Uranium at the Cretaceous-Tertiary boundary in Denmark

Uranium is significantly enriched (up to two orders of magnitude) in the Danish Cretaceous-Tertiary boundary beds relative to the underand overlaying sediments. Both the predominant oxic and some anoxic deposits have a high uranium content. To investigate the geochemical behaviour of the element, a series of sections was analysed for uranium by means of the delayed-neutron counting technique. Uranium contents in the carbonate rocks from different parts of the Danish Sub-basin are generally low but show slight regional trends. Experiments that involve cold acid extractions suggest that uranium is associated with the non-carbonate residues. The uranium distribution with depth in the offshore drill core from the Central Graben area (North Sea) suggests that the element is associated with clay in the Danian part. Cretaceous-Tertiary boundary beds from Stevns Klint and other localities in the Danish sub-basin have anomalously high uranium contents compared with the values for chalk. Uranium is not correlated with iron, non-carbonate carbon or aluminium. The highest uranium values within boundary sections are not found in the lower part of the sections as is the case for iridium. The only boundary beds that show typical anoxic depositional affinity have a total uranium accumulation that is one order of magnitude lower than that found in the oxic sections. High amounts of uranium within Cretaceous-Tertiary boundary beds are suggested to be related to diagenetic processes such as compaction and dehydration. Uranium is thought not to cause the extinctions at the Cretaceous-Tertiary boundary because of the relatively low contents found at the actual extinction level.     

Cosmic particles (micrometeorites) and nanospheres from the Cretaceous-Paleogene (K/T) boundary clay layer at the Stevns Klint Section,Denmark

This paper presents new data on numerous small metallic particles of iron, copper, Fe-Ni, Fe-Ni-Co, and Fe-Cr alloys, magnetite, and aluminosilicate balls of cosmic origin found in the black clay boundary layer between the Cretaceous and Paleogene in the Stevns Klint Section (Denmark). The findings imply that a fall of an asteroid to Earth 65 Ma ago was accompanied with falling of finely dispersed metallic particles of extraterrestrial nature related to the asteroid fragments or to micrometeorites following the asteroid or to the intense supply of cosmic dust. The huge amount of finely dispersed matter that fell to Earth at that time should be considered in further reconstructions of events at the boundary of the Cretaceous and Paleogene.     

A preliminary investigation into calcareous dinoflagellate cysts and problematic microfossils from an expanded Cretaceous/Paleogene boundary section at Kulstirenden, Stevns Klint, Denmark

Located to the north of the Stevns Klint Peninsula (Denmark), Kulstirenden shows the transition from Cretaceous chalks to Danian carbonates across the Cretaceous - Paleogene (K/Pg) boundary. The K/Pg boundary at Kulstirenden is represented by the Fiskeler Member (Fish Clay), a streaked marl interval with a smectite rich, red oxidised layer at its base marking the boundary. The Fiskeler Member is important as it includes the iridium concentration linked to the bolide impact which may have caused the end-Cretaceous mass extinction and is at its maximum thickness at Kulstirenden (c.45 cm). Calcareous dinoflagellate cysts (Calciodinelloideae) have been investigated from within the fine fraction (45-125 μm) at Kulstirenden in order to understand the ecological implications of these enigmatic microfossils. Several species were found within the Fiskeler Member, including Orthopithonella collarisWendler et al. (2001, Rev. Palaeobot. Palynol. 115, 69-77). This species is of particular interest as it demonstrates reduced paratabulation and may indicate a transgressive period immediately after the K/Pg boundary event. O. collaris has been described as a morphotype formed under post-K/Pg environmental conditions and is, therefore, described as a “disaster” taxon that marks the K/Pg boundary at Stevns Klint. The distribution of this taxon is more extensive than previously documented, disappearing as carbonate sedimentation returned in the Cerithium Limestone Member of the Danian. Several calcareous microfossil specimens that were found cannot be associated with the dinoflagellates and display Bolboforma-like features. While the origins of Bolboforma are enigmatic, the current finding expands their stratigraphic range and suggests an appearance of this group of organisms found at Stevns Klint may give an insight into the inception of this group into the earliest Danian.     

