olelog

The geologic time scale was developed during the 1800s based on fossils (biostratigraphy). At that time it was thought that life began about 545 million years ago (when the first clearly visible fossils turned up), and the time from then to now was named Phanaerozoic. The name derives from the Greek words φαίνω and ζωή, meaning ‘make life appear’.



As the life time (ζωή/zoic) of certain species is used as markers, it is no wonder that mass extinctions played an important role in the time divisions. Phanaerozoic was/is divided into three ages: Palaeozoic (ancient life), Mesozoic (middle life), and Cainozoic (new life).

542 Ma - Paleozoic era - 251 Ma | 251 Ma - Mesozoic era - 65 Ma | 65 Ma - Cenozoic era - Present
(Ma = million years ago)

With the largest extinction of all, the Permian–Triassic extinction event, around 251 million years ago at the Permian-Triassic transition. And the Cretaceous–Tertiary extinction event (K-T extinction) around 65 million years ago. (The Mesozoic era between these two extinction events was the age of the dinosaurs, getting extinct around 65 million years ago).

An earlier attempt was made in the middle of the 1700s - sometimes attributed to the German geologist Abraham Werner (1749 – 1817) who set out a now obsolete theory about the stratification of the Earth's crust ("neptunism"). He (and others before and after him) divided the rocks of the Earth's crust into four types: Primary, Secondary, Tertiary, and Quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. The terms Tertiary and Quaternary lived on as the two main subdivisions of the Cainozoic, and "Tertiary" (now Palaeocene-Pliocene) and "Quaternary" (now Pleistocene-Holocene) remained in use as names of geological periods well into the 20th century (while the terms Primary and Secondary disappeared about 150 years ago). A good example is the K-T boundary (also termed the K–Pg boundary). K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit (or possibly Greek kreta), and T is the abbreviation for the Tertiary period (Pg = Palaogene).

At its 32nd Congress in Florence in 2004 the International Commission on Stratigraphy (ICS) decided to delete Quaternary from the geologic time scale and let Neogene continue until present. ICS is the only organization concerned with stratigraphy on a global scale. This decision was very much to the dismay of thousands of quaternary geologists. The around 50.000 members of INQUA (The International Union of Quaternary Research) demanded the Quaternary to be reinstalled with 2.6 million years as its base, and full status as a geologic period on par with Palaeogene and Neogene. And this was indeed the decision that ICS had to take on 29 June 2009, so that the Cenozoic now looks like this (with 2.588 million years as the base for the Quaternary):



The Tertiary does not show up on the latest official international stratigraphic chart from ICS, but is still (unofficially) used for Palaeogene + Neogene.

The term Quaternary was proposed by Giovanni Arduino in 1759 for alluvial deposits in the Po river valley in northern Italy. It was introduced by Jules Desnoyers in 1829 for sediments of France's Seine Basin that seemed clearly to be younger than Tertiary Period rocks. The Quaternary covers the time span of glaciations classified as the Pleistocene, and includes the present interglacial period, the Holocene. This places the start of the Quaternary at the onset of Northern Hemisphere glaciation 2.588 million years ago.

This post has been in the pipeline for some time. The Norwegian article mentioned below gave me the final inspiration to finish it.

In Norwegian:

• http://www.geo365.no/forskning/kvartartilbake/
  

In between I am also a bird watcher. As such I am fond of mangroves, and I have visited the mangrove areas in Senegal several times, mainly Sine-Saloum (usually staying in Toubacouta) and also once in Casamance (not always safe!).


Blue marker at Toubacouta in the Sine-Saloum delta and red marker near Kafountine in Casamance, where I took the photo below of pelicans some years ago.

In the Toubacouta I have witnessed how the mangrove forest is shrinking.

The Saloum delta region is under threat from coastal erosion and from the salinity of the soil. The mangrove forest is vital to this area; it prevents the soil from being washed away, supplies the essential nutrients for young fish and shelters the oyster colonies. The mangrove tree also provides a stock of medicinal plants used by locals and a significant source of income for the women who farm the shellfish. However, ever lower rainfall levels and chaotic exploitation of the forests have accelerated the decline of the tree population, with the resulting deterioration of the environment and dwindling resources.

I am therefor happy to see that a Senegalese environmental NGO has now announced that it had planted 34 million mangrove trees in three months in a project largely financed by French dairy giant Danone to offset its carbon footprint. According to the environmental organisation, Oceanium, some 34 million mangrove seedlings were planted between August and November 2009, 27 million in Senegal's southern Casamance region and 7 million in the Saloum river delta. Over 78,000 volunteers from 323 villages participated in the massive planting campaign. Without the mangrove forests the water becomes too salty to grow rice, a staple food for the Senegalese, fish die and the soil becomes exhausted.

