18 October, 2008

Field work preparations

These days I am doing my preparations for my mapping project. Usually one of the first things I do when going to an area I have not previously visited nor read much about is to learn the local stratigraphy, especially the lithostratigraphy. Knowing the terms and formation names makes it a lot easier to orientate in the literature and usually already gives a good, general clue about what kind of lithology I can expect to encounter in the field.

Lithostratigraphic Overview of Baden-Württemberg [5. Ausgabe Jan. 2004 (1. Ausg.1999), Bearbeiter: M. FRANZ & E. VILLINGER]

Above is an overview of the lithostratigraphy of the German state of Baden-Württemberg. In a simplified manner it can be subdivided into three lithostratigraphic areas, each with a slightly different sedimentation history in the Jurassic. You will notice simply by comparing the formation names that the three areas are starting to develop a divergent sedimentation regime sometime in the Upper Bajocian (Bajocium). I highlighted the lithostratigraphy relevant for my own mapping and placed a special emphasis on the Hauptrogenstein-Formation (a oolithic limestone complex) and the Opalinuston-Formation (mainly mudstones) which are the main targets and formations within my mapping area. The Opalinuston-Formation is named after the ammonite Leioceras opalinum (Reinecke, 1818). Hauptrogenstein means as much as "Main Fry Stone" referring to the similarity of the ooliths to fish eggs. The Hauptrogenstein can be sub-divided into Lower, Middle and Upper Hauptrogenstein and has a thickness of roughly 40 to 80 m in the Southern Upper Rhine graben region.

Overviews on the local stratigraphy can be freely downloaded on the website of the Landesamt für Geologie, Rohstoffe and Bergbau von Baden-Württemberg [State Office of Geology, Resources and Mining of the State of Baden-Württemberg].

A lot more blogs

Geoberg has recently made another good post about many palaeontological orientated blogs with some of those written in Spanish. I also discovered two blogs (The Life of Madygen and NÖLOGIC) among Geoberg's post that are authored by German students of my former university. Additionally there is a newly born German language blog by a student of geophysics from my own university. It's called A long way to go but written in German (auf Deutsch!). These blogs are fairly new so I am just as curious as you are of what they will develop into.

The three "German" blogs were added to my feed of German Geoblogs that you can see on the right.

13 October, 2008

Stuff I should read...

Here is what is currently on my high-priority reading list. That should increase the chances of me actually looking at it to 99% - I hope. It sounds interesting though and I won't be able to delay it forever.

Lorenz, Walter; Gwosdz, Werner:
Bewertungskriterien für Industrieminerale, Steine und Erden Teil 2: Karbonat- und Sulfatgesteine [Evaluation criteria for industrial minerals, rocks and clays. Part 2: Carbonates and Sulfate rocks] 1998.
Geologisches Jahrbuch Reihe H, Band H 4

Geyer, Otto F.;Gwinner, Manfred P.:
Geologie von Baden-Württemberg [Regional Geology of the State of Baden Württemberg, Germany] 1991. VIII

Ernst, Martin:
Stratigraphie und Fazies des Braunen Juras im südlichen Oberrheingraben (Blatt Kandern), [Stratigraphy and Facies of the Brown Jura in the Southern Upper Rhine Graben] 1990.
Jahresheft Geologisches Landesamt Baden-Württemberg, Heft 32, page 93-157

There are no online or downloadable versions. My excuses. This is good old paper.

12 October, 2008

Septarian Nodule - Solution of Weekend Fun No. 7

The first answer was already the correct one! Lockwood correctly identified the shown foto as a septarian nodule. Dispite the breccia like appearance the cement is orange calcite (just tested it with a bit of acid). Also the components are carbonate rich mud. A bit more accurate septarian nodules are concretions in carbonate rich sedimentary rock like clays and marls that develop cracks due to desiccation. They are said to form due to local enrichment of carbonate because of decomposition of organic matter. Usually the cavities are filled by calcite but cases of quartz and other minerals that can be precipated at low temperatures are also known. The minerals form from circulating solutions. Congrats to Lockwood!

10 October, 2008

Weekend Fun No. 7

After a long hiatus another implementation of the Weekend Fun puzzles! I've been searching through my pet rocks and I found this one. It is just right I think for asking: What is it and how does it form? I left away scale and other clues. The shown sample has been found in Germany by a friend of mine some years ago. Which isn't really any help because these can be found worldwide as far as I know. Have fun guessing! I'll solve this weekend fun puzzle sunday or monday depending on the number of comments unless someone get's it right first. Good luck!

09 October, 2008

En Morrenas

Since I already met Patricio in person I thought it would be about time to also had his spanish-language blog to my blogroll on the right. The blog is called En Morrenas meaning as much as "in moraines". I don't recall if he explained on the blog why he has that name but the real-life anecdote was entertaining. Anyways, if you are interested in Peru and some glacial geology go take a look!

