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Geological Dating

 
 
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Author Solivagant
Partaker
#46 | Posted: 13 Oct 2013 15:02 | Edited by: Solivagant 
Bialowieza - Holocene
The area was glaciated by the German-Polish Ice sheet during the Pleistocene. The forest only grew after the last ice age. "The forest area dates back to 8000 BC" https://sites.google.com/site/geo121wikifall2012/home/belovezhskaya-pushcha-bialowiez a-forest-poland-belarus

Malpelo - Miocene
"Malpelo Island is composed of Miocene pillow lavas, volcanic breccias, and basaltic dikes that have been dated as being 16 to 17 million years old. This island and the underlying and underwater Malpelo Ridge were created along with the Carnegie Ridge in the Late Miocene by a very complex interaction between the Cocos-Nazca Spreading Centre and the Galápagos hotspot" (Wiki)

Author Solivagant
Partaker
#47 | Posted: 14 Oct 2013 02:53 
Los Katios and Darien - both Early Pleistocene

Darien Was "the bridge between the two continents of the Western Hemisphere, which has emerged from below sea level on several occasions in the distant past, most recently in the early Pleistocene." AB)

Los Katios Acted as "a filter or barrier to the interchange of fauna between the Americas during the Tertiary and Pleistocene. lt is thought to be the site of a Pleistocene refuge, a hypothesis supported by the high proportion of endemic plants" (AB)

Author Assif
Partaker
#48 | Posted: 14 Oct 2013 03:08 
The Ishtmus of Panama was created 3 million years ago, aos both Darien and Los Katios are Gelasian (early Pleistocene could also mean Calabrian).

Author Solivagant
Partaker
#49 | Posted: 14 Oct 2013 03:39 | Edited by: Solivagant 
Assif:
The Ishtmus of Panama was created 3 million years ago,

Hi Assif - I did quite a lot of "investigation" on this matter without being able to discover any really specific dating.

This paper indicates that the Isthmus was created across the Miocene/Pliocene eras from 15Ma to 3Ma
http://www.academia.edu/400648/The_closure_history_of_the_Panama_Isthmus_Evidence_fro m_isotopes_and_fossils_to_models_and_molecules

This article indicates that the theory of "Pleistocene Refuges" mentioned in the AB for Los Katios has been overtaken/modified by later research/knowledge.
http://www3.geosc.psu.edu/~pdw3/2003_KnappMallet_Perspective.pdf

This article describes the Peistocene area with particular reference to the Los Katios area (among others in Colombia)
http://digitallibrary.amnh.org/dspace/bitstream/handle/2246/3087/N2294.pdf?sequence=1

As far as I can see none of them specifies the period within the overall timescale across which the "Great American Interchange" took place nor the possible arid periods during Pleistocene galciations which might have created "Refuges".

Your suggestion that it took place in the Gelasian age - i.e in the earlier Pleistocene coincides with my assignment to "Early Pleistocene" (as also in the AB for Darien) - It appears that some transfer could have taken place beforehand as the bridge came and went - but it seems reasonable to assume that the majority took place "relatively" soon after the current creation of the bridge but do you have any references? . Particularly ones which specifically describe it as Gelasian? To date I just do not find this term being used by academics

Author Solivagant
Partaker
#50 | Posted: 14 Oct 2013 05:16 | Edited by: Solivagant 
I am having problems with Mt Nimba!!

A few quotes
"The Mount Nimba range is ...of Precambrian basement rock, predominantly granites. ..The range is a striking example of erosional processes. The sharp relief of the mountains, with their grass-covered summits, precipitous slopes and flat open piedmont, is formed by a ridge of iron-quartzite emerging from softer metamorphic rocks. Weathering also left a gigantic sheet of hard iron-quartzite jutting out of the eroded piedmont schists and granite gneiss... giving very poor soils ... (which) explain the treeless grassy summits as well as the belt of savanna at 500-550 m around the mountains above which the forests take over." http://www.eoearth.org/view/article/154709/

"This area is unequalled as an illustration of the theory of erosion levels" (AB)

"Mount Nimba is part of an ancient mountain range, the Guinean range, which was upthrust between the end of the Jurassic and the end of the Eocene (Lévêque 1997). Since then, erosion has worn away the softer schists and granito-gneiss, exposing the underlying ore-containing quartzite (Lamotte 1983)."