• http://www.terradaily.com/reports/Senegalese_NGO_plants_34_million_mangroves_to_offset_carbon_emissions_999.html
  
• http://www.unesco.org/csi/region/desert.htm
  
• http://www.irinnews.org/Report.aspx?ReportId=80906
  
• http://www.grist.org/article/roll-up-for-the-worlds-largest-mangrove-planting-project/
  
• http://www.google.com/hostednews/afp/article/ALeqM5goTwIeIviSzpU__HDlZnGyyP0Scg
  

With static google maps geotagging now has become possible on this blog, where I cannot use JavaScript. So far it seems to work OK, but I still have to experiment a bit.



Any helpful suggestions are of course welcome

A couple of months ago I wrote about a new hypothesis by Egholm et al. according to which the maximal mountain height correlate closely with climate-controlled gradients in snowline altitude rather than with tectonic activity. In Denmark this hypothesis seems to have lead to a heavy discussion about the uplift/erosion history of the Norwegian mountains between geologists at the University of Århus versus geologists at the University of Copenhagen, and I am looking forward to hear more about this dispute at the Nordic Geological Winter Meeting in Oslo in January.



But how about the Alps? A paper in the latest volume of the science magazine "Tectonophysics" (No. 474, S.236-249) seems now to prove that today's uplifting of the Alps is driven by strong climatic variations. The formation of the Alps through the collision of the two continents Africa and Europe began about 55 million years ago. By now the Alps are shrinking just as quickly in height, as they are growing. Due to the erosional work of glaciers and rivers about exactly the same amount of material is eroded from the Alps as added by uplifting.

Swiss geodesists, who have been measuring the Alps with highest accuracy for decades, have observed, that the Alp summits, as compared to low land, rise up to one millimetre per year. Over millions of years a considerable height would have to result. Researchers from the GFZ German Research Centre for Geosciences have calculated that the mountains eroded concurrently at almost exactly the same speed.

Though the Alps are constantly rising, it is no longer the plate forces but the strong climatic variations since the beginning of the so-called quaternary glacial before approximately 2.5 million years, to which mountain slopes in particular have been reacting so sensitively. To-days rise is attributed to the melting of Alpine glaciers.

Well, today it is probably just a question of isostasy, i.e. gravitational equilibrium between the earth's lithosphere and asthenosphere, meaning that the Alps "float" at an elevation which depends on their thickness and density. The burning question is, why the Alps stopped “growing”, where they did, during their collision phase. Was this only a question of isostasy or was the “snowline effect” at work?

• http://www.physorg.com/news176643920.html
  
• http://www.livescience.com/environment/091105-alps-grow-shrink.html
  
• http://www.eurekalert.org/pub_releases/2009-11/haog-ata110509.php
  
• http://www.sciencecodex.com/are_the_alps_growing_or_shrinking
  

Few people know where Franz Josef Land is, or have ever heard of it. Except for a few Russian army border guards, Franz Josef Land is totally uninhabited. It has no native inhabitants. This is not because the area is small - Its 191 islands have a total area of 16,134 km². It is however situated far up north in the Arctic - and was furthermore completely closed to visitors for roughly 60 years until 1991. It is the most northerly group of islands associated with Eurasia and the Eurasian continental plate. Gakkel Ridge further north is normally seen as on the border zone between The Eurasian and the North American plate.

The situation may change now that the sea ice in the Arctic is melting and icebreakers in a few years perhaps no longer may be needed to reach the islands (Most of the Russian icebreakers in the area are - as far as I know - nuclear icebreakers). Since 2005 cruises are organised from Murmansk.

The archipelago is dominated by Jurassic to Tertiary basalts, but there are also late Triassic and Jurassic sediments lying in near horizontal strata. Fossil tree trunks show that the climate here was warmer in the Mesozoic. The basalt layer above the Jurassic sediments is up to 500 m thick and part of a Large Igneous Province (LIP) formed in the Cretaceous, and called the High Arctic Large Igneous Province (HALIP). This is a major Late Cretaceous large igneous province located in the Arctic. It includes the Ellesmere Island Volcanics, Strand Fiord Formation, Alpha Ridge, Franz Josef Land and Svalbard. These areas were closer to each other in the Cretaceous - since then the spreading ridge (Gakkel Ridge) has brought them further apart. A multitude of tectonic fault lines has broken the archipelago into many relatively small islands.

The age of the HALIP volcanic rocks is rather uncertain, but a long period of magmatism between ca. 136 and 80 million years ago has been suggested for the whole LIP.

From 15 June 2009 the archipelago became part of the newly established Russkaya Arktika National Park.

• http://maps.unomaha.edu/maher/svalbard/wwwHALIP/
  
• http://www.largeigneousprovinces.org/06apr.html
  
• Google Books - Bradt's Spitsbergen Guide