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Posts tagged with "sedimentology"

Biogeomorphology - Braiding vs. Meandering Rivers

Thursday, 8. October 2009, 15:23:26

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Biogeomorphology is the study of interactions between living organisms (ecology/biology) and the development of landforms (geomorphology). Organisms affect geomorphic processes in a variety of ways. For example, trees can reduce landslide potential where their roots penetrate to underlying rock, plants and their litter inhibit soil erosion, biochemicals produced by plants accelerate the chemical weathering of bedrock, and marine animals cause the bioerosion of coral.



A braided river consists of a network of small channels separated by small and often temporary islands called braid bars or aits or eyots. Braided rivers are relatively rare today. I only remember to have seen them in barren (glacial) environments.

At the beginning practically all rivers were braided. A literature compilation and fieldwork on fluvial deposits show that, prior to effective plant colonisation, Cambrian to Early Silurian fluvial deposits were largely braided-river sand-sheets passing into sandy coastal and offshore deposits.

After trees and deep roots developed late in the Early Devonian, meandering rivers became more common, and today they are the norm.

Sedimentologists have generally dismissed or underestimated the importance of vegetation on riverine landscapes, although the few pristine modern rivers illustrate the intense effects of vegetation.

Late Palaeozoic plants fundamentally and irrevocably changed environments on land.

Reference:
Gibling and Davies
Rivers and Plants: Evolving Fluvial Systems through the Paleozoic
IAS 2009 27th Meeting, Book of Abstracts, p, 183



PS:
The trick to create meandering channels in the lab is indeed to plant alfalfa seedlings to give the banks some cohesion. See
http://scienceblogs.com/highlyallochthonous/2009/10/how_to_build_a_meandering_rive.php
An experiment that stresses the importance of living organisms in river morphology.



Academics

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Source-Sink Systems

Wednesday, 5. August 2009, 07:06:17

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Geology is first and foremost what you see in the field, but now and then you need to theorise. I cannot imagine any pleasure in sedimentology without plate tectonics, and that is probably a main reason why I (occasionally assumed to be a sedimentologist) am fascinated by plate tectonics. That is to me the start of the so-called rock cycle. Plate tectonics give rise to uplift - to building of (high) mountains. The uplifted rocks weather and erode, and the weathered and eroded material is either deposited in situ or transported away.

The simplest case of sediment transport is by gravity. Rock falls and landslides. Scree deposits are a regular sight in mountainous areas (where they make climbing and walking difficult), but they are rarely seen in old sediments.

Transport of particles in water is however the most important of all sediment transport mechanisms, not only by streams and rivers but also by ocean currents.

The next important transporting medium is air. Loess is a good example of airborne deposits, with very fine-grained particles. In a desert with practically no rainfall, it is a pleasure to see what wind can do with sands.

Maybe we tend to forget ice as a sediment transport medium, although in the region where I was born, you cannot miss it with all the moraines from the Ice Age. Glaciers act much like a conveyor belt carrying debris from the top of the glacier to the bottom where it deposits it in end moraines. Glacial erratics
can also be extremely spectacular.

The source-to-sink system comprises all areas that contribute to erosion, transportation and deposition of sediments within an erosional-depositional system - from catchment headwater to deep-marine basin floor fan. You can divide the source-to-sink system into four segments as done in a recent paper in Basin Research.

Here is an illustration from that paper

showing the segments: catchment, shelf, slope, and basin floor. The segments are related so that long-term modification (on geological time scales) by erosion and deposition in one segment will affect one or several remaining segments, causing lengthening and flattening of the segments and overall development of the entire system. The basin floor (deep ocean floor) is the ultimate sink (in the sedimentary record). Later, however, the buried sediments can be reused via the rock cycle and plate tectonics, so that they can be uplifted to build new mountains as sedimentary, metamorphic or fully re-melted igneous rocks.

From cradle to the grave - from erosion to deposition - from source to sink. That is indeed a basic concept.

