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Geological Dating

 
 
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Author Solivagant
Partaker
#61 | Posted: 15 Oct 2013 03:48 
I came across this document about filling the Geological Gaps etc - we may well have seen it before but I don't particularly remember it. http://www.geoconservation.com/conference/Docs/WHGeol.pdf
It includes a partial assignment of WHS (as of 2004) to Geological time periods.
2 issues arise
a. Some differences in periods chosen.
They have divided the Palaeozoic. We perhaps should consider?
b. Some diffferences in assignment.
Grand Canyon - they have assigned to Permian (Palaeozoic) -but we have it much later in Miocene.
Mammoth Cave - they have as Carboniferous we have as Cretaceous
There may be some other differences but I was getting lost with all my "tabs" so it seems better to record this "so far"!!

I have cut and pasted the list here - with blank periods as in the original and with my inserted "groupings"
Quaternary - Naracoorte (Australia) 170k years
Pliocene
Miocene - Riversleigh (Australia)15/25m years
Oligocene
Eocene - Messel Pit (Germany) 27/29m years
Palaeocene

MESOZOIC
Cretaceous - Dinosaur Park (Canada) 75m years
Jurassic - Dorset/E.Devon (U.K)
Triassic - Dorset/E.Devon (U.K.) , Ischigualasto-Talampaya (Argentina), Monte San Georgio, (Swit))

PALAEOZOIC
Permian - Grand Canyon (USA)
Carboniferous - Mammoth Cave (USA) 300m years
Devonian - Miguasha (Canada) 370m years
Silurian
Ordovician - Gros Morne (Canada) 500m years
Cambrian - Burgess Shale (Canada) 520m years

Precambrian

Author elsslots
Admin
#62 | Posted: 15 Oct 2013 07:47 | Edited by: elsslots 
Solivagant:
Grand Canyon - they have assigned to Permian (Palaeozoic) -but we have it much later in Miocene.


I think this can be explained due to the same "erosion" discussion that we had earlier. They date the original rocks, not the moment the erosion (canyon building) took place.

Crit viii states:
The Precambrian and Paleozoic portions of this record are particularly well exposed in canyon walls and include a rich fossil assemblage. Numerous caves shelter fossils and animal remains that extend the paleontological record into the Pleistocene.

Author Solivagant
Partaker
#63 | Posted: 15 Oct 2013 09:57 | Edited by: Solivagant 
It appears that there is a lot of academic (and religious!!) debate about the time taken to erode the Grand Canyon and when it started - complicated by issues of uplift, level of the Gulf of California, differential erosion, whether Noah was around etc etc. The answer appears to be that it started somewhere between 70Ma and 20Ma - and that it probably reached its general current proportions around 1.2 Ma ("The base level and course of the Colorado River (or its ancestral equivalent) changed 5.3M years ago when the Gulf of California opened and lowered the river's base level (its lowest point). This increased the rate of erosion and cut nearly all of the Grand Canyon's current depth by 1.2M years ago")

Whatever the geoconservation document which I cited says I see little benefit in dating the Grand Canyon by the age of its exposed rocks!! But which erosion period we should take I just don't know
a. When the erosion started
b. When the greatest amount took place
I think we just have to choose 1 and provide enough info in the Text to explain the rest

We could of course adopt this view :- " I also want you to realize that when someone asks me whether the flood of Noah created the Grand Canyon, I have to say that I don't know." - A Christian Science Ministry Web site!!!! I never appreciated how many "Young Earth Creationists" there were on the Web

Author elsslots
Admin
#64 | Posted: 15 Oct 2013 10:33 | Edited by: elsslots 
Solivagant:
1.2M years ago

this would mean Early Pleistocene; "feels" too late somehow
with 70Ma (the other end of the spectrum) we're at Cretaceous...

Author Solivagant
Partaker
#65 | Posted: 15 Oct 2013 12:00 | Edited by: Solivagant 
elsslots:
with 70Ma (the other end of the spectrum) we're at Cretaceous...

http://cloud.media.wenatcheeworld.com/uploads/epaper/2012/11/30/ww_20121130_a007.pdf
and
http://www.theguardian.com/science/2012/dec/11/grand-canyon-paper-date-debate

examples of a widely syndicated story from late 2012.

No answer to our problem but it does indicate the sort of "debate". I have seen the phrase "Proto- canyon" used for the early manifestation - which leaves the "real" canyon for the Early Pleistocene

Author elsslots
Admin
#66 | Posted: 15 Oct 2013 12:30 | Edited by: elsslots 
I've got a new quest for you, Solivagant: Monarch Butterfly Biosphere Reserve !

