Response of deep-sea benthic foraminifera to Miocene paleoclimatic events, DSDP Site 289

Changes in the Miocene deep-sea benthic foraminifera at DSDP Site 289 closely correlate to the climatically induced variations in deep and bottom waters in the Pacific Ocean. In early Miocene time, oxygen and carbon isotopes indicate that bottom waters were relatively warm and poorly oxygenated. Benthic foraminiferal assemblages are characterized by various species inherited from the Oligocene. Expansion of the Antarctic icecap in the early middle Miocene, 14–16 m.y. ago, increased oxygen isotope values, produced cold, more oxygenated bottom waters and lead to a turnover in the benthic foraminifera. An Oligocene—early Miocene assemblage was replaced by a cibicidoid-dominated assemblage. Some species became extinct and benthic faunas became more bathymetrically restricted with the increased stratification of deep waters in the ocean. In mid-Miocene time, Epistominella exigua and E. umbonifera, indicative of young, oxygenated bottom waters, are relatively common at DSDP Site 289. Further glacial expansion 5–9 m.y. ago lowered sealevel, increased oceanic upwelling and associated biological productivity and intensified the oxygen minima. Abundant hispid and costate uvigerines become a dominant faunal element at shallow depths above 2500 m as E. umbonifera becomes common to abundant below 2500 m. By late Miocene time, benthic faunas similar in species composition and proportion to modern faunas on the Ontong-Java plateau, had become established.     

Pliocene benthic foraminifera from the Blake Plateau: Faunal assemblages and paleocirculation

Relative abundance of benthic foraminifera have been analyzed from core V26-145 from the Blake Plateau. The investigated sequence represents the time interval between 1.8 and 4.6 Ma. In order to determine how different sieve sizes influence the relative abundance patterns, three sediment size fractions were studied separately. It becomes difficult to maintain consistent taxonomic concepts in the fraction 63–125 μm, partly because this fraction contains high abundances of juvenile forms. However, the 63–125 μm fraction holds high abundances of the important small speciesEpistominella exigua. Due to these reasons only the two larger fractions (125–250 μm and >250 μm) were considered meaningful to analyze for relative abundance patterns. An analysis of the two larger fractions (>125 μm; >250 μm) shows no consistency in relative abundance patterns.The relative abundance patterns for the 34 most common species in the size fraction >125 μm were analyzed by means of correspondence analysis. Three benthic foraminiferal assemblages (I, II, and III) were recognized and these can be associated with water masses. Assemblage I is associated with the Florida Current and consists of shallow water species (Amphistegina gibbosa, Compressigerina sp. A,Discorbinella biconcavus, Islandiella teretis, Reussella atlantica, andSiphonina pulchra). Assemblage II contains key species for North Atlantic Deep Water (NADW) (Cibicidoides kullenbergi, Epistominella exigua, Globocassidulina subglobosa, Lenticulina peregrina, Oridorsalis umbonatus, andPlanulina wuellerstorfi). The third assemblage (III) contains species associated with the Antilles Current (Bolivina rhomboidalis, Cassidulina obtusa, Cassidulina vortex, andNuttallides umbonifera). The correspondence analysis reveals an alternation in dominance between Assemblage I and Assemblage II prior to 3.3 Ma, suggesting lateral oscillations between the Florida Current and NADW. At about 3.3 Ma Assemblage I disappears and Assemblage III increases in importance, suggesting an increasing influence of the Antilles Current in the upper part of the record.     

A model for improving the precision of paleobathymetric estimates: an example from the northwest Gulf of Mexico

Intraspecific variation in test morphology of ten commonly occurring, benthic foraminiferal species collected from 47 stations and from water depths ranging from 53 to 3230 m in the northwest Gulf of Mexico were subjected to canonical discriminant analysis in order to statistically define an a priori bathymetric zonation. Three species (Bolivina subspinescens, Gavelinopsis translucens, and Uvigerina peregrina) had intraspecific variation capable of statistically dividing the bathyal zone into six contiguous 200 m intervals. Statistical analysis of the remaining seven species (Bolivina albatrossi B. lowmani, Cassidulina subglobosa, Cibicidoides pachyderma C. robertsonianus, Epistominella exigua, and Qridorsalis umbonatus) divided the bathyal zone into five contiguous 250 m intervals. The statistical differences in morphologic variability found in this study appear to be the organism's physiologic response to biogeochemical changes in sea floor habitat as they transcend various water masses. As such, the statistical analyses is a direct measure of the effect of those environmental factors, allowing better resolution and reliability of paleodepth estimates and geodynamic modelling than that commonly attained through faunal association.     

