There is an interesting dispute going on at Benny Peiser’s CCNet among some eminent scientists about the date of the Cretaceous/Tertiary (K/T) boundary. It’s not an issue that I’d ever thought about very much – although my 5-year old granddaughter has gotten interested in dinosaurs and asked me why they are “extincted”. (She’s the one that thought that Bon Appetit would be a good name for a restaurant for dogs.) The dispute caused one party, Jan Smit, to propose that the other party, Greta Keller, send thin sections of her critical sections to an independent analyst. Keller thought that this was a ridiculous proposal, saying:
Instead, Smit has called for “testing” Keller’s forams to demonstrate that they are dolomite crystals… If Smit wants to carry out such a foolish “test”, I say go ahead and use your own slides.
Without knowing anything of the debate, Keller loses me here. If an exploration geologist responded in an equivalent way to a request for an independent analysis of a drill core, you should call your broker instantly and short the stock. Now in fairness to Keller, there seems to be a lot of ingrained academic expectations of immunity from ongoing due diligence and it might be a little early to short the stock. However, to a draw a more general moral, surely Smit’s request can be construed as a form of ongoing peer review. If Smit doesn’t get anywhere with Keller, I think that the next step should be writing the journals involved and asking them to intervene.
Here is some of the recent correspondence at CCNet (and there are some other interesting comments there as well.)
Jan 23, 2006 Jan Smit: SCHULTE’S K/T BOUNDARY IS CORRECTLY PLACED AT BRAZOS RIVER: AT THE BASE OF CHICXULUB EJECTA
Keller, Adatte and Harting mount their horses again in their quest for the holy grail: the denial that the Chicxulub impact is the K/T boundary impact, notwithstanding truckloads of positive evidence, to which Schulte et al. recently added another piece.
The Chicxulub impact coincides with the mass-extinctions and caused the worldwide iridium anomaly. In all our former debates (CCNet, 1 November 2003
http://www.geolsoc.org.uk/template.cfm?name=NSG2345809234541) Gerta Keller c.s. have consistently refused to answer to this evidence, or dismiss it with a simple sweep of the hand.
The focal point of Keller, Adatte and Harting is their critique on Schulte’s placement of the K/T boundary in the Brazos river sections. As Keller states: “…does not justify the arbitrary assignment of the K-T boundary to the base of the event deposit in contradiction to the globally accepted defining criteria”.
But wait a minute! It is Keller, Adatte and Harting that make the crucial error of placing the K/T boundary at the first appearance of the Paleocene foraminifers, neglecting “globally accepted criteria”
Schulte’s assignment is not arbitrary, his K/T boundary placement is fully in agreement with the official K/T GSSP in Tunisia. Keller et al. claim the K/T boundary should be placed at the first occurrence of Paleocene foraminifers. Yet this is NOT the case at the K/T stratotype (GSSP) in Tunisia, where the first occurrence of Paleocene foraminifers is 5-20 cm (depending on who is cited), probably thousands of years above the K/T boundary. Therefore Keller’s statement is highly misleading. This first appearance criterion is an approximation, there are other criteria. As for biostratigraphy, the mass-extinction of foraminifers and nannofossils approximates the K/T boundary much more accurate. The official K/T boundary is DEFINED at the base of a 2-3mm thin iridium-rich layer. The K/T boundary does coincide, like elsewhere, EXACTLY with the mass-extinction of the vast majority of Maastrichtian foraminifers.
So far so good, the mass-disappearance of the Cretaceous planktic foraminifers at Brazos River coincides with the base of the event beds in Brazos River, as Schulte wrote. To state, as Keller does; “…. the remainder consists of dark laminated shale similar to the late Maastrichtian sediments below the storm event deposits” is misleading. Even untrained freshman students armed with a simple hand lens can easily distinguish the foram-loaded sediments below the event beds from the darker, foram poor sediments above the event bed.
