Dust flux, Vostok ice core

Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Wednesday, February 10, 2016

Karst features of Guilin, part 1

Guilin is a small town (as far as China is concerned) in Guangxi Province, whose main claim to fame is it is one of the most spectacular examples of karst topography in the world.

Karst topography viewed from the Li River, south of Guilin.

The karst terrain covers over 5,000 square km and has formed by a combination of rapid uplift (courtesy of the collision between the Indian Plate and the southern Eurasian Plate, combined with erosion and dissolution of the carbonate deposits that covered the area. The result is a flat plain, interspersed with steep sided peaks that often exceed 50 m in height, which occur individually or in small clusters.

Viewed from within Guilin, from the peak in the old walled city.

The flat plains are intensely farmed or developed. The hills are too steep for development, but often have temples or pagodas at the top.

These peaks have been of great cultural significance for hundreds, perhaps thousands of years. Apart from the temples built at the peak, the base (and often various patches some height above the base) of many of these peaks have been decorated with poetic or religious inscriptions, dating back many centuries.

Although there are more than one erosional mechanism active in the formation of karst topography, dissolution of the carbonate rock is critical. Both surface and ground waters quickly become saturated with carbonate, normally causing some dissolution and an uneven surface. Carbonate rocks are somewhat permeable, meaning water flows through them quite easily. When two different masses of water meet, even if both are saturated in carbonate, the resulting mixture is always undersaturated, leading to dissolution at the water table, where meteoric water encounters groundwater.

Diagram showing that corrosion (dissolution) occurs at the surface, at the water table, and at interfaces between different bodies of groundwater. From Scholle, et al. (1989).

Corrosion begins in the mixing zones between bodies of water with differing chemistry, and is most intense along pre-existing lines or zones of weakness. Zones of weakness can include both fractures and bedding planes. When this dissolution begins, it is commonly influenced by regional stress fields.

Carbonate "pavement" near Marmora, Ontario, showing dissolution along lineaments related to the local tectonic stress field.

As dissolution proceeds, the caves and crevasses tend to get larger. Random areas within the carbonate will be more resistant to dissolution, possibly due to chemical variability, but also because if fractures are more or less randomly distributed, there will be some large areas with relatively few fractures. These resistant regions end up as the remnants of undissolved rock that end up as the peaks around Guilin.

Moon Hill, near Yangshuo.

Since dissolution is such an important factor in the formation of this landscape, we will see a variety of local features in rocks of the area that reflect dissolution.

Luckily, the Chinese like these sorts of rocks and tend to put them on display everywhere. These examples were in Shan Lake park (site of the twin towers, which were not made of silver and copper after all).

Tuesday, February 9, 2016

A little stratigraphic correlation

The sidewalks in Guilin are paved with fossiliferous shales.


Gastropod. Part of my shoe for scale.

More bryozoa (bottom), a gastropod (centre, top), and an orthoceratid (upper left), which is a kind of cephalopod.

A large orthoceratid, and at least one brachiopod.

A rugose coral (also called a horn coral).

Various crinoid ossicles (echinoderms).

A tabulate coral. I had found a better example, but can't find the photo (or maybe it was blurred and deleted).

A couple of brachiopods, with the section cut through both valves, plus assorted fossil debris.

What is interesting to me is how similar this collection of organisms is to that of Devonian sediments near Port Colborne, Ontario.

Actually, the following photos are from various sites near where I have described--but some of these are nearly 30 years old (from slides) so I may not really remember where they are from.

Rugose corals from the Port Colborne quarry.

A tabulate coral from the Port Colborne quarry.

These fossils are Devonian in age, and more closely resemble the corals in Guilin than other corals from my image collections of Ordovician age. The other fossils don't (to my unpracticed eye) seem to have changed much over the same interval.

I asked one of the locals where the sidewalk tiles come from. She claimed that they were quarried nearby, but not from any of Guilin's famous dragon's teeth. Although I did notice quarries on a few of them.

Sunday, February 7, 2016

Thousand-year-old university in China

The Yuelu Academy in Changsha.

An overview of the campus. Nice place. The snow is from that same storm that got me in Wuhan.

Lectern of the main lecture hall.

A nice, collegial passageway.

Period wood-cut, showing that even a thousand years ago, professors sometimes had to be brought back to the campus in wheelbarrows.

Confucian temple on campus.

No idea about student fees, administration, or tenure.

Saturday, February 6, 2016

Lack of creative destruction in Changsha

All across China, massive construction programs have rebuilt entire cities. Older areas, with their tangle of alleyways have been demolished to make way for organized blocks of high-rises.

Not so much in Changsha, which is in Hunan Province. I find the city a little difficult to get around, because much of downtown is still a warren of alleyways. On the plus side, some of these have been gentrified and are filled with interesting architectural details.

You can have your neighbour over tea without them leaving home. Just hand a teacup across to their balcony.

Modern art gallery.

Woman drinking tea.

The biggest problem in getting around is the city hasn't upgraded its transit information. I use a Chinese map app on my phone, which tells you what transit to take to get from your current location to some other selected location. Changsha is the only city in China I've found where this doesn't work--the real bus routes differ from the ones in the app.

Why don't I drive, you ask?

Because driving in China is still pretty much like this:

Thursday, February 4, 2016

The two towers in Guilin

The pagodas of the Sun and Moon are supposedly the top tourist attractions within Guilin, China.

I'll let you decide which is which.

Local information claims that the tower of the Sun is made of copper. I'm not sure if they just mean the eaves, or if the tower is clad in copper. But just for fun, let's say the entire tower is pure copper. 

I'll check it out tomorrow morning and let you know.

No word on what the tower of the Moon is made of. My guess is silver.

I took a motorcycle cab from the train station to the hotel--well, at least to the vicinity of the hotel. The driver couldn't find it. The ride was only mildly terrifying, except for that one time when the driver decided to cut into traffic by jumping off the sidewalk into a gap between the curb and a taxi that looked much too narrow for my suitcase, then gunned the engine to cut in front of the cab. The weaving in and out of traffic afterwards was quite relaxing.