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Stinnesbeck-1994-Geo See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/291069062 Deposition of channel deposits near the Cretaceous-Tertiary boundary in northeastern Mexico: Catastrophic or... Article in Geology · January 1994 DOI: 10.1130/0091-7613(1994)022<0953:DOCDNT>2.3.CO;2 CITATIONS READS 7 55 14 authors, including: Jan Smit Philippe Claeys Vrije Universiteit Amsterdam Vrije Universiteit Brussel 166 PUBLICATIONS 4,570 CITATIONS 310 PUBLICATIONS 3,483 CITATIONS SEE PROFILE SEE PROFILE Wolfgang Stinnesbeck Gerta Keller Universität Heidelberg Princeton University 266 PUBLICATIONS 3,773 CITATIONS 319 PUBLICATIONS 10,344 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Exp 364 View project Iodp exp 364 chicxulub crater drilling View project All content following this page was uploaded by Jan Smit on 21 January 2016. The user has requested enhancement of the downloaded file. Downloaded from geology.gsapubs.org on January 21, 2016 FORUM Deposition of channel deposits near the Cretaceous-Tertiary boundary in northeastern Mexico: Catastrophic or "normal" sedimentary deposits?: Comments and Replies and Is there evidence for Cretaceous-Tertiary boundary-age deep-water deposits in the Caribbean and Gulf of Mexico?: Comment and Reply COMMENT capable of transporting fine sand on the floor of the deep Gulf of Mexico before the waves were finally damped out. J. Smit, Th. B. Roep Keller et al. (1993, p. 780) concluded that the clastic beds at Department of Sedimentary Geology, Free University, Mimbral and DSDP Sites 536 and 540 "were probably deposited by de Boelelaan 1085, 1081 HV Amsterdam, Netherlands turbidite or gravity flows." Superficially, the K-T clastic unit resem- W. Alvarez, Ph. Claeys bles a turbidite fan, which is not surprising, because both turbidites Department of Geology and Geophysics, University of California, and tsunami deposits are emplaced by currents of decreasing Berkeley, California 94720 strength, carrying large amounts of suspended material. A. Montanari In normal turbidites, currents are unidirectional. In 15 outcrops Osservatorio Geologico di Coldigioco, 62020 Frontale di Apiro of the K-T clastic unit, stretching over 1200 km from Alabama to (MC), Italy Poza Rica in Mexico, currents were repeatedly bidirectional, dif- fering by 180° (Fig. 1 in supplement; see footnote 1). The conti- The Chicxulub structure, in the subsurface of the northern Yu- nental shelf was nearly flat; there is no evidence for narrow canyon catán peninsulá, is a strong candidate to be the long-sought impact walls or restricted basins anywhere, and therefore if the clastic units crater corresponding to the Cretaceous-Tertiary (K-T) boundary were to represent turbidity currents, they had to be running uphill (Hildebrand et al., 1991). In two relatively recent articles some of us part of the time, which seems unlikely. Bidirectional currents, on the have described unusual clastic sediments from Arroyo el Mimbral in other hand, are entirely consistent with surges of individual tsunami northeastern Mexico (Smit et al., 1992) and Deep Sea Drilling waves. Project (DSDP) Sites 536 and 540 in the Leg 77 area of the Gulf of In all K-T clastic units around the Gulf of Mexico, there is a Mexico (Alvarez et al., 1992). We interpreted these clastic sedi- striking contrast between the sediment composition of the unit 1 ments as (1) the product of tsunami-generated water disturbances, channels, poor in quartz and feldspar but rich in spherules, and units (2) resulting from impact at Chicxulub, and (3) deposited precisely 2 and 3, where foraminifera and quartz-feldspar detritus dominate at the biostratigraphic K-T boundary. Subsequently, Keller et al. over rare spherules. If they were turbidites, the K-T clastic beds (1993) and Stinnesbeck et al. (1993) reported their own studies of would require two different source areas to explain the difference in the Mimbral and Leg 77 sites. They concluded (1) that the clastic composition in all the K-T outcrops stretching 1200 km from Ala- sediments were not deposited by a tsunami event, (2) that they bama to Poza Rica. That is extremely unlikely for turbidites, but contain no evidence for a nearby impact, and (3) that they were not consistent with tsunami wave origin. deposited at the biostratigraphic K-T boundary. We have chosen to stress in this Comment only the most fun- Evidence for Impact damental problems we find in the three principal conclusions of Unique, bubble-rich spherules are found in the K-T clastic bed Keller et al. and Stinnesbeck et al. An additional list of 18 detailed from northeastern Mexico (Alvarez et al., 1992; Smit et al., 1992) criticisms is available.1 through Texas (J. Smit, unpublished) to Alabama (Pitakpaivan and Hazel, 1992). We interpret these spherules as altered droplets of