But wait again! Keller c.s. deny that the iridium rich ejecta layer in the Pacific, Western Interior and the Tethys is the Chicxulub distal ejecta layer. According to them, that one should occur some 300ky, or between 4 and 12 meters below the KT boundary in the Tethys sections. Well, nobody has found any sign of such an ejecta layer outside the Gulf of Mexico and direct surroundings below the K/T boundary, although the Chicxulub impact is large enough to have produced such a global ejecta layer.
So why then should the Tethys-Pacific-Western Interior ejecta layer NOT be the Chicxulub ejecta layer? Keller states: “In fact, the Ir anomaly is never found in association with Chicxulub ejecta and no Chicxulub ejecta glass has ever been found and documented in K-T clay layers worldwide.”
Once again that is misleading, and hinges on a multitude of curious interpretations and twists.
Chicxulub glass has indeed almost nowhere been identified, because after 65 million years such glass, instable as it is, rarely survives that long. Pure glass has been found only at Beloc, Haiti, and extremely rare in the core of smectite spherules in Mimbral, Lajilla (Mexico). Glass devitrifies into a variety of secondary minerals over time, such as smectite, glaucony or goyazite (http://www.geo.vu.nl/~smit/tektites/dogiecreek.htm), but, on the other hand, its host structure is often preserved, like silicified wood from the petrified forest in Arizona preserves the original wood structure. Yet, because no wood was found, has anybody denied that the petrified forest ever was a forest with trees? The typical fingerprint of the Chicxulub glassy spherules and droplets is, therefore, not the presence of glass, but the presence of exquisitely preserved splash-forms and the remains of internal bubbles. Such forms have been found in the Pacific (GPC-3), Tethys (Agost) in the iridium-rich ejecta layer at the K/T boundary, and in the Western Interior (Dogie Creek). In the Western Interior these splash-forms occur in the sub-layer amalgamated to the iridium rich layer. The significance of the dual layer at the K/T boundary in the Western Interior is consistently downplayed or dismissed by Keller cs., yet is the prime evidence for tying the Chicxulub impact to the iridium-rich ejecta. “Schulte et al’s conflating the two events” is therefore fully justified. and supports the K/T boundary position at the base of the event bed, because the bubbly splash-forms occur abundantly at the base of the bed.
Additional evidence that the global iridium-rich layer is caused by the Chicxulub impact include shocked zircons from the iridium-rich part of the dual layer, whose age and isotopes are consistent with an origin from the Chicxulub crater (such shocked zircons are recently also found in Tethys sections)
Adatte’s comments on the sedimentology of Schulte are peppered with curious stratigraphic and sedimentologic concepts. Adatte considers the event beds a ” normal sedimentary succession”. This is a curious conclusion, regarding the presence of iridium and impact spherules in the beds. And the exquisite preservation of such “normal storm” beds in a regressive setting is highly unusual to say the least.
A statement of: “channel complex ……deposited in an incised valley …” is misleading. The event beds can be traced over more than a kilometer in the Brazos river bed. Its geometry is a blanket of sand rather than a confined channel.
“5 discrete storm beds …” can also read as: 5 discrete tsunami-surge beds, and “erosional surfaces” can also be caused by individual tsunami surges. These are not valid criteria to distinguish one from the other.
One can differ in opinion about the interpretation on the event beds being several storm beds, or the deposits from several tsunami waves. The sedimentary structures will be comparable, although not identical. However, the prime sedimentary structures justifying a storm interpretation are hummocky cross stratification HCS (oscillation driven, multidirectional). Such structures are widely quoted from the Brazos event beds (Yancey, Hansen), but are they real? Our observations of the event beds at low river levels, when the sandstones are exposed over a wide area do not agree with HCS, and display dominantly climbing ripple beds, the product of uni-directional currents from a high suspension load. (see http://sheba.geo.vu.nl/~smit/mexico/brazos.htm ). Such uni-directional climbing ripples are easily explained by tsunami wave surges that each may last for an hour or more.
Whether burrow-rich upper surfaces of sand layers indicate a colonization over a long period of time, or can be caused by quick re-burrowing by excavated (storm, tsunami) organisms trying to re-occupy their normal habitat remains an undecided question. Crab burrows (ophiomorpha) elsewhere in comparable deposits in NE Mexico (Lajilla, Penon http://sheba.geo.vu.nl/~smit/mexico/penon.htm ) burrow down from the event bed surface to the upper surface of sandstone layers up to 70 cm deeper down.