08 October, 2008

Travertine along the Lima coast

In my article about the geology of the Lima coast I omitted to mention one prominent feature of the Lima coast. That is the occurence of Travertine or better said calcareous tuff along the cliffs of the Lima conglomerate. As a matter of fact this is a common occurence along the entire coastline of exposed conglomerate and I am sure the formation is directly linked to it.

When walking or driving along the Costa Verde (green coast) of Lima - actually it has the charm of brown-grey concrete instead of being green in most places - it is impossible to miss the sometimes 10m large and several 10s of meters long Travertine curtains that usually originate somewhere in the lower or middle of the Lima conglomerate. From my few observations while driving by or from the opposite side of the street the occurence of Travertine seems to be connected to changes in grain size within the Lima conglomerate. Either they occure at the lower contact of finer layers of sand/silt or at the lower contact of layers of very coarse conglomerate. For more on the conglomerate itself please consult the other post.

Unfortunately I only took one mediocre foto of the Travertine.

Foto showing the contact of coarse and less coarse conglomerate with travertine close to Parque de Amor/Miraflores (the sand is recent wash-out debris)

Here are several scanned images I took in late 2004 on a previous visit to Miraflores/Lima.

Travertine views from large to small scale

In the above fotos you can see different perspective on the Travertine just below the Larcomar shopping and entertainment mall. I included a few remarks into the fotos. The white thingy in the lower right foto is half my student ID, about 11cm long. Going top to bottom and left to right you can see the layer of finer material being the focal layer for travertine occurence. Travertine forms at the lower contact of the finer material and covers the sedimentary layers below it. Dead plants remains still are in place and intergrown with the travertine. On one foto you can nicely see the individual roots still in place and the empty tube-like features of the travertine. The last foto illustrates how the travertine also is cementing the conglomerate pebbeles in some places.

It seems obvious that the formation of travertine is linked to changes in grain size and sedimentary lithology of the not well consolidated sediments. I could imagine the exposed layers of sand or silt to be the former groundwater aquifer of the Lima conglomerate. Travertine would thus form at the top of less permeable layers as documented in the fotos.

From locals I know that until 4o to 50 years ago the entire coastline of Lima was green, hence the name. Only in the last decades it changed from green to concrete brown-grey. That change occured at roughly the same time as groundwater production for drinking and agriculture increased significantly when more pumps were being installed (I must apologise for not having written sources available. Those will be added as soon as available to me.). Lima today has 8 to 9 Million inhabitants that all rely in groundwater or imported water from the mountains.

Combined with the age information of the Lima conglomerate from the previous post the travertine formation is at most Plio-Pleistocene in age and continued up to recent historical times. Considering the preservation of plant remains in the fotos I assume the shown exampels to be no older than a few decades to a few hundred years. Also they illustrate nicely the results of exploiting the groundwater resources beyond their ability of regeneration.

Perhaps some of you Peruvian geobloggers can find sources on this or know more from own work? I could not find online sources regarding this issue.

To anyone working on this: These are not the results of any study or detailed work. Only the conclusions I draw from driving by in a car and a single hour of looking at the rocks from a distance.

07 October, 2008

Home, a Congress, Geobloggers and Lima

Today after a stressing 24h travel from door to door I have safely returned home from my travels to Lima in Peru. It was again a wonderful experience to be in Lima and meet many old - and new - friends. As you can read in previous posts I flew to Lima in order to, besides visiting friends, attend the XIII Latin-American Geological Congress / XIV Peruvian Geological Congress and the SEG Workshop: "Geology of Pb-Zn Ore Deposits: The Present Perspective" by Richard Tosdale, David Leach, Lluís Fontboté y Larry Meinert. Both of these were excellent experiences and I was very impressed by the course. Sadly for some unknown reason Lluis Fontbote could not attend. Still - a great course! Congress itself took 4 days with little more than 1800 participants and more than 60 stands of geo-related companies (mostly mining and exploration services).

On the evening of the 29th of september Patricio, Luis, Miguel and I also managed to have our first Lima Geobloggers Meeting in Larcomar. Patricio even managed to make this nice logo which of course shows-up rather late (Internet connection from San Miguel/Lima was awful) on my blog but I like it.

So we met in the Hooters Bar (contrary to what the logo says...) in Larcomar, drank a nice Peruvian beer and had plenty to laugh about from personal and very hilarious geo-anecdotes of which we better not share the content online.

From left to right: En Morrenas, Lost Geologist, MiGeo and Geocosas.

It was great meeting you guys by the way!

The congress: It was awesomely big. Ok, it was my first big one. But still. I have a lot of people whom I promised to write. There are one or two possibilities that could develop into a master thesis, however, I prefer to celebrate once I have something concrete. Anyways, the presentations went on for 4 days in 4 different rooms 10 hours each day. Almost every kind of topic was somehow adressed with a focus on mining and mineral deposits and, of course, Latinamerican geology. If you are interested the programm is still online on their website. Also I heard the presentations will (or already are?) be uploaded to a website. I'll let you know once I know more.

The entire event was finalised by a nice dinner in a great Argentinian restaurant in Miraflores together with two kind professors from Brasil and a local geology student (hi Jenny!).