Early Carboniferous radiolarians from north-west Thailand: palaeogeographical implications

Moderately well-preserved radiolarian assemblages are described from bedded cherts south of Mae Hong Son, north-west Thailand. Twenty species and subspecies are identified, including one new species ( Archocyrtium sashidai Feng sp. nov.). The assemblages belong to the middle Early Carboniferous Albaillella indensis and Eostylodictya rota zones. The new data suggest that there was a pelagic basin between the Shan-Thai terrane and Gondwana during the Early Carboniferous. This implies, contrary to previous interpretations, that the Shan-Thai terrane had already rifted apart from Gondwana during the Early Carboniferous.     

Mississippian (early Carboniferous) radiolarian biostratigraphy of northern Thailand (Chiang Dao area)

Well-preserved Carboniferous radiolarian faunas were obtained from ribbon-bedded siliceous sediments (radiolarites) north of Chiang Dao city, Chiang Mai province, northern Thailand. These sediments are rich in identifiable radiolarian faunas, including more than 44 species and sub-species belonging to 15 genera. Among them, Albaillellaria and Latentifistularia are dominant, but few Entactinaria are present. Five Early Carboniferous radiolarian assemblage zones are recognised and compared to those of Germany, France and North America. They are, in ascending order: the Albaillella paradoxa gr. assemblage; the Albaillella indensis gr. assemblage: the Albaillella cartalla-Albaillella furcata furcata assemblage which includes the Palaeolithocyclia rota subassemblage; and the A. furcata rockensis-Latentifistula impella gr. assemblage. The age assignment of each assemblage is well-controlled by co-occurring conodonts, which are abundant during this time interval in the area. The Thai radiolarian assemblage zones are rather similar to those of Germany and North America, indicating that the albaillellarian form has a global distribution and can be readily used as a world key indicative fauna. These results also provide an additional data set indicating that distal oceanic deposits are present in northern Thailand from the Devonian to the Late Triassic, which provides evidence for a long-lived oceanic realm between the Indochina and Shan-Thai continental terranes (nearly 200 My).     

Ladinian radiolarian fauna from West Sichuan, China

A poorly preserved, but diversified radiolarian fauna was recovered from thin-bedded cherts occurring in the southeast of Daofu, Sichuan Province, southwestern China. Twenty-two radiolarian species belonging to 10 genera are identified and three new species (Paroertlispongus daofuensis n. sp., Falcispongus heinzi n. sp., Falcispongus pauliani n. sp.) are described. Falcispongus heinzi represents a transitional species between genera Oertlispongus inaequispinosus Dumitrica, Kozur and Mostler and Falcispongus Dumitrica. The fauna is divided into two assemblages, namely Muelleritortis cochleata and Oertlispongus inaequispinosus assemblages, which can be well correlated with the Ladinian radiolarian zones from Europe. The fauna indicates that basaltic rocks occurring in the Xianshuihe Belt were formed mainly during the Middle Triassic. Our results thus extend the previously known geological age of the Xianshuihe Belt to the Middle and Late Triassic interval.     

Cenozoic radiolarian paleobiogeography: Implications concerning plate tectonics and climatic cycles

A preliminary study of the paleobiogeographic patterns of radiolarian facies during the Paleogene and subsequent time shows that:(1) Through time radiolarian assemblages display distinct faunal provincialism reminiscent of modern faunal distributions correlated with planetary temperature gradients and surface oceanic conditions. The equatorial—tropical radiolarian fauna extended apparently unrestricted across the Pacific Ocean, the Caribbean Sea and the Atlantic Ocean through Early Miocene time. In the Caribbean Sea and the Atlantic Ocean, radiolarians reached their maximum abundance in the Eocene and Oligocene. Subsequently, they gradually declined to virtual disappearance in these areas in the early Miocene. Their Pacific counterparts remained practically undisturbed, except that post early Miocene assemblages there showed a marked trend toward decreasing test thickness. This trend has since been a worldwide characteristic of Neogene radiolarian assemblages and their modern equivalents. It is postulated that the disappearance of radiolarians in the Carribean Sea and the Atlantic Ocean at the end of the Paleogene is related to the onset of the emergence of the isthmus of Panama which interrupted the preexisting oceanic circulation between the Pacific and Atlantic Oceans.(2) Throughout the Paleogene there have been marked sequential fluctuations in the radiolarian assemblages of the Caribbean Sea which indicate intermittent incursions of higher-latitude fauna in this area. Associated with the faunal fluctuations are cyclic variations in the total carbonate of the sediment with patterns also comparable in duration to Pleistocene carbonate cycles in the equatorial Pacific known to have been induced by climatic changes. Based on similarities with Pleistocene climatic cycles in the equatorial Pacific and elsewhere, it is surmised that the faunal and lithologic fluctuations observed in Paleogene radiolarian sediments were also induced by the biologic and physico-chemical processes associated with worldwide changes in the climatic conditions of that time.     

