Cretaceous-Tertiary Boundary Clay Research Articles

High-resolution trace element chemistry across the Cretaceous-Tertiary boundary in Denmark

Closely spaced samples on millimeter scale across the Cretaceous-Tertiary boundary clay in Denmark were analyzed by instrumental neutron activation analysis. The results show a strong correlation between Cr and Ir while Co, Zn, As, Sb and Au are correlated with Fe. The elemental peaks for Ir-Cr and Fe are separated by 6 mm. The Fe peak is found in burrow-fillings at the lowermost part of the boundary clay. Chromite grains extracted from boundry clay in Denmark and New Zealand show a compositional common group. The composition points to an ultrabasic (kimberlitic) origin of the chromites. Tandem accelerator mass spectroscopy demonstrated, that there are no Ir carriers in addition to elemental carbon in the boundary clay from two localities in Denmark.

XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint

XAFS study of Zr in Cretaceous–Tertiary boundary clays from Stevns Klint

白亜紀-第三紀(K-T)境界粘土層に含まれる硫化鉱物のマイクロビーム蛍光X線マッピング

白亜紀-第三紀(K-T)境界粘土層に含まれる硫化鉱物のマイクロビーム蛍光X線マッピング

When the Sun died over northern Europe: the unique geology of Denmark's inland islands

Most geologists asked to comment on the geology of Denmark would probably think of Cretaceous Chalk and Pleistocene glacial deposits. Today, many will perhaps be familiar with the Cretaceous–Tertiary boundary clay at Stevns Klint, which has played a prominent role in the discussions regarding the mass extinction event at this time (the ever popular ‘end of the dinosaurs’). Few would perhaps think of volcanic or tectonic phenomena, although, in fact, outstanding localities for these processes are to be found here, documenting a time when dense volcanic ash clouds drifted over north‐west Europe.

Fireball passes and nothing burns—The role of thermal radiation in the Cretaceous-Tertiary event: Evidence from the charcoal record of North America: Comment and Reply

[Belcher et al. (2003)][1] reported that at six locations across North America quantities of charcoal in the Cretaceous-Tertiary (K-T) boundary clay are about an order of magnitude below background levels. They interpreted this absence of charcoal as evidence for the absence of a global

Review of the mineralogy of the Cretaceous-Tertiary boundary clay: evidence supporting a major extraterrestrial catastrophic event

AbstractThe proposed impact event at the end of the Cretaceous resulted in mass extinctions and subsequently significant variations in the geochemical and mineralogical composition of the sediments marking the K/T boundary. The impact-generated material derived from target rocks produced the ejecta layer deposits around Chicxulub crater, which were subsequently diagenetically altered to mainly smectite in marine sections and to kaolinite in continental sections. The fireball layer represents the cosmic dust dispersed and deposited globally and contains smectite derived from the alteration of microkrystites and the finest fraction. The lowermost Danian clay layer, recognized in marine sections, resulted from the sudden decrease in ocean productivity and represents a reduced sedimentation deposit. Its clay mineral associations depend on local environmental conditions and diagenetic processes. Overall, the diagenetic alteration of the boundary materials resulted in a significant modification of original signatures. The composition of the clay mineral phases can, however, still be evidence of the nature of the precursor materials providing evidence for an extraterrestrial impact event.

High iridium concentration of alkaline rocks of Deccan and implications to K/T boundary

We report here an unusually high concentration of iridium in some alkali basalts and alkaline rocks of Deccan region having an age of about 65Ma, similar to the age of the Cretaceous-Tertiary boundary. The alkali basalts of Anjar, in the western periphery of Deccan province, have iridium concentration as high as 178pg/g whereas the alkaline rocks and basalts associated with the Amba Dongar carbonatite complex have concentrations ranging between 8 and 80 pg/g. Some of these values are more than an order of magnitude higher than the concentration in the tholeiitic basalts of Deccan, indicating the significance of alkaline magmatism in the iridium inventory at the Cretaceous-Tertiary boundary. Despite higher concentration, their contribution to the global inventory of iridium in the Cretaceous-Tertiary boundary clays remains small. The concentration of iridium in fluorites from Amba Dongar was found to be <30 pg/g indicating that iridium is not incorporated during their formation in hydrothermal activity.

Determination of Platinum‐Group Elements and Forty Two Other Elements in Two Candidate Danish Cretaceous‐Tertiary Boundary Clay Reference Materials by INAA, ENAA and RNAA

Ruthenium, rhodium, palladium, osmium, iridium and platinum (PGEs) and forty two other elements in two candidate geological Cretaceous‐Tertiary boundary clay reference materials taken from the Fish Clay, Stevns Klint, Denmark, were determined by a combination of neutron activation analysis (NAA) consisting of instrumental, epithermal and radiochemical NAA with or without nickel sulfide fire assay preconcentration. The accuracy of the experimental values was assessed by the comparative analysis of the certified reference materials.

