The origin of the clay minerals at the Cretaceous/Tertiary boundary in Denmark
} Department of Geological Sciences, Case Western Reserve University, Cleveland, Ohio 44106 JAMES L. ARONSON T HUGH T. MILLARD, JR. U.S. Geological Survey, M.S. 424, Denver Federal Center, Denver, Colorado 80225 ELIZABETH GIERLOWSKI-KORDESCH Freie Universität Berlin, Institut fir Palaeontologie, Schwendener Str. 8, D-1000 Berlin 33, West Germany
ABSTRACT We cannot reject the impact hypothesis chemically to the somewhat variable chemistry summarily, because shocked quartz with mul- of the microtektite-like spherules in the Fish The distinctive Mg-smectite that is the tiple planar sets is distinct to the K/T bound- Clay, which were taken to represent unaltered predominant clay mineral in the Cretaceous/ ary, and this distinctive shocked quartz has ejecta (Varekamp and Thomas, 1982). Kastner Tertiary (K/T) boundary marl at Stevns Klint, not yet been identified in distal volcanic teph- and others (1984) concluded that this unusual Denmark (that is, the Fish Clay), which has ras or flows. If shocked quartz is of impact Mg-smectite originated as a direct isochemical been previously believed to have formed from origin, then the collision of either a smaller alteration of impact ejecta. If true, then this dis- impact-derived glass, is also present in the asteroid, or a comet, is more consistent with tinctive Mg-smectite would be expected to be a upper of two marls of probable early Danian the relatively small amount of impact-derived significant component in smectite-dominant age at Limhamn Quarry, Sweden, approxi- material in the Fish Clay. Alternatively, if K/T-boundary marls close to Stevns Klint, such mately 8 m above the K/T boundary. This shocked quartz is proven to be formed by as Nye Kl0v and Kj
Geological Society of America Bulletin, v. 101, p. 702-710, 3 figs., 4 tables, May 1989.
702
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 ORIGIN OF CLAY MINERALS AT CRETACEOUS/TERTIARY BOUNDARY, DENMARK 703
Sweden are described in various papers (see The occurrence of these marls within this lime- which are shown in Figure 1. The actual K/T Birkelund and Bromley, 1979). K/T boundary stone, and its elevation at approximately -50 m, boundary marl is layers II-V, layer I being the marls were collected at Stevns Klint, Nye Kl0v, permits us to correlate with either the lower 8 m uppermost Maastrichtian chalk and layer VI and Kjolby Gaard. A Danian marl was collected of Danian limestone or with the lower of the two being the lowermost Danian chalk and lime- 10 m above the K/T boundary at the Dania middle Danian mound sequences. Although Hol- stone. Layer II is a light gray marl, <0.5 cm thick. Quarry near Manager, Jutland. land and Gabrielson noted the presence of two Layer III is composed of two units: a basal thin In addition to the marl collected from Dania, distinct marls, 1 and 2 m below the K/T bound- (0.5 cm thick) red-orange clay containing coarse two non-K/T boundary marls (=5 cm thick) ary at Limhamn, which would be close to the spheroidal pyrite overlain by fissile black clay were collected from the north wall at the -60 m quarry floor (-60 m along the west wall), it is without obvious continuous lamination. We did level from Limhamn Quarry, Limhamn, Swe- unlikely that our marls are the Maastrichtian not analyze the red-orange clay in this study. den. The stratigraphy at Limhamn has been de- marls, on the basis of elevation and facies associa- Hansen and others (1986, 1988) described this scribed recently by Holland and Gabrielson tion. We therefore call the two marls collected layer as consisting of filled burrows. Shocked (1979). The K/T boundary at Limhamn is a the "lower" and "upper" marls, respectively, of quartz has been found within the thin (1-3 mm), hardground, and the Maastrichtian is almost probable early Danian age. We note that two rust-colored, spheroidal-pyrite layer at the base completely under water; only the uppermost 3 m marls are present in the eastern wall approxi- of layer III (B. F. Bohor and G. A. Izett, 1988, are exposed presently along the west wall, mately 200 m east of the sampled location in a written commun.) for which reason Bohor and according to Holland and Gabrielson. We were similar stratigraphic sequence, but we did not Izett have referred to this rust-colored layer as the confined to collecting from the eastern half of the check the correlation between these two "impact layer." Ir increases 50 times from layer II quarry. The marls we collected are enclosed in exposures. through layer III (Kastner and others, 1984). chalky bioclastic micritic limestone, which con- Bulk samples of the K/T boundary marls were Apparently, layer II was deposited before tains fragments of branching bryozoans and cor- collected from Nye Kiev (2-3 cm thick) and shocked quartz. We place the boundary between als. The bedding is discontinuous and displays a Kjelby Gaard (3-5 cm thick), and bulk samples layers III and IV at the first upward appearance complex interfingering geometry. On a macro- of the Danian marls were collected from the of obvious and continuous lamination in layer scopic scale, these beds appear to be original Limhamn Quarry (<5 cm thick) and from the IV; the color of layer IV changes upward contin- depositional slopes that dip gently as much as Dania Quarry (3-4 cm thick). Several samples uously from dark brown to light gray. The 15°, and they most likely represent the flanks of were microstratigraphically collected from the boundary between layers IV and V is a distinct bryozoan mounds which are the predominant Stevns Klint K/T boundary (that is, the Fish change from a light gray marl to a white-colored facies in the lower and middle Danian at Lim- Clay), as described below. chalky marl, with irregular lenses of white chalk hamn and are not noted in the Maastrichtian, approximately 1 cm above this boundary. Christensen and others (1973) subdivided the according to Holland and Gabrielson (1979). Fish Clay into six smaller layers or beds (I-VI), Five bulk samples of the Fish Clay were col- lected from outcrops approximately 200 m north and approximately 50 m south of Hojerup Church, and these samples are referred to as "Fish Clay A-E." The correlation of these sam- D8 ples to the Fish Clay stratigraphy is noted in Figure 1. Fish Clay A and Fish Clay B are identi- D7 cal samples of the dark brown fissile clay above C3 X D6 laminated, black to grey the rust-colored layer in layer III. Fish Clay C fissile clay was divided into three smaller subsamples: CI (a C2 D5 .E D4 non-laminated dark brown clay at the base of layer IV), C2 (gray D3 upper layer IV), and C3 (light gray marl, upper- > CI mm black clay oc„ 02 most layer IV). Fish Clay D was divided into < c CO light grey-white
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 704 ELLIOTT AND OTHERS
TABLE 1. MAJOR-ELEMENT ANALYSES OF CLAY MINERALOGY FOR <2 AND <0.125 (jm FRACTIONS
Sample Size Clay Major-element analyses (wt. %) fraction {/im) mineralogy*
TiO, AUO, Fe20,t CaO MgO Na,0 Totals
Dania Quarry <2 I/S (74% exp.), illite (Danian) I/S (69% exp.), illite 0.24 18.13 5.50 0.06 <0.125 Kj0lbv Gaard Smectite, illite, tr. quartz <2 (K/T boundary) <0.125 Smectite 0.66 16.25 0.12 4.68 2.20 85.56
Limhamn Quarry (lower Danian) Upper marl <2 Smectite Smectite 56.88 0.38 16.50 <0.125 I/S (64% exp.), illite <2 I/S (77% exp.), illite 52.39 0.23 9.36 0.28 <0.125§ Nye K10v Smectite, tr. illite, quartz (K/T boundary) Smectite 57.28 0.67 16.36 0.09 <0.12<2 5 Stevns Klint (K/T boundary) Fish Clay B1 2-20 Illite, feldspar, quartz, smectite <2 Smectite, tr. ¡Kite <0.125 Smectite 56.84 0.54 15.89 0.80 0.05 5.90 0.21 2.82 83.05
Fish Clay E <0.125§ Smectite 45.32 0.46 16.25 0.69 2.46 4.99 0.38 0.01 70.56 Kastner and others <2 Smectite 60.00 0.67 17.07 4.66 2.17 7.08 91.65 (1984)
Maastrichtian chalk I/S (82% exp.), illite
U.S.G.S. standards
SCo-l 63.70 0.59 13.42 5.48 2.61 2.45 2.71 0.90 91.86 SCo-l (accepted) 63.40 0.62 13.70 5.22 2.64 2.76 2.82 0.95 92.11
MAG-I 49.81 0.73 15.56 7.58 1.40 2.70 3.59 3.68 85.05 MAG-1 (accepted) 51.20 0.75 16.46 1.38 3.13 3.72 3.91 80.55
G-2§ 60.12 0.49 10.67 2.36 1.22 0.65 4.24 3.91 83.66 G-2 (accepted) 69.19 0.53 15.34 2.68 1.98 0.78 4.51 4.15 99.16
* Pre-dominant clay mineral listed first; tFe as Ii^O^; ^analyzed by induction coupled plasma.
