Maastrichtian Assemblages Research Articles

Biostratigraphie, paléoécologie et zones d’acmé des foraminifères planctoniques au passage Crétacé-Paléogène dans la Téthys (Tunisie et Espagne) et l’Atlantique (France)

Biostratigraphical high-resolution analyses and quantitative data confirm that deposition is continuous across the K-Pg transition in several sections in Tunisia (El Kef, stratotype section) and Spain (Agost and Caravaca sections) located in the Tethyan realm and the Bidart sections in the Atlantic realm, without any relevant hiatus. The Upper Maastrichtian assemblages of planktic foraminifera from these sections are largely dominated by small biserial heterohelicids. They are associated to common species having planispiral test (i.e. globigerinelloids), trochospiral test (i.e. hedbergellids, rugoglobigerinids globotruncanids), to rare triserial heterohelicids (i.e. guembelitriids) and trochospiral species showing tubulospines (i.e. schackoinids). Stratigraphical ranges of these diverse taxa through the late Maastrichtian in the Tethyan and Atlantic realms show very few changes in the planktonic foraminiferal assemblages and most of the species are present in the Abathomphalus mayaroensis biozone. By our high-resolution sampling and the intensive research for the A. mayaroensis index species in the uppermost Maastrichtian samples, we confirm that this species is omnipresent up to the top of the Maastrichtian. Therefore, A. mayaroensis is present in almost all samples which are late Maastrichtian in age, but this species became very scarce in the uppermost Maastrichtian samples. This scarceness could be due to a climate cooling. A sharp decrease in relative abundance of the deep dwellers species, like as Abathomphalus intermedius and A. mayaroensis as well as in other keeled globotruncanids is observed at the studied sections from the Tethyan realm (indicative of low latitude) across the latest Maastrichtian. At the K/Pg boundary, all the globotruncanids disappeared. They are considered specialists living in tropical-subtropical deep seawater habitat. At this boundary, large and ornate heterohelicids also disappeared. Therefore, all the studied sections show that about 90 % of the Maastrichtian species became extinct according to a catastrophic mass extinction pattern. Only about 10 % crossed the K/Pg boundary and survived during the earliest Danian. The minor difference in the number of disappeared taxa is related to their latitude location or environment paleodepth. The changes in the species relative abundance, observed in the successive planktic foraminiferal assemblages, make it possible to recognize the Acme-stage 0 typical of the upper Maastrichtian interval. It is characterized by the highest species richness of Globotruncanids and heterohelicids specialists of tropical to subtropical marine conditions, the Acme-stage 1 typical of the Guembelitria cretacea Zone, and in particular of the Hedbergella holmdelensis Subzone dominated by “opportunists” species belonging to Guembelitria, the Acme-stage 2 which corresponds to the Pv. eugubina Zone dominated mainly by specimens belonging to Palaeoglobigerina and Parvularugoglobigerina and the Acme-stage 3 which characterizes mainly the Ps. pseudobulloides Zone dominated by biserial species belonging to Chiloguembelina and Woodringina.

Benthic foraminifera across the Cretaceous/Paleogene boundary in the Southern Ocean (ODP Site 690): Diversity, food and carbonate saturation