Fish otoliths from the Priabonian (Late Eocene) of North Italy and South-East France - Their paleobiogeographical significance

The study of the Late Eocene (Priabonian) otolith associations from Possagno, North-East Italy, and from the Synclinal d’Allons in Haute Provence, South-East France, allows for the reconstruction of a teleost fauna of 55 taxa, which is the most diversified assemblage presently known from the Upper Eocene Paleo-Mediterranean basin. Thirty-six taxa are identified at the species level, and five of those are new: “genus Alepocephalidarum” astrictus, “genus Lophiiformorum” canovae, “genus Agonidarum” sudans, “genus Uranoscopidarum” cochlearis and Aseraggodes laganum. In the Synclinal d’Allons, the otolith associations reflect a tropical to subtropical neritic environment with a few mesopelagic fishes. At Possagno, the associations indicate an environment that changed from one that was deep and exposed to the pelagic realm and then evolved to a more shallow sea with a well-diversified benthic life and less mesopelagic fishes. A paleobiogeographical analysis of all known data on Priabonian otoliths, worldwide, shows clearly a western Atlantic (Louisiana) and an eastern Atlantic-Paleomediterranean association. In the eastern Atlantic-Paleomediterranean association, the Aquitaine association not only differs from the Possagno-Allons association in function of its more distant geographical position, but also by its stronger oceanic character in the southern part of the basin, and by the occurrence in the north, of a very shallow water facies (Saint-Estephe Formation) that contains some taxa which are known nowhere else in the Priabonian. The Ukraine fauna is characterized by a high number of species, which have an Oligocene record in other European sites. The northern geographic location of Ukraine, combined with the good connections to both the North Sea Basin and the Turgai street can provide the explanation. Many Oligocene species (or their close relatives) probably already existed at Eocene times in more northern regions, but could penetrate only in more southern European seas since the strong cooling at the beginning of the Oligocene.     

The Radiolarian biotic response during OAE2. A high-resolution study across the Bonarelli level at Bottaccione (Gubbio, Italy)

In order to improve our understanding of the radiolarian biotic response and the palaeoceanographic changes associated with the Late Cenomanian oceanic anoxic event (OAE2), a high-resolution radiolarian study was carried out across the Bonarelli level at its typical locality (Bottaccione section, central Italy). Our results confirm that a drastic radiolarian faunal change took place during the OAE2. The radiolarian turnover took place within the median part of the Bonarelli level, associated with an interval of high organic matter preservation, but relatively low values of silica. Therefore, this part constitutes a critical period in the evolutionary history of Radiolaria. A synthesis of all data available in the Umbria-Marche basin suggests that the lower part of the Bonarelli level (and underlying limestones) records mainly radiolarian extinctions (ca. 41%), while its upper part (and overlying limestones) records mainly first occurrences (ca. 35%). Our results improve understanding of the paleoecology of the family Saturnalidae, which would seem to prefer oligotrophic environments.     

Morphological characteristics of boreal radiolarians from the Triassic and Late Cretaceous: Comparative analysis

When comparing boreal radiolarian assemblages of the Triassic and Late Cretaceous, significant differences in their morphotypic composition are recognized. In particular, Triassic assemblages are dominated by spherical morphotypes, including pylomate forms of the genus Glomeropyle, while Late Cretaceous assemblages are dominated by prunoid morphotypes without polar spines (genera Prunobrachium and Amphibrachium). It is concluded that, in the course of evolution, high-latitude radiolarian assemblages considerably changed both taxonomically and morphologically. Therefore, it is impossible to determine the uniform morphological and taxonomic characters describing boreal assemblages of the entire Mesozoic. Features of boreal radiolarian assemblages are unique to each geological epoch.     