in the K/T boundary marls at Stevns Klint (both minor amounts of discrete illite were detected though differing, both sets of results agree with layers II and III), Nye Kldv, and Kjelby Gaard. even in the <0.125 ¿im fraction (Table 1 and Fig. respect to the unusually high MgO content of this We agree with previous determinations, except 2). The clay mineralogy of the lower marl at smectite. that we observed trace amounts of discrete illite Limhamn is similar to the clay mineralogy of the The major-element analyses of the <0.125 /um and quartz in the bulk clay fractions (<2 fim) of Danian marl from the Dania Quarry (Table 1) fractions of the other K/T marls, and the upper these marls. We note that smectite is the predom- and to the clay mineralogy reported previously Limhamn marl, are of Mg-smectites. As shown inant clay mineral in the <0.125 /^m fraction of for a Maastrichtian marl 8.4 m bellow the K/T in Table 1, their values of Si, and Al, Mg, and K, layer II, whereas Christensen and others (1973) boundary at Kjalby Gaard (Rampino and Rey- are similar to each other and distinct from the characterized the <2 /¿m fraction as being I/S nolds, 1983). composition of the finest fraction of the Dania (30% expandable). The mineralogy of the 2-20 We also analyzed the minor amount (0.5%) of Quarry marl. Because of insufficient material, the /nm fractions of Fish Clay B (layer III) is illite noncarbonate siliciclastic material present in a <0.125 (im fractions of layer II and of the lower (mica), feldspar, and quartz, with trace or minor sample of Maastrichtian chalk from Stevns Klint. Limhamn marl were analyzed for their major amounts of smectite. Given the minor amounts of It is predominantly I/S, 82% smectite layers, with elements using an induction coupled plasma discrete illite in the <2 /urn fractions, further trace discrete illite in the < 1 /¿m fraction. The atomic emission spectrophotometer (ICP), and separations to the submicron size fractions were clay mineralogy is similar to that of the lower these data are also listed in Table 1. Except for required to exclude the coarser-grained illite. Limhamn and Dania Quarry marls, and its 2-20 Si02 and AI2O3, our ICP results are reasonable The clay mineralogies of the two Danian ixm fraction also consists of illite (mica), quartz, for both these samples as verified by our ICP marls from the Limhamn Quarry differ from and feldspar. results for layer III of the Fish Clay and for the each other significantly. The upper Limhamn G-2 interlaboratory standard, which were run as marl is very much like the K/T marls described Major-Element Analyses internal controls. The Mg and K contents of the above; smectite is the predominant clay mineral, layer II smectite, which is stratigraphically below only minor amounts of discrete illite were The major-element analyses of our <0.125 the "impact zone," are comparable to the Mg and detected in the <2 jum fraction, and discrete illite fim fractions and Kastner and others' (1984) K contents of the layer III, Nye Kl«)v, Kjelby was not detected in the <0.125 /um fraction. In data from the < 2 ftm carbonate-free fraction Gaard, and upper Limhamn marl smectites. contrast, the clay mineralogy of the lower marl at from the Fish Clay are summarized in Table 1. K-Ar Dates Limhamn is predominantly mixed-layer illite/ Our analyses are on a dry basis; we did not
smectite with 64% and 77% smectite layers in the determine H20 and H20+. Kastner and others' The K-Ar dates are summarized in Table 2. <2 and <0.125 jum fractions, respectively, and total is 91.19%; our totals ran 83%-85%. Al- Dates measured from an authigenic smectite or
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 ORIGIN OF CLAY MINERALS AT CRETACEOUS/TERTIARY BOUNDARY, DENMARK 705
illite/smectite reflect the mean age of illitization containing the Mg-smectite from Nye Kiev and whole-rock samples from within layers IV and V or time-integrated age of illitization. Argillaceous from the Limhamn Quarry upper marl. A series above the position of peak iridium determined sediments typically contain both detrital and of <0.125 and <0.25 /nm size fractions, which herein. authigenic components, and the latter are present are nearly pure smectite, was analyzed as well Rusty iron oxide-stained laminae and wisps in larger amounts in the finest submicron frac- from Fish Clay A and C to determine if the were visible in our sample of Fish Clay D. These tions (for example, Aronson and Hower, 1976). Mg-smectite itself is a carrier of noble metals in irregular rust-colored zones are less than a mil- The K-Ar dates for the Fish Clay decrease with the Fish Clay. The results are given in Table 3. limeter thick and probably formed either diage- grain size. The dates range from 329 Ma for the The Ir contents of the submicron smectitic netically or by chemical weathering. A small coarse 2-20 urn fraction of Fish Clay B to 50 Ma fractions from Fish Clay A and C1-C3 are con- amount of this rust-stained material (50 mg) was for the <0.25 /urn fraction of Fish Clay A. The siderably enriched (as high as 61 ppb), demon- collected carefully from layer IV by scraping and disparity of dates of the finest size fractions strating firmly that the main carrier of Ir at was analyzed. It is highly enriched in all the noble between Fish Clay A (50 Ma) and B (73 and 76 Stevns Klint is of submicron size. The iridium metals, especially Ag and Pt. Ma) might be attributable to Fish Clay B having contents of these fractions increase stratigraphi- The upper Limhamn marl and, for compari- a trace amount of the coarser, detrital illite as a cally upward from 50 ppb Ir at the top of layer son, a sample of the Permian Kupferschiefer result of the processing of a larger sample. III (Fish Clay A) to 61 ppb Ir at the base of layer Shale were analyzed. The Limhamn upper marl IV (Fish Clay CI), then decrease to 10.5 ppb at is nearly devoid of Ir (0.06 ppb), whereas the Noble-Metal Analyses the top of layer IV (Fish Clay C3). Our peak Kupferschiefer Shale contains an amount of Ir iridium concentration in the submicron fractions (0.6 ppb) that would almost be considered an The concentrations of noble metals Ag, Au, Pt, occurs approximately at the boundary between anomalous concentration comparable to the Ir and Ir were determined on a whole-rock basis layers III and IV, which is consistent with pre- concentrations of some K/T boundary samples from the series of samples subdivided from Fish vious whole-rock analyses (for example, Kastner containing just over 1 ppb (for example, Nye Clay D and on bulk samples of the boundary clay and others, 1984). We measured 10-20 ppb Ir in Kiev and the south Atlantic sites collated by