"Mount Nimba is formed from Precambrian granite, schists, granito - gneiss and other rocks, including iron containing quartzite. Mountains were shaped in the end of Jurassic - end of Eocene and since then have been heavily eroded."

So we have
a. Its pre-Cambrian bedrock origins
b. It creation as part of a mountan range betwee "the end of the Jurassic and the end of the Eocene" (a very long period and beyond any of our individual time periods)
c. Its subsequent Erosion - time period not speciified but, presumably ever since!
d. The fact that it is its erosion which is its most special aspect and which really therefore ought to determine its time period!!

Any ideas??

Author clyde
Partaker
#51 | Posted: 14 Oct 2013 07:14 
well done to Els and all for the new Timeline section! Interesting.

just a question though ... how come Luang Prabang is considered as 20th century?

Author elsslots
Admin
#52 | Posted: 14 Oct 2013 09:59 
Solivagant:
c. Its subsequent Erosion - time period not speciified but, presumably ever since!
d. The fact that it is its erosion which is its most special aspect and which really therefore ought to determine its time period!!

I had a similar problem with Purnululu. Erosion takes forever, but it is impossible to determine when the rocks have eroded into the current, recognizable shape. I choose to use the date of the rock origins. Erosion must have started not long after that, especially since we're talking about millions of years here.

Author elsslots
Admin
#53 | Posted: 14 Oct 2013 10:04 
clyde:
how come Luang Prabang is considered as 20th century?

there could be arguments in favour of 19th century as well, but the AB evaluation opens with a clear statement that the city got its unique townscape (mix of Lao, Vietnamese and French) between 1915 and 1925

Author clyde
Partaker
#54 | Posted: 14 Oct 2013 10:38 
Ok that makes sense then. Luang Prabang is a really beautiful town and I really hope it doesn't lose its charm because of mass tourism. It would be a pity.

Author Solivagant
Partaker
#55 | Posted: 14 Oct 2013 13:30 | Edited by: Solivagant 
St Kilda - Palaeocene
"Created as part of the British Tertiary Volcanic province during the volcanic activity of the Palaeocene and early Eocene (c63-52Ma) which accompanied the early stages of the opening of the N Atlantic. " http://www.kilda.org.uk/kildanomdoc/level3p1.htm

Gough and Inaccessible – Early Pleistocene
Gough Island –"4 main periods of volcanism are recognised. Older Basaltic 2.4 -.52Ma, Intrusion of aegerine-augite trachyte plugs 0.8-0.47, voluminous trachyte extrusion 0.3-0.12 Ma and finally to eruption of the Edinburgh Basalt 0.2-0.13Ma". Inaccessible – "..... a volcanic superstructure built up during the last three million years"

(The Volcanism actually covers all 3 Pleistocene periods but I have chosen "early" for timeline purposes - the text provides a fuller picture)

Author hubert
Partaker
#56 | Posted: 14 Oct 2013 18:21 
Looks great, the new Timeline feature. Though it is obviously not easy for some sites to find an appropriate reference for the assignment.
As I'm not a specialist in geology, I would start with a few rather easy sites:

Danube Delta (Romania) - Holocene
"The modern Danube Delta began forming after 4,000 BC in a gulf of the Black Sea, when the sea rose to its present level. A sandy barrier blocked the Danube gulf where the river initially built its delta. Upon filling the gulf with sediments, the delta advanced outside the barrier-blocked estuary after 3,500 BC building several successive lobes." (Wiki)