Upper Albian planktic foraminifera and radiolarian biostratigraphy (Nebeur – northern Tunisia)

Preliminary lithostratigraphic and biostratigraphic data recovered from Upper Albian pelagic successions of the Jebel Srassif area (Tunisian trough) reveal the presence of a moderately well preserved radiolarian fauna. This fauna is fossilized in blackshale beds of Rotalipora subticinensis, R. ticinensis and the lower part of the R. appenninica foraminifer zones. Thirty-five radiolarian morphotypes were identified. A correlation established with foraminifer planktic biochronology allows us to distinguish three radiolarian assemblages. The close association between organic-rich deposits and the radiolarian bloom can be interpreted as productivity proxy triggered by semi-enclosed basin configuration and an intensified upwelling currents provided by a possibly halokinetic-induced hydrothermalism.     

Biostratigraphie des brachiopodes et âge carixien (Pliensbachien inférieur) des calcaires à grands bivalves en Algérie occidentale

Recent researches on the Lower Jurassic of Western Algeria allow to establish a lithostratigraphic standard correlating the different members and formations developed in the Ouarsenis and Tlemcen Mountains, the Oran High Plains, the Nador and Ksour Mountains. The position of the large bivalve limestones (= Lithiotis limestones) is well established in the different lithologic successions. This facies is widespread in Western Algeria where it is interbedded with brachiopod marker beds, indicating short periods of maximum flooding. The large number of collected brachiopods are distributed into four “faunas” (assemblages) ranging from the Late Sinemurian (= Lotharingian) to the Early Pliensbachian (= Carixian). These faunas have been dated by the age of the species that they have in common with the NW european and western tethyan provinces. These chronological data are confirmed by rare ammonites. All these results evidence the age of the large bivalve facies in Western Algeria. They are contained in the Middle to Late Carixian (Demonense and Dilectum Zones). This datation is in conformity with that known from the Eastern High-Atlas (Bou Dahar). Consequently, the large bivalves cannot be considered as “markers for the unique Domerian” as it has been too often asserted. The palaeontological part of our study shows that the multicostate Zeilleriids (several Tauromenia species from the Late Sinemurian to the Early Carixian) are older than the multicostate Terebratulids (Hesperithyris species from the Middle to Late Carixian).     

Radiolarian assemblages in surface sediments along longitude 175°E in the Pacific Ocean

This study of 24 surface sediment samples along longitude 175°E between latitudes 48°N and 14°S in the western Pacific Ocean documents the relationship between the modern distribution of radiolarian assemblages and present oceanographic conditions. Ninety-two species were classified into eight clusters by using R-mode cluster analysis. Q-mode cluster analysis was used to distinguish five geographical zones, which were interpreted to represent the Tropical, Southern Subtropical, Northern Subtropical, Transitional, and Subarctic climatic zones. Species richness, diversity, and equitability are highest in the Tropical and Transitional Zones. We attempted to formulate new regression equations considering ecological information on the vertical distribution of radiolarian species. Transfer functions were derived from regression analysis of radiolarian assemblages to observed Sea Surface Temperature (SST) values. The transfer functions have a standard error of 1.16 °C in the estimate of winter SST, 0.81 °C in that of summer SST.     

Middle and Late Triassic radiolarians from northern Tibet: Implications for the Bayan Har Basin evolution

During the Triassic, the Bayan Har Basin is a huge triangular basin surrounded by the North China Platform, South China Platform and Qingtang Terrane. It is filled by a Triassic turbidite sequence, the Bayan Har Group. For a long time, the series of Bayan Har Group in the eastern part of the basin were considered to be a Lower to Upper Triassic sequence, and in the western part, was attributed to the Upper Triassic. A well-preserved diversified radiolarian fauna was recovered from radiolarian chert and tuffite interbeds of the Bayan Har Group turbidites and adjacent stratigraphic units in the Hoh Xil area, northern Tibet. Sixty-seven species are identified and subdivided into two assemblages: late Anisian and early Carnian. Combined with the discovery of the Late Permian and Early Triassic turbidite in the Bayan Har Group in this area by Huang et al., it proves that all the Triassic is also present in the Bayan Har Group sequence in the western part. The evolution of the Bayan Har Basin may be traced back to the Late Permian. The massive sequence of the Bayan Har Group and its provenance indicate that the Kunlun and Qinling orogenic belts rapidly rise during the Middle-Late Triassic. The basin extended to the end of the Triassic, possibly locally to the Jurassic.     

