Monday, November 30, 2009

Mapping India: Land Degradation and Desertification

In the November 25 issue of Current Science, researchers from the Indian Space Research Organization release a map and some important estimates of the extent of land degradation and desertification affecting mainly dry, semi-arid and dry- sub humid areas of India.

Source: Desertification/land degradation status mapping of India

About 69% of the total land area of the country - about 228 million hectares - falls in one of these three climatic categories. The numbers from this mapping project is cause for concern. They indicate that land degradation has affected just under half the extent - 105 million hectares of these dryland regions,  roughly 32% of the land area of India.

The main processes of degradation are water erosion, wind erosion and vegetal degradation through deforestation and overgrazing. The paper gives the extents affected by various degradation processes grouped state-wise.

I wish they had included estimates of degradation by land use. For example how much of agricultural land in each state is being degraded, how much forest and so on. These have been no doubt calculated. They show up as classes on the map, but the paper does not present the results by type of land use affected.

If predictions about changing rainfall patterns over India because of climate change turn out to be accurate they will accentuate many of these degradation processes. Rainfall is predicted to fall in shorter more intense bursts over many regions of India. This would mean more powerful surface runoff and greater soil erosion.

Regions of country which are hot and arid like Gujarat and Rajasthan are likely to get hotter and drier. That would mean more stress on vegetation and great wind erosion.

I come back to the National Action Plan For Climate Change (15 MB) There are 8 missions or strategies to deal with climate change. None of these directly includes the problem of land degradation and desertification in dryland regions. However the National Water Mission, National Mission for a Green India and the National Mission for Sustainable Agriculture seem to have the right overlapping goals that could be focused to address this problem.

I mentioned earlier about the estimates of land degradation according to land use. These numbers matter a lot. Farmers occupying dryland regions are usually poor farmers cultivating marginal lands. If you look at the above map, you will see large regions classified as Agriculture Unirrigated being affected by various processes of land degradation. These are farmlands that are out of the reach of irrigation canals and other State largesse.  Millions of farmers cultivate small land holdings, depending only on monsoons and groundwater. Warming and changing rainfall patterns will have a larger impact on these marginal farmers. Their livelihoods and the food security for large number of people in these drylands is at risk from continuing damage to the land.

The National Action Plan For Climate Change needs to single them out for special help.

Thursday, November 26, 2009

Charles Darwin Has Been Sighted In Pune

Its been 150 years - November 24th 1859 - that Darwin's book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life was published.

The British Library on Fergusson College Road, Pune, has a poster exhibit on the theory of evolution. There are 14 poster boards encompassing the gamut of thinking on evolution beginning with Charles Darwin's voyage to the Galapagos to his subsequent theories of common descent and natural selection to current understanding on topics like speciation, group selection, the evolution of attributes like musical ability  - which provides food for thought on whether every feature can be explained as an adaptation or whether some traits originate as spandrels or byproducts of the evolution of some other general feature - to recent thinking on the genome and the importance of mechanisms like epigenetics and gene regulation.

Source: British Council

Earlier on November 12th, biologist Madhav Gadgil gave quite a good talk on the relative roles of cooperation and competition in evolution. He spent quite a bit of time clarifying some common misconceptions about evolution, most notably the (mis)concept of an ideal type. That there is an ideal type or a narrow collection of attributes defining species and populations can be traced to essentialist thinking prevalent since...well since recorded philosophy of thought. One consequence of this thinking is that any individual of that group who exhibits variation outside that "ideal" or narrow range is considered an aberration of nature, a degenerate. Madhav Gadgil very eloquently dispelled that notion and stressed that variation is the norm of life, the fuel which drives evolution.

The sizable crowd which had gathered for the talk asked some thought provoking and challenging questions. There were more technical questions -  does the theory of the selfish gene underlie co-operation?...I don't quite remember Dr. Gadgil's answer but here is my take on this.  In his book The Selfish Gene Richard Dawkins argues that you can think of natural selection as acting on genes and not the individual. All genes are selfish since their "goal" is to replicate themselves at the expense of their alternative version. Can this explain co-operation?  Yes a very general sense if one is thinking of evolution in terms of gene selectionism then co-operation like any other attribute spreads through the spread of selfish genes.

There were also discussions on social Darwinism and how a clearer understanding of evolution - by removing misconceptions like racial purity and group superiority - can help us become a better society...never is local and ever changing and variation is everything....