Glycol-treated 16 20 0EGREES 29 Figure 2. X-ray diffraction traces of < 1 and <2 /¿m fractions (A) and of submicron fractions (B). S, smectite; I, illite; I/S, interstratified illite-smectite; and Q, quartz. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 706 ELLIOTT AND OTHERS Alvarez and others, 1982). Moreover, the Pt and TABLE 2. K-Ar DATES OF VARIOUS SIZE FRACTIONS FROM THE FISH CLAY AND MAASTRICHTIAN CHALK FROM STEVNS KLINT Au values of both upper Limhamn and the Kup- ferschiefer Shale are comparable to, if not higher Sample/size fraction K2O '"»Ar K-Ar age than, the concentrations of Pt and Au in the Fish (wt.%) (10-'°mol/g) (my.) Clay and Nye Kiev boundary marls. Crocket and Fish Clay A others (1988) also noted that the Pt and Au <2 fi m 0.35 24.00 0.710 135+11 contents in "background suite" shales were also 1-2 fim 0.35 18.60 0.607 120 ± 11 0.25-1.0 fim 0.37 19.25 0.559 102 ± 8 well within an order of magnitude of the concen- <0.25 (jm 0.18 11.29 0.134 50 ± 7 trations of Pt and Au at the K/T boundary at Fish Clay B Gubbio. It appears that parts-per-billion levels of 2-20 fim 2.62 13.620 329 ± 16 Pt and Au are present not only at the K/T 1-2 /im 1.31 64.44 3.428 173 ± 9 0.125-0.25 fim 0.45 24.10 0.621 93 ± 10 boundary, but also in the upper marl at Limhamn <0.125 /im 0.18 10.78 0.188 73 + 10 above the K/T boundary in Scandinavia and in <0.125 fim 0.18 12.09 0.202 76 ± 10 shales below the K/T boundary at Gubbio, as LP 6 (interlaboiatory standard)* 87.73 19.577 well as in the Permian Kupferschiefer Shale. 96.18 19.555 95.05 19.387 INTERPRETATION OF RESULTS Note: the Fish Clay A <0.25 fim is an unspiked argon determination. The X-ray diffraction and major-element •Accepted value for LP 6 is 19.25 x I0"10 mol/g by Odin (1982). analyses results indicate that the Mg-smectite, which previously was described as being present only in layers III and IV at Stevns Klint, is present analyses by Kastner and others (1984). This ism or is reworked from Late Cretaceous volcan- in the other Danish K/T marls, in layer II of the information alone, however, cannot distinguish ism. A volcanogenic origin for the Mg-smectite Fish Clay, and significantly, in the Danian upper between a volcanic and an impact origin for the must be re-examined. marl at Limhamn as well. The upper marl at Mg-smectite. Bentonites of volcanogenic origin have been Limhamn, however, is devoid of Ir (0.065 ppb Ir) documented in the Upper Cretaceous chalk sec- relative to the whole-rock concentrations meas- DISCUSSION tion in northern Germany. Earlier workers even ured from Nye Kiev (1.85 ppb Ir) and especially proposed that the Fish Clay itself is a bentonite from the Fish Clay, for which the whole-rock Ir Mg-smectite is not present exclusively at the (Rosenkrantz, 1955; Valeton, 1959, 1960). The has been determined to be as high as 69 ppb K/T boundary. Herein, we observed it to be smectitic character and the low Ir content of the (Ganapathy, 1980). These contrasting results present in the Danian upper marl at the Lim- upper Limhamn marl of probable Danian age underscore that Ir is present in the Stevns Klint hamn Quarry. In addition, it is present in layer II make it a good candidate for being a volcanic and Nye Kiev K/T boundary marls at anoma- of the Fish Clay before both peak iridium and bentonite or reworked bentonite as well. We did lously high concentrations. Given the low iri- shocked quartz in the Fish Clay, which are taken not notice any of the typical phenocryst mineral- dium value from the Limhamn upper marl, these by many to represent impact ejecta. We thus ogy to support this contention; however, in favor anomalous values are not a function of the high contend that the Mg-smectite is not derived from of volcanism coincident with the deposition of clay content in marls generally, which contrasts impact. Although Mg-smectite is also the pre- the black clay of layer III in the Fish Clay, we with the interpretation by Rocchia and others dominant mineral in these marls, impact-derived have discovered unusually large (to 1.3 mm), (1984 and 1987). phases such as shocked quartz are present in highly angular subhedral grains in the >50 //m The middle to late Paleozoic K-Ar dates on the minor amounts in the Fish Clay. This is contrary fraction of Fish Clay B (Fig. 3). These grains have 2-20 ¿im fraction of the Fish Clay indicate that to the commonly expressed views on the origin of two cleavage directions and are optically posi- the bulk of the potassium-bearing phases in this the K/T boundary clay, which imply that the tive, with a 2V of 75°; they are identified as fraction are detrital. The detritus in this fraction clay is altered from fallout ejecta. Rather, our labradorite plagioclase. This identification was was probably eroded from slates and schists in interpretations are consistent with the evolving verified from major-element analyses by electron the Caledonian orogenic belt and diluted by microstratigraphic picture of these K/T bound- microprobe (Table 4). The labradorite grains minor amounts of authigenic phases. The meas- ary layers presented earlier by Smit and Romein were presumably formed and dispersed by pyro- ured K-Ar ages of the clay fractions decrease (1985) for a series of K/T boundaries, and re- clastic basaltic volcanism. Although pyroclastic with grain size, corresponding to a decrease in the cently by Bohor and others (1987a, 1987b) and basaltic volcanism is relatively uncommon, proportion of detrital illite (mica) in these clay Izett (1987), who identified a thinner (on the scale younger abundant lower Tertiary basaltic tuffs fractions. This series of dates firmly indicates that of millimeters thick) "impact layer" contain- occur relatively close by at Hanklit, north Jut- the bulk of the 2-20 /um fraction of the Fish Clay ing shocked quartz within a thicker K/T-bound- land, Denmark (Pedersen and others, 1975). The is detrital; it is derived neither from impact nor ary clay unit on the scale of centimeters thick. high-MgO smectites and the labradorite plagio- from contemporaneous volcanism. Moreover, Mg-smectite is now documented in clase could be explained by the occurrence