Evidence for Tsunami Origin impact-melt glass, now almost entirely replaced by calcite and clay. Smit et al. (1992) described three subunits in the Mimbral clas- Although preserved glass is rare, glass has been recovered from two tic unit, interpreting the upward sequence as follows. Unit 1 was northeast Mexico K-T beds (Arroyo el Mimbral and Lajilla). Similar deposited by the first tsunami waves, which reworked impact ejecta glass, black and yellow, is abundant in the Haiti K-T boundary (Izett, that had just arrived on ballistic trajectories from Chicxulub, along 1991), and a few small fragments were recovered from the K-T bed with local rip-up clasts, and deposited them in discrete channels. at DSDP Sites 536 and 540 (Alvarez et al., 1992). Unit 2 represents backwash debris of continental-margin origin These K-T boundary glasses have a chemistry unlike that of any (sand, plant remains) shaken loose as tsunami waves washed up on igneous rocks we know of, but the high CaO (>23%) in the yellow the coast of Mexico. Unit 3 represents several passes of a seiche glass is compatible with impact melting and mixing of Yucatan plat- form carbonates and basement. The K-T glass has given a 40Ar/39Ar age of 65.07 ± 0.10 Ma, indistinguishable from that of the Chicxulub melt rock (Swisher et al., 1992). The Haiti and Mimbral glasses have low water content (<0.05 wt%), in the range of that of tektites and 1 GSA Data Repository item 9441, Supplement to a Comment, is available on request from Documents Secretary, GSA, P.O. Box 9140, at least an order of magnitude lower than that of volcanic glasses Boulder, CO 80301. (Claeys et al., 1993; Koeberl, 1992). In addition, Blum and Cham- Data Repository item 9441 contains additional material related to this Comment. GEOLOGY, October 1994 953 Downloaded from geology.gsapubs.org on January 21, 2016 berlain (1992) showed that the large variability in oxygen isotopic the case of a sudden mass extinction, this is misleading and ratios in the Haiti glasses (4.6%e) is too great to be achieved by should be abandoned. igneous processes. Blum et al. (1993) then showed that the Sr, Nd, and O isotopic signatures of the Haiti glass precisely match those of Conclusions the Chicxulub melt rock. Stinnesbeck et al. (1993) did not reference On the basis of the three main lines of evidence cited here and any of the studies of the glasses that point to impact origin, but cited the detailed criticisms presented in the supplement (see footnote 1), papers by Jehanno et al. (1992) and Lyons and Officer (1992) which we believe that Keller et al. (1993) and Stinnesbeck et al. (1993) attribute the Haiti glass to volcanism. have not made a good case for rejecting tsunami origin, impact Stinnesbeck et al. (1993) showed a spherule that appears to triggering, and K-T age for the clastic bed. We continue to be im- contain a foraminifer (their Fig. 3B), which would be incompatible pressed with Chicxulub and the K-T clastic unit around the Gulf of with an origin as a drop of impact melt. We find foraminifers only Mexico as strong confirming evidence for the K-T impact-extinction inside bubbles that have broken open (Fig. 2 in supplement), and we theory. suspect that their picture shows a slice cut at a high angle to the REFERENCES CITED plane that would show a bubble broken open. Alvarez, W., Smit, J., Lowrie, W., Asaro, F., Margolis, S. V., Claeys, P., Kastner, M., and Hildebrand, A. R., 1992, Proximal impact deposits at Evidence for a Biostratigraphic K-T Boundary Age the Cretaceous-Tertiary boundary in the Gulf of Mexico: A restudy of The theory that impact caused, or at least triggered, the K-T DSDP Leg 77 Sites 536 and 540: Geology, v. 20, p. 697-700. Blum, J. D., and Chamberlain, C. P., 1992, Oxygen isotope constraints on the mass extinction predicts that the evidence for impact should corre- origin of impact glasses from the Cretaceous-Tertiary boundary: Sci- spond precisely to the stratigraphic extinction horizon; otherwise ence, v. 257, p. 1104-1107. the theory is falsified. The papers by Keller et al. (1993) and Stin- Blum, J. D., Chamberlain, C. P., Hingston, M. P., Koeberl, C., Marin, L. E., nesbeck et al. (1993) purport to have established this diachroneity. Schuraytz, B. C., and Sharpton, V. L., 1993, Isotopic comparison of K/T Stinnesbeck et al. (1993) placed the biostratigraphic K-T boundary boundary impact glasses with melt rock from the Chicxulub and Manson impact structures: Nature, v. 364, p. 325-327. at Mimbral at the top of unit 3 and thus dated all of the clastic Claeys, P., Alvarez, W., Smit, J., Hildebrand, A. R., and Montanari, A., 1993, interval as Maastrichtian. K T boundary impact glasses from the Gulf of Mexico region: Lunar and At first it appears that these two papers provide detailed Planetary Science, v.
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