Maastrichtian-Danian Boundary Research Articles

Foraminiferal biostratigraphy of the upper Campanian–lower Danian of the Poty and Olinda cores in Pernambuco, northeastern Brazil

This study presents the foraminiferal biostratigraphy of the Upper Cretaceous–lower Paleogene succession of the Olinda and Poty cores in the Pernambuco-Paraíba Basin in northeastern Brazil. A total of 96 taxa of planktic foraminifera, belonging to 27 genera, that spanned the upper Campanian–lower Danian interval were recorded in this study, representing the following biozones: (1) Globotruncana aegyptiaca Interval Zone; (2) Gansserina gansseri Interval Zone; (3) Contusotruncana contusa Interval Zone; (4) Recemiguembelina fructicosa/Pseudoguembelina intermedia Interval Zone; (5) Pseudoguembelina palpebra/Pseudoguembelina hariaensis Interval Zone; (6) Plummerita hantkeninoides Interval Zone; and (7) Parvularugoglobigerina eugubina Total Range Zone/Igorina albeari Subzone (Pα–P3b). An informal subzone of benthic foraminifera, Alabamina dorsoplana/Epistomina supracretacea, was proposed for the Campanian strata in the lower part of the Gansserina gansseri Interval Zone, owing to the low recovery of planktic foraminifera in these deposits. In both core sections (Poty and Olinda), the Campanian–Maastrichtian transition was characterized by the occurrence of Pseudoguembelina palpebra. An erosive/non-depositional hiatus is recorded in the lower part of the Racemiguembelina fructicosa/Pseudoguembelina intermedia Zone within the Olinda core section. The Maastrichtian–Danian boundary is locally marked by the absence of the P0 zone, likely mixed with deposits corresponding to the Pα Zone.

Paleoenvironment, sequence stratigraphy, and sea level change in the upper Maastrichtian–Danian boundary interval in Gabal Aras, east Qena, Nile Valley, Egypt

The Cretaceous–Paleogene (K–Pg) boundary interval at Gabal Aras, Qena region (part of the southern Tethyan margin) was investigated in detail for calcareous nannofossil and foraminiferal (planktonic and benthonic) assemblages to characterize the surface and bottom sea water conditions. The K–Pg boundary is marked by a minor hiatus expressed by the absence of the lowermost Danian P0 and Pα planktonic foraminiferal zones. Benthonic foraminifera assemblages indicate moderately oxygenated bottom sea waters associated with oligo-mesotrophic conditions during early late Maastrichtian, and mesotrophic conditions during the latest Maastrichtian. The benthonic foraminiferal assemblage reflects a decrease in the food supply in the bottom sea water during the early Danian, while well-oxygenated and oligotrophic conditions dominated during late Danian. The late Maastrichtian surface water witnessed a general cooling trend that was interrupted by a warming episode that could correspond to the Late Maastrichtian Warming Event (LMWE). Acme of Thoracosphaera associated with increased abundance of Neobiscutum romeinii were observed within the upper part of NP1 Zone indicating stressful surface water conditions. The increase of the epifaunal foraminiferal taxa and the occurrence of Cruciplacolithus primus throughout NP2 and NP3 zones reflect a progressive return to normal marine conditions. In the framework of sequence stratigraphy, two third-order depositional sequences covering the K–Pg boundary interval were identified, interpreted, and correlated. The obtained sea-level curve was evaluated to assess whether it was controlled by the eustatic sea-level changes, regional tectonics, or both these factors.

Brachiopod extinctions in the Upper Cretaceous to lowermost Tertiary chalk of Northwest Europe

The white monotonous chalk from the Upper Cretaceous-lowermost Tertiary of Northwest Europe spans at least 24 million years and contains a rich, well preserved fauna of minute brachiopods. Based on taxonomical range charts and time-specific diversities this fauna is studied in terms of mean species longevity, rate of species origin and rate of extinction. The brachiopod fauna initially appears to have colonized the chalk sea in mid-Coniacian times. From there on there is a slow build-up of species diversity reflecting a gradual niche diversification of the chalk. A climax in adjustment and evolutionary stability is reached in Late Maastrichtian time. During the Coniacian-Maastrichtian interval mean rate of extinction is low (0.07 My-1) and mean rate of origination equally low (0.10 My-1). A sudden mass extinction at the Maastrichtian-Danian boundary, however, eliminated more than 70 per cent of the species. The most specialized species, in particular the secondarily free-lying species, apparently became extinct at the boundary. Only six species are known to cross the Maastrichtian-Danian boundary. These are all relatively featureless, non-specialized forms and gave, together with possible survivors in basin margin areas, rise to a rapidly formed highly diverse Early Danian fauna through adaptive radiation. The Early Danian fauna differs in taxonomic composition from the Maastrichtian fauna both on species as well as on higher levels. A dichotomous classification of extinction seems real for the brachiopods from the chalk as their mass extinction at the Maastrichtian-Danian boundary both quantitatively and qualitatively differ from their Late Cretaceous background extinction.