The impact of an asteroid at the Cretaceous/Paleogene (K/Pg) boundary triggered dramatic biotic, biogeochemical and sedimentological changes in the oceans that have been intensively studied. Paleo-biogeographical differences in the biotic response to the impact and its environmental consequences, however, have been less well documented. We present a high-resolution analysis of benthic foraminiferal assemblages at Southern Ocean ODP Site 690 (Maud Rise, Weddell Sea, Antarctica). At this high latitude site, late Maastrichtian environmental variability was high, but benthic foraminiferal assemblages were not less diverse than at lower latitudes, in contrast to those of planktic calcifiers. Also in contrast to planktic calcifiers, benthic foraminifera did not suffer significant extinction at the K/Pg boundary, but show transient assemblage changes and decreased diversity. At Site 690, the extinction rate was even lower (~ 3%) than at other sites. The benthic foraminiferal accumulation rate varied little across the K/Pg boundary, indicating that food supply to the sea floor was affected to a lesser extent than at lower latitude sites. Compared to Maastrichtian assemblages, Danian assemblages have a lower diversity and greater relative abundance of heavily calcified taxa such as Stensioeina beccariiformis and Paralabamina lunata . This change in benthic foraminiferal assemblages could reflect post-extinction proliferation of different photosynthesizers (thus food for the benthos) than those dominant during the Late Cretaceous, therefore changes in the nature rather than in the amount of the organic matter supplied to the seafloor. However, severe extinction of pelagic calcifiers caused carbonate supersaturation in the oceans, thus might have given competitive advantage to species with large, heavily calcified tests. This indirect effect of the K/Pg impact thus may have influenced the deep-sea dwellers, documenting the complexity of the effects of major environmental disturbance. • Benthic foraminifera and stable isotopes across the Cretaceous/Paleogene boundary. • Lower bathyal setting at Southern Ocean ODP Site 690. • Assemblage fluctuations in Maastrichtian, no forerunner events for extinction. • Low (<3%) species extinction and environmental disturbance across the boundary. • Danian assemblages affected by changing food flux, from different photosynthesizers. • Alternatively, they may indicate increased carbonate saturation in the oceans. • Carbonate supersaturation triggered by the extinction of pelagic calcifiers.

Nanofósiles Calcáreos y Bioestratigrafía del Cretácico del Sudeste de la Cuenca Austral, Patagonia, Argentina

Abstract CRETACEOUS CALCAREOUS NANNOFOSSILS AND BIOSTRATIGRAPHY OF SOUTHEASTERN AUSTRAL BASIN, PATAGONIA, ARGENTINA. This study presents the results of a quantitative analysis of the calcareous nannofossils recovered in five localities in the southeastern sector of the Austral Basin. On the basis of the assemblages recovered and its comparison with previous biozonations for the Austral Atlantic Ocean, it was possible to identify Valanginian—early Hauterivian, early Albian—middle Albian, late Albian—Cenomanian, Coniacian/Santonian—Campanian and late Maastrichtian assemblages. Two discontinuities evidenced by biostratigraphical hiatuses for the Cretaceous sequence were deduced: one for the late Hauterivian—Barremian and the other for at least the Turonian. The Early Cretaceous assemblages are comparable to those of the Falkland Plateau and they would be developed on an external platform having cold surface waters and high availability of nutrients. The Late Cretaceous assemblages are similar to those found ...

Low beta diversity of Maastrichtian dinosaurs of North America

Beta diversity is an important component of large-scale patterns of biodiversity, but its explicit examination is more difficult than that of alpha diversity. Only recently have data sets large enough been presented to begin assessing global patterns of species turnover, especially in the fossil record. We present here an analysis of beta diversity of a Maastrichtian (71-65 million years old) assemblage of dinosaurs from the Western Interior of North America, a region that covers approximately 1.5 x 10(6) km(2), borders an epicontinental sea, and spans approximately 20 degrees of latitude. Previous qualitative analyses have suggested regional groupings of these dinosaurs and generally concluded that there were multiple distinct faunal regions. However, these studies did not directly account for sampling bias, which may artificially decrease similarity and increase turnover between regions. Our analysis used abundance-based data to account for sampling intensity and was unable to support any hypothesis of multiple distinct faunas; earlier hypothesized faunal delineations were likely a sampling artifact. Our results indicate a low beta diversity and support a single dinosaur community within the entire Western Interior region of latest Cretaceous North America. Homogeneous environments are a known driver of low modern beta diversities, and the warm equable climate of the late Cretaceous modulated by the epicontenental seaway is inferred to be an underlying influence on the low beta diversity of this ancient ecosystem.