Last Interglacial stratigraphy at Ristinge Klint, South Denmark

Past environmental changes in the Baltic area are discussed on the basis of foraminifera and ostracods as well as pollen and spores in marine sediments in cliff sections at Ristinge Klint, Langeland, southern Denmark. The sediment succession represents Jessen & Milthers' (1928) pollen zones d-g or Andersen's (1961, 1975) zones E2-E5, and a correlation with the annually laminated Bispingen sequence indicates that the sequence spans about 3400 years. Marine conditions seem to have occurred at c. 300-365 years after the beginning of the Eemian Interglacial, close to fully marine conditions developing by c. 2500 years. This early date of the marine ingression pre-dates that of most previous studies in the region by several hundred years, but it post-dates the initial marine ingression in the easternmost Baltic. A marked change in salinity at c. 650 years after the beginning of the Eemian was presumably caused by an opening of the Danish Belts. An indication of a major alteration in current activity is registered at c. 3000 years after the beginning of the interglacial. The recognition of the relative timing of these events may be significant for the understanding of the opening of connections between the North Sea, the Baltic and the White Sea.     

Sedimentation pattern in Central Anatolia at the Cretaceous-Tertiary boundary

In the Central Anatolia region of Turkey, a mixture of sedimentary and tectonic melanges cover extensive areas, bordering the north, north-west and west of the Kir?ehir Massif. Broadly the age of this melange is Mesozoic; however it includes olistoliths whose ages range from Carboniferous to Cretaceous. A series of interconnected basins existed within the “melange belt” during Late Cretaceous-Early Tertiary times. They have been infilled, throughout the Lower Tertiary, by slump and mass-flow deposits, produced by active tectonic events. These events seem to be a natural continuation of the earlier stronger tectonics which produced the melanges.     

Chemical characteristics of the Cretaceous-Tertiary boundary layer at Gubbio, Italy

Platinum metals (Pd, Ir, Pt) and Au were determined by radiochemical neutron activation analysis (RNAA) on Cretaceous-Tertiary (K---T) boundary samples collected at Gubbio, Italy. In addition, about thirty elements were determined by instrumental NAA (INAA) for both the Cretaceous and the Tertiary layer samples, as well as the boundary clay samples. Iridium and other Pt metals were observed to be similarly enriched, relative to CI-chondrite, in the boundary layers, i.e., they occur in chondritic ratios. On the other hand, correlations among the metals are not very good, suggesting that Pt metals were not incorporated into clay materials in a single phase, but rather, they behaved separately according to their own solution chemistries. In the Gubbio section, the chemical composition does not change so much across the K---T boundary layer, except for Ir (and possibly other Pt group elements) and is very similar to that of the “North American shale composite (NASC)”. Arsenic and Sb were observed not to be anomalously enriched in the Gubbio K---T boundary layers. This implies that their abundances cannot be a clue in elucidating an event which must have happened at the K---T boundary period. NASC-normalized REE abundance patterns for the boundary samples show characteristic features due to some REE precipitation out of seawater. REE abundances are not variable among the Cretaceous, the Tertiary, and the boundary samples, suggesting that conditions for precipitation and sedimentation were similar across the K---T boundary at Gubbio.     

Lacustrine sedimentation and tectonics: an example from the Weichselian at Lønstrup Klint, Denmark

Sedimentological analysis of the Weichselian deposits exposed in the coastal cliff section at Lønstrup Klint, northern Jutland, Denmark, demonstrates the presence of four sedimentary units comprising fine-grained lacustrine and fluvial deposits of the latest Middle Wcichselian. The Lønstrup Klint section also shows an interplay between glaciotectonics and sedimentation. The two lower sedimentary units are separated by an erosional unconformity of pretectonic origin, whereas the upper two units are syntectonic. The glaciotectonic processes reflect the Late Weichselian expansion of the Scandinavian ice cap into northern Jutland. The sedimentary structures indicate high rates of deposition. The area underwent dramatic palaeogeographic changes from deep lake to proglacial fluvial plain in a time-span of a few thousand years.     