Reference:

Sømme et al.
Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systems
Basin Research (2009) 21, number 4 of August 2009, pp. 361–387
doi: 10.1111/j.1365-2117.2009.00397.x




AcademicsTop Blogs

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Polish Jura (Jurassic)

Sunday, 22. February 2009, 18:42:04

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I am back from a city trip to Krakow in Poland. In some way Krakow reminds me of Bali. Where Bali is full of temples, Krakow is full of churches, and they were in fact my primary goals. Less geology thus. Some of the old church walls are however made of limestone. Actually the reason of human settlement (back in the Stone Age) at Krakow was of a geological nature. It all started on the Wawel Hill, a small hill at the shore of the Vistula river. This was in fact the only place where I saw any geological outcrop. The hill is of Jurassic limestone and there even is a small karst cave, the Dragon Cave, where a fire-breathing dragon used to protect the hill. - A legend attributes the founding of Krakow to a mythical ruler Krakus, who built his settlement above a cave occupied by the ravenous dragon, Smok Wawelski.



The Jurassic period is the middle of the three divisions that make up the Mesozoic era. The Mesozoic era is the era when dinosaurs roamed the Earth. The dinosaurs became particularly well known after Spielberg’s film “Jurassic Park”. Most of the dinosaurs featured in “Jurassic Park” are not from the Jurassic period, but from the Cretaceous period, but who cares? “Cretaceous Park” does not really sell as a title.

The Jurassic is named after the Jura Mountains, situated mostly in France, but partly in Switzerland. I mainly appreciate the Jura for its outcrops of carbonate platforms, where you can see excellent evidence for the influence of Milankovitch cycles on sea level changes.



Now the funny thing is that there also is an area in Poland called Jura - in this case named after the Jurassic outcrops in that area. Do you follow me? - the Polish Jura is named after the Jurassic period, which again is named after the French/Swiss Jura. The Polish Jura Chain, also known as the Polish Jurassic Highland, or Kraków-Częstochowa Jurassic Highland Chain (Polish: Jura Krakowsko-Częstochowska, German: Krakauer-Tschenstochauer Juragebiet) is part of the Jurassic System of south–central Poland, stretching between the cities of Kraków, Częstochowa and Wieluń.

And now back to Krakow, via Spielberg. His film “Schindler's List” is a dramatized account of the true story of Oskar Schindler, a German businessman who saved the lives of more than one thousand Polish Jews during the Holocaust by employing them in his factories. It was filmed in Kazimierz, the old Jewish quarter in Krakow, from where the Jews were actually saved by Schindler’s so-called list. (And of course I walked through this quarter as well, but not out of geological interest).

• http://www.jura.info.pl/en/www/index.php?rid=2&sid=1




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Plattenkalk - Solnhofen

Friday, 5. December 2008, 10:46:00

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I ought to write about sediments or sedimentology more often, but my pictures from outcrops are seldom spectacular. When I show a picture like this one:

who cares about the limestone. Everybody stares at the fossil, which is understandable. Nevertheless I stand there with questions like: Why did it die just there? No oxygen available? How did it get fossilised? Why wasn’t it torn apart by scavengers or waves? What was the environment? How come that you can see so many tiny details? and so on... In short questions that might be answered by studying the sediments in which the fossil is found.

My picture is of one of the most famous fossils ever found - the Archaeopteryx lithographica, a link between dinosaurs and birds. I am happy to see that Munnecke et al. have paid the attention to the rock itself that it deserves in a paper published in the December 2008 issue of Sedimentology.



The limestone in which so far ten Archaeopteryx fossils were found are limestone successions of Upper Jurassic (Tithonian) age in the Solnhofen/Eichstätt area. They consist of alternate layers of thin-bedded, laminated, fine-grained, very pure (hard) limestone and softer (inter)layers with slightly lower carbonate contents that are also laminated and show a foliaceous weathering appearance. The extremely fine grained structure explains why so many fine details are visible in fossils from the area. It has also made some of these rocks perfect for lithography, that is one of the early methods of printing images using a flat stone with a completely smooth surface. In one of the geological museums at Solnhofen you can learn more about this printing process. This use of the rock lead to the naming of Archaeopteryx lithographica.