Reptilian assemblages from the latest Cretaceous – Palaeogene phosphates of Morocco: from Arambourg to present time

Arambourg was the first to conduct methodical vertebrate palaeontological studies in the Oulad Abdoun and Ganntour phosphatic basins of Morocco between the 1930s and 1950s. As early as 1935, he identified the main stratigraphical levels of the phosphatic series, characterizing them by a specific association of vertebrates (mainly selachians), and proposed stratigraphical correlations between the phosphatic levels of these two basins. During the last decade, due to a French-Moroccan program of collaboration, vertebrate fossils have been collected in great abundance. Here we present an updated overview of the latest Cretaceous to Ypresian reptilian faunas from the Oulad Abdoun and Ganntour basins, on the basis of published data and new field records. In addition to advances in the study of the already known taxa (i.e., squamates, crocodyliforms, plesiosaurs), recent field works reveal new major reptilian taxa that were unknown (or undescribed) at Arambourg's time: very abundant and diversified marine chelonians (Maastrichtian to Ypresian), scarce dinosaurs and pterosaurs remains (Maastrichtian), and a well diversified marine avifauna (Thanetian and Ypresian). A significant increase in the number of described taxa (52 versus 13) and an improvement of the quality of the specimens found (articulated skeletons versus isolated remains) is worthy of consideration. The Maastrichtian reptilian assemblages are dominated by mosasaurid squamates whereas those of the Palaeogene are by the mirroring crocodyliforms (dyrosaurids and eusuchians).

The “Tustea Puzzle”: Hadrosaurid (Dinosauria, Ornithopoda) Hatchlings Associated with Megaloolithidae Eggs in the Maastrichtian of the Hateg Basin (Romania)

Abstract Since 1991 when the coinciding occurrence of megaloolithid eggs and hatchlings of the hadrosaurid Telmatosaurus transsylvanicus was suggested by few limb bone remains found close to the first discovered eggs in the Hateg Basin, tens of eggs grouped in clutches together with neonate bones were unearthed within the place that become “Tustea nesting site”. In the meantime the original vertical escarpment near the village of Tustea was leveled and converted into a horizontal platform. By their external characters and eggshell microstructure all the eggs belong to the Megaloolithus oogenus, closer to M. siruguei; similarly, all the baby remains whose state of preservation allows their taxonomic assignment belong to Telmatosaurus transsylvanicus, one of the common dinosaur species from the rich Maastrichtian faunal assemblage of the Hateg Basin (Romania), and the basalmost hadrosaurid. Most of the baby remains consist of isolated bones and teeth, but partial skeletons with articulated elements were als...

Late Maastrichtian Volcanism in the Indian Ocean: Effects on Calcareous Nannofossils and Planktic Foraminifera

The biotic effects of volcanism have long been the unknown factors in creating biotic stress, and the contribution of the Deccan volcanism to the K–T mass extinction remains largely unknown. Detailed studies of the volcanic-rich sediments of Indian Ocean Ninetyeast Ridge Sites 216 and 217 and Wharton Basin Site 212 reveal that the biotic effects of late Maastrichtian volcanism on planktic foraminifera and calcareous nannofossils are locally as severe as those of the K–T mass extinction. The biotic expressions of these high stress environments are characterized by the Lilliput effect, which includes reduced diversity by eliminating most K-strategy species, and reduction in specimen size (dwarfing), frequently to less than half their normal adult size of both r-strategy and surviving K-strategy species. In planktic foraminifera, the most extreme biotic stress results are nearly monospecific assemblages dominated by the disaster opportunist Guembelitria, similar to the aftermath of the K–T mass extinction. The first stage of improving environmental conditions results in dominance of dwarfed low oxygen tolerant Heterohelix species and the presence of a few small r-strategy species ( Hedbergella, Globigerinelloides). Calcareous nannofossil assemblages show similar biotic stress signals with the dominance of Micula decussata, the disaster opportunist, and size reduction in the mean length of subordinate r-strategy species particularly in Arkhangelskiella cymbiformis and Watznaueria barnesiae. These impoverished and dwarfed late Maastrichtian assemblages appear to be the direct consequences of mantle plume volcanism and associated environmental changes, including high nutrient influx leading to eutrophic and mesotrophic waters, low oxygen in the water column and decreased watermass stratification.

