Small Geology of Lima coast

As you know I am currently in Lima, Peru. Lima is the capital of Peru and a crowded melting pot directly at the Pacific seaside. The seaside itself is pretty steep and vertical cliffs dominate the entire coastline here which of course provides for a magnificent view.

The coastline at Miraflores

Lima is situated on the alluvial fans of the Rimac and Chillon rivers. The palaofans are well exposed along the coastside in the cliffs that can be up to 80 m high. The Cordillera is the supplier of the pebbles and gravels that can be encountered here. Conglomerate clasts can be up to 80cm large at the coast. The Rimac river has a steep gradient of 1:25 and, according to my sources, thus is largly providing bedload transport. Clasts are mostly granites, diorites, gabbros and mesozoic to cenozoic volcanic rocks. The Lima Conglomerate has a thickness of up to 86m. It is interrupted in parts by lenticular sand- and siltstone lenses that likely represent estuarine incursions caused by sea-level variations.

One of the cliffs with erosional evidence and gullies forming. Note the lenses of finer material.

A sand lense in close-up. Note the deviation from the horizontal in the "layering".

According to what I read they can be subdivided into several layers which, by all honestly, I cannot see. The only difference is the average clast size which perhaps is not well exposed in Miraflores where I am. Neither could I observe the imbrication of the clasts and pebbles indicating flow directions and such alike. Well maybe I did but I have to stretch my imagination a lot to see it. There are no fossils

In terms of age we are talking Plio-Pleistocene here when sedimentation was affected by the movement of the Nazca Ridge towards the south proving for impulses of uplift and subsidence and the Lima anticline that blocks direct access for the Rimac river to the sea.

Movement of the Nazca Ridge. Taken from the source cited below.

The pebbles of the Lima Conglomerate get washed out and form the beach. The beach is only pebbles but it makes a great and amazing sound when the waves are washing over them and the water flows back. Klack-klack-klack...

Beach pebbles

If you like to read more take a look at the cited article.

References:

• Roux, J.P. et al (2000): Sedimentology of the Rimac-Chillon alluvial fan at Lima, Peru, as related to Plio-Pleistocene sea-level changes, glacial cycles and tectonics, Journal of South American Earth Sciences 13, 499 - 510

Secure arrival

Just letting you all know I safely arrived to Lima, Peru. I'm very close to the seaside in Lima and can see the big waves of the Pacific ocean. Congress will start in around 10 days. Till then I can do some relaxing, aclimatise myself and meet many friends. I also hope to take more useful fotos than last time of the very impressive cliffs of Lima along the coastside. I'm pretty sure all you sedimentologist would love those conglomerates that are exposed for several 10s of meters high.

Away again

It is again time to pack and travel. Tomorrow morning I will board my plane and fly to Lima, Peru, like I already talked about in other posts. New posts will likely be rare in that time but I am looking forward to 3 interesting weeks and a great geological congress at the end of the month. In early october I will be back home.

86th Annual Meeting of the German Mineralogical Society

Tomorrow, sunday 14th, is the opening ceremony of the 86th Annual Meeting of the German Mineralogical Society (DMG). Three days of symposias ranging from education and outreach over ore deposits to the preservation of monuments will offer a wide range of interesting activites. My fellow German Geoblogger Lutz will be presenting a poster on this meeting which was reason enough for me to spontaneously register and have my very first meeting ever! It will be a nice practise before attending the big congress in Lima at the end of this month. I will focus myself on visiting the ore deposits symposia which seems to offer some interesting presentations about MVT deposits in Germany and hydrothermal vein deposits.

Five most important minerals

After the 50 minerals meme Callan from the NOVA Geoblog is asking us what the 5 most important mineral are if we had to explain to a non-geologist.

Quartz: Many others already mentioned it. It is one of the toughest and most widespread minerals that everyone will get in touch with sooner or later. Also it is a major building stone of the continental crust and makes for nice juwelery in the form of amethyst, rock crystals and smokey quartz. Last but not least it is part of not just a lot of sedimentary rocks but also part of every computer or optical device in the form of silicium.

Feldspar: Is actually a group of silicate minerals, however most non-geo-educated people won't be able to seperate them anyways. Furthermore, they also compromise a large portion of the earths crust and are highly useful as a resource for ceramics, pottery (clay minerals also play a role here) and construction materials.

Calcite/Aragonite: Anyone taking a vacation in warmer climate will come across carbonate producing organisms like corals, crinoids, mussels and many others. Everyone likely heard of the Great Barrier reef or the Carrara marble. It can host great fossils and is widespread in many areas of the world. Also it is relatively easy to recognise. Last but not least it is a very important resource for a variety of economical activites like cement production, paints, filling material, glass and ceramics.

Olivine: Mentioned by Silver Fox it constitutes a major portion of the earth's mantle. One may find it in basalts which is what most people know. It can be beautifully green and of "gemstone quality". Olivine rich rocks are hosts to important ore deposits, i.e. chromium.

