(3) WHY BIOSTRATIGRAPHERS DON'T AGREE WITH JAN
Gerta Keller <gkeller@Princeton.EDU>
Jan Smit (CCNet Jan. 23) brings a spirited defense of Schulte et al.(CCNet Jan. 12) and his own work by rehashing old arguments (arguments, which have never been answered) he has made time and time again - arguments which have already been (n.b. only by Keller and her group) "demonstrated" to contradict empirical evidence (which is still flawed) 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 (wishful thinking ?) 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 (I said biostratigraphers only) . He puts himself up as expert in all, but has done no research (I did 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 ( I don't deride Peter Schultes PhD thesis, which is an excellent and in depth geochemical and sedimentological study of the KT boundary deposits in Mexico), Instead, he accuses with innuendo and slander the detailed and serious research ( I do indeed, as such research is neither detailed, nor serious, and based on "voodoo" sedimentological principles) done by multidisciplinary teams of experts as not knowing what they are doing whenever the results do not agree with his own (Uuuummm, that's normal scientific process, is n't it? If research does not agree on what you are working on since 1974, you start wondering if you are right or wrong. I checked and rechecked my results, and they came out like before. So I started to examine the science of Keller's group, and found serious and fatal flaws in their research) (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 (all of them? come on!) 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 (We agree here, (except in the region where this is all about: the Gulf of Mexico around the Chicxulub impact). 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 ( I am sorry, I adressed specifically these criteria (mass-extinction, iridium anomaly, base of boundary clay) with regards to the K/T boundary) - 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 (in el Kef, not elsewhere) on lithological criteria." (simply following the int strat comm rules) Evidently Smit assumes that lithological changes ( I said criteria, not 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 deposits. 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 ( I don't follow this, this is exactly what I think is correct, and has happened at the K/T boundary. So what's the disagreement?)
However, even the (?presence of 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 (?? in the GSSP at Kef yes, but anywhere else you have to use your correlation tools and common geological sense. As it happens, this invariably leads to a position of the K/T boundary at the base of a clay layer, except in the Gulf of Mexico). 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 (so what is the deal?).
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 (no true. There is a layer G and base I indicated by Hansen/Schulte that is extremely poor in biota, and poor in carbonate, although that is not obvious in the field because carbonate content is below 30% in all adjacent non event beds. Such carbonate layer would qualify for a clay layer, don't you think? ). But an Ir anomaly is present above (not above, but IN) the event deposit coincident with the first Tertiary species and a mm thin rust colored sandstone layer (Rocchia et al.,l996) (Not true again. This rust colored sandstone layer is compared to adjacent layers poor in iridium) . In addition, the global carbon-13 shift coincides (Not exactly, they are separated) with the Ir anomaly and biostratigraphic placement of the KT boundary. Yet, Smit and Schulte et al dismiss these accepted markers (not true again, we use these markers) and place the KT boundary at the base of the event deposits on the sole basis that they contain Chicxulub spherules (which coincides with the mass-extinction, a good biostratigraphic marker) .
They do the same in Mexico's sections where a clay layer and thin red layer with Ir anomaly (excuse me, that red layer is a fine sand, on the contrary poor in iridium) 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 (Nope, your abundant foraminifers in a micrite mud have almost disappeared below teh event bed ) 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 (not undisturbed, slumped) 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 (since when is the interpretation behind a microscope a proven fact?? it remains a human interpretation!), 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- (can't be, they first occur 5 cm above the KT boundary!) 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 (but not close enough!). 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) (Keller claims so, but she is the only one findimg them there) 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. (Not if you solely rely on microsope observations, ignoring lithological properties and abundance patterns) 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 (Here I dropped from my chair in astonishing amazement! This very disapearance is therefore equal to the by Keller much touted mass-extinction of tropical and specialized species. What better criterion can you use to define the KT boundary? It only so happens that that coincides with the base of the event bed, as Schulte and Smit have said from the beginning, and as Keller here admits). 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 (Oh No?!, why not? ).
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.
(The funny thing is, take away the event deposits, and our K/T boundary and Kellers K/T boundary almost exactly coincide! The event deposits are most likely caused by a series of tsunamis, with possibly a few storm deposits related to the event, lasting a few week time at most. These few weeks will not be discernible in other K/T sequences, where no such beds interfere. So what are we talking about, a difference of a few weeks in geological time??)
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.
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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
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