Catastrophic mass extinction and assemblage evolution in planktic foraminifera across the Cretaceous/Paleogene (K/Pg) boundary at Bidart (SW France)

A high-resolution biostratigraphic analysis of planktic foraminifers confirms that the Bidart section at the eastern margin of the Atlantic Ocean exhibits a continuous and complete Cretaceous/Paleogene (K/Pg) transition interval. The biozones and subzones recorded in this section are less expanded than their equivalent in Tunisian sections: El Kef (Global Stratotype Section and Point: GSSP for the K/Pg boundary) and Ellès (auxiliary section), but they are sufficiently thick to allow a detailed analysis of the evolution of the planktic foraminiferal assemblages across the K/Pg transition. Throughout the uppermost 4 m Maastrichtian, the planktic foraminiferal assemblages are highly diversified, containing up to 72 species. These Maastrichtian assemblages are rich in cosmopolitan taxa (70%), dominated by small biserial morphotypes which belong mainly to the genus Heterohelix which coexist with less abundant but highly diverse tropical and subtropical species. The extinction pattern at the Bidart section suggests a sudden catastrophic mass extinction at the K/Pg boundary which affected at least 53 out of 72 species. The species becoming extinct include globotruncanids (e.g. Contusotruncana spp., Globotruncana spp., Globotruncanita spp.) and complex heterohelicids (e.g. Racemiguembelina spp., Pseudotextularia spp., Gublerina spp.). At the Bidart section, only Archaeoglobigerina cretacea disappears 2 m below the K/Pg boundary event. Specimens of 18 small and even tiny Maastrichtian species, are found at the lowermost Danian. Only a few of these species belonging to the genera of Guembelitria, Hedbergella and Heterohelix are considered to be real “Cretaceous survivor species”, whereas the specimens belonging to the rest, are most probably reworked, because they differ in their preservation. Throughout lowermost Danian, the planktic foraminiferal assemblages are dominated by “opportunistic” species of the genus Guembelitria. These opportunists are associated to small and poorly diversified pioneer globigerinids ( Palaeoglobigerina spp. and Parvularugoglobigerina spp.). These assemblages became progressively more diversified across the early Danian containing species with cancellate walls ( Eoglobigerina spp., Parasubbotina spp., Subbotina triloculinoides and Praemurica spp.) and new taxa of biserial heterohelicids ( Woodringina spp. and Chiloguembelina spp.) suggesting a paleoenvironmental recovery.

The response of benthic foraminifera to the K–Pg boundary biotic crisis at Elles (northwestern Tunisia)

The high-resolution quantitative study of benthic foraminifera from the Elles section (NW Tunisia) that contains one of the most complete Cretaceous–Paleogene (K–Pg) boundary transition and spans about 357 kyr provides detailed data on the palaeoenvironmental turnover across the K–Pg boundary. Benthic foraminifera indicate outer neritic-uppermost bathyal depths without perceivable bathymetrical changes throughout. Uppermost Maastrichtian assemblages are well preserved and highly diversified, indicating stable environment and mesotrophic to weakly eutrophic conditions during the latest Cretaceous. Benthic foraminifera underwent a major faunal turnover in coincidence with the K–Pg boundary, where a dramatic and sudden decrease in the percentage of both infaunal morphogroups and buliminids, as well as in diversity, heterogeneity, and genus and species richness of the assemblages, are recorded indicating overall oligotrophic conditions. Benthic foraminifera do not show significant extinction at the end of the Cretaceous, with only about 3% of the species clearly becoming extinct together with the temporary disappearance of some taxa. A stepped pattern of faunal recovery and restructuring is recognizable during the lowermost Danian reflecting the gradual restabilization of the environmental conditions after the K–Pg boundary event. The nature and the abundance of food supply to the sea floor conditioned the faunal turnover in the earliest Paleogene which reflects not only a sudden collapse of the food web due to the extinction of calcareous primary producers, but also a major, rapid change in composition and abundance of food supply just after the K–Pg boundary. Short-term blooms of some opportunistic species within the G. cretacea Zone and the lowermost part of the Ps. pseudobulloides Zone would reflect instability in the benthic assemblages that might be related to the transfer to the sea floor of food supply not easily used by the benthos through short-term, large blooms or changes in abundance of opportunistic, various phytoplankton groups. The major environmental instability at the sea floor that just follows the K–Pg boundary event may have been thus related to changes in the phytoplankton composition and abundance and would have taken place over a period of about 25 kyr. Benthic foraminiferal assemblages appear to stabilize in the lowermost part of Zone Ps. pseudobulloides (∼ 65 kyr after the K–Pg boundary event). The sea floor ecosystem, at least at outer neritic-uppermost bathyal depths, may have recovered over a considerably shorter period than commonly suggested, even if the food delivery to the sea floor had not fully recovered the pre-K–Pg levels as indicated by the lower percentages of infaunal morphogroups and buliminids. This would be also in agreement with the rapid recovery of terrestrial ecosystems following the biotic crisis at the K–Pg boundary. The drastic change of benthic foraminiferal assemblages coincident with the K–Pg boundary at Elles and their staggered reorganization during the lowermost Paleogene are largely compatible with the catastrophic effects of a huge asteroid impact on Earth at the K–Pg boundary that severely destabilized the oceanic phytoplankton-based food web.