The Maastrichtian‐Danian in the SW Zagros Fold‐Thrust Belt (S. Iran): An Integration of Planktonic Foraminiferal Biostratigraphy and Gamma‐Ray Spectrometry

AbstractIn this study, the Maastrichtian‐Danian boundary was measured and sampled in two stratigraphic sections, the north and south flanks of the Dehnow anticline in Coastal Fars, Southern Iran. This boundary was also investigated in the drilled exploratory well‐1 in the same region. The lithology of the Maastrichtian‐Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozones are the Gansserina gansseri Interval Zone, and the Contusotruncana contusa Interval Zone, which indicates latest Campanian to middle Maastrichtian age for the upper part of the Gurpi Formation. In addition, the Eoglobigerina edita (P1) Partial Range Zone, Praemurica uncinata (P2) Lowest Occurrence Zone, Morozovella angulata (P3) Lowest Occurrence Zone and Globanomalina psudomenardii (P4) Taxon Range Zone represent a Danian to Thanetian age for the lower part of the Pabdeh Formation. From the absence of the Abathomphalus mayaroensis Interval Zone, Pseudoguembelina hariaensis Interval Zone, Pseudotextularia elegans Interval Zone, Plummerita hantkeninoides Interval Zone, Guembelitria cretacea (P0) Partial Range Zone and Parvularugoglobigerina eugubina (Pα) Total Range Zone, it can be deduced that there is a paraconformity across the Maastrichtian–Danian boundary in the studied area, this hiatus encompassing the late Maastrichtian and the earliest Danian. Danian deposits from the study area contain reworked glauconitized macrofossils, planktonic and benthic foraminifera of the Cretaceous. The obtained surface gamma‐ray spectrometry logs resemble the exploratory well‐1 gamma‐ray wireline log.

Cretaceous-Paleogene ostracods from the Paraíba Basin, northeastern Brazil

This work presents a detailed taxonomic study on the marine ostracods from the Paraíba Basin, northeastern Brazil, in wells from the wells Itamaracá-1IT-03-PE and Poty-1PO-01-PE, which record the Maastrichtian–Danian boundary. Besides the taxonomic data, this paper contributes to the paleoenvironmental knowledge of Cretaceous–Paleogene ostracods from the Paraíba Basin. The analysis of 98 samples of the well Itamaracá-1IT-03-PE and 59 samples of the Poty-1PO-01-PE resulted in the record of 34 ostracode species, all representative of a marine environment with normal salinity. Seven new species are proposed: Cytherella centrocompressa sp. nov.; Cytherella paraibensis sp. nov.; Neonesidea potyensis sp. nov.; Bythoceratina spinosa sp. nov.; Eucytherura ventrotuberculata sp. nov.; Langiella fauthi sp. nov. and Protobuntonia punctatum sp. nov.

A Cretaceous–Palaeogene boundary geological site, revealed by planktic foraminifera and dinoflagellate cysts, at Ouled Haddou, eastern external Rif Chain, Morocco

