take caution not to drop your samples into the scanner or scratch the plastic surfaces.

Saturday, January 17, 2009

Chinese Geoblogosphere

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Some recent visits from China to my blog and the recent post of Silver Fox on Looking for Detachment led me to start a small search for the Chinese Geoblogosphere. Surprised as I was I discovered a few geoscience related blogs in Chinese. I don't speak Chinese, google translation is...."funny" but they are obviously talking about geology there. I don't even know how to correctly translate the names of the blogs or their authors so I decided to simple post the links and my personal interpretation of what their names might be like. If you are Chinese and find my translation to be total nonsense please excuse my ignorance. I'd be most grateful for a correct name translation and I will correct them as soon as I can. The list is by no names complete I think. If you are not listed accept my excuse.

UPDATE: hawkman (see comments) was kind of enough to reply and inform me about the correct translations for the Chinese Geoblogs! Thanks a lot! Corrections included below.

Geography Time http://www.comgeo.net/

Shao-Ji-Cheng's Blog http://www.sciencenet.cn/u/Majorite/

Liu Jishun's Blog http://www.sciencenet.cn/u/yuelugj/

About Rock and other http://www.kongcuo.com/

Hawkman's Blog about earthquakes http://hawkman.tasuo.org/

GeoIdea http://www.geoidea.org/

365 Geo http://www.365geo.com/

It is a shame I don't understand a word of Chinese. The Google translation often provides very funny results.

Friday, January 16, 2009

A rock face

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One of the odd curiousities I came across while mapping november/december last year is this weird looking piece of sculptor work. It's a bit scary, no? Someone discovered limestone for "rock art".



I wonder who made it and especially when. The surface was not too dirty and I did not clean it. Sadly so far it remained the only mysterious artwork within my mapping area. It was quite a nice distraction for my supervisor (who saw it first) and me. Did any of you ever find something comparable during field work? Wild works of art in nature?

Wednesday, January 14, 2009

State Geological Surveys of Germany

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To guide the way to the German State Geological Surveys I now included links to the most important refernece sites under the point "Geologische Dienste Deutschlands". You will find a link to the BGR - Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute of Geosciences and Natural Resources) sort of a USGS, a link to the Landesamt für Geologie, Rohstoffe und Bergbau Baden-Württemberg who are proviving the theme for my mapping work and are comparely to a State Geological Survey in the US and finally the InfoGeo website, a central point to find all German State Geological Surveys in one place.

Saturday, January 10, 2009

Visited countries meme

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Another meme is spreading like a virus in the geoblogosphere, the visited countries meme! Other blogs have already been infected, like NOLÖGIC, Looking for Detachment, The Ethical Palaeontologist, Clastic Detritus, Highly Allochthonous, ReBecca's Blog and Hypo-theses.

Here is the anamnesis of my worldly travels. I touched the ground in less than 9% of the world. Way too little!!!

Also the visit to the USA is a bit of a cheat. I had to wait 8 hours in transit on a flight to Peru in the Forth Worth Airport in Texas.


visited 19 states (8.44%)

Friday, January 9, 2009

Limestone classification - naming your rock

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Something I should be doing a lot now is giving names to rocks I find in the field. Unfortunately a white, powdery substance also known as snow is preventing this. I figured I might share with you the joys of limestone classification. Perhaps it may help you understand my posts or pass that little exam ahead of you if you are a student. There are two widely used classifications of limestone rocks that have proven to be most practical, those of Dunham (1962) and Folk (1962).

Both

"Rely on the concept of textural maturity, where the texture is believed to reflect the energy level in the depositional environment"
(Wright, 1992).

I am doing field work and mapping in carbonates (mainly limestones, few marls) meaning I need an easily applicable method to name my sample in the field without knowing much about its history. The original Dunham classification is based on depositional texture and can easily be applied in the field without major equipment (magnifying glass, acid, a scale). Folk's classification may be more detailled but generally, with exceptions, requires a lab with thin sections or peels. For the above reasons I will restrict myself to introducing you to the expanded and revised Dunham classification of Wright (1992).

Dunham originally included five textural classes: mudstone, wackestone, packstone, grainstone and boundstone. A sixth class was included for rocks without recognisable depositional texture and termed crystalline carbonate.

In 1971 the Dunham classification was expanded by Embry and Klovan to include the size aspects of grains larger than 2 mm and the organical boundstone was extended to include frame-, bind- and bafflestone.

Wright revised this classification in 1992 and included diagenetic changes of depositional texture to further appreciate the impact of diagenesis on limestones. The terms mud-, float- and rudstone were revised and five diagenetic classes added: cementstone, condensed and fitted grainstone, sparstone and mircosparstone. In my own experience the diagenetic classes might require lab work though because they are not always easily recognisable in the field.

