Distribution Of Ostracods Research Articles

Late Silurian (Ludlow–Přídolí) microfossils and sedimentation in the Welsh Basin near Clun, Shropshire

The base of the Clun Forest Formation at Clun, Shropshire, has previously been taken to correlate with the base of the Downton Castle Sandstone Formation (Přídolí Series, upper Silurian) on the basis of brachiopod, bivalve, gastropod and ostracod faunas. The detailed distribution of microfossils (acritarchs, chitinozoans, conodonts and ostracods) is documented at Nantyrhynau Quarry, Clun, Shropshire, to test this correlation. Three new species of chitinozoans, Eisenackitina clunensis, Eisenackitina kerria and Angochitina paucispinosa, are described from the quarry. Macrofossil and ostracod distributions suggest that the correlation is correct. However, a typical Ludlow acritarch flora is present throughout the section and suggests that the basal part of the Clun Forest Formation is Ludlow in age. The mixture of characteristic Ludlow and Přídolí microfossils at Nantyrhynau Quarry may be the result of differing environmental conditions between the Ludlow (shelf) and Clun (basinal) areas at this time. Alternatively, the strata exposed at Nantyrhynau Quarry may represent a period towards the end of the Ludlow Series when there are no strata represented in corresponding shelf sections due to non-deposition or erosion. © 1997 John Wiley & Sons, Ltd.

Possible Passive Distribution of Ostracodes by High-Altitude Winds

Possible Passive Distribution of Ostracodes by High-Altitude Winds

Distribution and population dynamics of ostracodes (Crustacea, Ostracoda) in a karstic lake: Lake Banyoles (Catalonia, Spain)

Qualitative and quantitative benthic samples were collected monthly between December 1986 and December 1987 from several stations at various depths and basins in the karstic Lake Banyoles (Catalonia, Spain), to study the spatial distribution and seasonality of ostracodes. A total of eight ostracode species were found in the lake. Of these, Candona neglecta Sars, Isocypris beauchampi Paris and Cypria ophtalmica Jurine were the most common ostracodes at all depth stations. Darwinula stevensoni Brady & Robertson, Ilyocypris species (I. bradyi Sars and I. gibba (Ramdohr)), Cyprideis torosa (Jones) and Cyclocypris ovum Jurine, on the other hand, were confined to sublittoral and littoral areas of the lake.

Silurian-Early Devonian ostracodes from South America (Argentina, Bolivia): Preliminary investigations

Ostracodes are described from the “Cerro del Fuerte Section” and neighboring localities, all in the Precordillera de San Juan (northern Argentina, San Juan Province), and from sparse faunas in Bolivia (Chuquisaca, Tarabuco Province). Additional material comes from the collection of Thomas (1905). This preliminary study gives the first detailed description of ostracode assemblages in the Upper Silurian and Lower Devonian of the South American continent. Records of other abundant lower Paleozoic (Lower Ordovician to Lower Devonian) ostracodes in Argentina, Bolivia, Brazil, Peru, and Venezuela are also reviewed. Twelve different species, belonging to Palaeocopa (Beyrichiacea and Primitiopsacea) and to Binodicopa and Podocopa (Healdiacea, Thlip-suracea, Cypridacea) are described and a new genus is established (Australobollian. gen.). Ostracode distribution at Cerro del Fuerte attests to the presence of the Siluro-Devonian boundary within the upper Los Espejos Formation and confirms recent stratigraphical attributions mainly based on conodonts and brachiopods (Benedetto et al., 1992). The beyrichiaceanHemsiellaindicates a late Ludlow to Pridolian age for the lower part of upper Los Espejos Formation. The non-palaeocope“Thlipsurella-Phanasymmetria-Ranapeltis”assemblage found in the uppermost part of the formation indicates an Early Devonian (Lochkovian) age. The present study reveals the existence of faunal links at genus (Silurian) and probably species (Early Devonian) level between South America (Argentina, Bolivia), Laurentia, Avalonia-Baltica, and northern Gondwana. For example, close affinities (e.g.,Ranapeltissp. aff.rowlandiandThlipsurellasp. aff.ellipsoclefta)exist between the uppermost Los Espejos Formation (Argentina) and contemporaneous horizons in the North American Mid-Continent (e.g., Haragan Formation, Oklahoma; Shriver Formation, Pennsylvania). Two types of ostracode assemblages, “beyrichiacean-dominated” and “thlipsuracean-bairdiacean-cypridacean dominated,” are recognized in the Late Silurian–Early Devonian of Argentina and discussed relative to other assemblages known in Laurentia, Avalonia-Baltica, and northern Gondwana. Their paleoecological significance in relation to marine bathymetry is addressed.

