Mercury Increased in Three Different Spikes From Deccan Traps Across the K-T/K-Pg Boundary

Mercury enrichment and Hg isotopes in Cretaceous–Paleogene boundary successions: Links to volcanism and palaeoenvironmental impacts

Authors:

Sial et al

Abstract:

We investigate the use of Hg as a proxy for volcanism by studying four distal and two proximal sections in relation to the Deccan volcanic center, straddling the Cretaceous–Paleogene (KPg) boundary at (a) Højerup (Denmark), Bottaccione and Padriciano (Italy), (b) Meghalaya and Jhilmili (India), and (c) Bajada del Jagüel (Argentina). Hg sequestration by organic matter results in constant Hg/TOC ratio and linear correlation between Hg content of the sediments and total organic carbon (TOC).

Elevated Hg concentrations that deviate from this linear relationship represent most likely true Hg anomalies and these notable Hg/TOC spikes (all TOC <1 al="" also="" and="" are="" at="" between="" biozone="" bottaccione="" boundary="" cf2="" clear="" correlation="" foraminiferal="" found="" h="" hg="" i="" ii="" iii="" in="" jerup="" jhilmili="" kpg="" meghalaya="" no="" occurs="" p1a="" planktic="" section.="" sections="" spike="" sub="" subzone="" the="" within="">2

O₃ exists in any of the studied sections. The Hg anomalies probably result from strong volcanic episodes of the Deccan phase-2 (started 250 kyr before the KPg boundary and lasted for 750 kyr) that exhaled sulfuric aerosols, carbon dioxide and other toxic agents which reached a critical threshold, represented in true Hg enrichments in the paleoenvironments. The possibility that Hg enrichments resulted from anoxia scavenging on the seafloor and penetration downward into sediments is not supported in the stratigraphic record of Mo/Al ratios redox proxy.<1 250="" 750="" a="" aerosols="" agents="" al2o3="" also="" and="" anomalies="" anoxia="" any="" are="" at="" before="" between="" biozone="" bottaccione="" boundary="" br="" carbon="" cf2="" clear="" correlation="" critical="" deccan="" dioxide="" downward="" enrichments="" episodes="" exhaled="" exists="" for="" foraminiferal="" found="" from="" h="" hg="" i="" ii="" iii="" in="" into="" is="" jerup="" jhilmili="" kpg="" kyr="" l="" lasted="" meghalaya="" mo="" no="" not="" occurs="" of="" on="" other="" p1a="" paleoenvironments.="" penetration="" phase-2="" planktic="" possibility="" probably="" proxy.="" ratios="" reached="" record="" redox="" represented="" result="" resulted="" scavenging="" seafloor="" section.="" sections.="" sections="" sediments="" spike="" started="" stratigraphic="" strong="" studied="" subzone="" sulfuric="" supported="" that="" the="" threshold="" toxic="" true="" volcanic="" which="" within="">