So when did these butterflies enter the world? And when did they start migrating to these spots in Mexico?

Author Solivagant
Partaker
#67 | Posted: 15 Oct 2013 16:04 | Edited by: Solivagant 
elsslots:
I've got a new quest for you, Solivagant: Monarch Butterfly Biosphere Reserve !


Ok -
"It is thought that monarchs were originally tropical butterflies that underwent range expansion. Scientists are not sure how long the monarch's spectacular annual migration to Mexico has been occurring; it may be as old as 10,000 years (when the glaciers last retreated from North America) or as young as a few centuries." http://www.monarchlab.org/Lab/Research/Topics/Migration/WhereToGo.aspx

It appears that the microclimate of the small area in Mexico where they overwinter is the crucial factor for its choice by them - they are not particularly "wedded" to a particular species of tree as long as the trees provide the right environment re protection, ability to hang/cluster etc.. In geological timescales the climate must have changed many times . So there is no way the location could have stayed constant through the Pleistocene - "the distances and directions of monarch migrations in North America must have changed frequently during the interglacial and glacial episodes of the Pleistocene"
http://jeb.biologists.org/content/199/1/93.full.pdf

Another comment
"The last Pleistocene glaciations in North America instigated migration to Mexico in the east and to Californian coast and deserts in the west. In the western U.S., the overwintering colonies are smaller and more numerous, while in Mexico, they are few, but more spectacular" http://entnemdept.ufl.edu/creatures/bfly/monarch.htm

So I guess it must be Holocene - but exactly how recently within it isn't clear. Just think of the climate changes which would have occurred even through that period. Numbers can virutally die out in one place if the climate changes but just a few will have survived and multiplied somewhere else where they found suitable, if slightly different, conditions

Author Solivagant
Partaker
#68 | Posted: 16 Oct 2013 03:41 
Komodo - Early Pleistocene
"the ancestor of the Komodo dragon most likely evolved in Australia and spread westward, reaching the Indonesian island of Flores by 900,000 years ago. Comparisons between fossils and living Komodo dragons on Flores show that the lizard's body size has remained relatively stable since then"
http://www.livescience.com/9726-origin-komodo-dragon-revealed.html

Pitons - Middle Pleistocene
"Qualibou, also known as the Soufrière Volcanic Centre is a 3.5 X 5 km wide caldera on the island of Saint Lucia that formed approximately 32-39,000 years ago. This eruption also formed the Choiseul Tuff which covers the south east portion of the island.
The Pitons are two large lava domes that formed 200-300,000 years ago, some time before the formation of the caldera and since then other domes have filled the caldera floor. (Wiki)

Vallee de Mai - Paleocene
"at about 90Ma Madagascar parted from India and Seychelles. The isolation of the Seychelles was completed at about 65Ma when India and Seychelles drifted apart"

Author elsslots
Admin
#69 | Posted: 16 Oct 2013 12:09 | Edited by: elsslots 
I would like a second opinion on Ha Long Bay:
OUV = full range of karst formation processes on a very large scale and over a very long period of geological time

Possible age:
- Early Pleistocene (Pleistocene epoch of the Quaternary period: The process of erosion began dissolving the limestone-rich region of Hạ Long, after that, forming the limestone plain was most active )
- Middle or Late Pleistocene (middle and late Pleistocene Epoch: Period when the caves and grottoes of the area formed. )
- early Holocene Epoch The islands of today's Hạ Long Bay are basically remnants of these mountains, flooded. Rainwater flowed into crevices in the limestone that had formed from tectonic activity. This steady erosion constantly widened the cracks, eventually creating today's formations.

See nice timeline here:
https://en.wikipedia.org/wiki/H%E1%BA%A1_Long_Bay#Timeline_of_geologic_evolution

And page 65 of the nom file has a similar timeline. I tend to lean to Holocene, as then thë Bay was formed.

Author Solivagant
Partaker
#70 | Posted: 17 Oct 2013 01:13 | Edited by: Solivagant 
elsslots:
I tend to lean to Holocene, as then thë Bay was formed.


Me too. Clearly we have to guard against assigning "everything" to Holocene just because some aspects changed then to create what we see today. But in this case the "Bay" wasn't a Bay until then - which seems a pretty significant fact! The text can make it clear that the erosion took place throughout the Pleistocene - and the Wiki timeline link can also be provided to provide a fuller history.

