That Day 66 Million Years Ago

Just wanted to share this abstract of a paper detailing an outcrop from Baja California, Mexico, which preserves heterogeneous deposits resulting from the Chicxulub meteorite impact 66 million years ago. 

We report K-Pg-age deposits in Baja California, Mexico, consisting of terrestrial and shallow marine materials re-sedimented onto the continental slope, including corals, gastropods, bivalves, shocked quartz grains, an andesitic tuff with a SHRIMP U-Pb age (66.12 ± 0.65 Ma) indistinguishable from that of the K-Pg boundary, and charred tree trunks. The overlying mudstones show an iridium anomaly, and fungal and fern spores spikes. We interpret these heterogeneous deposits as a direct result of the Chicxulub impact, and a mega-tsunami in response to seismically-induced landsliding. The tsunami backwash carried the megaflora offshore in high-density flows, remobilizing shallow marine fauna and sediment en route. Charring of the trees at temperatures up to >1000°C took place in the interval between impact and arrival of the tsunami, which on the basis of seismic velocities and historic analogues amounted to only tens of minutes at most. This constrains the timing and causes of fires, and the minimum distance from the impact site over which fires may be ignited.

Raging forest fires, a tsunami and its backwash, hundreds of millions of tons of sediment mobilized as gigantic mixed debris flows, ecosystems laid waste.

What a catastrophic time! 

The paper is open access but be aware that it is a preprint, yet to be peer reviewed. 

Forest fire at the K-Pg boundary on the Pacific margin of Baja California, Mexico: timing and causes- Amanada Santa Catharina et.al. 2022.

Meteorite Impact May Have Triggered Largest Pulse Of Deccan Basalt Eruptions

What caused the mass extinction 65 million years ago?

a) It was a meteorite impact and the resulting environmental crises.
b) No,  it was the Deccan basalt eruptions and the resulting environmental crises.
c) It was both, the meteorite impact and the eruptions.

The two mechanisms were distinct. One, a calamity from space and the other a gigantic eruption whose cause was from deep within the earth.

Now, it seems they may be more intimately linked. The meteorite impact may have triggered the largest pulse of the Deccan volcanic eruptions. Be careful here. The impact did not initiate Deccan volcanism. That was caused by India rifting away from Madagascar (88 mya) and Seychelles (66 mya). The rifting and an unusually hot mantle underneath resulted in copious amounts of melt being generated in the mantle which found its way to the surface via the great tensional cracks formed when continents separate. The impact though may have resulted in increasing the permeability of the mantle underneath thus making it possible for larger amounts of magma to make its way to the surface.

Abstract- 2014 GSA Annual Meeting, Vancouver:

New constraints on the timing of the Cretaceous-Paleogene (K-Pg) mass extinction and the Chicxulub impact, together with a particularly voluminous and apparently brief eruptive pulse toward the end of the “main-stage” eruptions of the Deccan continental flood basalt province, suggest that these three events may have occurred within less than about a hundred thousand years of each other. Partial melting induced by the Chicxulub event does not provide an energetically-plausible explanation for this coincidence, and both geochronologic and magnetic-polarity data show that Deccan volcanism was underway well before Chicxulub/K-Pg time. However, historical data document that eruptions from existing volcanic systems can be triggered by earthquakes. Seismic modeling of the ground motion due to the Chicxulub impact suggests that the impact could have generated seismic energy densities of order 0.1-1.0 J/m3 throughout the upper ~200 km of the Earth’s mantle, sufficient to trigger volcanic eruptions worldwide based upon comparison with historical examples. Triggering may have been caused by a transient increase in the effective permeability of the existing deep magmatic system beneath the Deccan province, or mantle plume “head.” It is therefore reasonable to hypothesize that the Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai sub-group) lava flows that account for >70% of the Deccan Traps main-stage eruptions. This hypothesis is consistent with independent stratigraphic, geochronologic, geochemical, and tectonic constraints, which combine to indicate that at approximately Chicxulub/K-Pg time a huge pulse of mantle plume-derived magma passed through the crust with little interaction, and erupted to form the most extensive and voluminous lava flows known on Earth. High-precision radioisotopic dating of the main-phase Deccan flood basalt formations may be able either to confirm or reject this hypothesis, which in turn might help determine whether this singular outburst within the Deccan Traps (and possibly volcanic eruptions worldwide) contributed significantly to the K-Pg extinction.

Elsewhere in a GSA special issue on volcanism, impacts and mass extinctions more evidence that Deccan volcanism had a significant impact on the fauna and flora.

Chronology of the volcanic episodes is improving and pointing to a scenario wherein the volcanism coincided (or was causally connected) to within a hundred thousand years of the Chicxulub impact and overlapped the stratigraphic horizon defined as the Cretaceous -Paleogene boundary. Looks like everyone is going to be partially right on this one.

Multiple causes for the mass extinction.

Multiple Events Caused K-Pg Mass Extinction?

