Monday, October 4, 2010

Landscapes into Rock - Part 4

This post ends my summary of the Landscapes into Rock conference that took place in London, September 21-23, 2010.  Click here for previous posts.

Theme three – Landscapes into Rock – was obviously the central theme of the Conference. It was chaired by Sebastien Castelltort (ETH – Zurich) and Emma Finch (University of Manchester), it had eleven oral presentations and featured a very insightful “keynote of the keynotes” by Mike Leeder (University of East Anglia). Of interest for me was the research by Alex Whittaker et al using regional grain-size trends to derive information on the dynamics of the sediment routing system.

The high-point of the session was the keynote address by Mike Leeder. Mike put forth many interesting and provocative ideas:

  • the need to fully utilize the sedimentary record to test the landscape evolution models; 
  • the recent advances in speleothem and calcisol research that may provide the ability to isolate climate/vegetation forcing of the eroding landscape; 
  • the understanding of the link between the rate of tectonic evolution and how they induce major changes in the landscape; 
  • teleconection – the link between the eroding landscape and the downslope deposcape.

The fourth (and last) theme – Integrative studies of sediment routing systems and the petroleum systems - was organized by Ian Lunt (Statoil) and Mike Blum (ExxonMobil), and featured two presentation and two keynote speakers – Ole Martinsen (Statoil) and Peter Burgess (Shell and Royal Holloway University of London). For me, the highlight of this session was Peter’s overview of stratigraphic forward modeling in hydrocarbon exploration. Peter noted that stratigraphic forward models (SFM) are more mature but still have a limited predictive power. SFM prove most useful in their ability to quickly create multiple scenarios, to test hypotheses and ideas, to devise numerical experiments that illustrate how depositional systems work and through that to develop new plays and concepts.

On a less-formal side, the conference ended each day with a social hour, which involved a lot of discussion of the ideas presented during the day, accompanied by wine, of course.  The discussions were less formal, but certainly not less technical.  They were less flashy than the gathering that took place at Dolce & Gabbana one evening, just down the street from the Burlington House (picture below), but the social hour at the Landscapes into Rock conference were certainly more intellectually stimulating -- for me :)

Sunday, October 3, 2010

A day on the river

You are a geologist when you have fun digging trenches to see cross-bedding and when you enjoy photographing mud clasts on a Saturday afternoon.

I am a geologist, so is my SO, and this weekend we enjoyed a trip along the Trinity River; beautiful weather was a plus, and it made it for a great family outing.  We started with our canoe from the bridge across Trinity near Liberty, TX.  From here we went north for about 7 km in total (the red line shows our path for the day).
The first stop was on the opposite bank from the meander loop cut-off, indicated by the yellow arrow in the picture above.  A point bar with a lot of awesome features, worthy of any Geology 101 class: ripples and dunes...
... with awesome lineation in the coarse grain fraction oriented parallel to the transport direction (downstream is towards the top of the picture).
More ripples and dunes...
... mud cracks and the resulting mud-chips waiting for the next bank-full discharge to be washed away....
... unless of course your teenager will not remove them all by building mud-chip castles.

The mud cracks on the surface of this point bar developed in low areas, when water level was just above the edge of the depression where the mud accumulated.  Eddies formed in these low areas of the point bar, and these eddies brought in and deposited a thin layer of mud.  The mud cracks formed later after the water receded and the surface dried out.  Similar eddies carrying and depositing fine-grained material (but at a larger scale) were responsible for the deposition of a nice mud-drape on one of the point bars we stopped at further upstream.  The picture below shows the river bank with the water flow from right to left, and a protected area entered by an eddie, which deposited a beautiful mud-drape over the extent of the point bar exposure (arrows indicate the extent of the mud drape).

Well developed cross-bedding may be seen within the point bar succession....
... and ripple lamination, cross-bedding and wind ripples may be found in the right exposures on the point bars...
We had a blast: great weather, nice river, good canoeing, and cool sedimentary features.  You get the picture :)
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Comparative geology - the tale of two rivers

I recently went on a canoe trip along the Trinity River (our track is shown by the red snaky line in the picture below).  We spent the day looking at sedimentary features associated with modern river systems, and by doing so, thinking about processes at work in rivers, and the resulting rock architecture.  As geologists, we often study modern environments (like rivers, beaches, deltas etc) to gather clues that help us understand the rocks and the processes that formed them.

The trip to the Trinity (more details in this post) reminded me of the Arges River in Romania; if looked from above, both have a lot in common.
Note that the scale of the two satellite images are similar, so the size of the geomorphic features can be easily compared.  The width of the meander belt in the two images is similar.  Two abandoned meander loops (red arrows) have similar dimensions and shape.  Their paleo meander belts (active sometime in the recent past and still visible on the satellite image) have similar widths (black arrows).
The zoomed satellite photos show that the size of the active channels are similar.  The Arges shows better the point bars within the active channel, but this is only because the picture of the Trinity was taken at near bank-full stage, where most of the point-bars are submerged.
These two rivers, although in somewhat different settings, would most likely create a very similar rock succession.  I have to take a canoe trip along Arges sometime in the future, and at that point I will have on the ground pictures from the both locations.  Until then, wait for the next post on the Trinity, and enjoy the birds-eye view of the two rivers.
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