<1 250="" 750="" a="" aerosols="" agents="" al2o3="" also="" and="" anomalies="" anoxia="" any="" are="" at="" before="" between="" biozone="" bottaccione="" boundary="" br="" carbon="" cf2="" clear="" correlation="" critical="" deccan="" dioxide="" downward="" enrichments="" episodes="" exhaled="" exists="" for="" foraminiferal="" found="" from="" h="" hg="" i="" ii="" iii="" in="" into="" is="" jerup="" jhilmili="" kpg="" kyr="" l="" lasted="" meghalaya="" mo="" no="" not="" occurs="" of="" on="" other="" p1a="" paleoenvironments.="" penetration="" phase-2="" planktic="" possibility="" probably="" proxy.="" ratios="" reached="" record="" redox="" represented="" result="" resulted="" scavenging="" seafloor="" section.="" sections.="" sections="" sediments="" spike="" started="" stratigraphic="" strong="" studied="" subzone="" sulfuric="" supported="" that="" the="" threshold="" toxic="" true="" volcanic="" which="" within=""> Hg isotopes were analyzed in samples from all KPg boundary sections in this study and from Bidart, France, the latter for comparison. Hg isotopes yielded δ202Hg values ranging from −1 to −2‰ and Δ201Hg signatures from 0 to 0.05‰ (spike II in Højerup, Bottaccione and Meghalaya KPg boundary layers) consistent with volcanic emission of Hg (0 to −2‰). The δ202Hg in spike I in Meghalaya and Padriciano and spike III in Jhilmili is consistent with volcanic emission of Hg. Two samples from Bajada del Jagüel and four from Bidart, however, display isotope signals compatible with volcanic emission/chondrite Hg. The results of three other samples are characteristic for reworked sediment, soil and/or peat. Most of the data show small positive Δ201Hg, in favor of long-term atmospheric transport prior to deposition, supporting a volcanic origin for the Hg. The present study broadens, therefore, the potential use of Hg as stratigraphic marker and, moreover, confirms that in the critical KPg transition, Hg was enriched in paleoenvironments at three distinct stages during the Deccan phase-2.
<1 250="" 750="" a="" aerosols="" agents="" al2o3="" also="" and="" anomalies="" anoxia="" any="" are="" at="" before="" between="" biozone="" bottaccione="" boundary="" br="" carbon="" cf2="" clear="" correlation="" critical="" deccan="" dioxide="" downward="" enrichments="" episodes="" exhaled="" exists="" for="" foraminiferal="" found="" from="" h="" hg="" i="" ii="" iii="" in="" into="" is="" jerup="" jhilmili="" kpg="" kyr="" l="" lasted="" meghalaya="" mo="" no="" not="" occurs="" of="" on="" other="" p1a="" paleoenvironments.="" penetration="" phase-2="" planktic="" possibility="" probably="" proxy.="" ratios="" reached="" record="" redox="" represented="" result="" resulted="" scavenging="" seafloor="" section.="" sections.="" sections="" sediments="" spike="" started="" stratigraphic="" strong="" studied="" subzone="" sulfuric="" supported="" that="" the="" threshold="" toxic="" true="" volcanic="" which="" within="">

<1 250="" 750="" a="" aerosols="" agents="" al2o3="" also="" and="" anomalies="" anoxia="" any="" are="" at="" before="" between="" biozone="" bottaccione="" boundary="" br="" carbon="" cf2="" clear="" correlation="" critical="" deccan="" dioxide="" downward="" enrichments="" episodes="" exhaled="" exists="" for="" foraminiferal="" found="" from="" h="" hg="" i="" ii="" iii="" in="" into="" is="" jerup="" jhilmili="" kpg="" kyr="" l="" lasted="" meghalaya="" mo="" no="" not="" occurs="" of="" on="" other="" p1a="" paleoenvironments.="" penetration="" phase-2="" planktic="" possibility="" probably="" proxy.="" ratios="" reached="" record="" redox="" represented="" result="" resulted="" scavenging="" seafloor="" section.="" sections.="" sections="" sediments="" spike="" started="" stratigraphic="" strong="" studied="" subzone="" sulfuric="" supported="" that="" the="" threshold="" toxic="" true="" volcanic="" which="" within="">

Dr Gerta Keller Trumpets a Charge: Multiple Papers About Deccan Traps and the the K-Pg/KT Mass Extinction

Dr Keller has been leading an insurgency against the idea the Chicxulub impact was the underlying event that brought about the Cretaceous-Paleogene (K-Pg) Mass Extinction (formerly the KT Extinction).  This is rather contrarian to the generally accepted theory.  

The journal Paleaeogeography, Palaeoclimateology, Palaeoecology has an issue dedicated to how volcanic eruptions impacted (see what I did there?) past mass extinctions (or didn't as it may be).  That's the reason for all the volcano related posts this past week.  