First evidence of Late Carnian radiolarians from the Izmir-Ankara suture complex, central Sakarya, Turkey: implications for the opening age of the Izmir-Ankara branch of Neo-Tethys

Within the Late Cretaceous mélange complex of the Izmir-Ankara suture zone in central Sakarya area, north-western Turkey, a megablock with radiolarian cherts associated with basaltic pillow lavas has been dated by radiolarians. The studied radiolarian assemblage and conodonts yielded an early Late Carnian age. This age is the oldest obtained from the chert blocks all along the suture belt and has important implications for the rifting/opening age of the Izmir-Ankara branch of the Tethys ocean in north-western Turkey. Based on this new data, it is concluded that during the Late Triassic the Izmir-Ankara seaway was connected to the other Tethyan oceanic branches and deep enough to provide chert sedimentation and exchange radiolarians with the main open oceans. It is further suggested that the long-lasting misinterpretation of a Liassic rifting/opening of the Izmir-Ankara ocean should be revised.     

Le genre Nucleolites (Echinoidea, Cassiduloidea) du Bajocien à l'Oxfordien dans le Bassin de Paris : apport des données architecturales à la systématique et à la phylogénie

The classification of the Paris basin Bajocian-Oxfordian species of the genus Nucleolites is revised. A classic point of view, until now used by authors and mainly based on the general morphology of the test, is first developed. Then, this last is modified with new architectural data, which refer to the extraxial-axial theory concerning the structure of the apical system as well as the presence of supplementary and catenal plates. These architectural data are first used facing the general morphology of the test. Such approach leads to a new point of view for the classification of the species of the genus Nucleolites. The systematics is particularly significantly simplified. The deduced and proposed phylogenetic hypothesis shows that the genus Nucleolites is composed of two parallel lineages as soon as the beginning of the genus in the Bajocian: a group with a so-called “primitive” architecture, and a group with an “advanced” one. On and after the Late Callovian, the species with a primitive organisation give birth to advanced species, which continue in younger time. In this way, the genus Nucleolites may be paraphyletic since the Late Callovian onward.     

Radiolarian faunal turnover across the Oligocene/Miocene boundary in the equatorial Pacific Ocean

The global warming trend of the latest Oligocene was interrupted by several cooling events associated with Antarctic glaciations. These cooling events affected surface water productivity and plankton assemblages. Well-preserved radiolarians were obtained from upper Oligocene to lower Miocene sediments at Ocean Drilling Program (ODP) Leg 199 Sites 1218 and 1219 in the equatorial Pacific, and 110 radiolarian species were identified.Four episodes of significant radiolarian faunal changes were identified: middle late Oligocene (27.5 to 27.3 Ma), latest Oligocene (24.4 Ma), earliest Miocene (23.3 Ma), and middle early Miocene (21.6 Ma). These four episodes approximately coincide with increases and decreases of biogenic silica accumulation rates and increases in δ¹⁸O values coded as “Oi” and “Mi” events. These data indicate that Antarctic glaciations were associated with change of siliceous sedimentation patterns and faunal changes in the equatorial Pacific.Radiolarian fauna was divided into three assemblages based on variations in radiolarian productivity, species richness and the composition of dominant species: a late Oligocene assemblage (27.6 to 24.4 Ma), a transitional assemblage (24.4 to 23.3 Ma) and an early Miocene assemblage (23.3 to 21.2 Ma). The late Oligocene assemblage is characterized by relatively high productivity, low species richness and four dominant species of Tholospyris anthophora, Stichocorys subligata, Lophocyrtis nomas and Lithelius spp. The transitional assemblage represents relatively low values of productivity and species richness, and consists of three dominant species of T. anthophora, S. subligata and L. nomas. The characteristics of the early Miocene assemblage are relatively low productivity, but high species richness. The two dominant species present in this assemblage are T. anthophora and Cyrtocapsella tetrapera. The most significant faunal turnover of radiolarians is marked at the boundary between the transitional/early Miocene assemblages.We also reviewed changes in other microfossil assemblages in the low latitudes during the late Oligocene through early Miocene. The microfossil assemblages of major groups show sequential changes near the Oligocene/Miocene (O/M) boundary (23.8 Ma). Many extinction events and some first occurrences of calcareous nannofossils and many occurrences of radiolarians are found from about 24.8 to 23.3 Ma, and first occurrences of planktic foraminifers and diatoms followed from 23.2 through 22 Ma. Hence, the O/M boundary is identified as a significant level for microfossil evolutions.     