A few canards were repeated during the talk and discussion, most notably how Hitler was directly influenced by Darwin. He wasn't.  He had not read Darwin and had no understanding of evolution and neither did his coterie. Maybe there were a few people throwing around phrases like survival of the fittest but really a heady mix of a radical Christian sense of racial superiority and extreme nationalism more convincingly explain his conversion to arch fascist. Check out this article and this one for a humorous but informative take on the subject.

If you are in town go stop by the British Library. The exhibition runs until November 29th.

Tuesday, November 24, 2009

California Droughts And Carbonate Cycles

When I was a graduate student in the mid 1990's one of the hot research topics in carbonate sedimentology was the study of shallow marine carbonate depositional cycles. Sediments in shallow marine and even deeper environments  are deposited in packages or cycles during periodic sea-level rise and fall. There is a rhythmic beat to this, regulated by the waxing and waning of polar ice sheets or by periodic tectonic subsidence or by an internal clock beating to changing currents and sediment distribution patterns. The periodicity of these cycles is on the scale of tens of thousands of years.

Which of these mechanisms is dominant? That was the big question and the big fight.

GSA meetings used to be fun listening to rival research groups intellectually slug it out. Over the years the waning and waxing of ice sheets (allocyclicity) has been recognized as a common mechanism of generating sediment cyclicity but to give other processes their due, tectonic subsidence and autocyclicity i.e internal forcing due to self regulated sediment accumulation and distribution patterns are also recognized from specific environments.

We worry about a lot of other problems these days, global warming and its effects of rainfall being one. Scientists involved earlier in their career in the study of marine carbonate cycles have started paying attention to geological beats taking place on a much higher frequency.

Isabel Montanez who has published a lot on marine carbonate cycles has a paper with graduate student and colleagues on the rhythmic precipitation of carbonate minerals within cave stalagmites from the Sierra Nevada mountains of California.

Late Pleistocene California droughts during deglaciation and Arctic warming - Earth and Planetary Science Letters

And here is the Science Daily press release.

Cave stalagmites form by minerals precipitating from water dripping from the roofs of caves. Growth speeds up during the rainy season and slows or stops during the dry periods. Growth bands can thus reflect yearly growth much like tree rings. This allows scientists to resolve changes taking place over tens of years. One fairly long stalagmite can record growth over hundreds to few thousand years. In this study the scientists have a record of stalagmite growth - radiometrically calibrated - over a time interval from about 16.5 thousand to about 8.8 thousand years ago covering the end of the last ice age.

During this time interval the climate record from Greenland indicates alternating warm and cold periods lasting a few hundred to a few thousand years.  In California the chemical composition of the stalagmite measured over the same time period indicates that during the Greenland warm periods California became drier while Greenland cold periods corresponded with a wetter California.

How do you find this out? Of major interest are the variations in the oxygen isotopes and to a lesser extent the carbon isotope composition of the calcite in the stalagmite.

A graphic makes the geochemical life of oxygen isotopes easier to conceptualize.

Source: SAHRA

The ratio of two oxygen isotopes  18O and 16O are measured. The notation d18O  refers to the ratio of  18O to 16O. The more negative value of d18O   means enrichment in 16O. 16O being the lighter isotope is preferentially enriched in the vapor phase. So if it rains only a little then the precipitation is going to be enriched in 18O. If it rains a lot i.e. if most of the moisture in the air condenses then eventually the rains will become more and more enriched in 16O.

This is called the rain out or amount effect.

This oxygen in the rain eventually ends up in the mineral calcite precipitating on the floor of the cave. In the graphic above substitute initial precipitation and later precipitation taking place in different places to less rain and more rain taking place at the same location. 

Drier conditions will result in the mineral calcite that makes up the stalagmite growing from relatively 18O enriched water (elevated d18O ) and wetter periods will result in growth from relatively 16O enriched waters (depleted d18O).   These changing values are encoded in the calcite growth bands of the stalagmite. The scientists have found with disturbing implications for future California climate that in the past, a decline of ice sheets and warmer climate resulted in a drier California. History is giving us a warning about the expected rainfall patterns over California.

A quick note on carbon isotopes. Here two isotopes 13C and 12C are measured. Organic carbon is enriched in the lighter isotope because plants preferentially take up the lighter isotope during photosynthesis. During wet periods when the ground above the cave roof supports a lot of vegetation, the water seeping through the vegetation will incorporate a lot of the lighter isotope. During dry periods the water seeping through the cave roof will have relatively less of the lighter isotope. So dry periods will have an elevated d13C value (ratio of 13C and 12C).