Deep-Sea environments across the Cretaceous/Paleogene boundary in the eastern South Atlantic Ocean (ODP Leg 208, Walvis Ridge)

Sediments recovered at ODP Site 1262 on Walvis Ridge (eastern South Atlantic Ocean, paleodepth ∼ 2500–3000 m) offer an opportunity to look into the nature and cause(s) of the benthic foraminiferal turnover across the Cretaceous/Paleogene (K/Pg) boundary at abyssal depths at a location relatively remote from the location of the asteroid impact on the Yucatan peninsula. Late Maastrichtian assemblages were diverse and heterogeneous, reflecting oligo- to mesotrophic conditions at the sea floor. As at other locations, there was no significant extinction of benthic foraminiferal species at the K/Pg boundary, but the diversity and heterogeneity of the assemblages decreased precipitously. The percentage of infaunal buliminid taxa decreased rapidly, but the total percentage of infaunal taxa remained essentially unchanged. Benthic foraminiferal accumulation rates (BFAR) dropped at the boundary itself, and fluctuated strongly later in the Danian. After the K/Pg boundary, opportunistic taxa increased in relative abundance, and diversity and heterogeneity strongly fluctuated. There thus is no clear agreement between three proxies which have been used to indicate a high food supply to the sea floor: percentage buliminids, percentage infaunal taxa, and BFAR. This discrepancy might indicate that the food supply changed in character (e.g., type of food, temporal variability in flux), but did not show a long-term, large net change in total amount. The strong fluctuations in BFAR, heterogeneity and diversity indicate that environmental instability started at the K/Pg boundary, and persisted through planktic foraminiferal zones Pα and P1a. In lower planktic foraminiferal zone P1b, agglutinated species of the genera Spiroplectammina and Clavulinoides, thought to be infaunal and indicative of increasing levels of food supply, increased in relative abundance while the relative abundance of buliminids remained low. Possibly, agglutinated taxa took over at least part of the infaunal niche in the Paleocene, as a result of the rise in the calcium carbonate compensation depth. Towards the upper part of the studied interval (lower planktic foraminiferal Subzone 1c), benthic foraminiferal assemblages stabilized, with heterogeneity almost back to Maastrichtian values, although diversity and BFAR did not fully recover.

Sedimentology and palynology of the Calafate Formation (Maastrichtian), Austral Basin, Southern Patagonia, Argentina

The Calafate Formation crops out in south-western Santa Cruz Province, Argentina, and displays a stacking of asymmetrical coarsening–fining-upward cycles. These cycles are interpreted as the product of short-lived transgressive-regressive events in which the coarsening upward part represents sedimentary aggradation with a stable or decreasing sea level. Sedimentological and palynological analyses indicate nearshore marine conditions. Even though the existence of an estuary or incised valley cannot be determined, this is the most probable palaeogeographic model. Based on dinoflagellate cysts, the base of the section is considered to be not older than Maastrichtian. The presence of the oyster Ambigostrea clarae (Ihering) occurring together with the dinoflagellate cyst species Manumiella druggii (Stover) Bujak and Davies and Eisenackia circumtabulata Drugg in the middle part of the section indicates an age no older than late Maastrichtian. According to sedimentological data, deposits representing the Cretaceous–Palaeogene transition would have been eroded, which is confirmed by the presence of Grapnelispora loncochensis Papú. This megaspore is a consistent component of the Maastrichtian assemblages from Patagonia.

