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).

Monday, April 20, 2015

Xiaogoubei Geological Park

Just back from a day-trip to Xiaogoubei Geological Park, just north of Jiyuan, in the western part of Henan province. Unfortunately, the group that I was travelling with was not very interested in the geological highlights of the park, so we stuck mainly to the scenic areas. Hopefully I'll be able to go back in a few weeks and source some of the interesting boulders that litter the park.

Once again, we got off the loess plain--and my expectation that this would be another escarpment (as near Huixian Xigou) were shattered by the boulders of a very striking reddish conglomerate that litter the valley on the way up the road to the park.

There are also some very nice blocks of sandstone among the detritus in the river valley.

Dribbling little waterfalls feed into the main river channel.

All the steep slopes add up to one thing-falling rocks.

This could ruin your day. I was going to crawl under there and have one of my companions photograph me with my feet sticking out, but thought better of it. With my luck, the rock would just shift a little bit.

I'm having a bit of trouble putting the geological history of the park area together. It seems that the area is part of the North China Block. Driving up to the park it seemed we passed through a series of sheared metamorphic rocks, but within the park proper, most of the rocks at the base of the mountain are andesites, usually with one or two generations of amygdaloidal bodies. The most prevalent set of amygdaloidal bodies is composed of silica, some of which qualify as agate. Another less common set is a reddish chert. Some stones carry both sets.

The amygdaloidal bodies are the irregular white flecks in the grey rocks.

Andesites typically form during continental collision, or the assembly of small crustal pieces into a larger continent. Sometimes after the blocks have accreted together, they split (or 'rift') apart again.

Such a rifting event happened here about 1.5 billion years ago. Rifting is recorded first by some pillow basalts (which record the eruption of basic magmas directly into the sea) as a new ocean began to form, followed by erosion and infill of the rift basin with the reddish conglomerates noted above.

Pillow basalts with the loveliest scale a geologist could want.

Conglomerate with a not-so-lovely scale.

Presumably  the coarse sandstone boulders that litter the valley come from a unit atop the conglomerates.

'Herringbone' cross-bedding in sandstone from a loose boulder in the park.

I'll have to post more on this place later, but will just leave you with one interesting feature in the park. One of the bridges was a sort of suspension bridge composed of disarticulated wire baskets, each hanging separately from a set of cables. As is normally the case in China, it is up to you to recognize the dangers involved and act appropriately.

My main regret was not being able to wait around to see how one of the families with strollers crossed it.

No comments:

Post a Comment