High Precision Ru, Pd, Ir, Pt, Re and REE Determinations in the Stevns Klint Cretaceous-Tertiary Boundary Reference Material (FC-1) by Isotope Dilution Multiple Collector Inductively Coupled Plasma-Mass Spectrometry

We present high precision Ir, Ru, Pt, Pd, Re and rare earth element (REE) determinations by isotope dilution multiple collector-ICP-MS on the Cretaceous-Tertiary boundary sedimentary reference material FC-1. Samples for platinum-group element measurements were digested in Carius tubes followed by acid digestion. The platinum-group elements were subsequently separated by anion exchange chemistry and determined by multiple collector-ICP-MS. The accuracy of the platinum-group element analyses have been verified by comparative analyses of the reference materials WITS-1 and GP13 (sample size 0.5-1 g). Replicate analyses of FC-1 (sample size 0.2 g) exhibit good reproducibility (RSD < 5%) for all the analysed platinum-group elements. REE data also exhibit excellent reproducibility (RSD < 0.5%), which indicates that this sample is homogeneous for the determination of the platinum-group elements and REE at the 0.2 g level.     

Stevns Klint Fish Clay (FC-1): Preparation of, and Preliminary Results for, a Candidate Reference Material

The collapse of a section of the cliff at Stevns Klint, Denmark in 1986 provided a unique opportunity to collect about 50 kg of Fish Clay representing the Cretaceous-Tertiary (K-T) boundary layer. In this paper, details of the preparation of this sample are presented, together with preliminary analytical results to support the development of this sample as a reference material, particularly for the determination of iridium and the other platinum-group elements in clays and sediments associated with K-T boundary studies and in other environmental samples collected to study the effects of automobile exhaust catalysts.     

Trace-element patterns at the Cretaceous-Tertiary boundary—Consequences of a large impact

The earlier discovery of high concentrations of iridium and osmium at the very base of the Tertiary in marine pelagic sequences, has led to the hypothesis that the impact of a large projectile on Earth terminated the Mesozoic era.This paper describes the distribution of other trace elements in samples closely spaced around the Cretaceous-Tertiary boundary. We found an enrichment of Co, Cr, Ni, As, Sb and Se, and a depletion of the rare earth elements (REE), coupled with the anomalously high concentration of Ir and Os. Also, in the enrichment layer, problematic sanidine spherules occur which may be spheres, ablated from the impacting projectile or microtektites.The REE depletion could not only be demonstrated in the basal millimetres of the relatively thick (～ 10 cm) boundary marl bed of the Barranco del Gredero section, Caravaca, Spain, but also in the boundary clay of the Stevns Klint section—the “Fiskeler”—Denmark. In these boundary clay beds are also the highest concentrations of Ir recorded [44 and 86.7 ppb (1 ppb = 10^?9 g/g), respectively].This REE depletion is tentatively connected with the low REE concentration in common meteorites. In that case the basal millimetres are dominated by a meteoritic component and represent a “fall-out” layer of the impact event. This in turn would imply low terrestrial dilution at impact on Earth, suggesting that the projectile might have fallen into the ocean.Identification of the projectile remains speculative; especially the high As, Sb and Se anomalies are problematic. These latter may point to a projectile of uncommon composition, possibly a comet.An integrated scenario of a possible sequence of events is presented, chiefly based on the interpretation of micropaleontological, lithological, geochemical and stable isotope data of the studied sections.The direct and indirect effects of an impact leading to mass extinction constitute a complicated problem and may comprise a sudden temperature rise, a poisoning by cyanide or arsenic, and a few years suppression of sunlight, or preferably, a combination of these effects.     

Depositional environment and development of Danian bryozoan biomicrite mounds (Karlby Klint, Denmark)

The lower Danian bryozoan mounds exposed in the cliff at Karlby are described. Analyses of some sixty samples taken from a single mound reveal that the limestone is composed of about 30% of bryozoan fragments in a fine grained matrix. The texture and the grain-size distribution show that two distinct sedimentary facies can be recognized: (1) the northwestern flank and the basins with fine bryozoan fragments, a relatively small amount of matrix, and grain-supported texture; (2) the southeastern flank and the summit with coarse bryozoans, a larger amount of matrix and partly mud-supported texture. It is shown that the differences in the size of the bryozoan fragments are due to adaptations to changes in the water-movement rather than a result of significant transport. Thus, currents were roughly from the southeast producing more agitated water on the southeast flank and the summit and more gentle water on the northwest flank and in the basins. The unusual relationship between the velocity of the water-movement and the sedimentary facies is caused by an influence of the bryozoans on the depositional environment. On the southeast flank the higher current velocity favoured the growth of bryozoans, resulting in a relatively dense cover that was able to trap and bind the matrix. On the northwest flank the currents were slower and less favourable for growth, and the ability of the bryozoans to bind the sediment was correspondingly smaller.     