Biotic effects of impacts and volcanism

The biotic effects of late Maastrichtian mantle plume volcanism on Ninetyeast Ridge and Deccan volcanism mirror those of the Cretaceous–Tertiary (KT) mass extinction and impact event. Planktonic foraminifera responded to high stress conditions with the same impoverished and small-sized species assemblages dominated by the disaster/opportunists Guembelitria cretacea, which characterize the KT mass extinction worldwide. Similar high stress late Maastrichtian assemblages have recently been documented from Madagascar, Israel and Egypt. Biotic effects of volcanism cannot be differentiated from those of impacts, though every period of intense volcanism is associated with high stress assemblages, this is not the case with every impact. The most catastrophic biotic effects occurred at the KT boundary (65.0 Ma) when intense Deccan volcanism coincided with a major impact and caused the mass extinction of all tropical and subtropical species. The Chicxulub impact, which now appears to have predated the KT boundary by about 300 kyr, coincided with intense Deccan volcanism that resulted in high biotic stress and greenhouse warming, but no major extinctions. The unequivocal connection between intense volcanism and high stress assemblages during the late Maastrichtian to early Danian, and the evidence of multiple impacts, necessitates revision of current impact and mass extinction theories.

Calcareous nannofossil biostratigraphy and paleoecology of the Cretaceous–Tertiary transition in the central eastern desert of Egypt

The Gebel Qreiya and nearby Wadi Hamama sections of the central Eastern Desert are among the most complete K/T boundary sequences known from Egypt. The two sections were analyzed spanning an interval from l.83 Myr below to about 3 Myr above the K/T boundary. A 1-cm-thick red clay layer at the K/T boundary at Gebel Qreiya contains an Ir anomaly of 5.4 ppb. The high-resolution study and well-preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the K/T transition in Egypt. Four zones ( Micula murus, Micula prinsii, NP1, and NP2) were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern Tethys region. Latest Maastrichtian assemblages are abundant and diverse, though Cretaceous species richness progressively decreased across the K/T boundary. Dominant species include Arkhangelskiella cymbiformis, Micula decussata and Watznaueria barnesae, with high abundance of dissolution-resistant M. decussata reflecting periods of high environmental stress. Thoracosphaera blooms mark the K/T boundary and are followed by an acme of the opportunistic survivor Braarudosphaera bigelowii, the first appearance of the new Tertiary species Cruciplacolithus primus, and an acme of Coccolithus cavus/ pelagicus. These successive abundance peaks provide the basis for subdivision of the Early Danian Zones NP1 and NP2 into five subzones. Correlation of selected nannofossil taxa from the Egyptian sections with those from various onshore marine and deep-sea sections provides insights into their paleoenvironmental and paleoecological affinities.

The Cretaceous/Palaeogene (K/P) boundary at Aïn Settara, Tunisia: restructuring of benthic foraminiferal assemblages

Benthic foraminiferal assemblages, in contrast to planktic foraminifera, generally did not suffer mass extinctions at the Cretaceous/Palaeogene (K/P) boundary; extinctions were fewer in deeper water. However, the outer shelf, upper bathyal section at Aïn Settara, Tunisia, records a dramatic change in the structure of benthic foraminiferal assemblages across the K/P boundary. At the level of extinction of planktic assemblages and enrichment in Ir and other geochemical anomalies, highly diversified, low‐dominance Upper Maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages, strongly dominated by epifaunal morphogroups. This extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply. This, in turn, is the consequence of a sudden collapse in primary productivity, probably resulting from the impact of the K/P asteroid.

Late Maastrichtian to early Danian calcareous nannofossils at Elles (Northwest Tunisia). A tale of one million years across the K–T boundary