Planktic foraminifera and organic-walled dinoflagellate cyst investigations in the Ouled Haddou outcrop (eastern external Rif Belt) in northern Morocco, revealed a continuous sedimentation and a complete record of the Cretaceous–Palaeogene (K–Pg) transition. Both planktic foraminifera and dinoflagellate cyst assemblages observed in the studied Maastrichtian–Danian boundary interval are diverse and well-preserved and contain numerous chronostratigraphically significant bio-events that have allowed a high resolution biostratigraphic analysis, based on the first and last occurrences of index species and also on the massive disappearance and abundance changes of different taxa. Planktic foraminifera allow correlation of the studied interval with the uppermost Maastrichtian Abathomphalus mayaroensis Zone and the lower Danian Guembelitria cretacea, Parvularugoglobigerina eugubina, Parasubbotina pseudobulloides and Subbotina triloculinoides zones. A mass extinction of planktic foraminifera is observed at the end of the Abathomphalus mayaroensis Zone. This mass extinction is followed by three renewal steps of planktic foraminifera in the basal Danian. The Cretaceous–Palaeogene boundary is placed just above the mass extinction of Globotruncanids and Heterohelicids and below the first appearences of earliest Danian markers genera Globoconusa, and Parvularugoglobigerina.According to dinoflagellate cysts, the recognition of the latest Maastrichtian and earliest Danian is based on global bio-events, including the first occurrence of the latest Maastrichtian species Disphaerogena carposphaeropsis, Glaphyrocysta perforata, and Manumiella seelandica, the latest Maastrichtian acme of Manumiella seelandica, and the first occurrence of the earliest Danian markers Carpatella cornuta, Damassadinium californicum and Senoniasphaera inornata. The dinoflagellate Damassadinium californicum Zone characterizing the Danian in the Northern Hemisphere is recognized in this section. The Cretaceous–Palaeogene boundary is placed, at the same position determined by Planktic foraminifera, immediately above the acme of Manumiella seelandica and the last appearance of few Cretaceous taxa such as Dinogymnium spp. and Alisogymnium euclaense, and directly below the first occurrences of Carpatella cornuta, Damassadinium californicum and Senoniasphaera inornata. However, in contrast to calcareous planktic foraminifera, dinoflagellate cysts did not undergo a mass extinction at the K–Pg boundary, but shows important changes in the relative abundances of different species or groups of morphologically related species.Both planktic foraminifera and dinoflagellate cyst assemblages suggest deposition in subtropical to warm temperate province, but in an austere sea environments under a regressive regime during the uppermost Maastrichtian and open sea environments under a transgressive regime during the lower Danian. Dinoflagellate cysts indicate relatively stable warm conditions during the upper Maastrichtian, followed successively by cooler conditions in the uppermost Maastrichtian and at the K–Pg boundary, a gradual warming alternated by 3 rapid successive cooling pulses in the lower most Danian, and then a gradual returning to relatively warm conditions.The Ouled Haddou section needs to be preserved as a geoheritage site, because it is the sole Moroccan section with a good quality and an easy access, and hosts a complete registration of the Cretaceous–Palaeogene boundary transition.

Palynological characteristics of the sediments of the Malokuril’skaya formation (Maastrichtian-Danian), Shikotan Island

A spore-pollen assemblage was established for the first time in the sediments of the Malokuril’skaya Formation (Khromova Bay, Shikotan Island, Lesser Kuril Range, Kuril island arc system). This find enabled dating of the sediments of the uppermost part of the Malokuril’skaya Formation, which, based on this data, are referred to the Maastrichtian-Danian boundary. The assemblage of radiolarian species was identified for the entire section of the Malokuril’skaya Formation. In sediments of the lower part of the section, members of the Inoceramus group were described. These findings add new information to the paleontological characteristics of the Malokuril’skaya Formation. Moreover, our work allowed detailed correlation of the palynological assemblage studied with coeval palynological assemblages of adjacent areas. The similarity of Cretaceous-Paleogene sections of the Ust-Palanskaya (West Kamchatka), Uchir (Sakhalin Island) and Malokuril’skaya Formations, the Upper Cretaceous basement and the Cenozoic cover of the underwater Vityaz Ridge support the shared history of the development of the entire transition zone from the marginal Sea of Okhotsk to the Pacific at the Maastrichtian-Danian boundary.

New species of organic-walled dinoflagellate cysts from the Maastrichtian–Danian boundary interval at Ouled Haddou, northern Morocco

Slimani, H., Louwye, S. & Toufiq, A., September 2012. New species of organic-walled dinoflagellate cysts from the Maastrichtian–Danian boundary interval at Ouled Haddou, northern Morocco. Alcheringa 36, 341–358. ISSN 0311-5518. Seven new dinoflagellate cyst species and subspecies, previously figured under open nomenclature, from Maastrichtian and Danian deposits of Ouled Haddou (eastern external Rif Chain) in northern Morocco are formally described, and their stratigraphic ranges are clarified. Conosphaeridium lifum sp. nov. and Kenleyia chabaka sp. nov. have fibrous and reticulate wall surfaces, respectively. Oligosphaeridium saghirum sp. nov. is a small cyst with funnel-shaped distal process extremities. Spiniferella cornuta subsp. kacira subsp. nov. and Fibrocysta brevispinosa sp. nov. are distinguishable by their very short processes. Riculacysta chaouka sp. nov. is characterized by its perforate spinose ectophragm. Andalusiella bacita sp. nov. is a small and spindle-shaped cyst with only a single antapical horn.