Ostracodes et stratigraphie du néogène et du quaternaire méditerranéens

A stratigraphical chart of marine ostracoda from Lower Miocene to Recent is established. Selected species (approximatively 220) are those morphologicaly well characterized and known from different parts of the Mediterranean area. It appears that: • lower Miocene ostracodes are still poorly known; • specific diversity is high during the Tortonian and the Lower Messinian before the complete disappearance of marine Mediterranean species during the Upper Messinian évaporitic episodes; • during the early Pliocene, about half of the Upper Miocene marine species are reintroduced with the Atlantic waters; other species migrate for the first time in the Mediterranean Sea by the same way; • at the end of the Pliocene or at the beginning of the Pleistocene several species known in Mediterranean since the Middle Miocene or before, such as Cytherella sp. gr. transversa and Ruggieria tetraptera, as well some “nordic guests” such as Hemicythere villosa and Cythere lutea, appear. This work is an opportunity to confirme a Late Miocene age for the Neogene of Skyros (Aegean Sea), to assign the “Upper Pliocene” of Terquem to the Lower Pleistocene and to refute the existence of a pliocene psychrosphere.     

Radiolaria as a reflection of environmental conditions in the eastern and southern sectors of the Indian Ocean: A new statistical approach

Cluster analysis and species abundance plots of radiolarian abundance counts from core tops from the eastern Indian Ocean between 12° S and 31° S, and the southern Indian Ocean between 31° S and 62.5° S, demonstrate the existence of environmentally-related provinces supporting distinct taxa assemblages. These provinces are closely associated with currents in the eastern sector of the Indian Ocean and with fronts in the southern sector.The radiolarian assemblages correlate strongly with salinity-normalised total alkalinity (NTA) at the sea-surface, with temperature, salinity, and density from the sea-surface to 300 m, and with dissolved oxygen and nitrate and phosphate concentrations from the sea-surface to 100 m. Palaeo-reconstructions of these parameters at the sea-surface have been made for six Last Glacial Maximum (LGM) samples from five eastern Indian Ocean cores. The LGM sea-surface temperature estimates are comparable with those based on planktonic foraminiferal counts of the same samples obtained by other researchers. The reconstructions show that, since the LGM, density increased markedly along the Western Australian coast south of 20° S but changed little further from the Western Australian coast. By contrast, phosphate concentrations were marginally lower than modern values along the Western Australian coast south of 20° S but more than twice modern values in the other LGM samples.The utility of various regression and calibration techniques is discussed. It is concluded that, probably due to the effects of differences in radiolarian habitat, ocean currents, and/or environmental gradients, only one method, weighted averaging — partial least squares, is reliable in a study area of this size and complexity. If other methods are to be used, the study area must be partitioned into at least two separate regions with the major split between the eastern and southern sectors of the Indian Ocean.     

Middle and Upper Triassic radiolarite components from the Kcira-Dushi-Komani ophiolitic mélange and their provenance (Mirdita Zone,Albania)

The Middle Jurassic Kcira-Dushi-Komani Mélange in the northwestern Mirdita Ophiolite Zone contains blocks of Triassic oceanic crust, radiolarites and open marine limestones. We describe the microfacies and present biostratigraphic data from radiolarite clasts and blocks and from basalt-radiolarite blocks with preserved autochthonous sedimentary cover. The radiolarians yield Middle to Late Triassic (Late Anisian to Late Norian) ages for the oceanic realm from which the ophiolite and radiolarite blocks and clasts derived. Together with limestone blocks, the provenance areas of the components in the Kcira-Dushi-Komani Mélange are determined as the distal shelf and the ocean floor of the Neotethys. In the course of ophiolite obduction, the components were transported by mass movements into newly formed trench-like basins in front of the westward propagating nappe stack. These basins were later incorporated in the nappe stack forming the typical features of a syntectonic mélange. Our radiolarian biostratigraphic data confirm Late Anisian formation of the Neotethys Ocean, parts of which became closed in the Middle Jurassic. The data clearly speak in favour of one Neotethys Ocean to the east, from which the Mirdita ophiolites derived as far-travelled nappes.     