A detailed study of calcareous nannofossils of the Elles section (Tunisia) was extended over an interval of about 1 Myr including the K–T boundary. The late Maastrichtian assemblages are rich and well preserved. Pulses of surface water cooling, probably related to episodic upwelling are revealed by the increase in abundance of cool water taxa (mainly Kamptnerius magnificus, Nephrolithus frequens, Gartnerago spp.) in certain late Maastrichtian samples, paralleled by a decrease of the warm water species Watznaueria barnesae. A sensible decrease in abundance of Arkhangelskiella cymbiformis and its return to smaller specimens was also recorded at Elles, probably as the result of surface water productivity changes in the latest Maastrichtian. Some Maastrichtian samples at Elles contain Neobiscutum romeinii and Chiasmolithus? sp. These taxa, formerly thought to be Tertiary coccoliths, are here considered as truly Maastrichtian occurrences. As at El Kef, the Danian of Elles is characterised by successive blooms of surviving and newly evolved species. Though the abundance of calcareous nannofossils rapidly reached the same level as in the Maastrichtian, the lower diversity still points to a mesotrophic, poorly stratified marine environment. The reworking versus survivorship of Cretaceous species found in Danian samples remains an unresolved question, but a hypothesis of survivorship is also strengthened by the presence of several coccospheres of W. barnesae and Bidiscus rotatorius well above the boundary. The effect of the marine environmental change across an expanded K–T boundary section as Elles appears complex if seen through calcareous nannofossils. From a geological point of view, the K–T boundary floral turnover at Elles seems dramatically synchronous with the signatures of an extraterrestrial impact, superimposed on long-term, background environmental and climatic changes. However, a precise succession of events based on appearance/disappearance of nannofossil species across the Cretaceous/Paleocene transition is far from being unanambiguous.

Terrestrial palynomorph biostratigraphy of the Cypress Hills, Wood Mountain, and Turtle Mountain areas (Upper Cretaceous - Paleocene) of western Canada

Three cored test holes were drilled to study the stratigraphic interval spanning the Cretaceous-Tertiary boundary: one in the western Cypress Hills near Elkwater, Alberta; a second in the eastern portion of the Wood Mountain area near Killdeer, Saskatchewan; and a third on the western edge of Turtle Mountain near Goodlands, Manitoba. The terrestrial elements of the palynological assemblages are discussed. The Maastrichtian assemblages encompassed the Scollardia trapaformis Zone and two new subzones, Myrtipites scabratus - Aquilapollenites delicatus var. collaris and Porosipollis porosus - Aquilapollenites notabile within the Wodehouseia spinata Zone. The Paleocene zones encountered include the Aquilapollenites reticulatus Subzone of the W. spinata Zone, the previously described Wodehouseia fimbriata and Momipites wyomingensis zones, and the newly defined Tricolporopollenites kruschii Zone. These provide a biostratigraphy for the cored intervals which can be related to polarity chrons. The observations made demonstrate that existing zonations are not applicable basin wide, as there are chronologically distinct disconformity-bounded sequences in western and eastern basin sectors. Apparent diachronisms within the preserved assemblages were documented by earlier entry levels within the Momipites lineage and a significant upwards extention in the range of W. fimbriata in the eastern part of the basin.

Upper Cretaceous palaeoenvironments and benthonic foraminiferal assemblages of potential source rocks from the western African margin, Central Atlantic

Abstract Upper Cretaceous benthonic foraminiferal assemblages, clay minerals, kerogen types and carbonate microfacies are examined in organic-rich sediments from western African coastal basins along a latitudinal transect extending from southern Morocco to Nigeria. Samples from onshore sections of the Tarfaya Basin, southern Morocco, from DSDP Site 369, from offshore commercial wells on the Casamance Shelf, Senegal, from DSDP Site 367, from ODP Site 959 and from onshore sections of the Benue Trough in Nigeria, are analysed. Organic-rich sediments from these sites are characterized by smectiterich clay mineral assemblages, high amounts of marine organic matter and a typical benthonic foraminiferal biofacies dominated by buliminids and bolivinids. Benthonic foraminifera provide robust proxy indicators of palaeoproductivity and organic matter flux to the seafloor. The palaeobiogeographic distribution of benthonic foraminiferal biofacies can be used to identify areas and stratigraphic intervals of hydrocarbon accumulation. Lower Turonian benthonic foraminiferal assemblages exhibit extremely low diversity and are strongly dominated by a Gabonita biofacies, in contrast to Coniacian to Maastrichtian assemblages, which display higher diversity and contain numerous species of Buliminella, Praebulimina, Afrobolivina, Bolivina and Orthokarstenia . The palaeobathymetric distribution of these high productivity benthonic foraminiferal biofacies reflects the establishment of a productivity driven oxygen minimum zone along the western African shelf, associated with an upwelling system active off coastal Africa during most of the Late Cretaceous. The extent of the high productivity equatorial belt appears to have shifted latitudinally during the Late Cretaceous as sea level and circulation patterns changed. The zone of highest productivity was broadest in the Early Turonian, when it coincided with the maximum sea-level rise and highest atmospheric temperature in the Late Cretaceous.