On late Maastrichtian-early Danian water masses and lithologic and foraminifer assemblages in different tectonic zones of the Mountainous Crimea

This paper presents data on the structure of reference sections of the Maastrichtian-Danian boundary beds and the assemblages of benthic and planktonic foraminifers enclosed in these rocks. These are based on examination of the reference sections in two different structure-facies zones of the Mountainous Crimea: the Kacha Uplift and Indol-Kuban Trough. The strongly different lithologic and foraminifer assemblages in these sections indicate the presence of completely different water masses in the shelf part of the marine basin with water depths varying from those of the middle-lower sublittoral zone (in the Belbek, Beshkosh, and Chakhmakhly sections in the southwestern part of the Mountainous Crimea) to those of the pelagic environment on the continental slope and at the continental rise (section in Mount Klement’ev in the Indol-Kuban Trough). These assemblages indicate the sedimentation environment in the transition zone between the Kacha shelf and the deep-water Black Sea Basin.

Sedimentogenesis in Maastrichtian-Danian basins of the Russian plate and adjacent areas in the context of plume geodynamics

[1] The sediment composition and sedimentation conditions of Maastrichtian and Danian deposits in the vast territory of the Russian plate and adjacent regions of North Eurasia were studied. The succession of Late Cretaceous carbonaceous conditions of sedimentation in the Early Paleocene is noted in the major part of North Eurasia sedimentary basins. In some areas of the Lower Volga region and of the Northern Cis-Caspian basin, a radical change occurred in the sedimentation conditions at the Cretaceous-Paleogene boundary: Lower Paleocene siliceous formation replaced Maastrichtian carbonaceous formations. It is assumed that in this case the silica mass delivery into the basin was caused by tectonic rejuvenation of faults system at the border between the Russian platform and the CisCaspian basin under the large impact events. At the Maastrichtian–Danian boundary and above in the Danian, the increase of magnetic susceptibility of rocks is commonly noted for the major part at the expense of enrichment of rocks with iron in paramagnetic compounds (ferric hydrooxide and iron-containing clayey minerals) similar to metal-bearing sediments and to a lesser degree at the transport of terrigenous material addition in the period of large Early Paleocene regression. In the sediments, microspherules of metallic iron are noted that are most likely of cosmic meteoric dust.

Mapping of the Maastrichtian-Danian boundary in the coastal area of Køge Bugt by gamma- and resistivity logging

The Maastrichtian-Danian boundary surface has been mapped by geophysical logging of water supply borewells in the coastal area of Koge Bugt south of København. The transition from bryozoan limestone of Danian (earliest Palaeogene) age with a variable apparent resistivity between 100 and 250 Ohmm to chalk of Maastrichtian (latest Cretaceous) age with a relatively stable apparent resistivity in the range 60-80 Ohmm is easily detected on most resistivity logs. Gamma logs show a characteristic anomaly with two peaks in the uppermost Maastrichtian chalk approximately 8-10 meters below the Maastrichtian-Danian boundary. This gamma anomaly is caused by a layer of marl, which is found persistently in the whole area between Kobenhavn and Koge. The marl is probably equivalent to the Kj~lby Gaard Marl, known from outcrops of uppermost Maastrichtian chalk in northwest Jylland. A preliminary contour map has been prepared displaying the elevation of the boundary surface between the Danian limestone and Maastrichtian chalk below. This map shows that the limestones are weakly folded with structures very similar to those observed in the outcrops of Stevns Klint and also detected by recent seismic studies of the limestone basement in 0resund. The structures can be interpreted without introducing major vertical displacements along faults.

Recovery of North Caucasus foraminiferal assemblages after the pre-Danian extinctions

Abstract The planktonic changes associated with the Maastrichtian-Danian boundary are described from successions in the North Caucasus, Russia. The extinctions recorded in the benthonic fauna are less sudden than those recorded in the plankton, with many pre-dating the end of the Maastrichtian. The Danian benthonic fauna contains a number of survivor taxa with few new species. The recovery interval for the benthonic fauna was much shorter and the increase in diversity occurred earlier than that of the planktonic fauna. Within the Globorotalia angulata Zone the recovery of the foraminiferal assemblage was almost complete.