A 350-ky radiolarian record off Lüderitz,Namibia—evidence for changes in the upwelling regime

The study of radiolarian assemblages from Core MD 962086 provides new information on the variability in the upwelling intensity and origin of upwelled water masses over the past 350 ky in one of the major filamentous regions of the Benguela Upwelling System (BUS), located off Lüderitz, Namibia. The use of key radiolarian species to trace the source of upwelled waters, and the use of a radiolarian-based upwelling index (URI) to reconstruct the upwelling intensity represent the first use of radiolarians for paleoceanographic reconstructions in the BUS. These radiolarian-based proxies indicate strongest upwelling during Marine Isotope Stages (MIS) 3, 5, and 8, which compares well with other studies. While during MIS 3 and 8, the radiolarian-based proxies indicate the influx of waters of Southern Ocean origin, they also point to the increased influence of tropical waters during the lower portion of MIS 5. During MIS 2, 4 and 6 the radiolarian assemblages indicate generally lower upwelling intensities, although this signal is complicated by the increased occurrence of organic carbon in the sediments during these intervals. During MIS 2 there appears to be less of an input of Southern Ocean waters to the BUS, although during the also glacial MIS 4 and 6, there is evidence for an increased influence of cold Antarctic waters. The comparison of the results from Core MD 962086 with other studies in the BUS area indicates a non-uniform pattern of upwelling intensity and advection of cold, southern waters into this system during MIS 2. Weaker upwelling signaled by the radiolarian-based proxy in MIS 4 is in contrast to other studies that indicate higher productivity during this time period. In general, the data show that there is a strong spatiotemporal complexity in upwelling intensity in the BUS and that the advection of water into it is not strongly tied to glacial–interglacial variations in climate.     

New analysis of the Pleistocene carnivores from Petralona Cave (Macedonia, Greece) based on the Collection of the Thessaloniki Aristotle University

New taxonomic study of the “old collection” of Carnivora from Petralona Cave, associated to the well-known hominid skull, housed in the Geology School of the Thessaloniki Aristotle University since 1960, revealed 11 species (Canis arnensis, Lycaon lycaonoides, Vulpes praeglacialis, Ursus deningeri, U. spelaeus, U. arctos, Pliocrocuta perrieri, Pachycrocuta brevirostris, Crocuta crocuta, Panthera leo spelaea, and Felis silvestris), which are described in detail. The species composition is typical of the eastern part of the European Mediterranean and may be divided into three biostratigraphic assemblages: early Middle Pleistocene, late Middle Pleistocene and Late Pleistocene.     

Biostratigraphy and paleoceanographic significance of Paleocene radiolarians from offshore eastern New Zealand

A 100-m-thick Paleocene sequence of mainly pelagic sediments at ODP Site 1121, on the eastern flanks of the Campbell Plateau, contains few to common radiolarians of relatively low diversity in the lower 40 m (Early to early Late Paleocene) and abundant, diverse radiolarian assemblages in the upper 60 m (mid-Late Paleocene). The 150 taxa recorded from the entire Paleocene interval are thought to under-represent the actual species diversity by at least one half as many morphotypes have not been differentiated below the level of genus. Assemblages in the lower 40 m are similar to those described from onland New Zealand and DSDP Site 208 (northern Lord Howe Rise); they are correlated with South Pacific radiolarian zones RP4 and RP5. Assemblages in the upper 60 m differ from other known Late Paleocene assemblages in the great abundance of plagiacanthids and cycladophorids. Similarities are noted with later Cenozoic cool-water assemblages. This upper interval is correlated with South Pacific zone RP6, as revised herein, based on comparison with faunas from Site 208 and Marlborough, New Zealand. The interval is also correlated with the upper part of North Atlantic zone RP6 (RP6b–c) based on the presence of Aspis velutochlamydosaurus, Plectodiscus circularis and Pterocodon poculum. Other species, such as Buryella tetradica and Buryella pentadica, are valuable for local correlation but exhibit considerable diachroneity between the Pacific, Indian and Atlantic Oceans. An age model for the Paleocene interval at Site 1121, based on well-constrained nannofossil and radiolarian datums, indicates that the rate of compacted sediment accumulation doubles from 15 to 30 mm/ka at the RP5/RP6 zonal boundary. In large part this is due to a sudden and pronounced increase in accumulation rates for all siliceous fossils; radiolarians and larger diatoms increase from <100 to >10 000 specimens/cm²/ka. This apparent increase in biosiliceous productivity is age-equivalent to a mid-Paleocene cooling event (57–59 Ma) identified from global stable isotope records that is associated with the heaviest δ¹³C values for the entire Cenozoic.