And since when is a sequence boundary observable as such in an outcrop? A sequence boundary is a stratigraphic interpretation, not a fact. What is frequently observed at a postulated sequence boundary, is a burrowed hardground surface with evidence for a hiatus, and a transgressive sequence on top. Such sedimentary sequence has not been found in Brazos river at the base of the event bed.
So Keller, Adatte and Harting make a lot of noise, but present very little substance, and are plain wrong at a number of issues.
Prof. Dr. J. Smit
dept. of Sedimentology
de Boelelaan 1085
Jan 26, 2006 Gerta Keller: WHY BIOSTRATIGRAPHERS DON’T AGREE WITH JAN SMIT
Jan Smit (CCNet Jan. 23) brings a spirited defense of Schulte et al.(CCNet Jan. 12) and his own work by rehashing old arguments he has made time and time again – arguments which have already been demonstrated to contradict empirical evidence in various publications. Here I will only address his claim that is relevant to the Schulte et al. paper, namely that the KT boundary at Brazos is correctly placed at the base of the event deposit based on the presence of Chicxulub spherules. His many other claims, including sedimentation, sea level systems tracts and KT spherules being the same as Chicxulub spherules, make little sense and have no scientific basis.
On CCNet Jan. 24 he continues pulling the wool over non-experts eyes by attempting to denigrade paleontologists (as Luis Alvarez has done in the past) by labeling them as little more than drawing “their conclusions behind the microscope, fully neglecting sedimentological and field aspects.” In this derogatory statement he includes anyone who disagrees with him – the sedimentologists, mineralogists and geochemists along with the biostratigraphers. He puts himself up as expert in all, but has done no research and published no studies on biostratigraphy for more than 20 years, nor has he published any in-depth studies on sedimentology, mineralogy or geochemistry comparable to the ones he derides, Instead, he accuses with innuendo and slander the detailed and serious research done by multidisciplinary teams of experts as not knowing what they are doing whenever the results do not agree with his own (that includes his comments on sedimentology, mineralogy, sea level, and geochemistry in CCNet Jan. 23).
In todays CCNet he raises a red herring by asking “Why can biostratigraphers not agree on the K-T boundary?” In fact, biostratigraphers do agree on the placement of the K-T boundary. More than any other boundary, the K-T boundary is very easily identified and there is hardly ever any disagreement among biostratigraphers on its placement. It is only when ideology and circular reasoning interfere that there are disagreements. Smit uses circular reasoning by claiming that Chicxulub is the K-T impact, therefore wherever Chicxulub ejecta is found must be the K-T boundary. In the process he dismisses the geochemical, lithological and stratigraphic criteria – while at the same paying them lip service as in his CCNet comment.
Let us first analyze Smit’s arguments in CCNet Jan. 24. He states that “What biostratigraphers forget is that boundary stratotypes are NOT defined on biostratigraphic criteria, but are a “golden spike” in a sedimentary succession, chosen on lithological criteria.” Evidently Smit assumes that lithological changes are time correlative, but anyone who has taken Geology 101 knows that lithological changes are time transgressive. A lithological succession changes with the local environment – it can therefore not become a globally correlateable boundary. Only when a lithological change is induced by a global event, such as the KT clay layer, the KT carbon-13 shift, the late Cenomanian carbon-13 shift in association with global anoxia and organic-rich sediments, can lithology be used as one of the criteria in conjunction with the geochemical markers.
However, even the KT clay layer and basal red layer with its Ir anomaly is dependent on local environments and its absence doesn’t necessarily mark the absence of the KT boundary. By Smit’s argument the KT boundary must always be placed at the base of the KT clay layer. All biostratigraphers agree and follow this practice, especially if this clay layer also records an Ir anomaly and the global shift in carbon-13 values.