The biostratigraphy and palaeobiogeography of Upper Cretaceous-basal Tertiary ostracods from North Africa, Mali and Congo

A stratigraphic range chart of Upper Cretaceous (Cenomanian to Maastrichtian) Ostracoda from North Africa is presented. A second chart compares the stratigraphic and geographic distribution of ostracods in North Africa, West Africa and Congo. Comparisons of Upper Cretaceous-basal Tertiary ostracods faunas in North Africa, Mali and Congo demonstrate connections between those regions providing a supporting argument for the existence of a trans-Saharan sea during the latest Cretaceous and early Tertiary.

A quantitative method of palaeolake-level reconstruction using ostracod assemblages: an example from the Bolivian Altiplano

This paper provides quantitative information concerning the response of ostracods to environmental variability in order to reconstruct past environments. Ostracod faunas from modern sediments of Bolivian lakes and swamps were studied. Ostracod distribution is controlled by several ecological characteristics such as lake-level and water chemistry. Statistical results indicate that three transfer functions (on water depth, Total dissolved Salts and water in Mg/Ca ratio) can be developed, from ostracod species frequencies in lacustrine sediments, with some restrictions for the two last ones.

Distribution and ecology of Recent ostracodes from Mansar Lake, Jammu

Distribution and ecology of Recent ostracodes from Mansar Lake, Jammu

Holocene Palaeosalinity in a Maya Wetland, Belize, Inferred from the Microfaunal Assemblage

A 5.4-m sequence of peat and marl overlying a basal clay in a northern Belize wetland was studied to assess salinity changes over the past 7000 yr. The distribution of ostracods, gastropods, and foraminifers revealed initially freshwater conditions in a terrestrial wetland, changing to at least mesohaline conditions by about 5600 yr B.P. The mesohaline conditions corresponded to the formation of an open-water lagoon (and precipitation of a lacustrine marl) that was contemporaneous with rapidly rising sea level in the area. A mangrove peat filled the lagoon by 4800 yr B.P. probably as a result of increasingly shallow waters as sea level rise slowed and marl precipitation continued. A new lagoon began to form sometime after 3400 yr B.P. Freshwater ostracods and gastropods found in the marl of this lagoon suggest that it formed under near-limnetic conditions. Freshwater input likely resulted from massive deforestation by the Maya that began by 4400 yr B.P. Subsidence of the mangrove peat likely permitted the formation of a lagoon. A peat has filled the lagoon since at least 500 yr B.P.

The distribution of ostracodes in the Přídolí, upper Silurian, of the Prague Basin, Czechoslovakia.

The distribution of ostracodes in the Přídolí, upper Silurian, of the Prague Basin, Czechoslovakia.