Palaeobathymetric zonation of foraminifera from lower Permian shale deposits of a high-latitude southern interior sea

Foraminifera are documented from the type section of the Quinnanie Shale in order to interpret their bathymetric distributions in a shallow high-latitude interior sea during the Kungurian. The marine setting was a narrow elongate half-graben (Merlinleigh Sub-Basin of the Southern Carnarvon Basin) in the Western Australian portion of eastern Gondwana. The Quinnanie Shale is part of the Byro Group of formations that display pronounced shale–sand cyclicity recording frequent changes in bathymetry. The type section of the Quinnanie Shale shows an overall progradational pattern in lithofacies, and consists of five ‘cycles’, each culminating in a prominent sandstone bed. Foraminifera are abundant in the shale and are almost entirely siliceous (organic-cemented) agglutinated types that probably dominated the original fauna of the interior sea. Hierarchical cluster analysis of samples taken every meter through the 162-m-thick type section is used to distinguish ten biofacies, each defined by a different set of dominant agglutinated species. Although biofacies frequently change up-section, there is an overall trend that is related to the progradational trend suggested by the lithofacies. Based on comparisons between lithofacies and biofacies, a palaeobathymetric zonation is established for the foraminifera. This zonation, the sparse macrofauna, and the lithofacies suggest that the interior sea was stratified in terms of salinity and dissolved oxygen levels, and the water was generally hyposaline. Most of the agglutinated foraminiferal species have analogous morphotypes present in modern confined estuaries and interior seas and this points to great conservatism in the evolutionary and ecological development of this component of interior-sea faunas. Aaptotoichus quinnaniensis sp. nov., an organic-cemented agglutinated foraminifer, is described from the Quinnanie Shale type section.     

Macroscale ecotone effects for the stream macrobenthic fauna and communities of the eastern Novosibirsk region

It is suggested that the eastern Novosibirsk region appeared as a margin between the Western and the Eastern Palaearctic zones in regard to the faunas of stream communities of rheophilic invertebrates. The western (European) elements of the fauna prevail in the lowland areas; but both faunas, eastern and western, combine at Salairsky Ridge. In addition, some differences between these two faunas are observed, when the species of the western origin dominate in the soft-bottom and phytophylic communities and refer to the European fauna. On the other hand, the eastern Siberian species are the key elements in the rhithral (hard-bottom) communities and somehow in krenal communities. Seventeen regional types of rheophilic communities are described.     

Stepwise postglacial migration of benthic foraminifera into the abyssal northeastern Norwegian Sea

Accumulation rates of individual species (SpecAR) and relative abundances (percentages) of benthic foraminifera of an AMS ¹⁴C-dated high resolution sediment core from the Norwegian Seas (water depth: 2707 m) provide a record of the faunal fluctuations from the last glacial maximum across the Weichselian deglaciation to the Holocene. During glacial times, the total foraminifera accumulation remains at a very low level (< 100 specimens cm⁻² kyr⁻¹) and is dominated by two endofaunal species: Oridorsalis umbonatus (Reuss) and Siphotextularia rolshauseni (Phleger and Parker) and reworked specimens of the genus Elphidium. The following deglaciation period exhibits an increase of the AR of the total fauna at 14 kyr B.P. The species distribution is marked by the last appearance of S. rolshauseni and the first postglacial appearance of suspension feeding Cibicidoides wuellerstorfi (Schwager) 13 kyr B.P. The absolute maximum of benthic foraminiferal AR (2750 spec cm⁻² kyr⁻¹ occurred near 9 kyr B.P. at the end of the deglaciation. This maximum also marks the re-appearance of the agglutinating species Cribrostomoides subglobosus (Sars). The post-glacial interval is characterized by a twofold reduction of the total accumulation of benthic foraminifera. The species distribution shows two new species: Ammobaculites agglutinans (d'Orbigny, at 6 kyr B.P.) and Epistominella exigua (Brady, at 3.5 kyr B.P.). The total AR indicates benthic activity during glacial times was at a low level. It was significantly higher during the Holocene with an abrupt increase of benthic foraminiferal abundance from 10 to 9 kyr B.P. The Stepwise re-invasion into the postglacial deep-sea environment maybe related to specific habitat preference.     