But let us examine whether Smit and Schulte et al. follow this practice as they proclaim. For example, at Brazos there is no distinct KT clay layer. But an Ir anomaly is present above the event deposit coincident with the first Tertiary species and a mm thin rust colored sandstone layer (Rocchia et al.,l996). In addition, the global carbon-13 shift coincides with the Ir anomaly and biostratigraphic placement of the KT boundary. Yet, Smit and Schulte et al dismiss these accepted markers and place the KT boundary at the base of the event deposits on the sole basis that they contain Chicxulub spherules.
They do the same in Mexico’s sections where a clay layer and thin red layer with Ir anomaly is present above the event deposits, such as at El Mimbral, La Sierrita, La Parida and others. This KT clay and Ir anomaly also coincides with the mass extinction in planktic foraminifera and the first appearance of Tertiary species within a few cm above it. But as at Brazos, Smit and Schulte et al place the KT boundary at the base of the event deposit on the basis that the presence of reworked Chicxulub spherules there marks this as the KT boundary. They ignore Smit’s much touted identifying criteria (CCNet Jan. 24) and the fact that the original Chixulub spherule ejecta is interbedded in undisturbed marine marls 4-5 m below the event deposit (BBC Horizon 2004: What didn’t kill the dinosaurs). It is clear that while paying lip service to the defining criteria, they in fact only use their belief that the presence of Chicxulub spherules at the base of the event deposit places the KT boundary there because they assume that Chicxulub is the KT impact. The age of this impact, however, appears to predate the KT by about 300 ky (Keller et al., 2002, 2003, 2004a,b).
Smit and Schulte et al. thus conveniently dismiss lithological and geochemical data when it doesn’t fit their belief of where the boundary should be placed to be consistent with the hypothesis that the Chicxulub impact is the KT killer.
What about Smit’s slander of biostratigraphers? Who use only subjective criteria, who can never agree on first and last appearance datums? Smit trots out the brief keywords on the KT as selected by Jim Ogg for the latest ICS web page. These keywords include the Ir anomaly, the mass extinction in the major microfossil groups and dinosaurs (the latter is especially controversial and not a defining criteria since few dino bones if any can be found at the KT boundary). Jim Ogg obviously didn’t include all marker criteria for the KT boundary in his keywords. Notably absence is the carbon-13 shift, and the first appearances of Tertiary species, which are indeed key bio- and chemo-markers of the KT boundary. But neither are Chicxulub impact spherules mentioned as identifying citerion as Smit would have us belief.
Smit takes Oggs keywords as support to dismiss any and all biostratigraphers who employ the first appearances of Tertiary species as one of the markers of the KT boundary at Brazos – that indeed includes every study done by microfossil biostratigraphers to date. Even Schulte et al.s dinoflagellate expert on his team, Michael Prauss (see CCNet, Jan. 23), who excused himself from this paper. This agreement among biostratigraphers for the placement of the KT boundary in the Brazos section alone shows that evidently biostratigraphy works very well across different microfossil groups. The close coincidence of the first Tertiary species with the carbon-shift and the Ir anomaly – all above the event deposits – makes it rather clear that the KT boundary is not at the base of the event deposits.
Smits erroneously claims that:” They all five (Prauss, Tantawy, Keller, Adatte, Harting) mistakenly stress that the ONLY criteria based on first occurrences of Paleocene biota should be used..” This is at best misrepresentation by Smit since all biostratigraphers have made it clear that faunal turnovers from Cretaceous to Paleocene assemblages and the carbon-13 shift mark the placement of the boundary,
Biomarkers, first and last appearances of species and acmes, appropriately tested globally form the basis of biostratigraphy and age dating in conjunction with paleomagnetic and radiometric dates. At the K-T boundary, the mass extinction of tropical and subtropical planktic foraminifera marks a unique event. Equally unique is the first appearance of Tertiary species in foraminifera, as well as nannofossils and dinoflagellates. Smit stated that this occurs within the first 5 cm above the extinction horizon and Ir anomaly at El Kef, which is indeed very close. In fact, the first Tertiary forams appear already in the first 1 cm of the KT clay in the smaller than 63 micron size fraction (Keller et al., 1995; 2002) and coincident with the carbon-13 shift. Yet he exclaims: “Where she recognizes that first appearance of Danian species DO NOT coincide with the K/T boundary!?” Evidently he has not kept up with biostratigraphic KT studies over the past decades.