The author was concerned with the proper name for these rocks. Lithographic limestones may sound appropriate, but only a small portion of plattenkalk limestones, namely less than 1% from the classic Solnhofen occurrences, is usable for lithographic techniques. The German word plattenkalk means something like platy limestone, but this term (platy limestone) appears too wide. In 2005 Röper defined plattenkalk as all carbonate marine sediments, in which bioturbation – for whatever reason – partially or completely stopped, so that the primary lamination and fine stratification of the sediments is preserved. (Bioturbation means stirring or mixing of sediment or soil by organisms, especially by burrowing, boring, or ingestion). Now this lack of bioturbation is another reason that the fossils are so well preserved.

The monotonous appearance of these fine-grained mudstones, in particular the softer layers, made it difficult to study them in detail, even with the use of normal microscopes. Todays techniques with electron microscopical examination has made better studies possible.

There is a general agreement that the plattenkalk was deposited in individual basins at the northern margin of the Tethys Sea, where 30 to 90 m thick successions accumulated. The fine lamination of the plattenkalk indicates that life was absent in the bottom of the basins. Possible causes for hostile conditions at the bottom include oxygen depletion, possibly in conjunction with a toxic hydrogen sulphide regime, or hypersaline conditions. Hydrogen sulphide is a smelly nuisance known from stink bombs or rotten eggs. It is a highly toxic gas which hinders respiration just like carbon monoxide. The posture of the dead Archeopteryx indicates damage to the brain, maybe due to suffocation or poisoning. The poor creature died a long, slow death, unable to breath properly.

Plattenkalk successions like these are rare, but often famous, and include examples from the Ordovician of Scandinavia, the Devonian of Germany, the Carboniferous of Montana, the Permian of eastern Greenland, the Triassic of Spain and the Cretaceous of Italy. The most famous example of plattenkalk is probably, however, this Upper Jurassic occurrence of the Solnhofen (or Eichstätt) plattenkalk series. The Altmühl valley is often visited by fossil hunters, but my experience tells me that you have to hunt for several hours to find anything worth collecting (if any at all). Instead enjoy the landscape and the limestone and (coral) reef geology, and not least the splendid geological museums with beautiful (local fossil) collections spread over the area.

Reference:
Diagenesis of plattenkalk: examples from the Solnhofen area (Upper Jurassic, southern Germany) by Munnecke et al. in the December 2008 issue of Sedimentology (doi: 10.1111/j.1365-3091.2008.00975.x).

• http://my.opera.com/nielsol/blog/2007/06/14/interdisciplinarity
• http://my.opera.com/nielsol/blog/2008/03/18/most-famous-fossil-i-was-in-berlin-all-last-week-the-timing-was-not-optimal





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Salt Tectonics

Monday, 15. September 2008, 08:38:46

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(a.o in the Subhercynian Basin north of the Harz Mountains, Germany)

In Late Permian (something like the last five to seven million years of the Permian Period, which ended around 251 million years ago) a substantial area of the North Sea and north west Europe was covered by sea, the so-called Zechstein Sea.

The sea was situated around the equator. It was fed by rivers and ocean flooding once in a while, which flushed salty water into the sea. Since the climate was warm and arid, evaporation equalled or exceeded the inflow, concentrating the salts in the sea. In this way a large thick deposit of salt was accumulated. A sediment layer that it largely present in today’s underground (of the area in question). When sand and other sediments are compacted they become denser than pure salt. Under the pressure from the sediments above the salt becomes rather fluid and thereby mobile, and because the salt is less dense than the overlying rocks (density inversion) the salt will try to rise upwards (positive buoyancy). The best known of such salt movements (halokinisis with a fine word) are salt domes (also known as diapirs). Here is a cross section of an area with salt domes in north western Germany. The zechstein is shown in blue.


The zechstein has significant economic importance in the North Sea Oil province. The salt is impermeable and many oil or gas fields include structural traps associated with a salt dome. (For the information of my North American readers I may add, that similar salt structures are also of economic importance (for oil and gas) in the Gulf of Mexico - A belt of salt domes lies beneath the surface of the Gulf of Mexico. Over 500 mushroom-shaped geological structures formed as the Gulf separated from the Atlantic Ocean).

