Yamagata graben

[soubriquet 0]

A graben is a fault-bounded basin surrounded by high ground. The central Yamagata basins (there are at least three) are an enigma to me. Normally, grabens collect sediment shed off the high ground as the basin goes down and the mountains go up.

 

Other than the stuff in transit down the rivers, there are virtually no sediments here. Wherever you look in any stream bed, you find bedrock. Every landform is erosional, and in 4 years of looking I've only found one packet of fossils.

 

In 25 years I've never seen a system like this. South Island NZ is the closest I've come to something this dynamic, but it still doesn't compare.

 

Incroyable.

[soubriquet 0]

You don't have to answer this. Just musing.

 

What the sediments tell me is that Yamagata is going up, even the parts that are going down. Hmm.

[stemik 14]

 Originally Posted By: soubriquet

A graben is a fault-bounded basin surrounded by high ground. The central Yamagata basins (there are at least three) are an enigma to me. Normally, grabens collect sediment shed off the high ground as the basin goes down and the mountains go up.

Sensei, why would the basin go down if its colleting sediment...surely it seems to be the other way round...

[soubriquet 0]

Not quite sure I understand you, but I'll plough on regardless.

 

We geonerds use a very woolly concept known as "base level". I've never seen a truly satisfactory definition, but it effectively implies a "threshold", and relies on the fact that (except for glaciers, a special case) stuff doesn't move uphill.

 

What is happening here is the basin is going down relative to the mountains going up, but it is like sitting down in the lift. The whole caboodle is going up.

 

I'll refer everyone back to "O level" physics and add the reminder that stuff moves downhill (potential energy).

 

Circularly, the lack of sediments tells me that although the floor of the basin is going down relative to the surrounding mountains, it is going up relative to sea level (base level).

 

I hope that's clear hahahaha

 

(One of the nicest things in my life was a student coming to me 18 months after I'd finished teaching him sedimentology. "I've been thinking about what you said, and it's really simple").

[me jane 0]

Amazingly, I think that is clear... but it would be GSCE Physics for me

[tsondaboy 0]

Your key word is "Miocene Tectonic inversion"

[soubriquet 0]

Well dang me, I thought I'd be mumbling to myself

 

Thanks for that, tsonda. I don't access to any geological literature here, but I can still spot a rock, even if I can't get my feet into focus anymore. I'm glad I also have half a wit left.

 

In a landscape utterly dominated by pyroclastics, I've found a tiny treasure of lake/river sediments, packed with plant fossils.

[ex-lurker 0]

That is definitely a key word.

[tsondaboy 0]

Soubs PM me your email and I ll try to send you some papers in Pdf.

[soubriquet 0]

Thanks. Done

[tsondaboy 0]

Got it. I ll try to gather some papers and send you, but this might take some time because I am a bit busy right now.

[soubriquet 0]

Thanks mate. Theres no hurry. I appreciate any you can gather.

[soubriquet 0]

Thanks tsonda. Pdf's have arrived.

[tsondaboy 0]

have fun!

 

Next time I will sent you some Geo-porn too.

[soubriquet 0]

But you have...

 

It's nice to come to a new area without preconceptions and find my speciality observations (sediments and landscapes) fit precisely with the local experts' models.

 

Miocene tectonic invertion indeed. That means the stuff that was going down (the basins) is now going up.

[tsondaboy 0]

You still have it in you soubs.