This is also evident in his comment: “As member of the subcommission on the K/T GSSP, I pledged for NOT ACCEPTING the first appearance of e.g. E. eugubina, of C. primus, knowing that these markers first occur 4-25 centimetres above the iridium anomaly…” (Disclosure: I was also a member of that subcommission). No biostratigrapher proposed on that commission that the first appearance of P. eugubina mark the KT boundary. The first appearance of this species has always been (at least for two decades) the index fossil for the P0/Pla boundary in the early Danian! Smit’s claim makes it clear that he is not familiar with biostratigraphy – while at the same time dismissing it. If Smit had carefully read Tantawy’s comment on CCNet, he would also have seen that C. primus is not a KT defining criterion. But a host of first and last appearances of species and faunal turnovers are including the nannofossil “Biantholithus sparsus the calcareous dinoflagellate Thoracosphaera operculata, the sudden change in nannofossil assemblage, the last appearance of Ankhangelskiella cympiformis and Micula decussata and/or the first appearance of Cyclagelosphaera alta.” Is Smit really so out of it with the current status of biostratigraphy? Or just arrogant in dismissing all that doesn’t fit his hypothesis?
Based on the above arguments Smit states “Biostratigraphically, the K/T boundary is therefore better defined and approximated by the major extinction horizon, and this level is in Brazos river below the event beds.” There is just one small problem with this criterion at Brazos – there is no conventional mass extinction. Planktic foraminifera, define this mass extinction in marine fossils with all tropical and subtropical species extinct (2/3 of the total assemblage) by KT time and the survivorship of environmentally tolerant taxa. At Brazos, biotic stress is very high through the late Maastrichtian because the area was a very shallow sea (less than 80m estimated by Schulte et al) excluding most specialized species. In this environment species diversity is therefore very low, 20-30 species in any given sample below the event bed, as compared with 55-60 species in normal marine environments (Keller, l989). Some specialized species (e.g., globotruncanids and rugoglobigerinids) are sporadically present and these disappear at the unconformity at the base of the event deposit. The event deposit and sediments above it were deposited in even shallower seas leading to even greater biotic stress, as evident by the sharp increase of benthic species in the benthic/planktic ratio. In this high-stress environment the disappearance of the rare and sporadic specialized species at the unconformity below the event deposit cannot be assumed to represent the KT mass extinction as Smit claims.
In contrast, the carbon-13 shift and Ir anomaly both of which coincide with the first appearance of Danian planktic foramifera, nannofossils and dinoflagellates and faunal turnovers from Cretaceous to Paleocene assemblages well above the event deposit reliably mark the KT boundary. Prauss, Tantawy and I have independently studied the microfossils in the core KT1/KT2 of Schulte et al. and found that the boundary is coincident with the carbon-13 shift at 1.6 m above the event deposit. Thus, three independent studies based on different microfossil groups all agree on the placement of the KT boundary. They agree because the KT faunal and floral turnovers and the carbon-13 shift are unique. The same was observed in other sequences at Brazos (e.g., KT3 core, and CM outcrops, Keller, l989; Barrera and Keller, l990). Smit and Schulte et al. conveniently ignore this evidence.
Now consider that reworked Chicxulub ejecta is always well below the KT and at the base of the event deposit. Based on the empirical evidence this is a clear case of two separate events – the KT and Chicxulub impacts.
Gerta Keller, Department of Geosciences, Princeton University
Barrera, E., and Keller, G., l990. Stable isotope evidence for gradual environmental changes and species survivorship across the Cretaceous-Tertiary boundary. Paleoceanography 5(6), 867-890.
Keller, l989. Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktic foraminifera from Brazos River, Texas. Paleoceanography 4, 287-332.
Keller, G., Li, L. and MacLeod, N., 1995. The Cretaceous/Tertiary boundary stratotype section at El Kef, Tunisia: How catastrophic was the mass extinction? Paleogeogr., Paleoclimatol.,
Paleoecol., 119: 221-254.