And now to the Harz Mountains (in Germany) and the area to the north of it. The Harz was formed by an uplift, which affected the whole area of the Harz. The uplift started during the lower Cretaceous (140-97 million years ago) and stopped in the upper Cretaceous (97-67 million years ago), but most of the uplift happened during the Subhercyne Phase (83 million years ago). At that time Africa had started moving northwards, and thereby shortening (compressing) the crust between Africa and Scandinavia. Numerous predominantly NW-SE (so-called Hercynian) faults were created, including at the northern and southern rim of the Harz Mountains. Looking at a map of Northern Germany you may notice that many rivers follow the same NW-SE trend.

The large hercynian fault at the northern rim of the Harz Mounatins is called the Harznordrand Thrust (fault). In an area affected by thrust tectonics (like the hercynian thrust faults), buckling of the overburden layer will allow the salt to rise into the cores of anticlines (the opposite of synclines). Such anticlines formed north of the Harznordrand Thrust, and on both sides of the anticlines you can now see tilted strata dip away from the anticline. This is also the case in my photo below from the Hoppenstedt Quarry (4 km west of the town of Osterwieck). The strata are here dipping 30-40° to the SSW away from the Fallstein Anticline.


The quarry exposes limestones of the Cenomanian and Turonian (that is in the Upper Cretacious period - Turonian 93.5 ± 0.8 – 89.3 ± 1.0 miilion years ago and Cenomanian 99.6 ± 0.9 – 93.5 ± 0.8 million years ago). These limestones were deposited (100-90 million years ago) on the bottom of the Chalk Sea that I wrote about here and here. The 80 m thick succession in the quarry was deposited without major gaps within 10 million years, which means an average of 8 m per million year.

Reference concerning the Hoppenstedt Quarry:
  • EDGG, Heft 237 – Excursion Guidebook – 26th IAS Regional Meeting / SEPM-CES SEDIMENT 2008 – Bochum
    Field trip POST2 – Syntectonic sedimentation in front of a late Cretaceous growth fault – the Harz Mountains and the adjacent Subhercynian Basin (Germany) by T. Voigt and H. von Eynatten.


Note: Once again I have made an extremely long and complex story extremely short in the hope of highlighting some principal relationships.





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Panama # 2

Monday, 11. August 2008, 12:46:05

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In Gulf Stream born 3 million years ago? I wrote about what happened at the Panama isthmus about 3 million years ago.

But how was the situation in what is now Central America before then? Mainly based upon sedimentology Kirby et al. try to get a better grip on the last 30 million years in an open access article in PLoS ONE: Lower Miocene Stratigraphy along the Panama Canal and Its Bearing on the Central American Peninsula.

Here is the opening paragraph from their introduction:

The palaeogeography of Central America has changed profoundly over the past 30 million years (m.y.), from a volcanic arc separated from South America by a wide seaway, to an isthmus that connected North and South America by 3 Ma. The formation of the Isthmus of Panama was important because it allowed the mixing of terrestrial faunas between the two continents, as well as physically separating a once continuous marine province into separate and distinct Pacific and Caribbean communities. The formation of the Isthmus of Panama also ultimately led to profound changes in global climate by strengthening the Gulf Stream and thermohaline downwelling in the North Atlantic.



The palaeogeographic nature of southern Central America before the isthmus has been much disputed. Much of the discussion relates to the relative and absolute timing of some of the sediment formations along the Panama Canal (see the paper for this discussion).

As part of the Central American volcanic arc, the Panama microplate formed through subduction of various oceanic plates during the Cretaceous (145 to 65 million years ago) and Cenozoic (65 million years ago to the present). This microplate lies between the Cocos and Nazca plates to the south, the Caribbean plate to the north and the South American plate to the east. See tectonic map below.



A short-lived strait - the Culebra Strait - may have existed across the Panama Canal Basin sometime between 21 and 19 million years ago (on the first map in this post light grey represents the outline of tectonic plates containing continental or volcanic-arc crust. Dark grey represents land above sea level). The earliest evidence for a terrestrial connection between Panama (but NOT South America) and North America is 19 million years ago. After that the authors found no evidence for the disruption of the southern Central America peninsula until 6 million years ago, when there is evidence for a short-lived strait across the Panama Canal Basin. The existence of a peninsula for much of the Miocene (about 23 to 5 million years ago) has implications for our understanding of the tectonic, climatic, oceanographic and biogeographic history related to the formation of the Isthmus of Panama.