Ecology and Distribution of Ostracoda in Pyrenean Springs

Ecology and Distribution of Ostracoda in Pyrenean Springs

Associations d'ostracodes des marges téthysiennes et atlantiques marocaines de l'albien au turonien

Morocco situated in north-western Africa, lies at an important faunal cross point of the Atlantic and the Tethyan oceans. The marine ostracod faunas are controlled by eustatism. Atlantic influences are clear in Aptian and Albian times. In the Cenomanian, Tethys played the predominant role and towards the west tethysian faunas reach regions located some distance from the present Atlantic coast. The study of the middle Cretaceous (Albian to Turonian) ostracod associations, on tethysian and atlantic margins, allows us to establish the following facts: faunal relations between european and south-tethysian margins are moderate but constant from the Albian to the Turonian. Common species are numerous and the proximity of the european and eurasiatic plates facilitated exchanges; studies of the ostracod faunas in the north-tethysian mid-Cretaceous demonstrate endemic faunas. Relations between west-european and south-tethysian margins are almost non-existent. In the Barremian to the upper Cenomanian-lower Turonian period, faunal relations were established between the moroccan atlantic margin and the south-tethysian margin, under the influence of similar sedimentologic and climatic conditions. Faunas common to the east atlantic margin, the west atlantic margin and the south tethysian margin, are seldom seen, but seem to be present, in Albian-Turonian times, during and after the opening of the South-Atlantic Ocean and the establishment of its communication with the North-Atlantic Ocean. The synthesis of paleobiogeographic data and the dynamics of ostracod assemblages reveal, in middle Cretaceous times, a “North-African-Middle-East” paleobiogeographical province established since the lower Cretaceous and extending to the south-tethysian margin. The biogeographical homogeneity of the ostracod associations suggests similar living conditions along the whole expanse of the margin and the absence of important morphological barriers that would prevent possible migrations of benthic faunas (the spreading of these faunas was kept under control by tethysian and atlantic currents). The distribution of other paleontological groups (benthic foraminifera and rudists) bears out the existence of this province. The colonization of the North-African-Middle-East province depends on paleobiogeographic and geodynamic factors (linked with the positions of the continental margins and with the evolution of the mid-oceanic ridges), paleoceanographic factors (the positions of emerged blocks and the evolution of oceanic areas), and paleoclimatic factors (sea water temperature determining the latitudinal distribution of the ostracod genera). In the study of provincialism, the distribution of ostracods is influenced not only by local factors of depositional environments (for example; sedimentation, substratum, feeding, temperature, salinity…), but also by global events associated with the distribution of continental and oceanic masses (for example; depth of sea waters, ocean currents…).

Lacustrine ostracodes as hydrochemical indicators in lakes of the north-central United States

The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 μS cm-1) to saline water (17 000 μS cm-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.

Distribution of Ostracodes in the Upper Cretaceous (Late Santonian Through Middle Maastrichtian) of Alabama and Mississippi

ABSTRACT The large-scale distribution of ostracodes in the Upper Cretaceous deposits of Alabama and Mississippi was studied quantitatively to assess their usefulness in paleoecology and biostratigraphy. The data base consists of 10,174 ostracode valves that were extracted from 34 samples from the Eutaw Formation, including the Tombigbee Sand Member, the Mooreville Chalk, the Blufftown Formation, the Demopolis Chalk, the Ripley Formation, including the Cusseta Sand Member, the Prairie Bluff Chalk, and the Providence Sand. These formations range from late Santonian through middle Maastrichtian in age. The facies range from lagoonal oyster reefs through inner neritic sands and middle neritic marls to outer neritic, nearly pure chalk. About 300 specimens were randomly picked from each of the samples. Only samples of nearly the same age were compared to each other for the paleoecological analysis. Data on encasing sediment and associated micro- and macrofauna were used to determine paleoenvironmental conditions, and the interpretations were compared with those of the published literature. The results of the study suggest that ostracodes are excellent paleoecological indicators and show great promise in the dating of nearshore deposits that lack the more commonly used planktonic foraminifera. The chronostratigraphic ranges of most of the species and corresponding biostratigraphic zonations have been published previously. Certain species, such as Cythereis bicornis Israelsky, 1929 and Ascetoleberis plummeri (Israelsky, 1929), are found along a wide range of paleoenvironments, even inner neritic environments which either lack or contain relatively few numbers of planktonic foraminifera, and are restricted to a fairly narrow chronostratigraphic range. These taxa are particularly useful because their ranges can be calibrated by planktonic foraminifera and coccoliths in offshore deposits, then extended into nearshore areas. Moreover, many of the most useful taxa, for example Ascetoleberis plummeri, are easily recognizable by the nonspecialist.