Keller, G., Adatte, T., Stinnesbeck, W., Luciani, V., Karoui, N., Zaghbib-Turki, D., 2002. Paleoecology of the Cretaceous-Tertiary mass extinction in planktic foraminifera. Paleogeogr., Paleoclimatol., Paleoecol., 178, 257-298.
Keller G., Stinnesbeck W., Adatte T. and Stueben D. 2003. Multiple impacts across
the Cretaceous-Tertiary boundary. Earth-Science Reviews 1283: 1-37.
Keller, G., Adatte, T., Stinnesbeck, W., Rebolledo-Vieyra M., Urrutia Fuccugauchi, J., Kramar, G., and Stueben, D., 2004a. Chicxulub predates the K/T boundary mass extinction. Proceedings of the National Academy of Sciences 101, 3753-37-58.
Keller, G., Adatte, T., Stinnesbeck, W., Stueben, D., Berner, Z., Kramar, U., Harting, M., 2004b. More evidence that the Chicxulub impact predates the K/T mass extinction. Meteoritics & Planetary Science 39 (7), 1127-1144,
Keller, G., Adatte, T., Berner, Z., Harting, M., and Stueben, D., 2005. Chicxulub impact predates K-T boundary in Texas and caused no mass extinction. 7th International Symposium on the Cretaceous 5-9 Sept. 2005, University of Neuchatel, Switzerland, Scientific Program and Abstracts, P. 118-119.
Remane, J., Keller, G., Hardenbol, J., Ben Haj Ali, M., l999. Report on the international workshop on Cretaceous-Paleogene transitions. Episodes 22(l), 47-48.
Rocchia, R., Robin, E., Froget, L. and Gayraud, J., l996. Stratigraphic distribution of Extraterrestrial markers at the Cretaceous-Tertiary boundary in the Gulf of Mexico Area: Implications for the Temporal Complexity of the event. In: The Cretaceous-Tertiary Event and other Catastrophes in Earth History, Geol. Society of America, Special Paper 307, P. 279-286.
Schulte, P, Speijer, R., Mai, H., Kontny, A. (2006) The Cretaceous-Paleogene (K-P) boundary at Brazos, Texas: Sequence stratigraphy, depositional events and the Chicxulub impact. Sedimentary Geology, 184, 77-109
Department of Geosciences
Princeton NJ 08544, USA
The Chicxulub Debate:
Jan 27, 2006 Jan Smit: K/T AND CHICXULUB: TAKE AWAY THE EVENT BEDS AND ALL THE K/T BOUNDARY CONCEPTS MERGE
Gerta Keller spills a bunch of strong words in CCNet 26 Jan, but in the end, after you take away the smoke screen, almost completely agrees with Schulte and Smit about the placement of the K/T boundary!
Keller admits that tropical and specialized species disappear at the base of the event bed at Brazos river. This a major criterion to place the K/T boundary below the event beds at Brazos River.
But the funny thing is, take away the event beds, (that whatever mechanism you propose, have been deposited in a very short time), and the K/T boundary favoured by Keller and the K/T position favoured by Schulte/Smit are almost one and the same.
There are many arguments to make the iridium layer and Chicxulub ejecta one and the same but Keller never adressed them.
Neither has she ever shown any inclination to have her so-called Maastrichtian foraminifers (1) in the Yaxcopoil-1 core in the Chixulub crater tested. I have amply demonstrated (2) these to be inorganic dolomite crystals, yet Keller uses these to show that Chicxulub is older than the K/T boundary.
It is a pity she has not done so, because I think also full professors at Princeton are not beyond good scientific principles: Testing!
For detailed comments on Keller’s CCNet 26 Jan comments, see:
Prof. Dr. J. Smit
dept. of Sedimentology
de Boelelaan 1085
Jan 31, 2006 Gerta Keller: FORAMS OR DOLOMITE RHOMBS: THE MERRY-GO-ROUND ON CHICXULUB
I’m starting this morning with a big smile on my face after reading Jan Smit’s latest comment. He has gone way beyond science into the realm of fantasy – claiming that we almost completely agree with the placement of the K/T boundary – and further claiming that ” I have amply demonstrated these (Maastrichtian planktic foraminifera in Yaxcopoil-1) to be inorganic dolomite crystals”.