* http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002791
* http://www.physorg.com/news136614198.html
* http://www.terradaily.com/reports/Isthmus_Of_Panama_Formed_As_Result_Of_Plate_Tectonics_999.html





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Mass Extinctions related to Sea Level Change?

Tuesday, 17. June 2008, 12:37:38

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A new study, titled Environmental determinants of extinction selectivity in the fossil record, and published online 15 June 2008 in the journal Nature, suggests that sea level changes and related sedimentation differences over the course of geologic time is the primary cause of the world's periodic mass extinctions during the past 500 million years.

Crashing asteroids and sky-darkening super volcanoes have often been blamed over the last 60 years or so, but according to Peters, the author of the paper, changes in ocean environments related to sea level exert a driving influence on rates of extinction, which animals and plants survive or vanish, and generally determine the composition of life in the oceans.

Since the advent of life on Earth 3.5 billion years ago, scientists think there may have been as many as 23 mass extinction events, many involving simple forms of life such as single-celled microorganisms. During the past 540 million years, there have been five well-documented mass extinctions, primarily of marine plants and animals, with as many as 75-95 percent of species lost.

In the course of hundreds of millions of years, the world's oceans have expanded and contracted in response to the shifting of the Earth's tectonic plates and to changes in climate. (Geologists talk about transgression when sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. The opposite of transgression is regression, in which the sea level falls relative to the land and exposes former sea bottom.)

Peters measured two principal types of marine shelf environments preserved in the rock record, one where sediments are derived from erosion of land and the other composed primarily of calcium carbonate, which is produced in-place by shelled organisms and by chemical processes.

• http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature07032.html
• http://www.news.wisc.edu/releases/14562
• http://www.thetechherald.com/article.php/200825/1243/Sea-level-factor-in-mass-extinctions
• http://www.sciencedaily.com/releases/2008/06/080615142247.htm
• http://www.terradaily.com/reports/Ebb_And_Flow_Of_The_Sea_Drives_Big_Extinction_Events_999.html
• http://www.scientificblogging.com/news_releases/mass_extinctions_not_asteroids_but_sea_sediment_says_study

In this connection I would like to mention that when the dinosaurs died out at the mass extinction around 65 million years ago the global sea level had been extremely high, and most of northern Europe covered by sea, with no high mountains in the neighbourhood. In fact one-third of Earth's present land area was submerged at the peak of the Cretaceous transgression (sea level rise). With a low erosion rate only little material was brought to the sea, which therefor had very clear water, with excellent living conditions for micro-organisms with calcium carbonate shells. Thick layers of chalk were formed on the bottom of the “Chalk Sea”. And today the Cretaceous chalk cliffs stand out at the coast of England, Northern France, Germany, and Denmark. Only closer to the coast and islands sand and clay was deposited. (The image is reused from my post on Dresden and Sandstone)

In Denmark the Cretaceous/Paleogene boundary (where the mass extinction took place) is marked by a thin layer of clay, the so-called Fish Clay.

PS: Brian at Clastic Detritus has just published a post on the same paper. See it here.



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Sahara - from Green to Desert

Sunday, 11. May 2008, 08:41:44

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Around 14,800 years ago, a strengthening of the summer monsoons - moist tropical Atlantic monsoons from south-west - led to a dramatic climatic change in North Africa and created a “green Sahara”. How did this North African humid period come to an end and lead to the the world’s largest warm desert today. Was it abruptly or gradually?

The drying of the Sahara in the Holocene, that is approximately the last 11,550 years, is widely believed to have been an abrupt event, completed within a few hundred years, but new research published in Science of 9 may 2008 indicates that it happened gradually over the last 6000 years.

The authors of Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years studied a sediment record from Lake Yoa in northern Chad. Lake Yoa is one of the very few Saharan lakes in which sediments have accumulated without a break during the Holocene. Despite its extremely arid location, the lake is fed by ancient groundwater and therefore does not dry up.