Tobin et.al. have published work on a K-Pg section from Antarctica. From the latest issue of Palaeogeography, Palaeoclimatology, Palaeoecology:

Although abundant evidence now exists for a massive bolide impact coincident with the Cretaceous–Paleogene (K–Pg) mass extinction event (~ 65.5 Ma), the relative importance of this impact as an extinction mechanism is still the subject of debate. On Seymour Island, Antarctic Peninsula, the López de Bertodano Formation yields one of the most expanded K–Pg boundary sections known. Using a new chronology from magnetostratigraphy, and isotopic data from carbonate-secreting macrofauna, we present a high-resolution, high-latitude paleotemperature record spanning this time interval. We find two prominent warming events synchronous with the three main phases of Deccan Traps flood volcanism, and the onset of the second is contemporaneous with a local extinction that pre-dates the bolide impact. What has been termed the K–Pg extinction is potentially the sum of multiple, independent events, at least at high latitudes.

I don't have access to the paper so just some general thoughts.

Gerta Keller and colleagues have also challenged the theory that a single meteorite impact caused the mass extinction 65 mya. Except, their theory is that the bolide impact everyone is familiar with, which is the Chicxulub impact event in Yucatan Mexico took place about 300,000 thousand years before the peak Deccan volcanism. They base this on observations made on K-Pg boundary sections in Mexico and Texas and some work in India published in Journal of the Geological Society of India and Earth and Planetary Science Letters which support a link between Deccan volcanism and regional extinctions.

So, was the Chicxulub meteorite impact before the peak Deccan volcanism as Keller and colleagues say or was it 200,000- 300,000 thousand years after Deccan volcanism as this new paper by Tobin et. al. suggests. The famous iridium anomaly observed in many K-Pg boundary sections has been dated to after the main phase of Deccan volcanism indicating that there was a meteorite impact some time after peak volcanism.

Or were there two impacts with the Deccan volcanism sandwiched in between? It does seem that the single bullet theory for the K-Pg mass extinction is under serious threat.

Science Daily summary of Tobin et.al.' s paper. 

Field Photos: Red Layers Within Deccan Lavas And Mass Extinction

I'll lead you into the field photos in a minute, but I just want to comment on something else first.

Prof. Gerta Keller and her collaborators are at it again. Two new papers in the Journal of the Geological Society of India and Earth and Planetary Science Letters  have come out in recent months in support of the theory that the Deccan volcanism played a large role in the mass extinction that took place 65 mya.  The mass extinction resulted in biologically new conditions on earth and we recognize that formally by naming post extinction geological layers to represent the beginning of the Cenozoic Era.

I haven't read the papers but from following some early work of this group and the abstracts it is worth summarizing Prof. Keller's argument

1) The Chicxulub meteorite impact which is dated to around 65 mya and considered to be the main cause of the mass extinction occurred 300,000 years before the mass extinction and so couldn't have been the sole cause of the extinction. This conclusion is arrived at by studying Maastrichtian (latest Cretaceous) to Danian (earliest Cenozoic) sections near the impact crater in Mexico and Brazos river, Texas. The sections show a meter or so of sediment between the   impact breccia and the Cretaceous -Cenozoic boundary layer which is recognizable by C-13 shifts and an irridium anomaly, marking a pronounced environmental shift. Sedimentological analysis of the meter of sediment suggest normal quiet conditions of deposition and biostratigraphy suggests a time lag of about 300,000 years between the impact breccia and the boundary layer. The irridium anomaly thus points to a second meteorite impact.

2) On the other hand, the main pulse of the Deccan volcanism accounting for some 80% of lava volume erupted in the latest Maastrichtian in magnetic polarity zone C29R.  Planktic foraminifera and other ecological indicators from marine sediments spanning Maastrichtian to Danian deposited between lava flows in the Krishna Godavari basin show drastic drops in species richness, an indicator of extreme environmental stress. Formaminfera in Danian sediments between younger lava flows are represented by just a few species. These are survivor fauna. This then demonstrates a cause and effect relationship between the Deccan volcanism and environmental stress.

The mass extinction according to Prof. Keller had multiple causes, Chicxulub impact, then Deccan volcanism and then a second meteorite impact.

Most scientists working on this problem reject this scenario. This is not because they object to the premise that the Deccan volcanics would have been harmful. Their objection is to Prof. Keller's interpretation that the Chicxulub meteorite impact took place 300,000 years before the mass extinction. They interpret the meter or so sediment near the impact crater and the Brazos section as a tsunami deposit and not indicative of a long period of quiet conditions. And in many many sections spanning Maastrichtian to Danian around the world, there is no sediment between the impact layer (recognized by typical glass spherules and shocked quartz) and the boundary layer. No sediment therefore no time lag say the scientists and so Chicxulub meteorite impact coincides with the boundary layer and is the main cause of the mass extinction. Take a look at this great photo of the Cretaceous -Paleogene boundary layer at the Wooster Geologists blog.

Prof Keller argues that such sections wherein the impact layer coincides with the boundary layers are condensed sections i.e. there was no sedimentation at all in the interval between the impact and the mass extinction and therefore the two seem to appear the same! One problem has been the lack of high resolution dating which could separate these events and settle the issue. 