Biostratigraphy and depositional facies of the Cretaceous-Tertiary boundary strata in Amakusa-Shimojima,Kyushu, Western Japan

The Upper Himenoura Subgroup exposed in the island of Amakusa-Shimojima, Kyushu, Japan shows an example of the terminal Cretaceous stratigraphic record in the circum Pacific region. This sequence is a part of the Upper Cretaceous intra-arc basins of southwest Japan. Four cycles of upward coarse-graded facies are recognized. Each cycle consists of a basinal mud facies in the lower part and a tide-dominated shallow marine to brackish coarse clastic facies in the upper part. Biostratigraphic correlation chiefly based on ammonites, inocerami and trigoniids indicates that this sequence is Campanian to Maastrichtian in age. The occurrence of the above three fossils decreases upward and is terminated at the top of the sequence, being replaced by a molluscan assemblage similar to the Danian. This suggests that the sedimentation may have continued to the very end of the Cretaceous period and possibly to the beginning of the Tertiary.     

Sedimentology and extinction patterns across the Cretaceous-Tertiary boundary interval in east Texas

Biostratigraphic analysis of planktic foraminifera and calcareous nannofossils, as well as sedimentological and geochemical studies, suggests that the K-T boundary interval on the Brazos River in Falls County, Texas, has a complete Cretaceous section but that a hiatus probably exists in the earliest Palaeocene, representing as little as 35,000 years of time. Planktonic foraminifera, calcareous nannofossils and molluscs decline abruptly in diversity at the K-T boundary in conjunction with an increase in iridium levels. Molluscan assemblages are diverse and dominated by suspension feeders up to the K-T contact but are replaced by a very low diversity assemblage of predominantly deposit-feeders and carnivores in the Early Palaeocene. When both microfauna and macrofauna are considered, species that lived or fed in the water column (planktonic foraminifera, calcareous nannofossils, suspension feeding bivalves) suffered the highest mortality while benthic, dominantly deposit-feeding or carnivorous taxa (benthic foraminifera, carnivorous and deposit-feeding gastropods and bivalves) were less affected.Although the extinction appears massive and abrupt on the whole, some minor faunal irregularities (abnormal forminiferal tests and a slight molluscan diversity drop) occur about one meter below the K-T boundary. We don't as yet know whether these changes are part of normal background environmental fluctuations or whether they are related to the K-T mass extinction event.     

Planktonic foraminiferal turnover across the Cretaceous-Tertiary boundary in the Vajont valley (Southern Alps, northern Italy)

Planktonic foraminiferal analysis of the Erto section in the Vajont valley (Southern Alps, northern Italy) reveals a relatively complete succession across the Cretaceous–Tertiary (K–T) boundary. The turnover of planktonic foraminiferal fauna was studied for a stratigraphic interval spanning theAbathomphalus mayaroensisZonep.p., Pseudotextularia deformisZone,Guembelitria cretaceaZone,Parvularugoglobigerina eugubinaZone,Eglobigerina eobullioidesSubzone, andParasubbotina pseudobulloidesZonep. p.The extinction of most large, ornate, late Maastrichtian species occurs below a black ‘boundary clay’ (2–4 cm thick); however, part of the Late Cretaceous species, mainly heterohelicidids and hedbergellids, were found over an interval of more than 100 cm above the boundary. Although a relatively high number of species occur for the last time in the main extinction phase, the abundance of these outgoing species is less than 20% of the total population; unkeeled or weakly keeled, simple-shaped forms (heterohelicids, globotruncanellids, hedbergellids) constitute the bulk of the planktonic foraminiferal population both in uppermost Maastrichtian and lowermost Danian beds. The first Tertiary species (‘Globigerina’minutulaand ‘Globigerina’fringa) appear just above the ‘boundary clay’;Parvularuglobigerina eugubinaoccurs a few centimeters above. A marked increase in abundance and diversity in the Tertiary planktonic foraminiferal population occurs at the base of theEoglobigerina eobulloidesSubzone.     