The vegetation history of the surroundings is reconstructed from pollen. The reconstructed salinity values provide a record of changing precipitation. The input of atmospheric dust to the lake reflects wind regimes and the extent of vegetation cover in the surrounding landscape. The results show that vegetation and dust flux changed gradually over the past 6000 years, accompanied by the slowly weakening monsoon. The pollen source area implies that average north-easterly wind strength must have increased during this time, either because wintertime trade-wind circulation intensified or because a change in the mean position of the Libyan high-pressure cell now channeled low-level northeasterly flow more effectively through the Tibesti-Ennedi corridor.

Tibesti Mountains is a volcanic region to the west of Lake Yoa and the Ennedi Plateau, which is located to the east of the lake, is a sandstone plateau surrounded on all sides by sands, that encroach the deep valleys of the Ennedi.

However fast the drying occurred, it pushed people out of north-central Africa, and that climatically forced migrations might have led to the rise of the pharaohs and Egyptian civilization.

According to the lead author there are now signs of a tiny shift back towards greener conditions in parts of the Sahara, apparently because of global warming.

* http://www.sciencemag.org/cgi/content/short/320/5877/752
* http://sciencenow.sciencemag.org/cgi/content/full/2008/508/2?rss=1
* http://www.abc.net.au/science/articles/2008/05/09/2240138.htm
* http://www.nytimes.com/2008/05/09/science/09sahara.html?_r=1&partner=rssnyt&emc=rss&oref=slogin
* http://www.iht.com/articles/2008/05/09/africa/09saha.php
* http://www.redorbit.com/news/science/1378928/sands_of_sahara_moved_slowly/index.html?source=r_science



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Euxinic - do we need that word?

Saturday, 29. March 2008, 14:39:04

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Googling the combination “euxinic conditions” gave me 2060 hits, and the combination “euxinic sediments” 875 hits, so the term is obviously used, and it has been in use in geology at least since 1930.

Euxinic literally means ‘pertaining to the Black Sea’. The word euxinic comes from the old Roman (and ultimately from the Greek) name for the Black Sea (the Romans called it the Euxine Sea, Pontus Euxinus). So, before I go on, let us have a look at the conditions in the Black Sea.

The waters of the Black Sea are strongly stratified with an upper oxidised layer and a lower anoxic layer. Freshwater (green arrow) flows into the sea from rivers like the Danube, Dniester, Dniepr and Don. Sea-water (blue arrow) flows into the Black Sea from the Mediterranean via the street of Bosporus. Because of the different salinities and densities, the freshwater and sea-water mixing is limited to the uppermost 100-150m. The mixing between surface water and bottom water is strongly restricted, and the whole bottom water is exchanged only once in a 1000 years. Oxygen is needed for rotting of organic matter, so under anoxic conditions organic matter doesn't rot. As a result black, organic rich, sediments accumulate on the bottom. The Black Sea has got its name because such black sediments make the sea water dark. Unlike the Mediterranean, where visibility extends down to a depth of about 30 meters, visibility reaches only as far as about 5 meters in the Black Sea.

Rotting is a bacterial process, and occurs under aerobic conditions, aerobic means occurring only in the presence of oxygen. You also have bacterial activity under anaerobic conditions, that is it occurs in the absence of oxygen. During anaerobic conditions at the bottom of the Black Sea sulphate reducing bacteria strip the oxygen from sulphate and dump hydrogen sulphide (H2S) as a waste product (a sulphate ion consists of a central sulphur atom surrounded by four equivalent oxygen atoms). Some of the hydrogen sulphide may react with iron to form pyrite (FeS). Increase of pyrite in the sediments is an indication of the activity of sulphate-reducers.

So the term euxinic has to do with an environment of restricted circulation and stagnant or anaerobic conditions. Euxinic conditions are at the same time both anoxic, anaerobic and sulphidic. Euxinic conditions may lead to deposition of euxinic sediments like sapropel. Now there is another nice foreign word. Sapropel (a contraction of the ancient Greek words sapros and pelos, meaning putrefaction and mud, respectively) is a term used in marine geology to describe dark-coloured sediments (mud, slime, or ooze) that are rich in organic matter. Organic carbon concentrations in sapropels commonly exceed 2% in weight.