of the Danian upper marl at Limhamn, and in the basaltic volcanism during K/T boundary time in The 50 Ma date from Fish Clay A and the 73 pre-"impact layer," layer II, as well as in layer III the northern European region without invoking and 76 Ma dates of the finest-sized smectite from of the Fish Clay. It is not Caledonian-aged detri- an extraterrestrial source. Zoller and others Fish Clay B, although imprecise because of very tus. The K-Ar dates herein and the oxygen stable- (1983) showed that basaltic eruptions can pro- low K contents, are close to the stratigraphic age isotope data (Kastner and others, 1984) suggest duce significant amounts of aerosols with high and indicate that the trace amount of illite layers that it was formed authigenicallv. The least- iridium contents. It is thus conceivable from our in these smectites formed in early diagenesis. This contrived scenario concerning the origin of Mg- evidence, which suggests a basaltic progenitor of is consistent with an authigenic formation of smectite is that it either formed from K/T volcan- the Fish Clay, that the iridium anomalies at the smectite as interpreted from oxygen isotopic Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 ORIGIN OF CLAY MINERALS AT CRETACEOUS/TERTIARY BOUNDARY, DENMARK 707 TABLE i. NOBLE-METAL CONCENTRATIONS FROM THE K/T AND NON-K/T BOUNDARY MARLS noble metals in the finest submicron fraction (<0.125 /urn) points to at least two key prob- Concentrations (Au/Ir) sample* (Pt/Ir) sample* (ppb) lems that must be dealt with to understand the Ag Au Ir (Au/lr) chond. (Pt/Ir) chond. many chemical and physical phenomena asso- ciated with the K/T event: (1) the identification Fish Clay A. upper layer III of the Ir-bearing phases in these boundary lith- <0.25 fim 2l <0.8 ologies and (2) the identification of the factors Fish Clay C (alt <0.125 ßm fractions) that caused a high degree of variability in Ir C3 1070 4.1 10.5 57 1.32 2.7 C2 2240 6.1 26 31 0,79 0.6 contents between the different intraregional CI 2100 6.6 61 0.37 0.56 sites, such as Nye Klav and Stevns Klint, col- Fish Clay D (3-mm-thick horizontal slices; whole rock) lated by Alvarez and others (1982). Specula- Layer V tively, the iridium either (1) was incorporated D8 35 into the smectite itself as it formed from vitric Layer IV (black fissile clay) ash during the alteration of impact and/or vol- D7 134 1.9 11.9 <4 0.54 <0.2 D6 170 2.2 11.4 <5 0.65 <0.2 canic ejecta and/or (2) is within a trace submi- D5 310 3.6 13.8 <9 0.81 <0.3 D4 500 3.9 16.2 <10 0.85 <0.3 cron phase or phases yet to be identified in the D3 520 4.1 16.3 <10 0.84 <0.3 Fish Clay which could contain significant iri- D2 740 4.8 19.9 <12 0.81 <0.3 Dl 860 3.7 22.7 <9 0.55 <0.2 dium concentrations, such as particulate bolide Rust-colored stain in Fish Clay D5 material, organic carbon (Hansen and others, 3830 101 <4.1 1987; Schmitz, 1988), magnesioferrite (Bohor Nye Klov K/T boundary mail (whole rock) and others, 1987c; Smit and Kyte, 1984; Kyte 257 0.69 1.11 and Smit, 1986), or hypothetically, magnetite Limhamn Quarry upper marl (whole rock) formed authigenically (Lovley and others, 29 2.17 <40 1987), that could conceivably scavenge noble Kupferechiefer Shale. North Sea Core NAM 17 metals as it forms during diagenesis. 57 110 The peak iridium values at the K/T boundary Literature values for Fish Clay Ganapathy ( 1980) 47. 24. 0.62 0.25 vary significantly on an intrabasin scale, espe- 12.3 55. 17. 0.75 0.16 Kyte and others (1980) 3.4-6.6 18-46 23-69 0.39 0.69 0.50-0.76 cially in Denmark and in Italy (Alvarez and Kastner and others 0.94 1.01 others, 1982). The variable iridium (and other (1984) noble metals) may be a function of differences in •Values for the Au/Ir (0.296) and the Pt/Ir (1.99) ratios in CI chondrites are from Kastner and others (1984). the local depositional and redox environments. Relative to Nye Klav, iridium may have been concentrated in the Fish Clay at Stevns Klint K/T boundary in Scandinavia may not be due to rence in layer II signifies that the basaltic volcanic both physically, by deposition in the biohermal impact. From our study of the Scandinavian sites ash precursor of the Mg-smectite was arriving in troughs, and chemically, by the anoxic condi- alone, however, we cannot claim that basaltic the Danish basin prior to the deposition of tions (Ekdale and Bromley, 1984). The presence volcanism had a global effect. If the Mg-smectite shocked quartz and peak iridium in layer III. of relatively high iridium in the rust stains in is volcanic in origin as we contend, then its occur- The presence of high concentrations of the layer IV proves that Ir, and the other noble me- tals enriched in the stain, are highly mobile. Our results in Table 3 also indicate that the Pt/Ir and Au/Ir ratios within the Fish Clay whole-rock samples, in some cases, do not approximate the values for CI chondrites to within a half order of magnitude. If their source was chrondritic, then TABLE 4. MAJOR-ELEMENT OXIPE ANALYSES (WT. it) OF THE FISH CLAY FELDSPAR Oxide Wt % Si02 54.79 AI2O3 28.51 TiOj 0.02 CaO 11.20 FeO 0.21 MgO 0.02 BaO 0.01 Na20 5.01 K2O 0.37 Total 100.14 Note-, average of six analyses. The mode corresponding to this chemical composition is a labradorite with 53% anorthite, 44% albite, 2% orthoclase, with a remainder of diopside and quartz. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 708 ELLIOTT AND OTHERS the noble metals have been subjected to geo- the Toba eruption display a mosaicism inter- with our inference of a very high bolide-to-target chemical processes that have mobilized Ir. In preted to be caused by shock metamorphism ratio in the ejecta is compatible with either a general, the chemical mobility of the noble met- (Carter and others, 1986; Carter and Officer, meteorite much smaller than the proposed 10- als could have been an important process to 1987), and Carter and others noted that shocked km-diameter bolide or a less massive comet account for the difference in the parts-per-billion quartz and feldspar grains are present 2 m above (Hut and others, 1987) that excavated a rather concentrations of noble metals in these K/T and below the K/T boundary at Gubbio, Italy shallow crater in sandstone on the continent or boundary clays and their particularly high con- (Crocket and others, 1988; Hallam, 1987). Be- continental shelf. A close encounter with a centration in the Fish Clay as stressed earlier