And once again he has entered the realm of personal slander and accusations “I think also full professors at Princeton are not beyond
good scientific principles: Testing!” In the absence of science, hiding behind slander is the next best thing.
What riles Jan Smit so much about the Chicxulub Yaxcopoil-1 crater core? It is simple. Keller et al. (2004a,b) demonstrated that the impact breccia and the K-T boundary are separated by a 50 cm interval of sediments that contain (1) five thin glauconite clay layers, each of which represents deposition over tens of thousands of years, thus incompatible with tsunami or backwash deposition, (2) burrows and bioturbation, which could not be present if this were a tsunami or backwash deposit, (3) late Maastrichtian carbon isotope signals and the negative shift that marks the K-T, both indicating normal sediment deposition, rather than reworking, (4) chron 29r that marks the last 500 ky below the K-T and first 200 ky above it, (5) the presence of late Maastrichtian zone CF1 foraminifera, which span the last 300 ky of the Maastrichtian, (6) the mass extinction of Cretaceous planktic foraminifera, (7) the first appearance of Danian species immediately above it, (8) absence of Ir anomaly, probably because of erosion. All this evidence points to placement of the K-T boundary 50 cm above the Chicxulub impact breccia. And most importantly, it demonstrates that the Chicxulub impact predated the K-T boundary mass extinction.
All this evidence against the hypothesis that Chicxulub is the K-T killer riles Jan Smit, who maintains that the 50 cm interval represents a tsunami deposit, backwash and crater infill after the impact. Of all this evidence, which stands alone even without the forams, he is particularly upset about the forams, which he maintains do not exist and are just dolomite crystals. He has maintained this claim despite the fact that the two foram experts he has consulted have confirmed the presence of late Maastrichtian planktic foraminifera. Smit supplied core Yaxcopoil-1 samples to Antonio Arz, who documented late Maastrichtian forams (Arz et al., 2004). He then supplied his own set of samples (Disclosure: they are the same sample set as mine) to the Cretaceous foram expert Michele Caron, who confirmed the presence of abundant Late Maastrichtian foraminifera, including the zone CF1 index species Plummerita hantkeninoides, which spans the last 300 ky of the Cretaceous. But he rejected her results, sayingt “I don’t believe it”, just as he rejected Arz results.
Instead, Smit has called for “testing” Keller’s forams to demonstrate that they are dolomite crystals. Since Michele Caron has identified them in his own samples, which are from the same set as mine, he could perform this test easily. But he hasn’t. And there is a reason why. It doesn’t make sense. To the uninitiated this test may sound like a valid proposal. But it isn’t. The foraminifera in these dolomitized sediments are recrystallized, this means that the original calcite shells are replaced by dolomite. In fact, diagenetic replacement of original test shells is common in most sediments, but this doesn’t change the fact that the forams are there, only that the original shell calcite is gone. Now Smit proposes to test the foram shells and show that they are dolomite, rather than the original shell calcite. Of course they are replaced by dolomite – but they are still forams. But he wants you to believe that this is a legitimate test to determine whether forams identified as such by several foram experts are really forams. If Smit wants to carry out such a foolish “test”, I say go ahead and use your own slides. Michele Caron will be happy to show you the forams that you tell her don’t exist.
Department of Geosciences
Princeton NJ 08544, USA
The Chicxulub Debate:
Feb 2, 2002 Jan Smit: WHO IS MERRY-ING AROUND? A NEW APPEAL TO GERTA KELLER TO HAVE HER KEY-EVIDENCE OF CHICXULUB “FORAMINIFERS” TESTED
Since when is a call for objective, scientific testing “slandering in the realm of phantasy?” (G. Keller, CCNet, 31 Jan). Keller tries to hide behind a thin smoke screen in her refusal to let HER Chicxulub samples be scientifically tested.
