Deep-sea Ostracod Research Articles

Late Cretaceous and Cainozoic bathyal Ostracoda from the Central Pacific (DSDP Site 463)

Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct faunal assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some faunal exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively.

Response of deep-sea ostracod assemblages to Late Cretaceous palaeoceanographical changes: ODP Site 689 in the Southern Ocean

Twenty-six deep-sea ostracod species are described from the late Campanian to late Maastrichtian of ODP Site 689 in the Southern Ocean. Three are described as new:Cytherelloidea megaspirocostata,Agulhasina sudoceanicaandPennyella foveolata. Correspondence analysis identified three faunal sample groups. The first is mainly characterised byA. sudoceanica,Kirthesp. andCytherellasp. This is replaced, first temporarily (betweenc. 71 and 69 Ma) by a group mainly characterised byArgilloeciaspp. andC. megaspirocostata, possibly a consequence of a short-lived global palaeoceanographic event marked by increased ventilation and cooling of intermediate waters at site 689. It then reappears before finally being replaced by a third group largely characterised byEucytherecf.circumcostata,P. foveolataandDutoitella mimicaDingle. This final change is coeval with a marked increase in the faunal density of ostracods, probably owing to an increase in food supply. However, the oxygen isotopic records of benthonic foraminifera suggests that the replacement of the first ostracod group by the third is a result of the long term Maastrichtian cooling of intermediate waters at high latitudes. This replacement is also coeval with a gradual change in benthonic foraminiferal assemblages at site 689. It is suggested, therefore, thatPennyellaandDutoitellahad a greater potential of adapting to successively colder palaeoceanographical conditions thanAgulhasina. The former genera have a cosmopolitan deep-sea distribution today.

Benthonic ostracods and deep watermasses: A qualitative comparison of Southwest Pacific, Southern and Atlantic Oceans

Abstract The upper depth limits of the dominant cosmopolitan deep-water benthonic ostracod taxa present in five localities in the Southern Ocean (Kerguelen Plateau, Southeast Australian Continental Slope) and Southwest Pacific (Chatham Rise, Tasman Sea, Coral Sea) are compared to investigate the degree to which the position of intermediate and deep watermasses: Antarctic Intermediate Water (AAIW), Deep Water (DW) and Antarctic Bottom Water (AABW) control the vertical faunal succession. Although none of the taxa studied is restricted to one watermass, their upper depth limits appear to be closely related to the position of Antarctic Intermediate water (AAIW). Taxa showing the most consistent pattern include: Krithe (upper depth limit above AAIW), Poseidonamicus (upper depth limit in lower AAIW, but in underlying Deep Water on the Kerguelen Plateau) and Pterygocythere mucronalatum (DW, but in AABW on the Kerguelen Plateau). Bathyal (above approximately 1000 m) upper depth levels of taxa, species diversity, species turnover, and changes in the proportion of the dominant deep-sea taxa Krithe and Poseidonamicus match closely that of the Atlantic Ocean (Dingle and Lord, 1990). However, the upper depth limits of the abyssal taxa Poseidonamicus and Dutoitella appear to be very different in the Cape Basin, SE Atlantic, and the SW Pacific with respect to watermass characteristics. For example, in the Atlantic Poseidonamicus has its upper limit within Lower North Atlantic Deep Water (NADW) whereas in the SW Pacific it occurs consistently within the AAIW. These discrepancies in the upper depth level of abyssal taxa between the Pacific and Atlantic Oceans suggest that different watermasses or other environmental variables control their upper range in different oceanic basins. It follows that these differences must be taken into account if deep-sea ostracods are to be used as a reliable means to trace modern or reconstruct ancient watermass pathways between ocean basins.