Geological еvents at the Cretaceous – Paleogene boundary in Georgia (Caucasus)

A continuous section at Tetrickaro (South Georgia) of Maastrichtian-Danian shallow-marine paleontologically proved carbonate deposits is being described. Within the section, a boundary clay layer, 15 - 20 cm thick, has been established with anomalously high content of Ir (3.46-5.34 ng/g), with shock-quartz grains and reversed polarity corresponding to R-29 zone of the International Paleomagnetic Scale. Mass extinction of representatives of numerous marine macro- and micro-fossil groups has been established at the Maastrichtian-Danian boundary in Georgia. 18 species of inocerams, 16 species from 9 genera of ammonitids, 5 species of bellemnitids, 25 species from 12 genera of echinoidea, 6 species from 3 genera of orbitoids, 9 species from 3 genera of planktonic foraminifers and 60 species from 29 genera of calcareous nannoplankton have disappeared at the end of Maastrichtian.

Adaptive radiation, survival and extinction of brachiopods in the northwest European upper cretaceous-lower paleocene chalk

The Upper Cretaceous-lowermost Paleocene white, monotonous chalk of northwest Europe was deposited more or less continously through a period of at least 24 million years. It contains a rich, well-preserved fauna of minute brachiopods which comprises at least 80 species representing 28 genera and 14 families in the mid-Coniacian to Early Danian interval. In order to understand the adaptive patterns of this fauna, the time-specific diversities of the brachiopod fauna are broken down into taxonomic and environmental components. The brachiopod fauna apparently initially colonized the chalk sea bottom earlier than mid-Coniacian times probably as early as Cenomanian-Turonian times. From mid-Coniacian times, however, there was a slow build-up of both specific and generic diversity, whereas the number of families remained essentially constant. A climax in diversity was reached in the Late Maastrichtian. During the Coniacian-Maastrichtian interval mean rates of extinction and origination, and the percentage of turn-over are low for both species and genera. For families these rates are practically zero. A sudden mass extinction eliminated more than 70% of the species at the Maastrichtian-Danian boundary, more than 40% of the genera, but only about 1% of the families. A survivorship curve at the species level based on longevity history reveals an essentially linear trend indicating that new and old lineages became extinct indiscriminately through the mid-Coniacian to the top of the Early Danian, and that the mass extinction at the Maastrichtian-Danian boundary hit all lineages alike irrespective of their age. By comparing the variety of modes of life to brachiopod species richness at different times, major adaptive themes of the evolving brachiopod fauna and their degree of ecospace exploitation through time can be illustrated. Here are thus defined ten ecological groups of species each of which is defined without regard to their taxonomic composition. It appears that the main diversification took place preferentially in some ecological groups rather througout the Late Cretaceous, and that some groups rather than others were affected by the mass extinction at the Cretaceous-Tertiary boundary. Adaptive radiation took place primarily within a group of minute pedically attached mainly cancellothyridid brachiopods and within a heterogeneous group of secondarily free-living, hemispherical reclining brachiopods. These groups were also the most strongly affected at the Cretaceous-Tertiary boundary, the hemispherical reclining forms apparently became totally extinct and the minute pedically attached forms displaying very high rates of species turnover across the boundary. Environment apparently contributed only little to the large-scale evolution observed. Except for a complete, short-term cessation in chalk deposition at the Cretaceous-Tertiary boundary, the chalk sea represents an unusually stable environment through the iinterval studied. The fauna appears to have developed forms well adapted to the chalk already in Coniacian times. Species increase took place primarily by species packing within already existing ecological groups. The only major ecological novelty was the hemispherical reclining brachiopods which do not appear till later in the Late Cretaceous.

Background Extinction and Mass Extinction of the Brachiopods from the Chalk of Northwest Europe

The white monotonous chalk from the Upper Cretaceouslowermost Tertiary ofNorthwest Europe spans at least 24 million years and contains a rich, well-preserved fauna of minute brachiopods. Based on taxonomical range charts and timespecific diversities, this fauna is studied in terms of mean species longevity, rate of species origination, and rate of extinction. The brachiopodfauna initially appears to have colonized the chalk sea in mid-Coniacian times. From there on a slow buildup of species diversity reflects a gradual niche diversification of the chalk. Adjustment and evolutionary stability reaches a climax in Late Maastrichtian time. During the Coniacian-Maastrichtian interval, mean rate of extinction is low (0.07 My-1) and mean rate of origination equally low (0.09 My-1). A sudden mass extinction at the Maastrichtian-Danian boundary, however, eliminated more than 70% of the species. The most specialized species, in particular the secondarily free-lying species, apparently became extinct at the boundary. Only six species are known to cross the Maastrichtian-Danian boundary. These are all relatively featureless, non-specialized forms and, together with possible survivors in basin margin areas, gave rise to a rapidly formed, highly diverse Early Danian fauna through adaptive radiation. The Early Danian fauna differs in taxonomic composition from the Maastrichtian fauna both on species as well as on higher taxonomic levels. A dichotomous classification of extinction seems real for the brachiopods from the chalk as their mass extinction at the Maastrichtian-Danian boundaty both quantitatively and qualitatively differ from their Late Cretaceous background extinction.