Presence of an iron‐rich nanophase material in the upper layer of the Cretaceous‐Tertiary boundary clay

Abstract— We report new geochemical evidence from ten Cretaceous‐Tertiary (K‐T) boundary sites in North America and Europe, indicating the presence of a material remnant of a large asteroid or comet that struck the Earth at 65.0 Ma. Mössbauer spectroscopic data reveals that a ubiquitous iron‐rich nanophase material exists at the uppermost part of the K‐T boundary layer in the Western Hemisphere and in Europe in marine and continental fine‐grained sedimentary rock. The high surface‐to‐volume ratio of nanophase material suggests that it may be the carrier of the iridium abundance enhancement that marks the K‐T boundary. Even more provocative is the possibility that the discovered nanophase material is, for the most part, composed of the vaporized impactor after the impact‐generated high‐temperature vapor plume rose and cooled above the atmosphere.

Ru/Ir ratios at the Cretaceous-Tertiary boundary: Implications for PGE source and fractionation within the ejecta cloud

Ruthenium and Ir are the least mobile platinum group elements (PGEs) within the Cretaceous-Tertiary (K-T) boundary clay. The Ru/Ir ratio is therefore the most useful PGE interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay. The Ru/Ir ratio of European marine K-T sections (1.67 ± 0.38) is statistically different from that of the North American continental sections (0.76 ± 0.26). It is unlikely that this difference is due to secondary PGE remobilization, PGE input to the boundary clay during multiple impacts, or volcanic emissions. The global difference in Ru/Ir ratios in the boundary clay may therefore be primary. The positive correlation between distance from the Chicxulub impact structure, Yucatán, Mexico, and Ru/Ir ratio and the more than 1000°C difference in the condensation temperatures of these elements lead us to propose that fractionation of Ru from Ir during condensation from the ejecta cloud may have occurred, resulting in the global difference in Ru/Ir ratios.

Chalcophile elements and Ir in continental Cretaceous-Tertiary boundary clays from the western interior of the USA

This study presents data for Ir and the chalcophile elements As, Sb, and Zn in seventeen samples from continental K/T boundary layers in the western interior of the USA. The results show that in contrast to previously studied marine boundary clays, the continental boundary layers show no correlation between Ir and any of the chalcophile elements. Compared with average shale, the continental boundary layers are significantly to strongly enriched in Ir, As, and Sb, but show ordinary Zn concentrations. The Ir enrichments can be attributed to fallout of extraterrestrial matter, whereas As and Sb enrichments can be readily explained by the close spatial association of the boundary layers with coal and the abundance in the layers of jarosite, goethite, and other weathering products of pyrite. If compared to jarosite-rich coal-associated background samples, the boundary layers show much higher Ir concentrations but similar (or possibly slightly enhanced) concentrations of As, Sb, and Zn. The correlation between chalcophile elements and Ir in marine boundary clays, and the absence of such a correlation in continental boundary clays, concurs with the idea that a major fraction of the Ir in extremely Ir-rich (30–460 ppb Ir) marine boundary clays has precipitated from seawater that was enriched in Ir being derived from a vaporized asteroid.

Chemical species of iridium and other trace elements in the Cretaceous-Tertiary boundary clays and their implication

The geological samples: Cretaceous-Tertiary (K-T) boundary clays, meteorites, volcanic lava, and ultrabasic rock were separated into carbonate, metal, sulfide, oxide, silicate and acid-resistant residue by a selective chemical dissolution procedure developed in our laboratory. Some conclusions were drawn by analyzing the chemical speciation of anomalous iridum in the above samples and especially by studying the characteristics of mineral components in those residue phases. (1) It is impossible that the anomalous Ir was caused by geochemical enrichment; (2) The iridium enrichment in the K-T boundaries did not necessarily associate with kerogen; (3) The volcanic activity has participated in the extinction event at the end of Cretaceous; (4) Extraterrestrial impact was the trigger of K-T event. Then, we proposed a mixed model by which the extant anomalous Ir in K-T boundary clays was interpreted as a combined effect of extraterrestrial impact, volcano eruption and post-depositional redistribution.