Chalcosine/Chalcopyrite: Actually two different minerals but together the most important source of copper. After silver copper is the best electrical conductor and thus one of the most important metals in our society. Any electrical device needs copper. Additionally, together with tin it forms a very important alloy: Bronze.

50 minerals meme

Everyone seems to be jumping on the bandwaggon after Chuck from Lab Lemming started the 50 minerals you should have seen meme. Hmm..there is not much else to say but I might add some other minerals in a seperate addition underneath that I have seen in the wild for sure but are not listed here.

Bold for minerals seen in the wild, italic for in the lab or at uni.

Andalusite
Apatite
Barite
Beryl
Biotite
Chromite
Chrysotile
Cordierite
Corundum
Diamond*
Dolomite
Florencite
Galena
Garnet
Graphite
Gypsum
Halite
Haematite
Hornblende
Illite
Illmenite
Kaolinite
Kyanite
Lepidolite
Limonite
Magnetite
Molybdenite
Monazite
Nepheline
Olivine
Omphacite
Opal
Perovskite
Plagioclase
Pyrite
Quartz
Rutile
Sanidine
Sillimanite
Silver (native)
Sphalerite
Staurolite
Sulphur (native)
Talc
Tourmaline
Tremolite
Turquoise
Vermiculite
Willemite
Zeolite
Zircon

My personal additions that I think are important:

Amber (I know, technically it is not a mineral but...)
Anhydrite
Arsenic (native - wonderful garlic smell)
Chalcopyrite
Fluorite
Hauyne/Hauynite
Pechblende
Rhodochrosite
Siderite
Sylvinite (it tastes so..."delicious")
Vanadinite
Zinnwaldite

I am surprised how many I know. :-o

The Origin of the Rhume river/Die Rhumequelle

During my five week long stay in the Harz mountains I managed to undertake a few geology related tours. One of those took me and a friend to the Rhumequelle - the largest karst spring of Lower Saxony with a diameter of 20 m. Besides the main spring there are dozens of minor springs in the immediate vicinity of the Rhumequelle. Together with the main spring they have an average discharge rate of around 2.200 l/s with a maximum discharge of 5.900 l/s in rainy times and a minimum of 900 l/s in dry seasons. Only a small amount of the water derives from precipation. The largest amount comes from underground supply derived from the rivers Siebe and Oder who lose a significant amount of their water to karst ground water aquifers.

The spring itself is situated in the Zechstein-Dolomite (Upper Permian) that is jammed inbetween Lower Buntsandstein (Lower Triassic) clastic sediments by a major fault.

A small portion is used for drinking water. The water is of pure drinking water quality and aside from removing an excess of natural sulfate from it, it is directly pumped to the costumers. It is generally low on nutrients and other impurities but exhibits a fascinating blue colour that makes a wonderful constrast to the green of the surrounding trees.

View across the main spring of the Rhume with typical water colour.

If any of you should be close to it. It is well worth a visit!


References:

• Grimmelmann, W. (1992): Hydrogeologisches Gutachten Trinkwasserschutzgebiet "Pölder Becken", NLfB Archiv Nr. 100277, unpublished.
• Hermann, A. (1969): Die geologische und hydrogeologische Situation der Rhumequelle am Südharz, Jh. Karst u. Höhlenk., H. 9: 107 - 112, München.
• Röhling, H.-G. (2003): Die Rhumequelle im Eichsfeld - eine der größten Karstquellen in Mitteleuropa, Eichsfeld Jahrbuch, 11. Jahrg., 329 - 357, Duderstadt.

Survey on Geoblogs/Umfrage zu Geoblogs

Callan Bentley from the NOVA Geoblog is performing a survey of the Geoblogosphere for a presentation he is preparing for a meeting of the Geological Society of Washington. Anyone who is "geoblogging" is invited to partake in this survey. I am sure it will give us some interesting results.

Damit sich diese Nachricht auch in die kleinen aber feine deutsche Geoblogosphäre ausbreitet möchte ich auch auf deutsch darauf hinweisen, dass auf dem NOVA Geoblog von Callan Bentley eine Umfrage über Geoblogger und ihre Geoblogs läuft. Es wäre sicher schön, wenn nicht nur die nordamerikanischen Geoblogs in dieser auftauchen würden.

Painting Geologist

Totally not geology related I felt like sharing what seems to be becoming my new hobby to relax from studying and thesis preperations. I began painting. Just today I bought a set of 12 colours, paint brushes and paper. Not that I am losing my interesting in geology, however it is clear sometime the analytical-scientific needs to be shut down and put aside. I'm curious what kind of hobbies people out there have when they are not focused on doing geology. That would be interesting to know really. Perhaps you can leave some comments on that.

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It's an awful lot of fun to make paintings like that. In case you are wondering those above were made without any paint brushes.

Four Geoblogs

I added four more geoblogs to my link list. I found them some while ago already but didn't get around to include them, yet. Quite a varied mix, all highly interesting!

Sedimentary Basins and Petroleum Geology by Paul Wilson

GeoLibros by Make Stanne

Three months on the Long Mountain by Jess Deemer from California

Reporting on a Revolution by Suvrat Kher