Dr Keller's 'team' has a large number of articles in the publication.  Rather than do my traditional one-paper-per-post method, I am going to do a list here of each.  The reason being I don't buy her hypothesis that the Deccan Traps caused the mass extinction during the Maastrichtian.  I've posted as much since the evidence comparing mass extinctions already strongly tied to volcanic eruptions is rather different from what is present for the K-Pg Extinction.  I wrote as much in the Stop Dreaming post.  

That said, I am sure the Deccan Traps did cause some environmental impacts (see!), but they are insufficient to have caused the mass extinction.

While I admire tenacity, I think she has crossed over to religion.  However, rather than ignoring the recent papers, since they are peer reviewed papers in a respected journal, I am going to link to each here with a very short title and a description of each and a short comment.

Upheavals during the Late Maastrichtian: Volcanism, climate and faunal events preceding the end-Cretaceous mass extinction. Keller et al present their case the Maastrichtian Cretaceous was a time a climate upheaval and ecological degradation caused by the Deccan Traps with the ecology dominated by opportunistic, disaster taxa.  My comment: T rex.  Too big.

A multi-proxy approach to decode the end-Cretaceous mass extinction. Punekar argues there are multiple bits of evidence suggest the Deccan Traps caused the mass extinction at the K-Pg, especially the release of 12 to 28 teratons of carbon. Comment: Unfortunately, in the same journal edition, the OAE1 from the Early Aptian Cretaceous is stated to have been caused by the release of 20 teratons of carbon. The OAE1 was a mass extinction but a very, very mild one. Additionally, in a surprise result, calciferous plankton actually grow MORE with higher carbon dioxide levels, not less as was expected.

Tracing acidification induced by Deccan Phase 2 volcanism. Font et al ID some potential evidence of aquatic acidification at the end of the Deccan 2 Eruptions. These are located in India. Comment: Best to check to see how global this was before making a claim of global occurrence.

Palaeoenvironmental changes associated with Deccan volcanism, examples from terrestrial deposits from Central India. Fantasia et al present evidence of local impacts of the Deccan Traps caused stressed environment from India. Their claim is the DT caused environmental stress and could have made the Maastrichtian fauna vulnerable to a mass extinction at the end of the Cretaceous. Comment: Possible, but this could be completely local. Mount ST Helens did enormous damage locally, but only modestly globally.

Climatic fluctuations and sea-surface water circulation patterns at the end of the Cretaceous era: Calcareous nannofossil evidence. Thibault et al make the argument surface plankton became stressed and lost species during the proposed Deccan Warmings. However, 100k to 140k years before the K-Pg Boundary, the plankton had regained their species richness. Comment: Interesting. Given the problems of IDing what forminifers are what species I'd be cautious. The recovery would suggest whatever stress caused by the DTs had ended though.

Flood Basalts Don't Cause Mass Extinctions Through Sulphuric Acid

Selective environmental stress from sulphur emitted by continental flood basalt eruptions

Authors:

Schmidt et al

Abstract:

Several biotic crises during the past 300 million years have been linked to episodes of continental flood basalt volcanism, and in particular to the release of massive quantities of magmatic sulphur gas species. Flood basalt provinces were typically formed by numerous individual eruptions, each lasting years to decades. However, the environmental impact of these eruptions may have been limited by the occurrence of quiescent periods that lasted hundreds to thousands of years. Here we use a global aerosol model to quantify the sulphur-induced environmental effects of individual, decade-long flood basalt eruptions representative of the Columbia River Basalt Group, 16.5–14.5 million years ago, and the Deccan Traps, 65 million years ago. For a decade-long eruption of Deccan scale, we calculate a decadal-mean reduction in global surface temperature of 4.5 K, which would recover within 50 years after an eruption ceased unless climate feedbacks were very different in deep-time climates. Acid mists and fogs could have caused immediate damage to vegetation in some regions, but acid-sensitive land and marine ecosystems were well-buffered against volcanic sulphur deposition effects even during century-long eruptions. We conclude that magmatic sulphur from flood basalt eruptions would have caused a biotic crisis only if eruption frequencies and lava discharge rates had been high and sustained for several centuries at a time.