The main pulse of the Deccan volcanism lasted maybe half a million years or so and temporally does seem to coincide with the mass extinction. This would have resulted in at least severe regional environmental stress and extinction. The paper in Earth and Planetary Science Letters documents regional environmental effects. But would it have global impact?

A couple of months ago I was driving west of Pune (location in image below) and came across a road section that exposed several red clayey layers (red arrows) between lava flows. 

 These red layers locally known as red bole have been interpreted as weathering products formed during a hiatus in volcanic activity. Some are debris and soil that formed on top of a flow which then got fossilized due to burial by the subsequent flow. Others though are weathered tuffs or ash fall deposits. They have been found to contain basaltic shards (silicate glass that forms from sudden chilling of lava) diagnostic of an explosive pyroclastic origin. These explosive ash layers settled on lava flows and in a period of quiescence that followed got altered to a clay bearing layer.

These pyroclastic layers occur at regular stratigraphic intervals throughout the main Deccan volcanic phase. Ideas about their origins are not new. There is work dating back to the late 1970's by geologists from Pune (Dr. L.K. Kshirsagar - Ph.D thesis) that had recognized the pyroclastic nature of these layers. But the environmental connection to the mass extinction was not made then. There has been more recent work on these red layers and the idea is being floated around that such type of explosive volcanism may have resulted in columns of ash being ejected tens of km up to stratospheric levels and that would have influenced global climate leading to environmental perturbations.

 okay.. so finally here are the photos of these red layers. I can't say whether these represent in situ soils or ash fall deposits.

Long view of a red layer-

Close up of a red layer - 

Red layers containing broken blocks of basalt -

A rubbly top of a lava flow. You can see red material infiltrating through the cracks and opening between the basalt rubble. 

The Deccan volcanics are considered to be non explosive fissure type eruptions. Can explosive volcanic eruptions resulting in Plinian columns ( ash columns reaching great heights) form in such a volcanic setting? I am not a volcanologist but I have always associated such eruptions with classic volcanic cone formation. Have such cones and eruptive vents been identified in the Deccan volcanics?   Is this a problem of preservation, the cones being weathered away, or is it that cones need not always be associated with explosive volcanism? And were there enough of these episodes to have influenced global climate?

Remotely India # 5: Lonar Crater

Move over Chicxulub Mexico of dinosaur extinction fame, move over Meteor Crater Arizona.. I've got my own meteorite crater right here in my backyard.

Okay... okay.. this crater didn't transform the planet, didn't disrupt ecosystems or cause mass extinctions.. but there it stands, a beautiful round hole punched in the earth.. testimony to the fragility and exposure of our planet to bombardments from space.

Lonar Crater is a small crater formed by the impact of a meteorite. It forms a 1.88 km diameter depression in the Deccan Basalts in eastern Maharashtra near the town of Aurangabad about 8-9 hours drive from Pune. There is a relief of about 135 meters from the rim to the surface of the lake. The image below is a rendering of the relief of the region produced by draping a satellite image over a digital elevation model.

Source: Maloof et al 2009

For years there was some uncertainty on whether this depression represented a collapsed volcanic cone or whether it is of impact origin. Meteorite fragments have not been found at Lonar. But there always were doubts about the volcanic origin since geomorphic features of the crater such as its excellent preservation, a very thin sediment cover in the crater lake and immature river incision features surrounding the crater suggested a much younger origin than the ancient Deccan Basalts.

Now detailed studies of the deformation of basalt flows in the crater walls and evidence of impact shock from the presence of maskelynite a glassy phase formed by shock conversion of plagioclase feldspar has put that debate to rest. Several types of glassy spherules show that the crater formed due to a meteorite impact.  Below is a geological map of the lonar crater which shows the distribution of the ejecta blanket. Series Q are Quaternary features: Qb - beach, Qe - ejecta, Qf - forest, Qh - histosol, Qi - irrigated alluvial fan, and Qt - talus. Series T represent basalt flow in the crater walls. Coordinate are in Universal Transverse Mercator Projection.

Source: Maloof et al 2009

Dating the crater using various methods had previously suggested an age ranging from 12 thousand years to 65 thousand years. A recent study by Maloof et al 2009 carbon dated soils preserved underneath the ejecta blankets. The dates indicate a very young maximum age of about 12 thousand years for the impact. On the other hand another recent study using Argon-Argon dating method on impact melt rock has suggested an age of about six hundred and fifty thousand years. The consensus though seems to be leaning towards a much younger age for the crater.

The crater has  received a lot of attention from geologists. Its importance lies in its very recent origin. High erosion rates on earth wipe away bits and pieces of any feature, many times making a detailed reconstruction of events impossible. In Lonar crater though, impact features are well preserved and have proved useful in understanding cratering mechanisms. Its location within a basaltic terrain makes it a good analogue for small impact craters on the moon and other rocky planets. 

Ecologically too the crater is a unique place. The lake has high salinity levels and hosts a variety of extremophile bacteria.


The Geological Survey of India protects the crater and its rim but not all of the ejecta blanket. Urbanization and agriculture are slowly destroying it.

Digital Elevation Model of Lonar Crater derived from GPS measurments:

Source: Maloof et al 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.