Comments (here below) to: Gerta Keller, Thierry Adatte, Gerald Baum, Zsolt Berner, Reply to ‘Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas’ Comment by Schulte, Speijer, Brinkhuis, Kontny, Claeys, Galeotti, Smit, Earth and Planetary Science Letters (2008) in press, doi: 10.1016/j.epsl.2007.12.025

3.2. Separation of Ir anomaly and spherules

In the Brazos sections the reworked {1} spherule unit is at the base of the event deposit and always separated {2} from the two small (0.4-0.6 ppb) and the main (1.5 ppb){3} Ir anomalies. Schulte et al. [2] creatively explain this separation as rapid fallout of the spherules after the Chicxulub impact, followed by much later settling of the iridium. They thus ignore the evidence of multiple horizons of trace fossils{4} and truncated burrows{5} that indicate deposition of the event beds occurred over a long time period marked {6} by repeated colonization of the ocean floor alternating with storm deposits {7}[1, 12], as also observed in Mexico [8, 13]. In areas where the spherule layer and the Ir anomaly are in close proximity, such as at El Kef{8}, they explain this as the two ejecta layers having merged in simultaneous fallout. This interpretation is the basis for correlating the El Kef Ir anomaly with the spherule unit at the base of the event deposit in Brazos-1 shown in their Figure 1. Why would the heavier spherules settle out simultaneously with the Ir in distant regions, but “considerably later” in proximal areas?{9} Distance does not make Ir settle faster or spherules settle slower. In addition, the clay, iron, or glauconite spherules at the El Kef section are in no way similar to those from the Chicxulub impact and there is no genetic link {10}. Our new study of the same Brazos-1 sequence shows that there is no paleontologic, geochemical, lithological or impact justification to place the K-T boundary at the base of the event deposit (Fig. 2). No faunal changes coincide with the Ir anomaly{12}. The K-T boundary is well-marked 1 m above the event deposit by the first appearance of Danian species, the negative δ13C shift{13} and the mass extinction{14}. As in the CMA-B section (Fig. 1), most species are present in the 20 cm above the boundary either due to reworking or survival.

1) The term "reworked" can be interpreted in two ways. In the Keller et al sense it is used to indicate reworking from an older layer of spherules. In reality all spherule layers in the Gulf area are reworked, because the spherule bearing layers display cross-bedding.
2) That is nothing new and already noticed in Smit et al 1992.
3) A misleading distinction in three peaks. If fact that whole interval is iridium enriched over an extended interval (see 3), be it that some samples are more enriched, but not at the same level. The most detailed analysis by Rocchia et al shows that the whole interval from base of the hard mudstone (Unit E/F) to at least 20-38cm above unit H has values of >0.3 ppb, anomalously high (15x) above background values of 0.02 ppb. That can mean only two things: sedimentation of interval E-base J (60cm) has occurred during settling of the iridium rich dust of the impact fallout (estimated a few weeks), or the tail part of the Ir distribution (presumably the non graded interval J) has been reworked from primary deposits in the hinterland (drainage area) towards the Gulf coast. That may take a little longer, but hardly more than a few years.
4) Indeed there are multiple horizons of trace fossils. The difference lies in the interpretation.
The burrows are all of a type commonly made by crustaceans, and all are basically confined to the very top of each cross-bedded sandstone layer, of which there are at least 3. John Warme has ample experience with these crabs and shrimps, and has observed that they can burrow lighting-fast into many substrates, certainly in loose, freshly deposited sands. This is fully compatible with interpretation of the sandstone layers as deposits of individual surges of a tsunami, where the shrimp and crab population of the Gulf coast seafloor were disturbed, but after the surge had plenty of time before the next one, estimated at about an hour, to bury again into the seafloor.
If you were a shrimp, would you not try to shelter in the seafloor after such an experience? I would!
5) Truncated burrows are to be expected when a later tsunami surge erodes the top of the preceding one, including the hastily made burrows.
6) From the foregoing it is clear that for such a long time period not a scrap of evidence remains.
7) For 'storm deposits' is little evidence beyond alleged HCS, Hummocky Cross Stratification, mentioned a.o. by Yancey 1996. However, HCS has not been found at Brazos! Cross-sections perpendicular to the main current direction can be easily be mistaken for HCS, but are in fact little troughs of climbing ripple intervals. Beside the sedimentological criteria, interpretation as a storm deposit(s) would be unusual, because up and down from the sandstones, no other stormbed have been observed.
8) This is comparing apples and pears. In a sweeping statement the spherules of e.g. el Kef and the Gulf are considered one and the same, while they are not. The spherules at el Kef are crystalline, and likely the consensates from the impact vapor cloud, while the spherules around the Gulf are close to tektites, and were once melted, not vaporized, and traveled much further.