by cause quartz with the definitive multiple sets of comet, or the impact of an asteroid as small as Schmitz (1983). planar features caused by shock metamorphism 0.4 km diameter, has been shown by modeling We are left with unanswered questions on the has not been found frequently in distal volcano- to affect the global environment catastrophically significance of the nonchondritic, and rather genic rocks, we cannot reject the impact hy- and reduce photosynthesis to 10~3 of normal high, noble-metal contents of a black shale that pothesis summarily at this time; however, our (Gerstl and Zardecki, 1982). As more informa- are similar on a gross level to those of the Fish results challenge aspects of this hypothesis. tion is gathered and interpreted on the K/T Clay. The organic black shale member of the Specifically, our results indicate that the bulk boundary event, like many geologic phenomena, Permian Kupferschiefer Shale is reported to con- of the Fish Clay is composed predominantly of it is seen to be a complex interaction of physical, tain parts-per-million levels of Pt, Pd, and Au in volcanic and detrital minerals. Impact-derived chemical, and biological phenomena not easily Poland (Kucha, 1982), as well as prominent Cu, phases are present in minor amoun ts in the Fish trimmed by Ockham's razor. Ag, Pb, and Zn sulfide mineralization (for ex- Clay. Grains of shocked quartz are concentrated ample, Jowett and others, 1987). The same in the millimeter-thin "impact layer" within a CONCLUSIONS processes responsible for variable enrichment of thicker K/T boundary marl (B. F. Bohor and the noble metals in black shales, like the Kupfer- G. A. Izett, 1988, written cominun.). If the (1) If one excludes the red-orange basal layer schiefer Shale, are likely to have controlled the shocked quartz is impact derived, and if most of III, which we did not analyze in this study and irregular distribution among the K/T boundary the Ir is derived from the bolide, then what little which contains the shocked quartz (B. F. Bohor marls at various localities as well. Furthermore, impact-derived material is present in the K/T and G. A. Izett, written commun.); the Fish Clay if it is considered that the Fish Clay is akin litho- boundary must have had a very high concentra- is composed predominantly of volcanic-derived logically to organic black shales, it is possible tion of Ir. Yet, that phase(s) has not been identi- and detrital phases. Mg-smectite of volcanic that significant amounts of its noble metals are fied, although carbon appears to concentrate origin is the predominant clay mineral in the derived from the same kind of nonimpact parts-per-million levels of Ir (Hansen and others, K/T boundary marls at Nye Kiev and Kjolby sources that contributed to the high metal 1987; Schmitz, 1988). In order to have had a Gaard, as well as at Stevns Klint as reported contents in the Kupferschiefer Shale. high Ir content, the globally distributed ejecta previously, and it is the predominant clay min- must have been dominated by bolide rather than At present, shocked quartz having the distinc- eral in the marl of probable early Danian age at by terrestrial target material to even a greater tive multiple planar sets has not been found as- Limhamn. Moreover, the Mg-smectite occurs in extent than the very high values (>0.1) modeled sociated with basaltic volcanism. It is highly layer II, which is stratigraphically below the by O'Keefe and Ahrens (1982) for high-speed unlikely that basaltic volcanism directly pro- presence of shocked quartz and peak iridium in ejecta. Generally, the small amount of ejecta and duced shocked quartz. Major acidic pyroclastic the Fish Clay. By contrast, the clay mineralogies the high Ir contents of the K/T boundary units volcanism, however, commonly predates and of the upper Limhamn marl and the K/T favor the possibility that the bolide was more of accompanies major episodes of basaltic volcan- boundary are distinct from those of the lower an iron meteorite, as concluded from the os- ism erupted through continental crust (for Limhamn marl and of the Dania Quarry marl. mium isotopic data (Luck and Turekian, 1983), example, Woldegabriel, 1987), and Loper and (2) The iridium (and other noble metals) in as opposed to being chondritic. In addition, the McCartney (1988) have indicated a theoretical the K/T boundary marls at Stevns Klint is pres- possibility of coincident basaltic volcanism de- mechanism for an explosive basaltic eruption to ent largely in the finest submicron fractions. creases and perhaps masks the sensitivity that disperse shocked quartz. At present, the evi- Either the iridium was incorporated into the geochemical analyses on the impact layer would dence is still being weighed in the literature as to smectite itself when it formed authigenically, or have in being able to infer the nature of the whether explosive acidic eruptions can produce iridium is present in very large parts-per-million target (for example, DePaolo and others, 1983). the multiplanar lamellae (see discussions by concentrations in unidentified trace phases in the Carter and Officer, 1987; Izett and Bohor, 1987; The ubiquitous shocked quartz in the K/T submicron size fraction. Our measurements Alexopolous and others, 1988) that are observed boundary units world-wide, and the lack of al- demonstrate that these metals can be remobil- in both terrestrial and marine K/T boundary most any other shocked phases in these bound- ized and concentrated in nonchondritic ratios by sections (Bohor and others, 1987b) and are ary units, seems incompatible with the proposed secondary alteration. There are significant claimed to be of impact origin. Shocked quartz impact by a very large bolide (10 km diameter, amounts of Au, Pt, and possibly Ir in the Kup- with multiple planar sets appears to be a distinc- Alvarez and others, 1980). Continental impact ferschiefer Shale relative to the K/T boundary. tive component of the K/T boundary (for ex- by a large bolide should have excavated deeply It is thus possible that some of the noble metals ample, Izett and Bohor, 1987; Alexopolous and into the continental crust and should have in the K/T boundary have been derived and/or others, 1988; discussion by Kerr, 1987), al- ejected other shocked phases (for example, concentrated by similar nonimpact processes though quartz with one planar set has been feldspar; Carter and others in Crocket and oth- which have produced high (parts per billion) found at the Toba eruption, other minerals in ers, 1988) in addition to quartz. This, together concentrations in the Kupferschiefer Shale. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 ORIGIN OF CLAY MINERALS AT CRETACEOUS/TERTIARY BOUNDARY, DENMARK 709 (3) The Mg-rich character of the smectite forming the irradiation. F. Asaro, B. F. Bohor, reduce the viscosity of the melt. U.S.G.S. standards of and the presence of labradorite feldspar (Fig. 3 G. Izett, M. Kastner, C. W. Naeser, C. T. Pill- MAG-1 and SCo-1 were prepared and analyzed as unknowns. Working curves for each element were de- and Table 4) in the Fish Clay indicate that vol- more, R. C. Reynolds, and B. Schmitz read and termined by analyzing a suite of 42 geochemical rock canism was basaltic in composition and commented on an earlier draft. standards, data for each having been compiled (includ- pyroclastic. ing SCo-1 and MAG-1) by Abbey (1983). (4) Physical models of the impact must ac- Where there was an insufficient amount of material count for the predominance of nonimpact- for XRF analysis, these clay fractions were analyzed APPENDIX 1. METHODS using an induction coupled plasma atomic emission derived phases in the K/T boundary marls, their spectrophotometer (ICP). The ICP analyses were per- large intrabasin and interbasin variability of Large amounts of Fish Clay A and B (50 and 65 g, formed by Sharon Matis of BP America, Warrensville noble-metal contents, and the presence of thin respectively) and smaller amounts (20-25 g) of Fish Research Center, Cleveland, Ohio. For ICP, 0.1000 g (millimeter thick) shocked-quartz-bearing "im- Clay C1-C3 and Fish Clay E were processed for clay was dissolved in a mixture of hydrochloric, nitric, and pact zones" or layers within the thicker (cen- mineralogical and chemical analyses. Coarse pyrite in hydrofluoric acid in a Teflon-lined Parr Bomb at 125 °C for 48 hours; 15 ml of saturated boric acid and timeter thick) K/T boundary units. these samples was excluded by hand. The clay miner- alogies were determined on the <2 and <0.125 Mm deionized water was added to make a 50.0-g solution. (5) At present, our results together with the fractions from X-ray diffraction patterns, and the This solution was analyzed using a Jarrell-Ash Induc- ubiquitous presence of shocked quartz in the major-element concentrations were determined on the tion Coupled Plasma Spectrometer, which was cali- brated using a series of inhouse standard solutions, K/T boundary world-wide are most compatible <0.125 /um fractions. Unlike previous studies, the including 100 ppm silicon and aluminum standard with a scenario of a continental impact by a <0.125 ix m fractions were obtained to exclude the coarser detrital components, such as illite and quartz. solutions, to analyze a wide variety of elements. relatively small metal-rich bolide occurring si- U.S.G.S. standard G-2 was prepared and analyzed as In order to obtain smectite separates free from ce- an unknown. The results for the clay fractions, and for multaneously with pyroclastic basaltic volcan- ments and to disaggregate them completely from G-2, including the accepted values for G-2 as listed by ism in the proto-North Atlantic region. Alterna- coarser detrital phases, these samples were treated Flanagan (1969), are shown in Table 1. tively, if (1) multiplanar shocked quartz is found chemically following the procedures outlined by Jack- Conventional K-Ar ages were measured on various to be the result of explosive pyroclastic volcan- son (1979). Carbonates were removed from these marls using a mild IN acetic acid-sodium acetate size fractions of Fish Clay samples A and B. Potassium ism and (2) if sufficiently intense and/or buffer solution at pH 4.5 at 50 °C over a period of 1 to was determined by flame photometry using a lithium widespread major basaltic volcanism can be 3 weeks. Free iron oxides were removed using a buf- internal standard. Argon isotopic compositions were 38 found to have occurred coincident with the K/T fered sodium citrate-sodium dithionate-sodium bi- measured together with an aliquot of Ar spike using boundary outside Scandinavia (such as the Dec- carbonate solution (pH 7.3) with additions of sodium an MS-10 mass spectrometer in the static mode on line to the Case Western Reserve University argon extrac- can Traps), then a volcanic scenario might be hyposulfite. Organics were removed from Fish Clay A, B, and C1-C3 by repeated treatments of 50% H202 tion line. The argon contents of the smectite separates sufficient to explain the K/T boundary event. at 50 °C. The sand, silt, and fine-silt fractions were were measured without an Ar spike, owing to the low separated by screening and centrifugation. The result- radiogenic argon content. The unspiked argon ant <2 ¡xm suspension was separated into various determinations rely on the nearly constant yield ACKNOWLEDGMENTS micron and submicron size fractions down to <0.125 of extracted argon and sensitivity of the MS-10 jitm using a continuous-flow Sharpies centrifuge. All mass spectrometer before and after the unspiked We thank Graham Bell and Risto Rttkonen submicron fractions analyzed further were dialysed in determinations. of Cementa AB Malmo, Sweden, for their as- deionized water for 3 to 5 days. Some organic matter The clay fractions of Fish Clay A and Fish Clay sistance in allowing us to collect the Limhamn was judged to be present in some of the Fish Clay C1-C3 and the whole-rock samples from Fish Clay D, samples after the chemical pre-treatment, based on the the K/T boundary at Nye Kiev, and the upper Lim- Quarry marls. This study was funded by grants gray color. We verified this through commercial car- hamn marl were analyzed for noble metals Ag, Au, Ir, from the Case Western Reserve University bon analysis (Galbreath Laboratories, Knoxville, Ten- and Pt. For the analyses, 0.2- to 0.8-g samples were (CWRU) Graduate Alumni Fund and from the nessee). A sample collected from the base of layer IV irradiated for 40 hours in the central thimble of the CWRU Chapter of Sigma Xi. The time for writ- contains 28.8% CaC03 and 1.55% organic carbon be- U.S. Geological Survey TRIGA reactor (thermal neu- 13 2 ing the results was funded by National Science fore chemical treatments. After chemical treatments, tron flux = 1.5 x 10 n/cm /sec). Only 50 mg of the the <0.125 fim fraction from this