On of the "surprises" to me so far with this exercise is its clarification of just how many "Natural" sites have only emerged "relatively" recently

Author Assif
Partaker
#71 | Posted: 22 Oct 2013 10:43 
Re: Lagoons of New Caledonia

It is now assigned to Oligocene, but that's the time when the island emerged. The reef for which the site got inscribed is much later, probably similar in age to Belize Barrier Reef (Holocene), and Great Barrier Reef (Middle Pleistocene).

Author Solivagant
Partaker
#72 | Posted: 22 Oct 2013 17:06 | Edited by: Solivagant 
Assif:
The reef for which the site got inscribed is much later, probably similar in age to Belize Barrier Reef (Holocene), and Great Barrier Reef (Middle Pleistocene).

I had been researching the New Caledonia Lagoons time period when the Oligocene proposal was made. I was a bit surprised but "bowed out" at that point! As a non-geologist I had come to the conclusion that the geology of New Caledonia is complex, covers many periods and is still the subject of research and theorisation. Hence my uncertainty and reluctance to make a choice!

However, I agree with Assif that Oligocene doesn't seem to be justified – other than by the fact that the island only made its last rise above sea level during that time. We have another example of a natural site which owes its present day form to many different periods and therefore requires us to choose that period which gave it the largest part of its OUV

I note in particular that France nominated it under 4 criteria but that IUCN rejected the "Earth science" criterion viii ("based on the occurrence of geodynamical processes that sculpture the surface of the Earth – including obduction, subduction, erosion, sedimentation and variations in sea levels.. ........IUCN considers, however, that the nominated property does not meet criterion (viii) - Earth's history, geological and geomorphic features and processes")

Instead the site was inscribed under 3 natural criteria "(vii) – Superlative natural phenomena or natural beauty, (ix) – Ongoing biological and ecological processes. (x) – Biological diversity and threatened species". So we need to concentrate on when the environment for those species was most significantly formed. It is worth mentioning that the islands contain significant endemic land-based "biota". But they have not been inscribed for this – only for the reefs/lagoons and their ecology

So which period contributed most to those criteria in this case? Well the reefs seem to have been "up and down" across the Pleistocene and Holocene periods both from changes in sea level and from tectonic movements. As far as I can make out, neither period is mentioned in the Nom File – which emphasises the "non geological" aspect of the site

I found this paper which describes the entire geological history of New Caledonia but concentrates on the reefs. It contains 2 separate articles
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CC4QFjAA&url=h ttp%3A%2F%2Fnouvelle-caledonie.ird.fr%2Fcontent%2Fdownload%2F32607%2F250955%2Fversion %2F1%2F&ei=EapmUr6gEqHz0gXTmYCABA&usg=AFQjCNHZllvHmt3e-aVQr_NwQ6czyNznLA&sig2=I9zXZK5 JNhTv4N7Xm9AE2w&bvm=bv.55123115,d.d2k

It appears that the inscribed reefs cover a range of "types" as to depth, relationship to the sea etc etc. Another article concentrates on the "post Middle Pleistocene" aspects http://www.sciencedirect.com/science/article/pii/S1251805000886656 . The fact that the reefs include areas which were earlier river beds has been cited as a significant aspect. See also page 26 of the first article. Also this quote from http://archive.unu.edu/unupress/unupbooks/80505e/80505E02.htm "The Holocene sea-level rise has been followed by revival and renewed growth of coralline barrier and patch reefs offshore, thereby augmenting structures that had been developing intermittently through Pleistocene times, and the initiation of Holocene fringing reefs along the present coastline ..... However, the south-east coast near Yat is bordered by an emerged Pleistocene fringing reef up to 10 metres above sea level, and similar emerged reefs up to 20 metres above sea level encircle the Ile des Pins to the south. ....... the northern half of the west coast of New Caledonia is low-lying, consisting of gently sloping Pleistocene piedmont fans that have been partially submerged by the sea..",

Which takes us to the second article. See pages 33 onwards and in particular the map on page 37 showing sea levels at different periods and the dates of reef formation. Again we have "Old reefs" (Pleistocene) over 125k years old and "Post Glacial reefs" = "Modern" ie Holocene. Clearly water levels have altered significantly across the Holocene and it would appear that 10500 years ago the "lagoons" were all above water (1 of the articles hypothesises that there may have been brackish lakes). So – much of the "shape" of the lagoons is due to Pleistocene events, but today's lagoons would appear to have been (almost?) completely water-filled during the Holocene .

Author Assif
Partaker
#73 | Posted: 17 Jan 2014 21:30 
I am quite frustrated trying to find out the age of Uvs Nuur. Any help?

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