9) That is easily explained. Would the only 3 mm thick lamina with iridium and spherules be undisturbed, one would indeed expect to find the spherules below and the iridium anomaly above. However, on the scale of 3mm the spherules and iridium are completely mixed, and nobody has ever succeeded (or even tried) to analyse the upper from the lower part separately.
Also, "considerably later" means a few weeks at most. Regarding the sedimentation rates in el Kef (and other expanded) distal sections), this would amount to (4cm/1000years max sedimentation rate) only 0.0015 mm of sediment! No way this would be noticeable.

10) Oh yes, there is! The same Ir-rich lamina at Agost (Spain) contains both iridium anomaly, dumbbell shaped tektites identical to the Gulf spherules, and microkrystites. All in the same lamina.

11) That is bull.
Paleontologic? Just below the event-deposit (with spherules from Chicxulub) the amount of planktic forams is around 300/cm3. In the interval above the iridium anomaly <10/cm3. KT is marked by a mass extinction, coincident with the same drop in abundance in all section elsewhere. This drop should NOT qualify??
Geochemical? The KT boundary in el Kef (the GSSP of KT) is placed below the layer with the iridium anomaly. The iridium anomaly at Brazos is partially within (the top of) the event deposit. So KT should be below the event deposit, I would think.
Lithological? The Maastrichtian Corsicana marls are more Carbonate-rich and foram rich (see above) than any mudstones in 2.5m above the event deposit. Same as in any deep-water KT boundary section in the world below and above the KT boundary. Again a good criterion to place the KT boundary below the event deposit.
Impact justification? The spherules from Chicxulub impact are in the lower part of the event deposit, and the iridium anomaly begins in the upper part of the event deposit. As the KT boundary is placed below the iridium anomaly, (even if you do not consider for a moment the spherules due to circular reasoning) at el Kef, it should be the same at Brazos, ergo, below the event deposit.

12) More bull. The iridium anomaly starts within the event deposit. All of the event deposits contain reworked material. The last normal Maastrichtian marls are below the event deposit, so the level of change is between these marls and the event deposit (with excess Ir), not within mudstones where the faunas are already greatly reduced, or in the middle of the extended ir anomaly.
13) Not consistent. At el Kef the first appearance of Danian foraminifers is clearly 15 cm above the KT boundary, so that does not work. The negative ∂13C excursion at el Kef starts 35 cm above the KT boundary, so again appreciably above KT, and not applicable here.
14) But no demonstrable mass-extinction at this level according to both fig1 and 2?. So what is the criterion to place the mass-extinction here, while the large faunal abundance changes are between the event deposit and the Crasicana marls (see{11}) ? I dont get it.
Here below follow some comments on the reply by Gerta Keller, Thierry Adatte, Gerald Baum, Zsolt Berner (in Press) 2008 to <<Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas’, a comment by Schulte et al.>> , which is a critique on:
G. Keller, T. Adatte, Z. Berner, M. Harting, G. Baum, M. Prauss, A. Tantawy, D. Stueben, Chicxulub impact predates K-T boundary: New evidence from Brazos, Texas, Earth and Planetary Science Letters 255 (2007) 339-356

Smit, J., Montanari, A., Swinburne, N. H. M., Alvarez, W., Hildebrand, A. R., Margolis, S. V., Claeys, P., Lowrie, W., and Asaro, F., 1992, Tektite-bearing, deep-water clastic unit at the Cretaceous-Tertiary boundary in northeastern Mexico: Geology, v. 20, p. 99-103.

T.E. Yancey, Stratigraphy and depositional environments of the

Cretaceous/Tertiary boundary complex and basal section, Brazos

River, Texas, Gulf Coast Assoc. Geol. Soc. Trans. 46 (1996)


Climbing-ripple interval in the KT sandstone form the Brazos river bed that may resemble HCS. Yet these are climbing ripples, not pointing to storm-waves, but to uni-directional currents with extremely high suspension load, compatible with back-surge from a tsunami surge.