layer still contained "rust-colored stain" was available. The radiochemical Foundation Surficial Processes Program Grant 1.0% to 1.2% organic carbon. procedure, which was used to separate the noble met- EAR87-09392, awarded to J. L. Aronson. The clay mineralogies were determined using a No- als before counting, is described by Millard (1987). Bronwyn Weaver and Clarissa Gereby assisted relco 12045-1 X-ray diffractometer with 1° divergence The third fusion with the lead button was not per- formed with these samples. Ranges for the coefficients in the chemical pre-treatments, separations, and and receiving slits and CuKa Ni-filtered radiation, of variation (one standard deviation based on counting dialysis. Donald N. Schad shot the photomicro- scanned at 1° 26 per minute. The percent expandable, statistics) are 1% to 3% for Ag, 7% to 8% for Au, 2% to graph. Dr. Martin E. Kordesch assisted with or percentage of smectite layers, in illite/smectite was determined from the average of the percent expand- 5% for Ir, and 10% to 20% for Pt. field work at Stevns Klint. M. C. Yang and able layers derived from the 17 A peak/saddle The major-element chemistry of sand-sized grains G. Zagger examined the plagioclase grains, using intensity ratio, and the positions of the (001 )10/ was analyzed using a Chemica Electron Microprobe at a scanning electron microscope (SEM) with (002)17 and (002)]0/(003)l7 peaks (Reynolds and Los Alamos National Laboratory. Acceleration vol- energy dispersion X-ray spectroscopy. We thank Hower, 1970; Hower, 1981). tage was 15 KeV; beam current was 14.8 nA. Sharon Matis (BP America) for the induction The major-element concentrations were determined on the <0.125 jum fractions and on U.S. Geological coupled plasma analyses, Stanley A. Mertzman Survey (U.S.G.S.) standards using X-ray fluorescence for the X-ray fluorescence analyses, John Angus (XRF); the X-ray fluorescence analyses were done by for the use of the SEM, Giday Wolde-Gabriel of Stanley A. Mertzman at Franklin & Marshall College. REFERENCES CITED Los Alamos National Laboratory for the elec- For XRF, 3.6000 g of Li2B407 was mixed with Abbey, S., 1983. Studies in "Standard Samples" of silicate rocks and minerals: tron microprobe analyses, and the staff of the 0.4000 g of whole-rock powder and fused into a ho- Geological Survey of Canada Paper 83-15, 33 p. mogeneous disk using a 95% Pt-5% Au crucible and Alexopolous, J. S., Grieve, R.A.F., and Robertson, P. B., 1988. Microscopic U.S. Geological Survey TRIGA reactor for per- lamellar deformation features in quartz: Discriminative characteristics pan. Several drops of dilute Lil solution were added to ofshocked-generated varieties: Geology, v. 16. p. 796-799. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021 710 ELLIOTT AND OTHERS Alvarez, L. W., Alvarez, W. L., Asaro, F., and Michel, H. V., 1980, Extraterres- Hansen, H. J., Rasmussen, K. L., Gwozdz, R., and Kunzendorf, H., 1987, Rampino, M. R., and Reynolds, R. C., 1983, Clay mineralogy of the trial cause for the Cretaceous-Tertiary extinction: Science, v. 208, Iridium-bearing carbon black at the Cretaceous-Tertiary boundary: Cretaceous-Tertiary boundary clay: Science, v. 219, p. 495-498. p. 1095-1108. Geological Society of Denmark Bulletin, v. 36, p. 305-314. Reynolds, R. C., and Hower, J., 1970, The nature of interlayering in mixed- Alvarez, W., Alvarez, L. W., Asaro, F., and Michel, H. V., 1982, Current status Hansen, H. J., Gwozdz, R„ and Rasmussen, K. L„ 1988, High resolution trace layer illite-montmorillonite: Clays and Clay Minerals, v. 18, p. 25-56. of the impact theory for the terminal Cretaceous extinction: Geological element chemistry across the Cretaceous-Tertiary boundary in Den- Rocchia, R., Renard, M., Boclet, D., and Bonte, P., 1984, Essai d'évaluation de Society of America Special Paper 190, p. 305-315. mark: Revista Española de Paleontología n. Extraordinario, p. 21-29. la durée de la transition Crétacé/Tertiaire par l'évolution de l'anomalie Aronson, J. L., and Hower, J., 1976, The mechanism of burial metamorphism Holland, B., and Gabrielson, J„ 1979, Guide to Limhamn Quarry, in Birkelund, en iridium; implications dans la recherche de la cause de la crise biolo- of argillaceous sediments: 2. Radiogenic argon evidence: Geological T., and Bromley, R. G., eds., Cretaceous-Tertiary boundary events, I. gique: Bulletin de la Société Géologique de France, v. 7, p. 1193-1202. Society of America Bulletin, v. 87, p. 738-744. The Maastrichtian and Danian of Denmark: University of Copenhagen, Rocchia, R., Boclet, D., Devineau, J., Jehanno, C., and Renard, M., 1987, Birkelund, T., and Bromley, R. G., eds., 1979, Cretaceous-Tertiary boundary p. 142-151. Comparaison des distribution de l'iridium observées à la limite Crétacé- events, I. The Maastrichtian and Danian of Denmark: University of Hower, J., 1981, X-ray diffraction identification of mixed-layer clay minerals, Tertiaire dan divers sites européens: Mémoires de la Société Géologique Copenhagen, 210 p. in Longstaffe, F. J., ed., Clays and the resource geologist: Mineralogical de France, v. 150, p. 95-103. Bohor, B. F., Triplehorn, D. M„ Nichols, D. J., and Millard, H. T„ Jr., 1987a, Association of Canada Short Course Handbook 7. p. 39-59. Rosenkrantz, A., 1955, Vidnesbyrd om vulkansk aktivitet i Grönland og Dan- Dinosaurs, spherules, and the "magic" layer: A new K-T boundary clay Hut, P., Alvarez, W., Elder, W. P., Hansen, T„ Kauffmun, E. G„ Keller, G., marks danien: Meddelelser fra Dansk Geologisk Forening, v. 12, site in Wyoming: Geology, v. 15, p. 896-899. Shoemaker, E. M., and Weissman, P. R., 1987, Comet showers as a p. 669-670. Bohor, B. F., Modreski, P. J., and Foord, E. E, 1987b, Shocked quartz in the cause of mass extinctions: Nature, v. 329, p. 118-126. Schmitz, B., 1983, Metal precipitation in the Cretaceous-Tertiary boundary Cretaceous-Tertiary boundary clays: Evidence for a global distribution: Izett, G. A., 1987, Authigenic "spherules" in K-T boundary sediments at Cara- clay at Stevns Klint, Denmark: Geochimica et Cosmochimica Acta, Science, v. 236, p. 705-709. vaca, Spain, and Raton Basin, Colorado and New Mexico, may not be v. 49, p. 2361-2370. Bohor, B. F., Foord, E. E., and Ganapathy, R., 1987c, Magnesioferrite from the impact derived: Geological Society of America Bulletin, v. 99, p. 78-86. 