A method for the quantification of bismuth and palladium in geological materials including Cretaceous-Tertiary boundary clays

A method was developed for the determination of Bi and Pd in geological materials. The elements are extracted into methylisobutyl ketone (MIBK) from 3 M HCl using ammonium pyrrolidine dithiocarbamate (APDC) as the ligand. The organic phase is analysed for both elements by graphite furnace atomic absorption spectrometry (GFAAS). The limit of detection (on the original rock sample) was 1 ng g −1 (ppb) for Pd and 200 ng g −1 for Bi. Detection limits could be reduced considerably by increasing the organic/aqueous phase ratios. The precision and accuracy of the method were tested by analysis of the standard soil GXR- 1 and Pt ore PTC- 1. Precisions of ±6.0% and ±5.2% and accuracies of ±2.5% and ±2.0% were reported for Bi and Pd, respectively. The method was employed to determine Pd and Bi in a Cretaceous-Tertiary (KT) boundary sequence from New Zealand. The correlation between Pd and Ir (determined elsewhere) concentrations was very good and showed that our method could provide a means of determining Pd rather than Ir, and using it as a marker for an extraterrestrial component in boundary shales. Bi concentrations (<4 ng g −1) were very low in the boundary material and these values lend credence to a theory that chalcophiles in KT boundary shales originate from ejecta from an asteroidal or cometary impact with carbonaceous shales in the Earth's crust. Such shales have a low Bi content but high concentrations of other chalcophiles such as As that are enriched in boundary material.

Global fire at the Cretaceous– Tertiary boundary

Cretaceous-Tertiary (K-T) boundary clays from five sites in Europe and New Zealand are 102-104-fold enriched in elemental C (mainly soot), which is isotopically uniform and apparently comes from a single global fire. The soot layer coincides with the Ir layer, suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled.

Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution

Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.

Mineralogy and Petrology of the Cretaceous-Tertiary Boundary Clay Bed and Adjacent Clay-Rich Rocks, Raton Basin, New Mexico and Colorado

ABSTRACT The Cretaceous-Tertiary (K-T) is preserved in a sequence of coal-bearing, fluvial rocks in the lower part of the Raton Formation (Late Cretaceous and Paleocene) at several sites in the east-central part of the Raton Basin. The K-T occurs at the top of a kaolinitic claystone commonly referred to as the boundary clay layer, in an interval of coal and carbonaceous shale. The is defined by the disappearance of certain fossil-pollen taxa. The clay layer also contains shocked quartz grains and abundance anomalies of iridium, chromium, and other elements. Each of these characteristics support the hypothesis of an asteroid impact at the end of the Cretaceous. Small goyazite spheres were also found in the clay bed; however, their origin is ncertain. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and thin-section petrography have shown that the clay bed exhibits unique mineralogic and petrologic characteristics not possessed by other clay-rich beds in coal-bearing rocks of the Raton Basin. The clay bed is composed primarily of well-crystallized kaolinite but also contains subordinate, randomly interstratified, mixed-layer illite/smectite, both of which appear to have been formed by the alteration of vitreous material in a coal-swamp environment. The bulk mineralogy of the clay bed is similar to that of other kaolinite-rich clay beds (tonsteins) that altered in coal swamps from airfall volcanic ash. The alteration process and diagenetic products of the host material in the cl y bed, however, differed from those of the tonsteins, resulting in a unique petrographic fabric. The clay bed is characterized by an overall imbricate fabric that may reflect an original vitreous material that included shards, bubbles, and spheres. The original fallout material of the clay bed first altered to cabbage-like microspherules, indicating a halloysite or allophane precursor, and then to well-crystallized kaolinite; the well-crystallized kaolinite is the diagenetic stable phase for these rocks at their maximum burial conditions. In comparison, the vitreous components of the tonsteins were altered directly to coarse vermicular and platey kaolinite. Alteration of the original fallout material in the bed was probably rapid, leading to hydrated, disordered, fine-grained clay minerals that formed into curled spherical or tubular shapes. The facto s that produced these unique fabrics in the clay bed existed at all K-T sites in the Raton Basin and were much different from those that formed the coarse platey and vermicular fabrics of ordinary tonsteins. The distinctive character of the clay may be due to the unique nature and chemistry of the fallout material and (or) physical or chemical conditions existing shortly after its deposition.