Palaeoecological preferences and geographical distribution of Late Maastrichtian deep‐sea ostracods in the South Atlantic

The distributional patterns of deep-sea ostracods in the terminal Cretaceous South Atlantic were examined from seven DSDP/ODP holes (356, 525A, 527, 528, 529, 698A and 689B). Many of the genera recorded in this study are previously known from Campanian-Maastrichtian deep-sea sediments. However, the recovery of Aversovalva, Hemiparacytheridea, Profundobythere, Mayburya and Legitimocythere reveals considerable similarities with the Tertiary deep-sea ostracod fauna of the Pacific and the North Atlantic. The underlying causes controlling the variation in faunal density among the various sites are likely to be related to variation in food supply and, to a lesser extent, to variation in oxygen levels, since all sites quantitatively assessed are regarded to represent oligotrophic, well-oxygenated conditions. A Q-mode principal component analysis with varimax rotation yielded a first component largely dominated by Bythocypris and significantly correlated with palaeotemperature; there is an increasing abundance of Bythocypris towards higher latitudes with a maximum abundance at Site 689 where the palaeotemperature was around 9°C. A species of the thermophilic genus Cytherelloidea occurs also at this site, probably as a result of a slow adjustment to colder conditions in the absence of a thermocline at that time. The second component is largely dominated by Krithe and significantly correlated with palaeotemperature and palaeodepth. Among the sites studied, Krithe is most common at Site 356, where the palaeotemperature was around 15°C; today, most representatives of this genus are psychrospheric and adapted to temperatures below 10°C.

Cainozoic and Recent deep sea cytherurid Ostracoda from south-west Pacific and eastern Indian Oceans: Part 1: Cytherurinae

From a largely unpublished database the systematics, geographical and stratigraphical distribution of Cainozoic cytherurine Ostracoda found in the deep sea environment of the eastern Indiall and south-western Pacific regions is presented. Eleven new species: ? Eucytherura anoda, Eucytherura batalaria, ? Eucytherura boomeri, Eucytherura elegantula, Eucytherura indianensis, Eucytherura multi tubercula ta, Eucytherura pacifica, Eucytherura parabatalaria, ? Eucytherura polydictyota, Eucytherura tumida and Hemiparacytheridea vanharteni are described. Five species are assigrwd lo previously established taxa and four species are left in open nomenclature due to paucity of material. MICHAEL A. AYRESS, ROBIN WHATLEY, SIAN E. DOWNING & KARIN J. MILLSON, 1995. Cainozoic and Recent deep sea cytherurid Ostracoda from the south western Pacific and eastern Indian Oceans, Part I: Cytherurinae. Records of the Australian Museum 47(2): 203-223. Deep sea ostracod studies which have examined the fine fraction (less than 250 micron aperture seive) of samples frequently report species of the Cytheruridae. That this family comprises very small species (less than 0.40 mm in length) explains why they are poorly represented in most published faunal lists of deep sea ostracods. This study indicates that the group is well represented in the deep-sea at least in the Indo-Pacific region and that this has been so throughout the Cainozoic. The present study is concerned with the Cytherurinae. A subsequent paper will describe the Cytheropterinae. Taxonomic knowledge of deep sea forms of the genera considered in this report, is based on material collected mainly from the Atlantic region (Maddocks & Steineck, 1987; Whatley & Coles, 1987; Coles & Whatley, 1989). Material collected from the deep IndoPacific and compiled through comprehensive studies undertaken in the Micropalaeontological Research Unit, Aberystwyth, Wales, is still incorporated in largely unpublished theses. To assimilate the nomenclature contained therein with the present taxonomic study it is considered useful to list all names-unpublished as well as published-that have been applied to these taxa during the course of our work. (Unpublished references are indicated by asterisk *). This valuable source of information, useful for improving our understanding of the systematics and zoogeography of the taxa, is the focus of this report.

Deep‐ocean paleoceanography and ostracodes

Ostracodes are small, bivalved Crustacea commonly preserved in deep‐sea sediments that are well suited for faunal, trace‐element, and isotopic analyses in paleoceanography of deep‐ocean environments. Twenty deepsea ostracode specialists from eight countries met at the U.S. Geological Survey National Center, Reston, Va., from July 12 to 14 at a workshop entitled “Recent Ostracoda from the Deep and Intermediate Ocean: Application to Paleoceanography.” The workshop was sponsored by the USGS Global Change and Climate History Program, and its major goal was to develop a data base on recent ostracodes from the world's deep‐sea environments and to fully realize their potential in deep‐sea paleoceanographic research.