I have checked the indexes of a few textbooks on oceanography and marine geology. They seem to do quite nicely without using the term euxinic. I have to know the term however to be able to read some of those $@^§* scientific papers!

Papers such as this one:
Euxinia as the cause of the end-permian mass extinction: Evidence from sulfur isotope chemostratigraphy
• http://gsa.confex.com/gsa/2005ESP/finalprogram/abstract_88807.htm
Relevant for my post a few days ago on How to kill 95% of all life?.
Oh ah, and yes, I forgot to say at the start: Google gave me 3,340 results for euxinia! - euxinia means euxinic anoxic conditions.

Euxenite, on the other hand, has nothing to do with euxinia, but is a lustrous, blackish-brown rare-earth mineral consisting primarily of cerium, erbium, titanium, uranium, and yttrium.

Words, words, words.



PS of 30 March 2008
Kim over at All of My Faults Are Stress-Related has started a discussion on possibly unnecessary or outmoded geology terms in the post Geology terms overdue for retirement?.

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A-bomb Blast Markers and Glaciers

Monday, 31. December 2007, 10:43:11

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Distinctive radioactive signals from fallout from atmospheric nuclear tests during the 1950s and 1960s are routinely used as event markers when analysing ice cores. And as sedimentological time markers in rivers as well for that matter. In 2006, a joint U.S.-Chinese team drilled four ice cores from the summit of Naimona'nyi, a large glacier 6,050 meters high on the Tibetan Plateau, and discovered that these signals were missing in their cores.

A reasonable conclusion is that this Tibetan ice field has been shrinking at least since the A-bomb test half a century ago.

The 7,694 meter high Mt. Naimona'nyi (also known as Gurla Mandhata) lies in the western tip of the mid-Himalayas in Burang County of the Tibetan Autonomous Region.

As the Tibetan glaciers release meltwater each year and feed the rivers that support nearly 500 million people in that region this is bad news. The loss of these ice fields might eventually create critical water shortages for people who depend on glacier-fed streams. If what is happening on Naimona'nyi is characteristic of the other Himalayan glaciers, glacial meltwater will eventually dwindle with substantial consequences for a tremendous number of people.


* http://researchnews.osu.edu/archive/radsignl.htm
* http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2007/2007121126010.html
* http://www.gov.cn/english/2006-11/10/content_438741.htm
* http://english.cas.cn/eng2003/news/detailnewsb.asp?infono=26273





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About.com Geology

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  • What's a Geopark?

    I've cared about geoparks for several years, so I made sure to attend a session on geoparks at the Geological Society of America meeting, on 19 October. The most important news to me was that the National Park Service is collaborating with the GSA on a formal proposal for establishing geoparks in th ...

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Geoblogosphere

"allgeo" via Chris

  • Today’s Ask-a-Geologist Question – Is being a ...

    We received this question from a 10-year old who is interested in what is it like to work as a geologist. Question: Is being a geologist fun, or is it drudgery? Do you have to stay away from your family for long periods of time? Answer: I think that being a geologist is a lot of fun.  One cool thin ...

  • Just another word for nothing left to do?

    When I was sixteen years old, I spent half a summer on a foreign exchange program. It was a big deal for me at the time- the first time I spent more than a fortnight away from my folks, the first time left the USA, the first time I drank beer and got tear-gassed. And the first week of that trip in ...

  • Smithers-man Goes for Toronto

    Article The guy who likes to pick 'technological winners' is running for mayor. We need him to scrape up enough money for the Pan-Am games!

  • NftFC #1: Assembling West Gondwana in the Neoprote ...

    This paper summarizes the assembly of the various mesoproterozoic blocks into West Gondwanaland. In this model, The SaoFrancisco/Congo craton first collides with the Rio de la Plata craton around 730 MA. This combined Sf-C-RdlP craton then collides with the Amazonia/ W. Africa craton at around 630 ...

  • Deer mauled by lions at DC Zoo

    Awesome! Deer in lion's den is fatally injured as crowd watches (Washington Post) Lily and I were actually at the Zoo yesterday, but we certainly didn't see this go down. YouTube video of the incident This reminds me: In other charismatic megafauna news, my Shenandoah trip on Saturday saw a black be ...

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