Laurisilva Madeira (Portugal) – Eocene or Oligocene or Miocene? I'm not sure about the rules in cases when a site extends over several periods.
"Fossil evidence shows that laurisilva flora once covered much of southern Europe in the Tertiary era, 15-40 million years ago, and what is now seen in Madeira is the largest surviving relict of a virtually extinct flora of great interest." (Advisory Body Evaluation)

Garajonay National Park (Spain) - Eocene or Oligocene or Miocene?
"Some 70% of the national part is woodland with Laurisilvia canaria dominant. The Garajonay National Park has a recorded flora of 450 species of which 34 are endemic to the island and of these, eight species are restricted to the national park. This type of vegetation assemblage resembles that of the Tertiary period which has largely disappeared from southern Europe due to climatic changes." - so, very similar to Laurisilva Madeira (ABE)

Donana National Park (Spain) – Miocene or Pliocene?
"The marshes of the Guadalquivir River constitute an example of geological processes during the Pleistocene. Donana contains the last marshes of the Guadalquivir unaltered by agriculture or development. The marshes result from a subsidence of the continental plate in the Upper Miocene and Lower Pliocene, which caused a depression later filled by fluvial and aeolic deposits. Deposition of a coastal sand bar and mobile dunes continue today." (Advisory Body Evaluation)

Primeval Beech Forests (Slovakia/Ukraine/Germany) - Holocene
"Beech reached Western and Eastern Carpathian territory in an Epiatlantic period 5.000 years ago." (Nomination file, 2007, page 33)
"Consecutively initiated from south to north, old forest habitats have been undergoing a development into extremely differentiated beech forest landscapes for some 6,000 years."
(Nomination file, extension 2011, page 11)

Author elsslots
Admin
#57 | Posted: 14 Oct 2013 23:56 
hubert:
Tertiary era, 15-40 million years ago

I would say Eocene, because of the 40 million years. If there's a long period, we take the start date just as with the cultural sites.

Author elsslots
Admin
#58 | Posted: 15 Oct 2013 00:16 
Correction:

Both islands of Madeira and La Gomera (Garajonay) seem to have been created much later:
- Madeira: The first phase of volcanic activity began about 18 million years ago was completed with the transition from the Miocene to Pliocene periods of the geologic timescale approximately 3 million years ago. This first phase was marked due to strong eruptions. In the second phase of volcanic activity, projected lava and pyroclastic sediments expanded, increasing the size of the island especially in the south, west and southeast, and at the tip. Two other phases formed the volcanic cliffs of the northern and southern shores, as well as the formation of basalts in Paul da Serra mainly because of a crack in Bica da Cana 550,000 years ago, where the last volcanic activity occurred.
- La Gomera: It arose about 10-12 million years ago, when huge blocks of the oceanic crust emerged from the ocean floor and different volcanic episodes increased its size

So the laurisilva must be of even a later date. The link you're referring to must be about laurisilva covering South European mainland

Author Solivagant
Partaker
#59 | Posted: 15 Oct 2013 02:35 | Edited by: Solivagant 
Iguassu/Iguazu - Early Pleistocene as being when it started? Some documents put the Falls as arising later but they seemed less "authoratitive" than the quoted link - 2cms pa for 2million years = c40kms which seems reasonable

"formed on the rim of the basaltic Paraná Plateau, Serra Geral Formation. This volcanic plateau formed in Lower Cretaceous period some 132 million years ago.. (The lava) "covered a former desert that was present in the region, and there were several stages to the lava flow (creating interlayered basalt with sandstone layers which has been subjected to various faults and tectonic movements.."Although no absolute ages exist on the evolution of the fluvial system, it has been suggested that the falls have been continuously wandering upstream to its present position by progressive headwater erosion at a rate of 1.4–2.1 cm/year in the last 1.5–2.0 million years" http://link.springer.com/chapter/10.1007/978-90-481-3055-9_11

Author Assif
Partaker
#60 | Posted: 15 Oct 2013 03:09 | Edited by: Assif 
I agree with Els that the earliest period has to be taken into account.

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