Global Change and the Biostratigraphy of North Atlantic Cainozoic deep water Ostracoda

Abstract. The biostratigraphical distribution of deep-sea (>1000m) Palaeocene to Recent benthonic Ostracoda, based on nannofossil NP and NN zones is presented. By excluding very rare species and those represented by juveniles, 184 species are used in constructing range tables from a total fauna for the interval of 230 species. The vertical distribution of these specimens clearly allows of the recognition of all the major stratigraphical units within the Cainozoic and is also sufficiently precise to distinguish most of the nannofossil zones. The principal criteria employed are the first and last appearances of taxa. While eminently possible to create a series of ostracod zones, it is argued that they are best employed in the recognition of particular levels within the existing nannofossil scheme. The interpretation of the range tables is complicated in places by large numbers of Lazarus taxa and also by the fact that many of the ‘originations’ actually record the arrival of immigrants from the Indo-Pacific.Graphs of both simple and cumulative species diversity, and of origination and extinction rates, are used to demonstrate major faunal events such as the first arrival in the area, during the Middle Eocene, of cosmopolitan deep-sea species, or the very marked, but stepped, Palaeogene-Neogene faunal turnover. The distribution patterns of the Ostracoda record such global changes as the formation of the psychrosphere and the inception of a marked thermocline but they do not, as other authors have suggested, indicate a dramatic faunal turnover at the Eocene-Oligocene boundary. The more vigorous circulation patterns of the Oligocene, related to the opening of the Drake Passage, are reflected in enhanced ostracod diversity at that time. Elevated late Oligocene extinction rates may be correlated with cooling consequent upon the growth of polar ice. Similarly, Lower Miocene low levels of diversity may be associated with the closure of the Iberian Portal and the effective isolation of the Tethys. The deep-sea ostracods do not, for the most part, record such events as the mid-Pliocene warming nor Quaternary climatic fluctuations.

Paleoceanographic events and deep-sea ostracodes : Benson, R.H., R.E. Chapman and L.T. Deck, 1984. Science, 224(4655):1334–1336

Paleoceanographic events and deep-sea ostracodes : Benson, R.H., R.E. Chapman and L.T. Deck, 1984. Science, 224(4655):1334–1336

Changes in Deep-Sea Ostracode Fauna from Eocene into Oligocene: ABSTRACT

A major change in deep-water oceanic circulation occurred near the end of the Eocene forming the present psychrosphere and basic two-level water-mass system. This event is especially felt in the South Atlantic and Indian Ocean as shown by ostracods found in DSDP cores. Faunas traceable back to the Cretaceous rapidly evolved into the modern deep-sea faunas at this time. Several important ornate genera undergo diachronous changes suggesting that the flooding of the world ocean basins with colder waters happened in stages. The displacement of Tethyan water masses coming from the north by newly formed Antarctic bottom waters can be followed by changes in the ostracods. End_of_Article - Last_Page 422------------

Deep-sea benthonic foraminiferal faunal turnover near the Eocene/Oligocene boundary

Eocene-Oligocene deep-sea benthonic foraminifera in D.S.D.P. Site 277 in the southwest Pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the Eocene/Oligocene boundary. Biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the Late Eocene to Early Oligocene sequence, while 18 taxa exhibit first or last occurrences. Comparison of the faunal changes in Site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera, and the overall faunal change preceding and subsequent to the bottom-water circulation event occurred gradually. The inferred water-mass event affected the relative abundance of one species, Epistominella umbonifera. The lack of major faunal changes at the Eocene/Oligocene boundary in Site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera, or a bottom-water temperature change less than 3°C.Examination of previously published benthonic foraminiferal biostratigraphic data from D.S.D.P. Sites 167, 171, 357, 360, 363, and 400A, and deep-sea ostracode data from D.S.D.P. Leg 3 show faunal changes occurred during discrete intervals in the Middle Eocene-Early Oligocene. The faunal patterns from these data and from Site 277 show that the Eocene/Oligocene cooling event did not cause rapid, catastrophic changes of the benthonic faunas of the open ocean, although significant faunal changes are associated with the water mass event in Sites 167, 171 and 400A.The benthonic faunal changes in Middle Eocene-Early Oligocene time are consistent with the gradual decrease of inferred bottom-water temperatures, based on previously published oxygen isotopic data. The δ 18O Eocene/Oligocene enrichment of 0.76‰ is a major event in the Southern Ocean oxygen isotopic record, but is considerably less in magnitude than the 1.75-2.00‰ change that occurred gradually from mid-Early Eocene to the Eocene/Oligocene boundary. The benthonic foraminiferal and isotopic data indicate that bottom-water circulation may have developed during the Middle Eocene to Early Oligocene interval, with the 3°C bottom-water cooling near the Eocene/Oligocene boundary representing part of this development.

