Radiolarian biostratigraphy and chronology of radiolarian events of ODP Leg 199 sites and EW9709 sediment cores

A generally rich radiolarian fauna ranging in age from Quaternary to early Eocene (Zone RP7) was found at five of the eight sites drilled during Ocean Drilling Program (ODP) Leg 199. Of particular interest are the stratigraphically complete assemblages that range in age from middle Miocene (Zone RN5) to early Eocene (Zone RP7), composites of Sites 1218, 1219, and 1220. At the same sites, multisensor track (MST) data show consistent cycles in gamma ray attenuation density, color, and carbonate content that can be correlated on a submeter scale from the early Miocene to early Eocene. In addition, the magnetic reversal records from these three sites allow construction of an absolute timescale. A series of 305 radiolarian morphologic first and last occurrences and evolutionary transitions for radiolarians were determined and correlated directly with the accompanying MST and paleomagnetic data, resulting in a detailed and accurate dating of events. Since many of the bioevents are found at more than one site, it was also possible to test their reliability within the study area. Twelve new species are described: Calocycletta (Calocycletta) anekathen, Dorcadospyris anastasis, Dorcadospyris copelata, Dorcadospyris cyclacantha, Dorcadospyris ombros, Dorcadospyris scambos, Eucyrtidium mitodes, Theocyrtis careotuberosa, Theocyrtis perpumila, Theocyrtis perysinos, Theocyrtis setanios, and Thyrsocyrtis (Pentalacorys) orthotenes.

Eocene and Oligocene radiolarian biostratigraphy from the Southern Ocean

Eocene-Oligocene radiolarians from Ocean Drilling Program Sites 699, 702, and 703, Leg 114 of the Subantarctic Atlantic were examined in order to extend the tripartite zonation for the recovered cores based on results of similar analysis of Leg 120 submarine sediments from the Indian Ocean. Correlation of the two oceans is made by examining 23 biohorizons and the three zones, Eucyrtidium spinosum, Axoprunum irregularis, and Lychnocanoma conica, in ascending stratigraphic order. One new species, Eucyrtidium nishimurae, is described.

Distribution of radiolaria in Oligocene to Pleistocene sediments of the North-West Pacific

Neogene stratigraphy of the tropical and subtropical Pacific on radiolaria is studied in the book. A detailed comparison of coeval systems from tropics and subtropics is given. A possibility of use of a uniform zonal scale in these areas is proved. Magnitude of changes of complexes on borders of Neogene zones is studied in detail. Six stages in development of radiolarians are identified in the tropics in Neogene. Stratigraphic levels, where the greatest changes of fauna occurred, are natural boundaries of these stages. 72 species of radiolarians (two of which are new) are described in the book.

Radiolarian stratigraphy across the Oligocene/Miocene transition in low latitudes

Recently the International Union of Geological Sciences (Commission on Stratigraphy, Working Group on the Paleogene/Neogene Boundary) proposed that the Oligocene/Miocene boundary be placed at the base of Chron C6Cn2n at 23.8 Ma on the Cande and Kent (1992) magnetic time scale, where it is approximated by planktic foraminifera at the first occurrence of Globorotulia kugleri, and by calcareous nannofossils at the last occurrence of Sphenolithus ciperoensis and the first and last occurrences of Sphenolithus delphix and S. capricornutus. Herein we show that, in terms of radiolarians, the base of Chron C6Cn2n can be correlated with the upper part of the Lychnocanoma elongata Zone between the last occurrence of Artophormis gracilis (23.94 Ma) and the first occurrence of Cyrtocapsella tetrapera (23.69 Ma). Since the proposed stratotype at Lemme-Carrosio (Italy) does not contain radiolarians at the boundary, we re-examined 13 DSDP sites and established the stratigraphic sequence of 29 first and last radiolarian occurrences and one evolutionary transition across the boundary. Nine of these sites contain both calcareous and siliceous microfossils and thus allow for an integrated biostratigraphy. Paleomagnetic stratigraphy is not available for any of the DSDP cores examined. However, use of Hodell and Woodruff's (1994) strontium isotope curve from DSDP Site 289 has permitted calibration of several low latitude microfossil datum levels against the geomagnetic polarity scale. Two new species, Lychnocanoma apodora and Eucyrtidium plesiodiaphanes, are described.