So rhythmic deposition or precipitation of carbonate cycles over a wide range of time scales gives us different types of information about earth processes.

Cycles deposited over tens of thousands of years in marine basins tell us about either external controls on sea-level rise and fall like the periodic changes in the earth axial tilt or orbital parameters. Or they tell us about local tectonics changes or other internal regulating mechanisms.

On a decadal scale, precipitation cycles of calcite in stalagmites, may tell us about changing rainfall patterns and warn us about future droughts and water shortages.

Occasionally they may even give us insights into social and cultural upheavals such as the rise and fall of Chinese dynasties. Check out this finding. Its uses the same isotope principles from cave deposits to unravel Chinese climate history over the last thousand years or so and its impact on the Tang, Yuan and Ming dynasties in China. 

None of these press releases though have actually explained the isotope effect.

Which kind of irritated me and prompted this post.

Sunday, November 22, 2009

Israel -Jordan Border: Rodents Too Behave Differently

This from a Science Daily press release on the differences in ecosystems and animal behavior across the Israeli Jordanian border :

....the differences between Israel and Jordan are primarily in the higher level of agriculture and the higher number of agricultural farms in Israel as opposed to Jordan's agriculture that is primarily based on nomadic shepherding and traditional farming. The agricultural fields on the Israeli side of the border not only create a gulf between habitats and thereby cause an increase in the number of species in the region, but they also hail one of the most problematic of intruders in the world: the red fox. On the Jordanian side, the red fox is far less common, so that Jordanian gerbils can allow themselves to be more carefree. The higher reproduction rate of ant lions on Israel's side is also related to the presence of another animal: the Dorcas gazelle. This gazelle serves as an "environmental engineer" of a sort, as it breaks the earth's dry surface and enables ant lions to dig their funnels. The Dorcas gazelle is a protected animal in Israel, while hunting it in Jordan is permitted and compromises the presence of the Jordanian ant lions' soil engineers.

Important lessons for conservation here.

Wednesday, November 18, 2009

Speeding Up Mineral Reactions To Fight Global Warming

The more familiar method of carbon dioxide sequestration involves capturing and pumping the gas into underground reservoirs where geological traps that have sealed natural gas for millions of years will serve to lock captured CO2 for eons as well.

Nature has published a paper by Jürg M. Matter and Peter B. Kelemen that proposes another method of CO2 sequestration, locking CO2 as carbonate minerals by reaction with a host rock.

Anthropogenic greenhouse-gas emissions continue to increase rapidly despite efforts aimed at curbing the release of such gases. One potentially long-term solution for offsetting these emissions is the capture and storage of carbon dioxide. In principle, fluid or gaseous carbon dioxide can be injected into the Earth's crust and locked up as carbonate minerals through chemical reactions with calcium and magnesium ions supplied by silicate minerals. This process can lead to near-permanent and secure sequestration, but its feasibility depends on the ease and vigour of the reactions. Laboratory studies as well as natural analogues indicate that the rate of carbonate mineral formation is much higher in host rocks that are rich in magnesium- and calcium-bearing minerals. Such rocks include, for example, basalts and magnesium-rich mantle rocks that have been emplaced on the continents. Carbonate mineral precipitation could quickly clog up existing voids, presenting a challenge to this approach. However, field and laboratory observations suggest that the stress induced by rapid precipitation may lead to fracturing and subsequent increase in pore space. Future work should rigorously test the feasibility of this approach by addressing reaction kinetics, the evolution of permeability and field-scale injection methods.

The advantage here is that the gas is converted into a solid phase and so exists in a more stable form. The principle may be sound but I'm going to think out aloud on bridging the very long distance between scientific possibility and its practical realization in the field for a country like India.

First come the political and economic issues with a scheme of this nature. Those hurdles are immense. India's stated position is of no mandatory limits on emissions, so there is no political urgency in examining CO2 sequestration projects like this one. And this method is going to be expensive as well. Transporting CO2 from emission points to suitable storage sites and then drilling and pumping gas in hard rock ain't going to come cheap. It might work if the price of emitting CO2 is very high. But under the current scenario in India with no limits or penalties on emissions there will be no economic incentives for polluters to even explore a scheme like this.

Besides, there are other urgent practical matters that need to be carefully thought out before rock masses can be given out for CO2 storage.