The last stages of dinosaur faunal history in Europe: a succession of Maastrichtian dinosaur assemblages from the Corbières (southern France)

AbstractWe report the discovery of a dinosaur assemblage in the non-marine Late Maastrichtian of the Corbieres region of southern France; this allows the reconstruction of the succession of dinosaur faunas during the Maastrichtian in western Europe. An Early Maastrichtian fauna dominated by titanosaurid sauropods was replaced by a Late Maastrichtian assemblage dominated by hadrosaurs. This important faunal replacement seems to coincide with environmental changes (documented by sedimentological and palynological evidence) which have been linked to a marine regression during the Maastrichtian. This suggests that sea-level changes influenced the evolution of dinosaur faunas in Europe during the Late Cretaceous, but were not sufficient to cause the final extinction of dinosaurs, for which other causes must be sought.

Palynology of the lower Lefipan formation (upper cretaceous) of Barranca de los Perros, Chubut province, Argentina part il angiosperm pollen and discussion

Abstract Angiosperm pollen are documented from nine outcrop samples from the Lefipan Formation, Barranca de los Perros, in the Chubut Province of southern Argentina. The material was collected from the lower part of the Lefipan Formation that contains a marine fauna of Maastrichtian age. Twenty‐seven angiosperm pollen taxa are described. Stratigraphic and geographic distribution of these taxa, and of pteridophyte and bryophyte spores and gymno‐sperm pollen from these samples, are compared with Campanian to Paleocene assemblages from southern South America, the Antarctic Peninsula, New Zealand and Australia. The Lefipan flora contains taxa in common with Maastrichtian assemblages to the south, but in overall aspect is dissimilar to the high latitude, wet temperate Weddellian conifer‐rich forest floras. The fern and angiosperm‐rich Lefipan palynoflora probably represents a shrubby angiosperm‐fernland vegetation with patchy wooded areas growing in warm temperate (to subtropical?) conditions.

Dinoflagellate assemblages and sea-level fluctuations in the Maastrichtian of southwest Georgia

Analysis of Maastrichtian dinoflagellate assemblages from the upper Ripley and Providence Formations in two cores from southwestern Georgia show changes that can be related to fluctuations in relative sea-level and in depositionla environments. Sediments in the USGS Ft. Gaines Core were deposited in transitional zone to nearshore and estuarine environments close to a major fluvial source, whereas co-eval sediments in the USGS Albany Core were deposited in middle to outer shelf environments, lateraly displaced away from any fluvial source. Lower Maastrichtian assemblages in the Ft. Gaines Core contain common Senegalinium obscurum and Cerodinium pannuceum. These point to overall transgressive conditions in the lower Providence, whereas decreases in percent marine phytoplankton indicate individual progradational episodes. The upper Providence of the Ft. Gaines Core shows a marked decrease in dinoflagellate species abundance and percent and absolute abundances of marine phytoplankton, with a concurrent increase in relative abundance of Achomosphaera-Spiniferites cysts. These indicators to a relative regression and shoreward movement of facies through the upper Maastrichtian. Lower Maastrichtian assemblages in the more seaward Albany Core are dominated by Chatangiella? robusta, Exochosphaeridium bifidum, and Cerodinium panneceum, and have a very high percent marine phytoplankton signal. These are interpreted to represent transgressive conditions with no progradation of the shoreline. The upper Providence shows high species abundance, increasing dominance by Achomosphaera-Spiniferites cysts, individual abundance peaks of several different species, and a decrease in percent marine phytoplankton, indicating an overall relative sea-level regression through the upper Maastrichtian. Comparison with dinoflagellate assemblages from Maryland suggest that high abundances of Areoligera cysts at about the lower/upper Maastrichtian boundary may reflect the level of maximum transgression in the middle of the Maastrichtian. Three new species are described: Florentinia perforata, Yolkinigymnium expansum, and Palambages trilicius.