Preliminary Research on Species Distribution of Planktonic Ostracods (Halocyprididae) in the Ross Sea, Antarctica

ABSTRACT This paper reports the results of preliminary research on planktonic Ostracoda collected during the first Italian Oceanographic Expedition to Antarctica (1987-88). A total of 311 samples at 33 stations (31 in Terranova Bay and 2 farther offshore in the Ross Sea) was collected. At each station, samples were taken at various depths from different layers (usually 50–100 m deep), and an integrated sample from the entire water column was collected. Ostracods-all conchoeciine Halocyprididae—were found in 272 samples (87% of the total); all the specimens (54,224) were examined individually. Taxonomic identification at the species level was made for adults (6,587, i.e., 12.15% of all individuals). Four species were identified (the highest density and the relative abundance are reported in parentheses): Alacia belgicae (4.00 ind·m–3, 82.69%), Metaconchoecia isocheira (1.30 ind·m–3, 16.65%), Alacia hettacra (0.13 ind·m–3, 0.61%), Metaconchoecia skogsbergi (0.07 ind·m–3, 0.05%). Some juvenile stages were tentatively identified as Paraconchoecia cf. brachyaskos. In almost all the stations the dominant species was Alacia belgicae, which seems to be a true Antarctic endemic species. It occurred in 2 distinct size ranges. Density distribution of both total ostracods and adults of the dominant species has been analyzed considering samples collected at different depth layers. In Terranova Bay, ostracod density did not show any sharply defined spatial distribution pattern. A positive correlation (P < 0.0001) was found between ostracod density and sampling layer depth. At most stations, densities were higher in intermediate and deep layers, where ostracods sometimes even assumed the role of the dominant planktonic component in terms of numerical importance. The distribution pattern by depth seems consistent with the detritivorous and carnivorous role of Ostracoda in the trophic structure of the Ross Sea zooplankton community.

Nonpalaeocope ostracod biostratigraphy of the type Wenlock Series, Silurian, of the Welsh Borderland

Abstract. Analysis of distribution, diversity and abundance of nonpalaeocope ostracods from the type Wenlock Series demonstrates that a major faunal change occurs around the Sheinwoodian-Homerian Stage boundary and that significant increases in faunal diversity occur at that boundary and in the late Whitwell Chronozone. Low abundance and low diversity in the late Sheinwoodian is interpreted to represent maximum water depth for the type Wenlock Series whereas the high diversity fauna of the late Homerian represents shallowest water conditions for this sequence. Many late Homerian species range into the Lower Elton Formation (early Ludlow) which suggests gradual ecostratigraphic change across the Wenlock-Ludlow boundary. Ancestor-descendant relationships for several lineages in the type Wenlock Series define lineage zones which essentially coincide with assemblage zones based on nonpalaeocope ostracods.

Ostracods as palaeoenvironmental indicators in the Lower Carboniferous Yoredale Series of northern England

Abstract. The ostracod fauna and vertical changes in its composition were examined in a shale sequence of the 5-Yard Limestone cyclothem (Yoredale Series) at a locality in Bishopdale, N. Yorkshire. The ostracod tax a are mainly confined to three superfamilies: Kirkbyacea, Healdiacea and Bairdiacea. The co-occurrence of several relatively short-ranging species such as Kirkbya quadrata, Cribroconcha insculpta and Bairdiolites elevatus suggests a Late Brigantian age. Four new species are described: Cornigella posteroextensa, ? Eriella minima, Rectobairdia bavarica and Roundyella binoda.Fluctuations in influx of terrigenous mud and water turbulence, related to delta growth, appear to have been the main environmental parameters that controlled the ostracod distribution and abundance along a nearshore-offshore gradient. Three different ostracod assemblages are recognized. A Roundyella-Cribroconcha assemblage, dominated by kirkbyacean and healdiacean ostracods, represents a quiet, nearshore environment with a fairly high depositional rate of terrigenous mud. A Bairdia assemblage, higher in the section, is dominated by bairdiacean ostracods that lived in a more turbulent, relatively offshore environment with less input of terrigenous sediment. A third, intermediate assemblage consists of almost equal amounts of bairdiacean and kirkbyacean ostracods, and reflects a transition from the Bairdia to the Roundyella-Cribroconcha assemblage.