There is no problem in India finding a suitable host rock. In Maharashtra and adjoining states of Madhya Pradesh, Andhra Pradesh there is half a million square km of Deccan Basalts, a rock rich in magnesium and calcium that will provide plenty of reaction surface and storage volume. This potential reservoir is up to 2 km thick in the central portions and along the western ghats. Other areas of the country too have mafic igneous rocks of the right composition that may extend to even deeper crustal levels.

However... where do you drill and store and to what depth before the project becomes too expensive?...

A crustal thickness of up to 1 km underlying cultivated areas must be kept untouched only for groundwater storage. That may seem excessive since groundwater is extracted mostly from the upper few tens to a hundred feet or so. But the Deccan Basalts and other mafic crystalline rocks have deeper aquifers too. Already these are being exploited by groundwater bore-wells that are reaching a few hundred meters in many parts of the country as demand for the groundwater increases.

Water in these crystalline rocks is stored and moves along fractures and cracks. Fracture systems in these rock masses penetrate to great depths and must be kept open if the rock is to act as an effective aquifer.  The danger is that gas pumped to depths even greater than 1 km may seep up through these deep penetrating fractures depositing carbonate minerals and plugging up the shallow permeability pathways for groundwater.

You could in principle go to very great depths say much more than 2 km, but at some point drilling through the hard crystalline rock will make the project uneconomic.

So then.... if the choice is between pumping CO2 into the crust to economically viable depths to keeping aquifers healthy, then the health of the aquifers must win out. Timely groundwater access improves crop yield and farmer income. The relation is direct and the benefits immediate. Risking reducing the  porosity and permeability of these rocks with carbonate minerals to attain a more nebulous benefit (for people who depend on groundwater) of lowered atmospheric CO2 content will be a suicidal course to take and I unfortunately mean that literally.  Groundwater irrigates a major share of cultivated areas and access to it offers the best chance of alleviating grinding farmer poverty in face of uncertain rains and lower crop yields due to increased temperatures.

So, no playing around with rock masses under cultivated areas...that might leave sections of the crust underlying wastelands, forests and urban areas as potential sites. Of these wastelands appear as the most promising sites in terms of the least political and civic resistance to such a project. This provided field experiments demonstrate the feasibility of this project and the political and economic conditions allow its implementation.

India's National Action Plan for Climate Change (15 MB) has very little to say about carbon sequestration. None of the eight missions or strategies meant to deal with climate change include carbon capture and sequestration.

It is under the political radar and it is expensive and India can best mitigate the effects of global warming by keeping the shallow crust fractured and permeable so as to act as an effective aquifer for groundwater.

My feeling is for India at least in the near term this method of preventing atmospheric CO2 buildup is a non-starter.

Thursday, November 12, 2009

Meteorite Impact Ended Banded Iron Formation Deposition

From the November issue of Geology:

Extraterrestrial demise of banded iron formations 1.85 billion years ago; John F. Slack and William F. Cannon

In the Lake Superior region of North America, deposition of most banded iron formations (BIFs) ended abruptly 1.85 Ga ago, coincident with the oceanic impact of the giant Sudbury extraterrestrial bolide. We propose a new model in which this impact produced global mixing of shallow oxic and deep anoxic waters of the Paleoproterozoic ocean, creating a suboxic redox state for deep seawater. This suboxic state, characterized by only small concentrations of dissolved O2 (~1 μM), prevented transport of hydrothermally derived Fe(II) from the deep ocean to continental-margin settings, ending an ~1.1 billion-year-long period of episodic BIF mineralization. The model is supported by the nature of Precambrian deep-water exhalative chemical sediments, which changed from predominantly sulfide facies prior to ca. 1.85 Ga to mainly oxide facies thereafter.

I don't have access to the full paper but if this holds up here is another example of how extraterrestrial matter has shaped the geological and biological evolution of earth.  A chance meteorite impact ends a prolonged process of iron oxide deposition and enables greater amounts of oxygen to accumulate in the oceans and eventually the atmosphere. That was a precursor for the evolution of more complex cell types like the eukaryotes.

Coincidentally in the October 29 issue of  Nature is another paper which hypothesizes that the earth was dry very early in its history and much of the earth's water and hence the ultimate source of the oceans has been derived from ice rich asteroid bombardment about 100 million years after the formation of the solar system. Science Daily has the summary.

Wednesday, November 11, 2009

Arctic: Carbon Sink Or Source?

