|DEBATES ABOUT BRAZOS RIVER CRETACEOUS TERTIARY (K/T) BOUNDARY CORES|
|Three abstracts presented at the GSA 2006 Annual meeting in Philadelphia, by Keller (2x) and Adatte deserve some comments|
CHIXCULUB IMPACT AND THE K/T MASS EXTINCTION (About the new Brazos
cores Mullinax 1 - 3)
K/T MASS EXTINCTION AND THE LILLIPUT EFFECT: CONSEQUENCES OF IMPACTS,
VOLCANISM AND CLIMATE CHANGE
Pennsylvania Geological Society Monthly Seminar – Free and Open
to the Public:
|Geological Society of America
Far more than a meteor killed dinos
There's growing evidence that the dinosaurs and most their contemporaries were not wiped out by the famed Chicxulub meteor impact, according to a paleontologist who says multiple meteor impacts, massive volcanism in India, and climate changes culminated in the end of the Cretaceous Period.
The Chicxulub impact may, in fact, have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University paleontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany. A final, much larger and still unidentified impact 65.5 million years ago appears to have been the last straw, exterminating two thirds of all species in one of the largest mass extinction events in the history of life. It's that impact ? not Chicxulub ? which left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles.
"The Chicxulub impact could not have caused the mass extinction," says Princeton University paleontologist Gerta Keller, "because this impact predates the mass extinction and apparently didn't cause any extinctions."
Keller is scheduled to present that evidence at the Annual Meeting of the Geological Society of America in Philadelphia, 22-25 October. The results of her research, which was funded by the National Science Foundation, will be discussed in two technical sessions and a public lecture sponsored by the Philadelphia Geological Survey.
May have, May have, May have is the basic message from Keller's Brazos core abstracts, but regarded closely, there is little evidence for these may have's.
Of the "mystery K/T impact" is very little evidence, if
any. Keller claims that this impact at K/T caused the K/T mass-extinction
and the worldwide iridium anomaly.
The best evidence for this is the widespread
dual impact layer in the western interior. In all K/T locations from
Saskatchewan to New Mexico, the K/T boundary is marked by a single
impact layer, that is divided into two sublayers:
Keller wisely(?) ignores this crucial evidence, because it would tumble her house of cards.
|Marine sediments drilled from the Chicxulub crater itself, as well as from a site in Texas along the Brazos River, and from outcrops in northeastern Mexico reveal that Chicxulub hit Earth 300,000 years before the mass extinction. Small marine animal microfossils were left virtually unscathed, says Keller.||The sediments in the Chicxulub crater and from Brazos river tell, in fact, a different story: All microfossils between the Chicxulub ejecta spherules and the iridium anomaly are reworked from the former seafloor, and are not representative for the sediments they reide in now (see below)|
|"In all these localities we can analyze the marine microfossils in the sediments directly above and below the Chicxulub impact layer and cannot find any significant biotic effect," said Keller. "We cannot attribute any specific extinctions to this impact." No one has ever published this critical survival story before, she said. Keller's research was funded by the National Science Foundation.||This image is from Keller's analysis of the new Brazos cores. We consider the Chicxulub impact and the "mystery impact" to be one and the same: the interval between the Event Deposit (Grey area) and the K/T boundary (red line) (in brackets) is then full of reworked specimens due to the currents of the tsunami waves, and should be discarded from analysis: they do not represent the environmet they were found in (see below)|
|If we take out this reworked interval, as I have done here, because it is only an instant of geological time (a few days at most) then the whole story is fully consistent with a mass-extinction at the K-T boundary, caused by the Chicxulub impact|
|The story that seems to be taking shape is that Chicxulub, though violent, actually conspired with the prolonged and gigantic eruptions of the Deccan Flood Basalts in India, as well as with climate change, to nudge species towards the brink. They were then shoved over with a second large impact.The Deccan volcanism did the nudging by releasing vast amount of greenhouse gases into the atmosphere over a period of more than a million years leading up tothe mass extinction. By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom, she says.||Giving scores for this beauty contest (conspiration): Deccan 1%; Chicxulub impact 99% mystery impact 99%, because they are one and the same!|
|"On land it must have been 7-8 degrees warmer," says Keller. "This greenhouse warming is well documented. The temperature rise was rapid, over about 20,000 years, and it stayed warm for about100,000 years, then cooled back to normal well before the mass extinction."||Stable isotope specialists (who are the ones creating the proxies for temperature) do not agree on this at all. New data from the ODP Leg 208 (and elsewhere) show a different story, one of slowly changing temperatures and stability up to the K-T boundary, and then bang! they are all numerically slaughtered at once, and most of them went extinct right away. Some of the less specialist species lingwere on for a (short) while, but soon succombed as well.|
|Marine species at the time suffered from the heat. Most adapted to the stress conditions by dwarfing, growing less than half their normal size and reproducing rapidly with many offspring to increase the chances for survival. The Chicxulub impact coincided with this time. By the time climate cooled back to normal, most tropical species were on the brink of extinction. Then the second large impact hit and pushed them over the brink ? many straight to extinction.||This story is not consistent with the story told from numerous complete seafloor sites from the ancient seas away from the Chicxulub crater. In these places (hundreds) there is not a trace to be found of an impact 300k before the K-T boundary, and dwarfing did not occur before the K-T boundary|