The distribution and habitat preference of ostracods (Crustacea: Ostracoda) in a coastal sand‐dune lake, Loch of Strathbeg, north‐east Scotland

SUMMARY. 1. Ostracods were a numerically abundant component of the benthos &gt;0.1 mm in size (up to 20% of the total) in the Loch of Strathbeg.2. Distinct assemblages of species were associated with some habitats: Cypridopsis vidua (Müller) and Herpetocypris reptans (Baird) with Eleocharis palustris (L.) beds; Cypria uphtalmica (Jurine), Candona Candida Müller and Cypria exsculpta (Fischer) with Phragmites communis Trin. beds; and Limnocythere inopinata (Baird) with open sand. In contrast, no distinct ostracod assemblage was associated with submerged beds of Chara aspera Detharding, or Myriophyllum spicatum (L.).3. The number of ostracod species and ostracod diversity increased from open sand through macroalgal and submerged macrophytes to emergent macrophyte habitats and was associated with increasing number of types of detritus.4. Laboratory experiments suggested that substratum particle size played a dominant role in determining the distribution of L. inopinata. This species preferred sandy sediments. The distributions of both H. reptans and C. vidua were affected by food supply and H. reptans also preferred fine‐grained sediments. The absence of these taxa from some habitats where food supply and sediment particle size conditions were suitable suggested that unmeasured factors played a role. A possible predatory exclusion of H. reptans from such habitats was indicated by a negative association of this species with a predatory mite.

The transition from Jurassic to Cretaceous in northeast Tunisia: biostratigraphic details and distribution of facies

At the end of the Jurassic the palaeogeography of northeast Tunisia was controlled by the presence of a series of positive areas aligned along the Zaress-Zaghouan axis which delimited two subsiding basins: the Tunisian Trough to the northwest and the Hammamet Trough to the northeast. These positive areas encouraged the development of reefs which, when traced laterally, are seen to be transitional to open marine facies. A biostratigraphy based on ammonite, calpionellid and ostracod distributions allows correlations between the different belts of facies.

Combined ostracod and planktonic foraminiferal biozonation of the Late Coniacian – Early Maastrichtian in Israel

Abstract. The distribution and zonation of planktonic foraminifera and ostracods during the Late Coniacian – Early Maastrichtian succession in Israel was studied in detail from six surface sections. The combination of contemporaneous biozones led to a more accurate age determination of the local ostracod zones, according to the Tethyan planktonic foraminiferal zonation. The configuration of the biozones of both taxa presents more datum lines for stratigraphic correlation of the Senonian strata of Israel. Three new ostracod species were described from Campanian sediments: Cytherelloidea zinensis, Loxoconcha hebraica and Cristaeleberis ordinata.

Les Ostracodes du Jurassique D'arabie saoudite centrale: Systématique, Répartition Stratigraphique et Paléogéographique

A biostratigraphic scale based on Middle Jurassicostracods it established and integrated into the existing ammonite zoning, complemented by data on nautiloids, brachiopods and echinoids, which provide a preliminary biostratigraphic setting. All the species encountered are described and sketched, but the nomenclature is in many cases left open, to allow further definition of species distribution world-side. The geographic distribution of ostracods suggests the existence of a South Tethys province during the Middle Jurassic, isolated from the North Tethys by an oceanic barrier.