M. B. Johansen 1987. Brachiopods from the Maastrichtian-Danian boundary sequence at Nye Klov, Jylland, Denmark. Fossils and Strata no. 20, 31st October, 1987. 99 pp. Oslo: Universitetsforlaget. Price 170.00 Norwegian crowns, US $25.50 (paperback). ISBN 82 00 02558 6.

Johansen M. B. 1987. Brachiopods from the Maastrichtian-Danian boundary sequence at Nye Klov, Jylland, Denmark. Fossils and Strata no. 20, 31st October, 1987. 99 pp. Oslo: Universitetsforlaget. Price 170.00 Norwegian crowns, US $25.50 (paperback). ISBN 82 00 02558 6. - Volume 126 Issue 3

Brachiopods from the maastrichtiandanian boundary sequence at Nye Kløv, Jylland, Denmark by Marianne Bagge‐Johansen, Fossils & Strata, Oslo, No. 20, 1987. No. of pages: 99. Price: 170NDK (soft covers).

Brachiopods from the maastrichtiandanian boundary sequence at Nye Kløv, Jylland, Denmark by Marianne Bagge‐Johansen, <i>Fossils &amp; Strata</i>, Oslo, No. 20, 1987. No. of pages: 99. Price: 170NDK (soft covers).

The Cretaceous-Tertiary boundary in a sector of the south limb of the Miranda-Treviño synclinal: the first appearance of chelonia and archosauria in the Basque country

This paper presents a study of the Cretaceous-Tertiary boundary in the Miranda-Treviño Synclinorium (Basque-Cantabric basin) where two main sequences have been recognised; the lower is regressive and theupper one has a marked transgressive trend. They are separated by a low angled un-conformity which is indicative of the Maastrichtian-Danian boundary. The lower sequence (S1) indicates a clear transition between the shoreface and backshore sub-environments. Bone accumulations are located in the sandy sediments of the upper foreshore and backshore, associated with ferrugenous hardgrounds and gypsum efflorescences. The upper sequence (S2) indicates the beginning of a marine transgression. It is composed a dominantly carbonate-rich sediments and the fauna suggests a deposition in environmental conditions ranging from stenohaline, to littoral, and to a coastal lagoon and inner carbonaterich platform. In the lower sequence (Maastrichtian Unit S 1 U 3), the following herpetofauna have been identified; an eusuchian alligator, and two dinosaurs (an ornithopod and a sauropod). Several plates of chelonia have been identified as? Adocus sp.

The Cretaceous—Tertiary boundary in Mangyshlak, U.S.S.R.

AbstractUpper Cretaceous carbonate sequences contain omission surfaces, hardgrounds and intercalations of ‘clays’. These ‘clays’ are largely associated with submarine biogeochemical carbonate dissolution that was caused by high biological productivity in the pelagic zone. The Maastrichtian-Danian ‘boundary clays’ probably accumulated during a maximum productivity that led to the exhaustion of nutrients, development of phenomena comparable to present-day red tides, and mass mortality of marine biota. There was a type of ecological break in the seas and oceans at the time of the Maastrichtian-Danian boundary.

End-Cretaceous Brachiopod Extinctions in the Chalk of Denmark

The results of a detailed study of the brachiopods of the most complete Cretaceous-Tertiary boundary in Denmark, Nye Klslashed circlev, show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario. The extinction is abrupt, coinciding with the Maastrichtian-Danian boundary. There is no warning in the form of decreasing density, decreasing diversity, or early extinction of specialized groups. The basal few meters of the Danian are almost devoid of brachiopods, and a Danian brachiopod fauna starts almost as abruptly as the Maastrichtian fauna disappeared. The new fauna is similar to the Maastrichtian as regards density and diversity, and at maximum six species are common to both stages. The northwest European Masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera. The mass extinction of these groups led to a total cessation of chalk production. The chalk is overlain by a thin clay bed deposited partly under anoxic conditions. This combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods. The surviving species included forms that could survive in well-aerated shallow marine waters on substrates other than chalk.