Thursday, July 29, 2010

Get Your Updated Geological Time Scale Here

Via The USGS has released an updated Geological Time Scale. One noteworthy revision is that the Ediacaran ( 635 mya - 542 mya) has become the first formally recognized geological unit (system) of the Proterozoic. Division of time into geological units like the now recognized Ediacaran  are based on some natural break in earth conditions.

In the case of the Ediacaran the unit is recognized on the basis of the unique fauna it contains - among the first examples of multicellular animals have been preserved in these strata and this unique fauna has been found to have a global distribution between 635 million years ago and 542 million years ago. That makes the Ediacaran worthy of a status of a formal geological division. The stratigraphic section in which these conditions are best represented and in which the beginning and end of these unique conditions are well preserved is called a type section or a stratotype. The type section for Ediacaran is in the Ediacara Hills Flinders Ranges of south Australia.

Other changes include revisions to the base of the Holocene series/epoch and the base of the Pleistocene series/epoch. You can download the USGS fact sheet on the revised Geological Time Scale here.

Tuesday, July 27, 2010

Video Of Rock Fall In The Himalayas

Via, a video of a rockfall in the Pangi Valley.

Pangi valley lies in the Chamba district of Himachal Pradesh between the Pir Panjal and Zanskar ranges very close to the border with Jammu and Kashmir and is a popular trekking destination.

Monday, July 26, 2010

Plate Motions: Is The Driver Bottom Up or Top Down?

Science Daily describes some modeling results of plate motions presented in the July 16 issue of Science: Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab.

What drives plate motion? Is is the forces of convection in the mantle below or is it the drag of the subducting plate along zones where two plate converge and one sinks below the other? The authors of the above paper suggest that it is the drag of the subducting plate that is more important.

From the press release:

Schellart and his team, including Stegman and Rebecca Farrington, Justin Freeman and Louis Moresi from Monash University, used observational data and advanced computer models to develop a new mathematical scaling theory, which demonstrates that the velocities of the plates and the plate boundaries depend on the size of subduction zones and the presence of subduction zone edges.

"The scalings for how subducted plates sink in the earth's mantle are based on essentially the same fluid dynamics that describe how a penny sinks through a jar of honey," said Stegman, who developed the computer models that helped the team reenact tens of millions of years of tectonic movement. "The computer models demonstrate that the subducted portion of a tectonic plate pulls on the portion of the plate that remains on the earth's surface. This pull results in either the motion of the plate, or the motion of the plate boundary, with the size of the subduction zone determining how much of each."

"In some ways, plate tectonics is the surface expression of dynamics in the earth's interior but now we understand the plates themselves are controlling the process more than the mantle underneath. It means Earth is really more of a top-down system than the predominantly held view that plate motion is being driven from the bottom-up."

Looking at the graphic above which shows different types of plate margins, the study in Science focused on areas of plate subduction using the Western North America as an example. Thinking about it more broadly I wonder what is happening at mid-oceanic ridges and regions where new plate boundaries are being formed like the northern part of the East Africa rift.  These are places where two plates or continental blocks are being pushed away from each other.

How much of a role does diverging convection cells in the mantle below play in these situations especially if there is no strong drag due to subduction at the other end of the plate; for example a situation like the Indian plate is experiencing today with a mature continental collisional zone at one end and a mid oceanic ridge at the other or  .. the evolving Red Sea and East African rift wherein mantle upwelling is generating tensional forces that stretches and thins and pushes away the overlying broken lithosphere blocks bottom-up a larger driver in these cases?

Monday, July 19, 2010

Indian Sedimentary Basins And Shale Gas

Over the last few months, several articles and papers have emphasized the potential role shale gas will play in India's hunt for energy. Shale gas is natural gas trapped in fine grained sediment.

Update May 18 2011: [ See post India Basin-Wise Shale Gas Estimates for estimates of shale gas from various Indian sedimentary basins.] 

These articles did not have any graphics so I am putting up a map of Indian sedimentary basins and a graphic depicting shale gas geological reservoirs.

Indian Sedimentary Basins

 Source: Geotimes

The basins of interest in terms of shale gas potential are the mostly marine Mesozoic and Cenozoic basins in Rajasthan and Gujarath and the Cenozoic basins of Assam. The Gondwana basins of central and eastern India are continental interior rift basins and are coal rich and have associated coal bed methane which if tapped could also play an important role in India's energy mix.