Upper Eocene to Middle Miocene ostracode faunas and paleo-oceanography of the North Coastal Belt, Jamaica, West Indies

The ostracode fauna of the Montpelier Group (Upper Eocene-Middle Miocene) exposed in the western part of the North Coastal Belt of Jamaica contains representatives of three paleo-environments. Allochthonous shelf and littoral species, characterized by abraded carapaces and eye tubercles, and a diverse group of archibenthal (slope) forms are present throughout. Species restricted to the World Ocean Psychrosphere (> 1000 m), notably Bradleya dictyon, Australoecia tipica, Agrenocythere hazelae and Macrocypris spp., first occur in sediments of earliest Miocene age (planktonic foraminiferal zone N4). Their presence establishes a minimum age for the entry into the Cayman Trench of frigid (<8–10°C) water masses drawn from the Atlantic thermohaline stratification.Upper Eocene and Oligocene assemblages are dominated by smooth, blind genera such as Krithe, Messinella and Bythocypris and lived in lower thermospheric conditions (10°C) at or near the base of the thermocline (700– 900 m). During the Early Miocene, downfaulting of the north island slope of Jamaica in response to southward tilting of the Nicaraguan Rise brought the Montpelier depositional site into contact with progressively deeper and colder water-masses. This subsidence culminated in the late Early Miocene; faunas of this age contain large numbers of Bradleya dictyon, Agrenocythere hazelae, Macrocypris sp. 1, Bairdia oarion and Bairdoppilata cassida. They suggest paleodepths of 1500–2000 m and the local presence of a 3–4° water-mass tentatively identified as the North Atlantic deep water. If this interpretation is correct, then the maximum sill-depth and water-mass configuration of the Miocene Cayman Trench have persisted to the present. Middle Miocene assemblages indicate a return to paleodepths of 1000–1500 m heralding the pronounced Upper Miocene to mid-Pleistocene tectonism which elevated Montpelier strata above sea level. An alternative view attributes the Miocene ostracode succession in the Montpelier to episodes in the development of the Atlantic circulation as recognized in the northeast Atlantic.Montpelier deposition took place either on a broad step intervening between the northern edge of the Clarendon Platform and the abyssal basins of the Cayman Trench or on a Tertiary analog of the existing north island slope. These results have emphasized the value of detailed taxonomic and morphologic studies of deep-sea ostracodes in geohistorical reconstruction.

Miocene deep-sea ostracodes of the Iberian Portal and the Balearic Basin

Discovery of deep-sea (psychrospheric) ostracodes in the Middle Miocene (Serravallian and Tortonian) of Andalusia, Spain, and in the cores of Site 372 of DSDP Leg 42a in the Balearic Basin east of Menorca indicates the presence of an opening (the Iberian Portal) between the Atlantic and the western Tethys basin complex at a depth estimated at more than 2000 m. Because of the concurrence of the ostracodes along a structural line marking the Prebetic and Subbetic boundary with the Meseta Massif, it is inferred and the rapidly shallowing ostracode faunas suggest, that this opening represents a structural trough closed by Alpine-type lateral movements during the Late Miocene (Messinian). During the Messinian “salinity crisis” the ostracodes to the east were nonmarine, while those on the western end of the line previously occupied by the trough remained marine.