It is not difficult to see through the all too transparent disguise when she exclaims at the end: “Go ahead and do a foolish test on your own slides”. When I would present an “unbiased” test of my own slides, then I would be foolish indeed.
By coincidence, I have just visited Michele Caron a few days ago at the Swissed meeting in Fribourg, and we have discussed at length with a microscope at hand whether the few foram-reminiscent forms in these slides are really the remains of foraminifers of not. Michele believes there are a few very badly preserved foraminiferal forms in there (deteriorated way beyond recognition at generic or species level) and I still have my doubts. However, Michele Caron has ample experience in identifying foraminifers in thin sections from the metamorphic “schistes lustrés” and she may have found a way to identify badly preserved specimens. But even if these forms turn out to be true foraminifers – and Arz et al 2004 have shown that there are a few reworked specimens in that core interval – then those occur in a cross-bedded sandstone and are, therefore, by definition reworked, and cannot be used for biostratigraphy.
About a year earlier I had sent to M. Caron, a renowned foraminiferal specialist, the thin sections I had made from that critical interval from impact to post-impact rocks for further analysis. I have done this to have my observations tested and to see if someone else could find foraminifers where I could not. Pure, simple, scientific testing by an experienced colleague, who had taken no stance in the debate.
Michele Caron spent weeks behind the microscope to find just a few examples that might be a badly preserved foraminiferal shell, and in one case she may be right. (See the images of these here: http://sheba.geo.vu.nl/~smit/forums/CCnetflareup.html).
Thus, when Keller quotes Michele Caron as having “… confirmed the presence of abundant Late Maastrichtian foraminifera”, she simply does not tell the truth. Nor has Caron found any “CF1 index species Plummerita hantkeninoides.”
Antonio Arz (1), who has also been “quoted” by Keller, has answered in a similar fashion in CCNet of 1 Feb. (Disclosure: Not I, but Antonio Arz has received the same sample set as Keller,
but he has dissolved all his sample material. My sample set was close, but offset from Keller’s, and cannot be used for one-on-one testing.)
I have provided M. Caron with a second set of polished thin sections, in which I earlier(2) demonstrated the zoned dolomite crystals, and I am curious to know what Caron will find in there.
Michele Caron had also earlier politely asked Gerta Keller if she could send her set thin sections to Fribourg, Switserland, so she could compare those with the set I had supplied. Thus far, Keller has failed to answer this request.
Keller, now for the first time, admits that all the calcite tests of her foraminifers in that critical interval were replaced by dolomite (3). Dolomitization, as every paleontologist knows, destroys very effectively the shape of fossils, especially microfossils, so nothing is left to recognize, and certainly not to the species level.
In the interval just above the claylayer in the Chicxulub core (794.11-793.85m) true Paleocene foraminifera are found. But also dolomite crystals can be found that are identical to the crystals in the interval 794.60-794.11m. Those crystals often pierce and destroy the foraminiferal test-walls, but never replace the original calcite wall (see http://sheba.geo.vu.nl/~smit/forums/CCnetflareup.html).
I therefore appeal again to Gerta Keller to send her set of thin sections to Michele Caron, so that all sample sets can be scientifically tested.
1) Arz J.A., Alegret, L., and Arenillas, I., 2004. Foraminiferal biostratigraphy and paleoenvironmental reconstruction at Yaxcopoil-1 drill hole (Chicxulub crater, Yucatan Peninsula). Meteoritics and Planetary Science 39(7), 1099-1111.
2) Smit, J., Gaast, S. J. v. d. & Lustenhouwer, W. T. 2004. Is the transition impact to post-impact rock complete? Some remarks based on XRF scanning, electron-microprobe and thin section analyses of the Yaxcopoil-1 Core, Chicxulub Crater. Meteoritics and Planetary Science 39(7), 1113-1126.
3) Keller, G. et al. More evidence that the Chicxulub impact predates the K/T mass extinction. Meteoritics and Planetary Science 39(7), 1127-1144 (2004).
Prof. Dr. J. Smit
dept. of Sedimentology
de Boelelaan 1085