Did the Chicxulub Impact Affect the Deccan Traps Eruptions?

State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact

Authors:

Renne et al

Abstract:

Bolide impact and flood volcanism compete as leading candidates for the cause of terminal-Cretaceous mass extinctions. High-precision 40Ar/39Ar data indicate that these two mechanisms may be genetically related, and neither can be considered in isolation. The existing Deccan Traps magmatic system underwent a state shift approximately coincident with the Chicxulub impact and the terminal-Cretaceous mass extinctions, after which ~70% of the Traps' total volume was extruded in more massive and more episodic eruptions. Initiation of this new regime occurred within ~50,000 years of the impact, which is consistent with transient effects of impact-induced seismic energy. Postextinction recovery of marine ecosystems was probably suppressed until after the accelerated volcanism waned.

Could the Chicxulub Impact Cause the Deccan Traps?

The asteroid that slammed into the ocean off Mexico 66 million years ago and killed off the dinosaurs probably rang the Earth like a bell, triggering volcanic eruptions around the globe that may have contributed to the devastation, according to a team of University of California, Berkeley, geophysicists.

Specifically, the researchers argue that the impact likely triggered most of the immense eruptions of lava in India known as the Deccan Traps, explaining the "uncomfortably close" coincidence between the Deccan Traps eruptions and the impact, which has always cast doubt on the theory that the asteroid was the sole cause of the end-Cretaceous mass extinction.

"If you try to explain why the largest impact we know of in the last billion years happened within 100,000 years of these massive lava flows at Deccan ... the chances of that occurring at random are minuscule," said team leader Mark Richards, UC Berkeley professor of earth and planetary science. "It's not a very credible coincidence."

Richards and his colleagues marshal evidence for their theory that the impact reignited the Deccan flood lavas in a paper to be published in The Geological Society of America Bulletin, available online today (April 30) in advance of publication.

While the Deccan lava flows, which started before the impact but erupted for several hundred thousand years after re-ignition, probably spewed immense amounts of carbon dioxide and other noxious, climate-modifying gases into the atmosphere, it's still unclear if this contributed to the demise of most of life on Earth at the end of the Age of Dinosaurs, Richards said.

"This connection between the impact and the Deccan lava flows is a great story and might even be true, but it doesn't yet take us closer to understanding what actually killed the dinosaurs and the 'forams,'" he said, referring to tiny sea creatures called foraminifera, many of which disappeared from the fossil record virtually overnight at the boundary between the Cretaceous and Tertiary periods, called the KT boundary. The disappearance of the landscape-dominating dinosaurs is widely credited with ushering in the age of mammals, eventually including humans.

He stresses that his proposal differs from an earlier hypothesis that the energy of the impact was focused around Earth to a spot directly opposite, or antipodal, to the impact, triggering the eruption of the Deccan Traps. The "antipodal focusing" theory died when the impact crater, called Chicxulub, was found off the Yucatán coast of Mexico, which is about 5,000 kilometers from the antipode of the Deccan traps.

link.

paper link.

Deccan Traps Geochronologically Synchronous With KT Extinction

U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction

Authors:

Schoene et al

Abstract:

The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply U-Pb zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that greater than 1.1 million km3 of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.