The USGS has quite an informative press release via and a graphic depicting how warming will affect the physical structure of the soil and permafrost in the Arctic region resulting in the release of carbon dioxide and methane.

Image: Zina Deretsky, National Science Foundation

There is still some uncertainty whether warming will result in the Arctic being a net source of greenhouse gases in the short term. Example warming could extend the growing season and this extra plant growth and the migration of the tree line northwards could end up sequestering more carbon dioxide than before. However sustained thawing and release of trapped gases over several decades may eventually overwhelm this balance and result in the Arctic becoming a net source of greenhouse gases.

Interesting statistic: Currently the Arctic releases about 50 million tons of methane per year. That might increase to several times more in the years to come. Methane is a more potent greenhouse gas than carbon dioxide, about 23 times more effective in trapping heat than CO2 on a 100 year time scale, so Arctic warming effects are a real cause for worry.

Friday, November 6, 2009

You'll Understand Homeopathy If You Understand Einstein

....Homeopathy - can it get more stupid than this...?

Warning: Advanced degree in physics and chemistry required to follow this discussion:

Now you know why those white pills pack so much punch! They are literally powder kegs of energy.

Thursday, November 5, 2009

Isolating Nuclear Waste At Yucca Mountain

BLDGBLOG has an interview with Abraham Van Luik, a geoscientist with the U.S. Department of Energy.

Its a long interview about isolating nuclear waste. Yucca mountain and its geology feature prominently.

Definitely worth reading.

Teaching Human Evolution In Pakistan Can Be Dangerous

Kenneth Chang of New York Times has written an interesting summary on the teaching and acceptance of evolution across Muslim countries and among Muslim immigrants in many western nations.

Atomic physicist Pervez. A Hoodbhoy went through a dramatic moment while lecturing at a university in Pakistan:

Pervez A. Hoodbhoy, a prominent atomic physicist at Quaid-e-Azam University in Pakistan, said that when he gave lectures covering the sweep of cosmological history from the Big Bang to the evolution of life on Earth, the audience listened without objection to most of it. “Everything is O.K. until the apes stand up,” Dr. Hoodbhoy said.

Mentioning human evolution led to near riots, and he had to be escorted out. “That’s the one thing that will never be possible to bridge,” he said. “Your lineage is what determines your worth.”

Its scary that this took place not at some isolated madrassa but at a national university. Overall acceptance of evolution - especially human evolution - is low in Muslim countries. The technological advancement engulfing these countries is not necessarily paralleled by a more scientific mindset among citizenry. Religious beliefs are playing a large role in driving a wedge between the two. Turkey is a great example. Just 2-3 decades ago creationism was not a factor affecting science education in Turkey. Today, the influence of Islamic parties is greater in society, evolution teaching is diluted at the school level and creationist textbooks are influencing biology syllabus.

The article does not mention Muslims in India but I doubt if attitudes towards evolution are significantly different among Indian Muslims.

And I wonder what the break up would be according to educational level and how it compared to Hindus.

Monday, November 2, 2009

End Cretaceous: How Many Impacts? How Many Iridium Anomalies?

Looking over the recent GSA geoblogosphere page I was alerted to a presentation by Shankar Chatterjee and colleagues on the Shiva crater, a hypothetical impact crater that Chatterjee claims is of end Cretaceous age and is likely responsible along with the Deccan volcanism for the mass extinction. He suggests that the Chicxulub impact event in Mexico also timed to the end Cretaceous did not alone cause the mass extinction.

Here is the abstract. The talk apparently got a skeptical reception. Chatterjee envisions the following scenario. The meteor hit the Indian continental plate and maybe initiated rifting between Seychelles and India.

Source: Chatterjee- Proc 30th Int. Geol. Congr. Vol 26, pp - 31-54

The crater is now broken up along the rift. Part of the structure lies along the Indian west coast and part of it along the Seychelles margin.

The argument is at present based mostly on the geometry and structure of the basins and rifted margins matching what a meteorite hit will produce if it hit the crust at a  shallow angle from the southwest.

But according to what I have read so far there is little direct local evidence of this being an impact crater. There is no core recovered from the supposed impact site and so no information available on whether the features that are seen at the Chicxulub crater in Mexico i.e. impact melt rock, high pressure quartz phases, chaotic breccia,  tsunami deposits and so on are present at this site too.  Also Chatterjee has not given as far as I know a convincing account of why various models of continental rifting, flood volcanism and denudational isostacy are inadequate explanations of the continental margin geology of west India and the Seychelles.