1988, Iridium, sulfur isotopes and rare earth elements in the Cretaceous- Cretaceous-Tertiary boundary, Caravaca, Spain: Earth and Planetary Izett, G. A., and Bohor, B. F., 1987, Comment on "Dyramie deformation of Tertiary boundary clay at Stevns Klint, Denmark: Geochimica et Cos- Science Letters, v. 81, p. 57-66. volcanic ejecta from Toba caldera: Possible rele\ance to Cretaceous/ mochimica Acta, v. 52, p. 229-232. Carter, N. L., and Officer, C. B., 1987, Reply on "Dynamic deformation of Tertiary boundary phenomena": Geology, v. 15, p . 90. Smit, J., and Kyte, F. T., 1984, Siderophile-rich magnetic spheroids from the volcanic ejecta from Toba caldera: Possible relevance to Cretaceous/ Jackson, M. L., 1979, Soil chemical analysis—Advanced course: Madison, Cretaceous-Tertiary boundary in Umbria, Italy: Nature, v. 310, Tertiary boundary phenomena": Geology, v. 15, p. 91-92. Wisconsin, M. L. Jackson, 895 p. p. 403-405. Carter, N. L., Officer, C. B„ Chesner, C. A., and Rose, W. I., 1986, Jowett, E. C., Rydzewski, A., and Jowett, R. J., 1987. The Kupferschiefer Smit, J., and Romein, A.J.T., 1985, A sequence of events across the Dynamic deformation of volcanic ejecta from Toba caldera: Possible Cu-Ag ore deposits in Poland: A re-appraisal of the evidence of their Cretaceous-Tertiary boundary: Earth and Planetary Science Letters, relevance to Cretaceous/Tertiary boundary phenomena: Geology, origin and presentation of a new genetic model: Canadian Journal of v. 74, p. 155-170. v. 14, p. 380-383. Earth Science, v. 24, p. 2016-2037. Valeton, V. H., 1959, Eine vulkanische Tuffanlage aus der Oberkreide von Christensen, L., Fregeslev, S., Simonsen, A., and Thiede, J., 1973, Sedimentol- Kastner, M„ Asaro, F., Michel, H. V., Alvarez, W„ and Alvarez, L. W„ 1984, Hemmoor/Niederelbe: Neues Jahrbuch für Geologie und Paläontologie ogy and depositional environments of lower Danian Fish Clay from The precursor of the Cretaceous-Tertiary boundary clays at Stevns Klint Monatshefte, p. 193-204. Stevns Klint, Denmark: Geological Society of Denmark Bulletin, v. 22, and DSDP Hole 465a: Science, v. 226, p. 137-143. 1960, Vulkanische Tuffiteinlagerung in der nordwestdeutschen Oberk- p. 193-212. Kerr, R. A., 1987, Asteroid impact gets more support: Science, v. 236, reide: Mitteilungen aus dem Geologischen Staatsinstitut in Hamburg, Crocket, J. H„ Officer, C. H., Wezel, F. C., and Johnson, G. D., 1988, Distri- p. 666-668. v. 29, p. 26-41. bution of noble metals across the Cretaceous/Tertiary boundary Kucha, H., 1982, Platinum-group metals in the Zechstein copper deposits, Varekamp, J. C., and Thomas, E., 1982, Chalcophile elements in Cretaceous/ at Gubbio, Italy: Iridium variation as a constant on the distribution Poland: Economic Geology, v. 77, p. 1578-1591. Tertiary boundary sediments: Terrestrial or extraterrestrial?: Geological and nature of Cretaceous/Tertiary boundary events: Geology, v. 56, Kyte, F. T., and Smit, J., 1986, Regional variations in spinel compositions: An Society of America Special Paper 190, p. 461-467. p. 77-80. important key to the Cretaceous/Tertiary event: Geology, v. 14, Woldegabriel, G., 1987, Volcanotectonic history of the central sector of the DePaolo, D. J., Kyte, F. T„ Marshall, B. D., O'Neil, J. R., and Smit, J., 1983, p. 485-487. main Ethiopian rift [Ph.D. dissert.]: Cleveland, Ohio, Case Western Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary Kyte, F. T„ Zhou, Z., and Wasson, J. T., 1980, Siderophile-enriched sediments Reserve University, 410 p. boundary sediments, Caravaca, Spain: Evidence for an oceanic impact from the Cretaceous-Tertiary boundary: Nature, v. 288, p. 651-656. Zoller, W. H„ Parrington, J. R., and Phelan Kotra, J. M„ 1983. Iridium site: Earth and Planetary Science Letters, v. 64, p. 356-373. Loper, D. E., and McCartney, K., 1988, Shocked quartz found at the K/T enrichment in airborne particles from Kilauea Volcano: Science, v. 222. Ekdale, A. A., and Bromley, R. G., 1984, Sedimentology and ichnology of the boundary, A possible endogenous mechanism: E.OS (American Geo- p. 1118-1121. Cretaceous-Tertiary boundary in Denmark: Implications for the causes physical Union Transactions), v. 69, p. 961-972. of the terminal Cretaceous extinctions: Journal of Sedimentary Petrol- Lovley, D. R., Stoltz, J. F„ Nord, G. L., and Phillips, E.J.P., 1987, Anaerobic ogy, v. 54, p. 681-703. production of magnetite by a dissimilatory iron-: educing microorgan- Flanagan, F., 1969, U.S. Geological Survey standards, II. First compilation of ism: Nature, v. 330, p. 252-254. data for the new U.S.G.S. rocks: Geochimica et Cosmochimica Acta, Luck, J. M., and Turekian, K. K., 1983, Osmium-187/ojmium-186 in manga- v. 53, p. 89-120. nese nodules and the Cretaceous-Tertiary boundary: Science, v. 222, Ganapathy, R., 1980, A major meteorite impact on the earth 65 million years p. 613-615. ago: Evidence from the Cretaceous-Tertiary boundary clay: Science, Millard, H. T., Jr., 1987, Neutron activation determination of iridium, gold, v. 209, p. 921-923. platinum, and silver in geologic samples: Journal cf Radiochemistry and Gerstl, G.A.W., and Zardecki, A., 1982, Reduction of photosynthetically active Nuclear Chemistry, v. 113, p. 125-132. radiation under extreme stratospheric aerosol loads: Geological Society Odin, G. S., 1982, Numerical dating in stratigraphy: New York, John Wiley & of America Special Paper 190, p. 201-210. Sons, 1,040 p. Hallam, A., 1987, End-Cretaceous mass extinction event: Argument for terres- O'Keefe, J. D., and Ahrens, T. J., 1982, The interaction of the Cretaceous/Ter- trial causation: Science, v. 238, p. 1237-1242. tiary extinction bolide with the atmosphere, ocean, and solid earth: MANUSCRIPT RECEIVED BY THF. SOCIETY JUNE 6, 1988 Hansen, H. J., Gwo2d2. R.. Bromley, R. G„ Rasmussen, K. L., Vogensen, Geological Society of America Special Paper 190, p. 103-120. REVISED MANUSCRIPT RECEIVED NOVEMBER 18, 1988 E..W., and Pedersen, K. R., 1986, Cretaceous-Tertiary boundary Pedersen, A. K., Engell, J., and Rensbo, J. G., 1975, Early Tertiary volcanism MANUSCRIPT ACCEPTED NOVEMBER 23, 1988 spherules from Denmark, New Zealand, and Spain: Geological Society in the Skagerrak: New chemical evidence from ash-layers in the mo-clay CASE WESTERN RESERVE UNIVERSITY GEOLOGY DEPARTMENT of Denmark Bulletin, v. 35, p. 75-82. of northern Denmark: Lithos, v. 8, p. 255-268. CONTRIBUTION 170 Printed in U.S.A. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/101/5/702/3380692/i0016-7606-101-5-702.pdf by guest on 24 September 2021