Magnesioferrite from the Cretaceous-Tertiary boundary, Caravaca, Spain

Magnesioferrite grading toward magnetite has been identified as a very small but meaningful constituent of the basal iron-rich portion of the Cretaceous-Tertiary (K-T) boundary clay at the Barranco del Gredero section, Caravaca, Spain. This spinel-type phase and others of the spinel group, found in K-T boundary clays at many widely separated sites, have been proposed as representing unaltered remnants of ejecta deposited from an earth-girdling dust cloud formed from the impact of an asteroid or other large bolide at the end of the Cretaceous period. The magnesioferrite occurs as euhedral, frequently skeletal, micron-sized octahedral crystals. The magnesioferrite contains29 ± 11 ppb Ir, which accounts for only part of the Ir anomaly at this K-T boundary layer(52 ± 1 ppb Ir). Major element analyses of the magnesioferrite show variable compositions. Some minor solid solution exists toward hercynite-spinel and chromite-magnesiochromite. A trevorite-nichromite (NiFe 2O 4-NiCr 2O 4) component is also present. The analyses are very similar to those reported for sites at Furlo and Petriccio, Umbria, Italy. On the basis of the morphology and general composition of the magnesioferrite grains, rapid crystallization at high temperature is indicated, most likely directly from a vapor phase and in an environment of moderate oxygen fugacity. Elemental similarity with metallic alloy injected into rocks beneath two known impact craters suggests that part of the magnesioferrite may be derived from the vaporized chondritic bolide itself, or from the mantle; there is no supporting evidence for its derivation from crustal target rocks.

Metal precipitation in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark

Alvarez et al. (1980) explained anomalous Ir concentrations in the Cretaceous-Tertiary (K.-T) boundary informal type sediment, the Fish Clay in Denmark, in terms of a global fall-out of extraterrestrial matter. However, geochemical and mineralogical analyses of the various sublayers in the clay, reveal that not only Ir, but also elements such as Ni, Co, Zn, Mo, As, Se, and Sb are substantially enriched in the clay. The enrichments may be due to precipitation of elements as sulfides at a redoxcline. The facts supporting this view are: 1. 1) the over-all chalcophile-element abundance pattern in the clay, 2. 2) the occurrence of a redoxcline, deduced from the distribution of organic matter and oxidized iron in the clay, 3. 3) the large amounts of small pyrite spheroids present at this redoxcline, 4. 4) the high concentration of trace elements in these spheroids. Also Ni, Co, and Ir, elements that have previously been presumed to have a meteoritic origin, are substantially enriched in the spheroids. A model is suggested in which metal-bearing pore solutions lose their metals by precipitation upon passing the boundary between the oxic Cretaceous chalk and the overlying, anoxic and hydrogen sulnde-rich Fish Clay. The great similarity in geochemistry and lithological appearance between several strongly Ir-enriched clays, suggest that the model may also be applied to other K-T boundary clays.

The Precursor of the Cretaceous-Tertiary Boundary Clays at Stevns Klint, Denmark, and DSDP Hole 465A

Results of detailed mineralogical, chemical, and oxygen isotope analyses of the clay minerals and zeolites from two Cretaceous-Tertiary (K/T) boundary regions, Stevns Klint, Denmark, and Deep Sea Drilling Project (DSDP) Hole 465A in the north central Pacific Ocean, are presented. In the central part of the Stevns Klint K/T boundary layer, the only clay mineral detected by x-ray diffraction is a pure smectite with > 95 percent expandable layers. No detrital clay minerals or quartz were observed in the clay size fraction in these beds, whereas the clay minerals above and below the boundary layer are illite and mixed-layer smectite-illite of detrital origin as well as quartz. The mineralogical purity of the clay fraction, the presence of smectite only at the boundary, and the delta(18)O value of the smectite (27.2 +/- 0.2 per mil) suggest that it formed in situ by alteration of glass. Formation from impact rather than from volcanic glass is supported by its major element chemistry. The high content of iridium and other siderophile elements is not due to the cessation of calcium carbonate deposition and resulting slow sedimentation rates. At DSDP Hole 465A, the principal clay mineral in the boundary zone (80 to 143 centimeters) is a mixed-layer smectite-illite with >/=90 percent expandable layers, accompanied by some detrital quartz and small amounts of a euhedral authigenic zeolite (clinoptilolite). The mixed-layer smectite-illite from the interval 118 to 120 centimeters in the zone of high iridium abundance has a very low rare earth element content; the negative cerium anomaly indicates formation in the marine environment. This conclusion is corroborated by the delta(18)O value of this clay mineral (27.1 +/- 0.2 per mil). Thus, this mixed-layer smectite-illite formed possibly from the same glass as the K/T boundary smectite at Stevns Klint, Denmark.

Response : Analysis of the Cretaceous-Tertiary Boundary Clay: Methodology Questioned

<i>Response</i> : Analysis of the Cretaceous-Tertiary Boundary Clay: Methodology Questioned