Any good textbook discussion carbonate rocks probably includes the following figure. The essential description and characteristics are shown in the figure and I recommend for anyone interested to either consult the original articles or any good textbook on carbonates for more detailled information than I will give in this post.


The revised classification of limestones (Wright, 1992)

You should keep in mind that textures in limestones are the result from the interplay of three major factors: depositional regime, biological activity and diagenesis.


A fundamental step in classification is seperating grain-support from matrix-support which is not always as easy as it may sound and depends on the two-dimensional aspect of how we look at a rock surface. As mentioned above the term mudstone was revised by Wright to calcimudstone to emphasise the difference from siliciclastic sediments and avoid confusion. Dispite similiar grain-size calcimudstone and Folk's micrite are not synonymous and should not be confused! Also you should not think that calcimudstone or wackestones are analogous to their siliciclastic counterparts. Hydraulic processes would not lead to such mixtures of fine and coarse grained materials (usually) as we can observe in wackestones. It might be interesting to remember that at least some packstones are likely compacted and dewatered original wackestones. Grainstones are matrix-free and grain-supported. Mud has either been removed or never formed, usually indicating high energy environments. However, they can also form by diagenetic processes, i.e. desiccation on exposure. Float- and Rudstones are basicly the coarse-grained counterparts of wackestone and pack- to grainstones. Due to almost synonymous usage and semantical problems Wright revised the original bindstones of Embry and Klovan and named them boundstone, like in the original Dunham classification that included all organical limestones into this class though. Beware not to confuse one with another! Also I am sure a few of you were wondering what happened to the bindstones on the above figures. The remaining biogenic textural classes did not change, however, Wright noted how the term bafflestone might be obsolete because it is virtually impossible to show that organisms baffled sediment.

Cementstone is almost totally composed of fibrous cement that is commonly replaced or recrystallised. Grains or in-situ biogenic materials do not form a framework.

Grain-supported textures are often changed in burial which produces partially sutured grains (condensed grainstones) or transforms all grain contacts to microstylolites (fitted grainstones).

Limestones that have lost their depositional texture due to recrystallisation or replacement are divided into sparstones and microsparstones, depending on their crystal size being larger or smaller than 10 microns. I still use crystalline limestone because they are rare and hard to tell apart where I am working.

To conclude remember this quote:

"There are too many papers that simply conclude that the carbonate rocks of a given study can be arranged according to the classification of one or more authors. All too often these workers have failed to recognize that a classification is a simple tool for organizing information, not the source of a conclusion" (Blatt et al. 1972).

Bold passages emphasised by me.

A very good read on carbonates and carbonate classification can be found here and on the USC Sequence Stratigraphy Web.


Important references used:
  • Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. Mem. Am. Assoc. Pet. Geol., 1: 108-121.
  • Flügel, E., 2004. Microfacies of Carbonate Rocks. Springer Verlag, Berlin Heidelberg, 976 pp.
  • Folk, R.L., 1959. Practical petrographic classification of limestones. Bull. Am. Assoc. Pet. Geol., 43: 1-38.
  • Wright, V.P., 1992. A revised classification of limestones. Sediment. Geol., 76: 177-185 doi:10.1016/0037-0738(92)90082-3

Wednesday, January 7, 2009

One year of being the Lost Geologist

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Exactly one year ago on January 7th, 2008, I began this blog with the first post. What a great and interesting first year of being the Lost Geologist! I hope I can keep on posting regularly for the next year, too, and expand both the quality of my writing and my interaction with the geoblogosphere.

Now if I wouldn't have been awfully busy the last few days with putting together a short presentation of results to my professor about my mapping project I would have had the time to make a nice, big anniversary post, however, my end of the year post already gives a good summary.

I am having a few nice posts in my mind though that I want to make in the next week all relating directly or indirectly to carbonates.

Tuesday, January 6, 2009

A new, very readable Dinosaur blog

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Recently I discovered the dinosaur blog by dino-gal aka Kay Buttler that I find to be very readable especially because I don't really understand the more scientific writing of plenty of other palaeo-blogs. I'm just not a "dead-animals-kind-of-guy" (although I find a lot of them in carbonates of course). Considering her enthusiasm she will surely become a great palaeontologist. Go read her blog and take a look at her website.

Thursday, January 1, 2009

First news for 2009

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Other geobloggers have already mentioned it on their blogs. A number of quality geoblogs have been inlcuded in a list of the 100 Best Blogs for Earth Science Scholars and I am delighted to have been notified that I also made it onto that list. Looks like 2009 started with good news!