Shale Gas Geological Reservoirs

Unlike gas reservoirs in coarser materials like sands, natural gas in shale is trapped in micro pores which may not be connected to each other i.e. they have low permeability and the gas is quite difficult to extract.

India's conventional natural gas reserves are growing with new discoveries mostly along the east coast Krishna Godavari offshore basins. Early estimates of these gas resources if proved correct may more than double in terms of energy equivalence India's proven reserves of about 5.6 billion barrels of oil. Unconventional resources like shale gas have the potential of adding substantially  more to these resources. Currently natural gas makes up a small portion of India's energy consumption pie (see fig on left) and the chance to move towards a cleaner emissions profile by substantially displacing coal in power generation (coal makes up about 70% of electricity generation) and eventually as fuel for transport makes these unconventional sources a critical energy resource of the future.

I don't know how much shale gas resources India has because there has not been a systematic evaluation of shale gas. India's current energy policy prohibits exploitation of shale gas and coal-bed methane. The sooner that policy changes the better for energy starved India.  

[Update Sept 3:] As a reader pointed out in the comments there is recent movement from the government on the exploitation of shale gas and coal bed methane. See this article. A policy on shale gas is likely to be out by next year, while the government has already auctioned of several blocks for exploration of CBM from various basins.

Still, there is one aspect of exploiting these resources that has not been touched upon by any of the articles I have come across and that is the environmental costs of extracting shale gas. Since this gas is locked up in impermeable layers one of the common methods of extracting it is by hydraulic fracturing of the rock. This involves injecting the shale with fluids and gels mixed with particulates like sand to keep the induced fractures open and enable migration of the gas along open fractures.

A new film "Gasland" discussed on Science Friday last month looks at some of the problems of hydraulic fracturing or "fracking" of the Marcellus shale that underlies large parts of Pennsylvania, New York and Ohio and West Virginia.  Chemicals used in the injecting fluid has been reported to contaminate groundwater in Pennsylvania. At least according to the film, the energy companies have been less than forthright about the chemical composition of the injecting fluids which the film claims includes carcinogens and neurotoxins.

All this should send warning signals about the way and means by which India goes about exploiting these shale gas resources.  Groundwater is as important a resource for India's economic development as is natural gas. Almost all drinking water needs in rural areas are met by groundwater. A significant majority, about 2/3, of arable area in India is irrigated by groundwater.  Contamination of large portions of the overlying aquifer will be nothing short of a catastrophe for farmers who have no other water supply but groundwater.

The exploitation of coal bed methane offers another avenue for social conflict. The Gondwana basins which are coal rich are forested regions and home to many tribal communities. There has been a long history in India of the government and private mineral companies riding roughshod over tribal rights. The current violent insurgency that is taking place along tribal regions of Chattisgarh, Maharashtra and Jharkhand has its roots in the rampant exploitation and callous indifference shown by the state and private companies towards tribal communities.

So, shale gas and coal bed methane offer a significantly large energy source but also open up the possibility of more environmental and social disruption.

Update May 18 2011: For latest estimates of shale gas see - India Basin-Wise Shale Gas Estimates.

Thursday, July 15, 2010

Monitoring Seismic Chatter

Nature News has a good article by Naomi Lubick on recent efforts to set up seismic arrays in Japan and northwestern U.S along the Cascadia subduction zone around the Olympic Peninsula Seattle area to monitor swarms of tiny earthquakes or tremors.

So far these swarms have not been connected to larger earthquakes and cannot be called precursors.. but that's what seismologists are hoping.. that ultimately we may be able to use the pattern of tremors to understand changes in stresses along major faults, giving us a better handle on the timing and location of bigger quakes.

The swarms in Japan seem to be spatially restricted along bands and one speculation is that the subduction of chains of seamounts may be triggering these swarms.

The earthquake swarms along the Cascadia subduction zone in the Olympic Penninsula seem to follow a time line..appearing every 12-14 months.

This regularity is an angle I am sure astrologers are going to be having a field day with ..keep a lookout for claims that these tremor swarms follow planetary cycles (possible for tiny disturbances?) and that you can "predict" big earthquakes by the pattern of these tiny ones.