Radiolarians from the Southwest Pacific

Radiolarians are very rare in all Leg 90 sites. They are relatively more frequent only in Neogene sediments from Sites 586 and 594, and in Eocene sediments at Site 592. In this chapter radiolarian abundances are recorded as comparative percentages for 92 Neogene morphotypes at Site 586B. Relative abundances only are estimated at Sites 592 and 594, where preservation is poor to moderate. A tentative correlation of radiolarian events at Hole 586B and Site 594 shows that only a few species can be found in both tropical and subantarctic areas. New evolutionary lineages are proposed. 1. Middle Miocene eucyrtids like Eucyrtidium teuscheri group evolved into a widespread species (E. teuscheri teuscheri) ranging from middle Miocene to Holocene and a temperate species (E. teuscheri orthoporus) ranging from middle Miocene to early Pleistocene. 2. Phormostichoartus pitomorphus appears to be a temperate descendant of the cosmopolitan P. fistula and disappears in early Pleistocene time. 3. The discovery of Lamprocyrtis daniellae n.sp. calls into question the lineage L. heteroporos -> L. nigriniae. 4. The evolution of Lamprocyclas maritalis from an ancestor group (L. aff. maritalis) is located in the early part of the Pterocanium prismatium Zone.

Radiolarian biostratigraphy in sediments of ODP Site 202-1237

Site 1237 is located on Nazca Ridge ~140 km off the coast of Peru and thus within the offshore region of the Peru-Chile Current. A total of 83 samples were used to provide an initial radiolarian biostratigraphic framework for Site 1237; radiolarians are present to Sample 202-1237B-19H-2, 58-60 cm (186.45 meters composite depth [mcd]) and are of good to fair abundance and preservation. Site 1237 is influenced by both subtropical and northward-transported southern latitude waters, has 55 ash layers within the uppermost 166 m, and has minimal to gross reworking. Shipboard paleomagnetic results showed that the upper 200 m spanned the last 12 m.y., and in the upper 100 mcd, the paleomagnetic inclination pattern could be directly correlated to the geomagnetic polarity timescale (GPTS). Tropical biostratigraphy was used to establish the zonal boundaries for Site 1237, and the paleomagnetic and radiolarian stratigraphy were well correlated.

Radiolarians from ODP Leg 116 holes

Cores recovered from three sites of Leg 116 were studied for radiolarians. Generally, radiolarians were absent from most samples prepared for examination. Moderate to well-preserved radiolarian assemblages are found only in the uppermost one or two cores that were the focus of this study. All of the radiolarian assemblages in the upper cores belong to the Buccinosphaera invaginata Zone of latest Quaternary age. However, there is one stratum where a few Miocene radiolarians are reworked into the modern assemblages. Local seamounts are suggested sources for the reworked radiolarians.

Microfossils detected in a block of ancient dense clay coated with a ferromanganese crust, Clarion-Clipperton Province, East Equatorial Pacific

The area in study is characterized by a regional stratigraphic hiatus from Early Miocene to Quaternary. Deposits from Late Eocene to Early Miocene occur on the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of Oligocene age, formed on surface layers of Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. Composition of found radiolarian and diatomaceous complexes proved that the crust formed in Quaternary on an eroded surface of Late Oligocene clay. In Quaternary Neogene sediments were eroded and washed away by bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the "Glacial Pleistocene". The erosion could be initiated by loosening and resuspension of surface sediments resulting from seismic activity generated by strong earthquakes in the Central America subduction zone. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area in study a common reason and a common Quaternary interval for formation of the following features is supposed: a regional stratigraphic hiatus, formation of residual nodule fields, and position of ancient nodules on the surface of Quaternary sediments.

Radiolarians from ODP Leg 134 sites

In the cores obtained during Leg 134 of the Ocean Drilling Program, radiolarians occur intermittently and usually in a poor state of preservation, apparently as a result of the region having been at or near the boundary between the equatorial current system and the south-central Pacific water mass during most of the Cenozoic. A few well-preserved assemblages provide a record of the Quaternary forms, and some displaced middle and lower Eocene clasts preserve a record of radiolarians near that subepochal boundary. There are less satisfactory records of middle Miocene and early Miocene to late Oligocene forms.

Radiolarian Paleogene biostratigraphy in the southern Indian Ocean, ODP Leg 120

During Ocean Drilling Program Leg 120, an almost complete Paleogene sediment section on the Kerguelen Plateau in the southern Indian Ocean was recovered. The biostratigraphy of radiolarians from these sediments at Sites 748 and 749 is studied. A biostratigraphic framework established in low and middle latitudes is not applicable because of the absence of most zonal marker species. Biogenic opal is present only in middle Eocene to Oligocene sediments, and three new zones-Lychnocanoma conica, Axoprunum (?) irregularis, and Eucyrtidium spinosum zones-are proposed. The Paleogene antarctic radiolarian fauna is different from that in low and middle latitudes. Three new species, Axoprunum (?) irregularis, Eucyrtidium cheni, and Eucyrtidium spinosum, are described.

Radiolarian fauna of sediment core MD96-2089 off Lüderitz, Namibia

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.

Benthic foraminifera extinctions in the Cenozoic record

In the late Pliocene-middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal-abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20-70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction? In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene-early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene-Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle-late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene-early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene-middle Pleistocene. Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.