Using Mercury Isotopes to Determine Volcanic or Meterorite Source for Mass Extinctions

High-resolution Hg chemostratigraphy: A contribution to the distinction of chemical fingerprints of the Deccan volcanism and Cretaceous–Paleogene Boundary impact event

Authors:

Sial et al

Abstract:

There is a renewed interest in volcanism as the major trigger for dramatic climatic changes at the Cretaceous–Paleogene transition (KTB), which were accompanied by a decrease in biodiversity and mass extinction. We have used Hg contents as proxy for volcanic activity at the classical localities of Gubbio (Italy) and Stevns Klint (Denmark) where the KTB layer is easily recognizable, and at a near-complete succession exposed at the Bajada del Jagüel locality in the Neuquén Basin, Argentina. These three localities display similar δ13Ccarb trends with markedly negative excursion at the KTB layer. Bulk-rock oxygen isotopes yielded similar pathways across the KTB layers in these localities and, if considered near-primary, the negative δ18O excursion at the KTB in Gubbio and Bajada del Jagüel suggest warming temperatures during this transition, whereas the negative excursion immediately followed by positive one at Stevns Klint points to a cycle of warm followed by colder climate. At Stevns Klint, Hg contents reach 250 ng g− 1 within the KTB layer (Fiskeler Member) and 45 ng.g− 1 at 1.5 m above that, while within the Scaglia Rossa Formation at Gubbio, three Hg peaks across the KTB are observed, one of them within the KTB layer (5.3 ng g− 1). Hg shows several peaks across the KTB in the Neuquén Basin, with up to 400 ng g− 1 in the Jagüel Formation. The phenomena that caused dramatic changes at the KTB probably expelled huge amounts of Hg into the atmosphere as recorded by these high Hg levels. A co-variation between Hg and Al2O3 in the studied sections suggest that Hg is adsorbed onto clays. Hg concentrations and also Hg isotopes are perhaps a powerful tool in the assessment of the role of volcanic activity during extreme climatic and biotic events, and in assessing the role of meteorite impact versus volcanism as the predominant cause of past global catastrophes and mass extinction.

Sulfur Very Important for Volcanicly Driven Mass Extinctions?

Microanalyses link sulfur from large igneous provinces and Mesozoic mass extinctions

Authors:

Callegro et al

Abstract:

Volcanic gases can have devastating impacts on Earth's environment and life. However, measurement of volatile elements in prehistoric magmas is challenging. We present a new method for determining sulfur contents in magmas using its concentrations in clinopyroxenes and an experimentally determined crystal-melt partition coefficient. Using this method we compared magmatic sulfur contents in the Paraná-Etendeka large igneous province (LIP; South America) and two other similarly sized LIPs, the Central Atlantic magmatic province (CAMP) and the Deccan Traps (India). We found that the CAMP and Deccan Traps, both associated with major extinction events, contained high magmatic sulfur concentrations, up to 1900 ppm. Conversely, the Paraná-Etendeka LIP, lacking significant environmental effects, had substantially lower magmatic sulfur concentrations, less than 800 ppm.

They ought to look at the Permian Extinction/Siberian Traps.  I am a bit surprised they did not.  And, again, the Deccan Traps have dinosaur fossils below, between and above the lava flows.

Did the Himalayas Start With the Deccan Traps?

Latest Cretaceous Himalayan Tectonics: Obduction, Collison Or Deccan-Related Uplift?

Authors:

Garzanti et al

Abstract:

Diverging interpretations and incompatible scenarios have been proposed for the early stages of Himalayan history. Numerous researchers have postulated that northern India was involved in ophiolite obduction, arc-continent, or continent-continent collision during the Late Cretaceous or Early Paleocene, but firm geological evidence was never produced. In this article we argue against orogenic events predating the Late Paleocene, when the Neotethys Ocean was still open. The Tethys Himalayan sedimentary record testifies to anorogenic evolution, primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of Deccan lavas and eventually followed by thermal subsidence. Major stratigraphic gaps in pelagic sediments suggest that such tectono-magmatic episode started to affect the base of the Indian Plate in the Campanian or possibly even in the Santonian, 10 to 20 Ma before the climax of Deccan flood-basalt eruptions. The abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the Indian subcontinent during the Maastrichtian was followed by progradation of coastal quartzarenites along the northern Indian margin in the Early Paleocene. Sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose. Felsitic volcanic rock fragments and Cr-spinels, many of which with the same geochemical fingerprint as Deccan spinels and newly found throughout the Maastrichtian to Danian succession, resisted the combined effect of subequatorial weathering and subsequent diagenesis, and testify that detritus from Deccan basalts reached the Indian passive margin as far as South Tibet. At the close of the Early Paleocene India drifted away from the Seychelles block, and thermal subsidence led to widespread carbonate deposition along the Tethys Himalaya. This article illustrates how mega-events of magmatic upwelling followed by lithospheric cooling may control passive-margin sedimentation and stratigraphic patterns, as occurred in northern India first in the Early Cretaceous and next in the latest Cretaceous/Paleocene.