A terrestrial scenario for the Cretaceous-Tertiary boundary collapse of the marine pelagic ecosystem

In this paper, we present an expansion of the model for marine ecosystem collapse at the Cretaceous-Tertiary boundary presented by Brinkhuis and Zachariasse (1988). A long-term sea-level drop at the end of the Cretaceous culminated in a short-term regressive pulse at K-T time. Deep-water production was curtailed, minimizing the vertical advection of nutrients and oxygen in the oceans. Consequently, a productivity crisis developed, which could only be survived by cosmopolitan shallow-dwellers, and the Oxygen Minimum Zone (OMZ) expanded. No sustained Oceanic Anoxic Event followed the K-T boundary event, since productivity had dropped to extremely low values. At K-T time, however, the short-term expansion of the OMZ, invoked by the combination of minimized oxygen advection and abrupt mass mortality, caused dysoxic conditions even to reach up to the shelves, as can be deduced from sedimentological, chemical and faunistic observations.     

新疆塔西南区海相白垩系—第三系界线的地球化学异常

新疆塔里木盆地西南地区海相白垩系—第三系的界线粘土层发现于依格孜牙组和吐依洛克组之间。这一层具有相当复杂的元素组合 ,存在诸多元素异常。它不仅是一条生物界线 ,而且是一条地球化学界线。这一异常事件层代表了白垩纪与第三纪之交的突变事件 ,具有全球的一致性和等时性 ,因而具有自然界线性质。     

The Cretaceous-Tertiary boundary on the cape fear arch,North Carolina,U.S.A.

Petrologic and faunal study of a 72.5 m continuous corehole drilled in southeastern North Carolina has provided an opportunity to study a relatively uninterrupted vertical sequence across the Cretaceous-Tertiary boundary. The following stratigraphic sequence occurs; upper middle Maastrichtian Peedee Formation, −65.8 m to −51.8 m below mean sea-level (BMSL), upper middle Maastrichtian Rocky Point Member of the Peedee Formation, −51.8 m to −27.4 m BMSL, and middle to upper (?) Eocene Castle Hayne Limestone, −27.4 m to −15.2 m BMSL (base of casing).The Peedee Formation consists of moderately indurated, very fine to fine, sandy foraminiferal biomicrite and sandy biomicrite. Silt-size zoned dolomite rhombohedra form up to 30% of the upper Peedee Formation and are most abundant where bioturbation is common. A diverse and well-preserved foraminiferal fauna indicates a middle to outer continental shelf environment.The Rocky Point Member conformably overlies typical Peedee Formation lithology and consists of well-indurated sandy, fossiliferous biomicrite that grades upward into sandy, pelecypod biomicrosparite, and finally pelecypod biomicrudite. The Peedee Formation and the Rocky Point Member represent an overall shallowing-upward sequence with the upper surface forming the Cretaceous-Tertiary boundary.The Castle Hayne Limestone disconformably overlies the Rocky Point Member and consists of lithoclast-bearing, bryozoan-molluscan biomicrudite grading upward into bryozoan biomicrudite. The Castle Hayne Limestone was deposited in an open, normal salinity environment between 30 m and 100 m in water depth.     

Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.     

Relationship between heavy metals and clay mineralogy of the modern sediment of salt marsh at the east coast of Wadden Sea, Denmark

Salt marshes play a significant roll in the marine and coast ecological systems. They can function as a sink for pollutants that would otherwise be harmful to the environment. Our investigation is mainly focused on clay mineralogy of the salt marsh sediment, metal associations in the environment of the modern （centennial） salt marsh sediment and possible relation between these metal associations and clay minerals involved. The studied salt marsh is located in the Skalingen Peninsula, West Denmark. About 85 percent of the deposited materials, including the heavy metals, was imported from the North Sea while only a small quantity of the materials was transported through the Varde River whose mouth is located about 10 km from the salt marsh, at the opposite side of the lagoon. A 25 cm high monolithic profile of the salt marsh sediment was collected and was cut into 1-cm slices. The rate of sediment accumulation, detailed grain size distribution, clay mineralogy, dating of the profile （^210Pb and ^137Cs）, content of organic matter as well as 17 metals： K, Ca, Ti, Mn, Fe, V, Cr, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Zr, Nb were investigated. Principal components and factor analyses demonstrated strong positive loadings for most of the studied metals, fine grain fractions as well as organic matter, indicating a close relation among these components. Mn, Fe, Ni, Cu, Zn, Rb were found best correlated to the clay fraction （〈2 microns）, which comprises primarily illite, kaolinite, minor chlorite and lesser smectite/illite mixed layer.