|As for how the dinosaurs were affected, that's a bit harder to say specifically, since dinosaurs did not leave a lot of fossils behind to tell the tale."Dinosaur fossils are few and far between," Keller said. "People love the dinosaurs but we can only really study what happened to them by looking at microfossils because these little critters are everywhere at all times. In just a pinch of sediment we can tell you the age, the prevailing climate, the environment in which it was deposited and what happened. It's remarkable."||True. BUT, Not when these precious
microfossils are reworked into a different environment! (as is the case
in Brazos river). Then they do not tell the
story about the sediments they now reside in, but the story about the
sediments they were removed from:
From the late Cretaceous seafloor before the Chicxulub impact
|What the microfossils are saying is that Chicxulub probably aided the demise of the dinosaurs, but so did Deccan trap volcanism's greenhouse warming effect and finally a second huge impact that finished them off. So where's the crater? "I wish I knew," said Keller. "There is some evidence that it may have hit in India, where a crater of about 500 kilometers in diameter is estimated and named Shiva by paleontologist Sankar Chatterjee from the Museum of Texas Tech University in Lubbock. The evidence for it, however, is not very compelling at this time."||If the Shiva crater were that large, abundant ejecta should have been found. They are not.|
|Comments on Press Release||Comments on Keller1||Comments on Keller 2||Comments on Brazos core website||Comments on "major findings at Brazos" (from Kellers Brazos core website)|
|The Major Findings at Brazos cores according to Keller (see website)||Comments on these major findings|
|1. The K-T boundary was recovered 80 cm above the upward fining of the event deposit in core Mullinax-1. The boundary was identified based on the characteristic K-T carbon-13 shift and the coincident faunal and floral turnovers from Maastrichtian to Danian assemblages.||No iridium analysis has been performed, so it is hard to determine the K-T boundary. The K-T boundary is not at this position. In the Brazos 1 outcrop in the Brazos river itself, the turnover to Danian assemblages is at the same level.|
|2. The ~100 cm interval between the K-T boundary and the event deposit contains exclusively late Maastrichtian microfossils, late Maastrichtian carbon-13 signals, and the same clay mineral and bulk rock content as in the late Maastrichtian below the event deposit. This indicates that deposited occurred during the latest Maastrichtian and that the event deposit is therefore a late Maastrichtian event.||This ~100cm interval is part of the event (tsunami) deposit (in Brazos-1 it is size graded), and contains reworked material settled from suspension after the passage of the tsunami waves caused by the Chicxulub impact. No wonder it contains exclusively material and signals from below the event deposit.|
|3. The event deposit (also commonly called impact-tsunami deposit) consists of discrete and separate depositional events separated by truncated burrows and changes in depositional regimes. This indicates that the event deposit was deposited over an extended time period and was probably caused by multiple (seasonal?) storm events.||Each of these discrete and separate depositional events are more likely deposited by individual tsunami waves or surges. The burrows are either escape structures from organisms trying to escape from the sediment load, or enter the event deposit from above after the tsunami's|
|4. The Chicxulub spherules in the event deposit are reworked from an older deposit. This is apparent by the abundance of glauconite, phosphate and clasts from the underlying sediments.||Chicxulub spherules are about the same size as the abundant glauconite and phosphate pellets (that are not known from the underlying sediment, but from the seafloor further inland), and are likewise reworked together with the primary spherule deposits, as the tsunami waves arrive later than the Chicxulub spherules|
|5. Clasts containing cemented clasts and spherules reveal an amazing history of Chicxulub spherules deposition at an earlier time, with subsequent erosion, lithification, clast formation, transport and redeposition at the base of the event deposit.||These clasts are known as "armoured" mudballs, also well known from several locations in Mexico. Those clasts are "semi-lithified", which means they were stiffer than the local seafloor muds, but still soft enough to pick a coating of spherules while they wallop in the spherule deposits in the tsunami currents.|
|6. A yellow altered glass layer about 45 cm below the event deposit may represent the original Chicxulub impact ejecta layer. This layer consists of smectite (Cheto) with rare relic glass still present with geochemistry consistent with Chicxulub impact glass.||This layer is probably a local weathering phenomenon. I have not seen it in outcrop, and numerous others have failed to find one, despite intensive searching. Why was this layer not observed in any of the (non-weathered) cores??. Cheto smectite can also originate as alteration of volcanic glass, of which many layers are found just across the border in Mexico.|
|7. The age of the yellow clay layer is indicated by planktic foraminifera as near the base of zone CF1, or about 300,000 years prior to the Chicxulub impact.||As the clay is a local weathering phenomenon, this information is moot.|
|8. These Brazos results are consistent with the earlier results from NE Mexico and the Chicxulub crater core Yaxcopoil-1 (Keller et al., 2003, 2004), which indicate that the Chicxulub impact predates the K-T boundary by about 300 ky.||These results are also consistent with an interpratetion of one impact at Chicxulub, which caused both the iridium anomaly and the event deposits. Keller refused her findings of Yaxcopoil-1 to be tested, so she must be afraid the truth will come out (See paper by Marcel Crok in CCNet)|