Gerta Keller Strikes Back: Maastrichtian Cretaceous a High Stress Environment due to Deccan Vulcanism

Late Maastrichtian–early Danian high-stress environments and delayed recovery linked to Deccan volcanism

Authors:

Punekar et al

Abstract:

Deccan volcanism occurred in three intense phases of relatively short duration: phase 1 spanning the paleomagnetic chron C30r/C30n boundary (planktic foraminiferal CF4), phase 2 in the latest Maastrichtian C29r (zones CF1–CF2), and phase 3 in the early Danian C29n (P1b). This study explores the nature of paleoenvironmental changes correlative with the three volcanic phases in central Egypt and the Sinai based on planktic foraminifers, stable carbon and oxygen isotopes.

Results show that high-stress assemblages dominated by Guembelitria blooms are prominent in, but not exclusive to, all three volcanic phases. These blooms are well known from the aftermath of this mass extinction in zones P0–P1a, the intertrappean interval between volcanic phases 2 and 3. Guembelitria blooms in CF4 (phase 1) are relatively minor (less than 45% ) although they comprise a substantial component of the planktic foraminiferal assemblages. Maximum Guembelitria blooms (greater than 80% of the total assemblage) are observed in CF1, which spans the last 160 ka of the Maastrichtian marked by rapid global climatic warming and cooling correlative with phase 2. Major Guembelitria blooms (50–75%) are also observed in P1b, which is marked by climate warming (Dan-C2 event) and a major negative carbon isotope excursion correlative with phase 3. This high-stress event precedes full marine biotic recovery after the mass extinction.

Sulfur and Chlorine in Late Cretaceous Deccan Magmas and Eruptive Gas Release

(kewl pic, huh?)

Large-volume pahoehoe lava flows erupted 67 to 65 million years ago, forming the Deccan Traps, India. The impact of these flood basalt eruptions on the global atmosphere and the coeval end-Cretaceous mass extinction has been uncertain. To assess the potential gas release from this volcanism, we measured sulfur and chlorine concentrations in rare glass inclusions inside crystals and on glassy selvages preserved within lavas. Concentrations range from ~1400 parts per million of S and 900 parts per million of Cl in inclusions down to a few hundred parts per million in the lava. These data indicate that eruptions of Deccan lavas could have released at most 0.103 weight % of S, yielding up to 5.4 teragrams of SO2 per cubic kilometer of lava. A more conservative estimate is 0.07 weight % of S and 0.04 weight % of Cl, yielding 3.5 teragrams of SO2 and 1 teragram of HCl for every cubic kilometer of lava erupted. The flows were very large in volume, and these results imply that huge amounts of S and Cl gases were released. The environmental impact from even individual eruptions during past flood basalt activity was probably severe.

hm. Another Vulcanists Strike Back Paper. Now the problem I have is not with the science wrt the geochemistry. It looks pretty good as far as I can tell. They did some very good work. This is the sort of science that needs to be done to test theories. That said, the only caveat is that they need to have it verified by another team. Like all scientific discoveries, it needs to be tested. otherwise, we would end up with a lot more fullerene at the PT Boundary embarrassments. That said, there needs to be more than merely sampling the lava flows from the Deccan Traps to back up this claim. There are two ways to test this idea - that out gassing from the Deccan Traps caused climate problems, namely erratic cooling, and acid rain.