Yet, end Cretaceous always fascinates.

Chatterjee think this impact occurred either simultaneously with the Chicxulub impact or it post-dates the impact in Mexico. I found this view point very interesting for the response it drew from Gerta Keller who is a strong proponent of the theory that the Chicxulub impact was not the primary cause of the K-T extinction. She is pushing for the Deccan volcanics being the real culprit.

Keller has been quoted rejecting Chatterjee's theory, saying there is no evidence for such an impact in Indian deposits. But she leaves a big question unanswered, one that is prompted by her own work and theory.

How do you explain the iridium anomaly associated with many K-T boundary sediments?

Keller contends that the Chicxulub impact took place about 300,000 years before the K-T boundary (read the debate here). The iridium anomaly at the K-T boundary is widely acknowledged - including Keller - to be of meteorite impact origin. In a previous paper she has proposed the possibility of multiple impacts to account for this iridium anomaly, even naming the Shiva crater as a potential candidate for a second impact site.

Now she seems to be against the Shiva impact theory and cites a lack of local evidence in Indian continental deposits for the Shiva impact event, but see....let me add an intriguing possibility... the Deccan volcanics complicate the stratigraphy and everything depends on the exact timing of the impact.  If the impact did not coincide with deposition of sediments and instead took place during eruptions, then all that evidence could be lost..obliterated within the lava flows. At end Cretaceous in the Indian continent these events, volcanism and sedimentation phases, alternated over periods of tens to a few hundred thousand years, and how can one be sure if the impact didn't coincide with a period of non-deposition and volcanism?

Given Keller's strong stance that there was no single smoking gun for the K-T mass extinction its a little bizarre that she is now dissing Chatterjee's hypothesis so readily and apparently rooting for the Deccan volcanics as the smoking gun!

So one impact definitely but how many more? ...still unanswered..

The most sympathetic view of Chatterjee's hypothesis was from The Economist who suggested that if the Shiva impact post-dates the Chicxulub impact, there should be two stratigraphically separated iridium enriched layers. The article pointed out to the Anjar deposits in west India as a site which might contain these two iridium anomalies.

I followed up on the work on the Anjar sediments. These are lacustrine (lake deposits)  inter-trappean sediments i.e. they are sandwiched between Deccan volcanic layers. Magnetostratigraphy indicates the sediments to be deposited in the latest Maastrichtian (the uppermost division of the Cretaceous) within the magnetic zone 29R (R- reversed magnetic field), which contains the K-T boundary at many locales. There are three iridium enriched layers each occurring below a clay rich bed.

Sounds like an ideal candidate in support of multiple impacts.

...Except there seems to be no evidence that these iridium anomalies are due to meteorite impacts or that they encompass the K-T boundary. Geochemical analysis shows that the section lacks the negative carbon isotope excursion that is characteristic of the K-T event found in terrestrial deposits elsewhere (see here). There is evidence in the form of high temperature low pressure cristobalite ( a variety of quartz) in the clay beds associated with the iridium (see here) that these could represent leaching and enrichment from a alkali volcanic tuff. Impact deposits should contain high pressure varieties of quartz.

Early alkali Deccan volcanics along the western margin of the rifted Indian continent are known to be enriched in iridium (see here) and leaching and secondary enrichment could form concentrated iridium layers.

Finally the sediment above the iridium enriched layers contain dinosaur egg shells and late Cretaceous ostracods (see here). Along with sedimentological features this indicates that the iridium layers at Anjar  predate the K-T extinction significantly and were formed in the early part of magnetic cron 29R.

It does not appear that these particular iridium layers are a result of the Shiva impact if it did occur. These deposits are well within the impact fallout zone for the Shiva impact and should have contained direct impact evidence like shocked quartz.

So....looks like many iridium layers but not all of them associated with the K-T boundary or with meteor impacts. 

The Chicxulub impact and the Deccan volcanism overlapped. The stratigraphy of end Cretaceous is going to be messy and it won't be possible to sort out events that took place with a few tens of thousands of years of each other and tie them to either an impact or volcanism. If there was a second impact its record could easily be amalgamated with that of volcanism and very hard to resolve within Indian continental deposits as an independent event .

Direct drilling and study of the recovered core from the Bombay High basin basement which is supposed to be the impact site should decide the issue

...if and when that data comes around.

My head is reeling with these details and nuances. I'll leave readers to sort through the evidence.