The first one is to go through the isotope ratios from the time period that the Deccan Traps are supposed to be erupting. There are multiple isotopes that can be used for determining whether or not the Cretaceous had an erratic climate in terms of temperature changes. The most famous is the ratios of oxygen isotopes. It should be noted that there needs to be isotopic shifts that are chronogeologically specific to the time period in question that support their hypothesis. IIRC, there was no shift in the isotopes that in that time frame. At least the ones wrt climate. I'll verify tonight with my copy of Mass Extinctions and Their Aftermath (every extinction in there has a nice discussion of the isotope ratios and shifts thereof).

It should be noted that one of the traditional bits of evidence that the climate was cooling was that the fact that the Cretaceous inland seas receded (the "Oceans of Kansas"). If you look at a temperature graph across the KT Boundary there's not much shift at least under the current research. Furthermore, the recession of the inland seas now looks like it may be because of the expansion of the Atlantic...something that was not caused by any climate changes (though the Atlantic did change the climate!)

The second test is to check whether or not there is evidence of a sulfur induced "impact" globally (and I don't mean an asteroid smashing either). Originally, this was suggested as one of the kill mechanisms for the asteroid/comet impact theory: the Yucatan has strata that are very high in sulfur content and the vaporization of that rock would have dumped all that sulfur into the atmosphere and came back down as acid rain. Now, in this case, the vulcanists are stating the Deccan Traps could have done this as well since the evidence is insanely stacked against the KT Extinction being anything like the PT Extinction where the PT has been pretty much sown up as being caused volcanically (please see my post, Stop Dreaming). In either case, if there was acid rain, there ought to be evidence of either chemical weathering or ph-sensitive species die offs.

At this point I am unaware of anything that has been published about chemical weathering related to sulfuric acid at the KT boundary or the globally distributed sections chronospecifically associated with the Deccan Traps. I could be wrong and perhaps some readers could point me to papers that might have been done taht I haven't seen. I don't believe that this has been looked at yet. However, I could be very, very wrong. However, should there be evidence of it, it's not proof that either the impact or the eruptions would have been the cause. The specific ratios of sulfur isotopes will have to be examined and compared with the ones from the Yucatan and those that the team that produced this paper have resolved. Since the Yucatan's sources of sulfur ought to be different and laid down over a longer time period than during the Deccan Traps, there should be a different ratio. Whichever matches the that evidence at the KT boundary would probably be the source...and that would be evidence of which caused the die off.

On the other hand, there ought to be a lot of die offs of critters that are specifically sensitive to changes in water pH. Freshwater fish and amphibians ought to have been disproportionately whacked by anything that dumped tons of sulfuric acid into their habitats. That would cascade up the food chain and munge anything associated with freshwater. Yet...yet...this didn't happen as far as we can tell. If you were associated with the brownwater ecosystems you largely marched through the KT Extinction in better shape than anyone else. This would suggest that the brown water ecosystems continued to have nutrient influxes even when the terrestrial environment had been devastated and whatever caused the die-off on land didn't effect the brown water ecosystem. Or couldn't. That would probably rule out a sulfuric acid kill mechanism from either model.

So where does this leave us? Probably not much different than we were before. There has been some nice geochemical work about the outgassing of the Deccan Traps. This is scientifically good and useful research. In reading the paper and the extrapolations that the vulcanists involved are trying to connect the Deccan Traps with climatic and biotic effects that are quite contrary to the one extinction event that has been linked to vulcanism.

In fact, these effects have been proposed by the impactists. That thought is...interesting. hrm.

As a parting thought, I have to wonder if they could extract out information about the carbon isotopes frm that same source as they did for the chlorine and sulfur. Just a thought.