Zoogeography and relationships of Australasian skates (Chondrichthyes: Rajidae)

Aim To investigate distributional patterns and derivation of skates in the Australasian realm. Location Australasia. Methods Genus‐group skate taxa were defined for this region for the first time and new systematic information, as well as bathymetric and geographical data, used to identify distribution patterns. Results The extant skate fauna of Australasia (Australia, New Zealand, New Caledonia and adjacent subAntarctic dependencies) is highly diverse and endemic with sixty‐two species from twelve currently recognized, nominal genus‐group taxa. These include the hardnose skate (rajin) groups Anacanthobatis, Amblyraja, Dipturus, Okamejei, Rajella and Leucoraja, and softnose skate (arhynchobatin) genera Arhynchobatis, Bathyraja, Insentiraja, Irolita, Pavoraja and Notoraja. Additional new and currently unrecognized nominal taxa of both specific and supraspecific ranks also occur in the region. The subfamily Arhynchobatinae is particularly speciose in Australasia, and the New Zealand/New Caledonian fauna is dominated by undescribed supraspecific taxa and species. The Australian fauna, although well represented by arhynchobatins, is dominated by Dipturus‐like skates and shows little overlap in species composition with the fauna of New Zealand and New Caledonia. Similarly, these faunas exhibit no overlap with the polar faunas of the Australian subAntarctic dependencies (Heard and Macdonald Islands) to the south. Skates appear to be absent from the Macquarie Ridge at the southern margin of the New Zealand Plateau. Their absence off New Guinea probably reflects inadequate sampling and the subsequent poor knowledge of that region's deepwater fish fauna. Main conclusions Skates appear to have existed in the eastern, Australasian sector of Gondwana before fragmentation in the late Cretaceous. The extant fauna appears to be derived from elements of Gondwanan origin, dispersal from the eastern and western Tethys Sea, and intraregional vicariance speciation.     

Paleoceanographic changes during the past 1.9 Myr at DSDP Site 238, Central Indian Ocean Basin: Benthic foraminiferal proxies

Deep-sea benthic foraminifera have been quantitatively analyzed in samples (> 125 μm size fraction) from Ocean Drilling Program (ODP) Site 238, to understand paleoceanographic changes in the Central Indian Basin over the past 1.9 Myr. Factor and cluster analyses of the 25 highest-ranked species made it possible to identify five biofacies, characterizing distinct deep-sea environmental settings. The environmental interpretation of each biofacies is based on the ecology of recent deep-sea benthic foraminifera. The benthic faunal record indicates fluctuating deep-sea conditions in environmental parameters including oxygenation, surface productivity and organic food supply. These changes appear to be linked to Indian summer monsoon variability, the main climatic feature of the Indian Ocean region. The benthic assemblages show a major shift at ∼ 0.7 to 0.6 Ma, marked by major turnovers in the relative abundances of species, coinciding with an increased amplitude of glacial cycles. These cycles appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the Central Indian Ocean Basin.     

Late Cretaceous bioconnections between Indo‐Madagascar and Antarctica: refutation of the Gunnerus Ridge causeway hypothesis

Aim To evaluate the Gunnerus Ridge land‐bridge hypothesis, which postulates a Late Cretaceous causeway between eastern Antarctica and southern Madagascar allowing the passage of terrestrial vertebrates. Location Eastern Antarctica, southern Indian Ocean, Madagascar. Methods The review involves palaeogeographical modelling, which draws upon geological and geophysical data, bathymetric charts, and plate tectonic reconstructions, and the evaluation of stratigraphically calibrated phylogenetic analyses to document ghost lineages of select taxa. Results The available geological and geophysical evidence indicates that eastern Antarctica’s Gunnerus Ridge and southern Madagascar were separated for the entire Late Cretaceous by a vast marine expanse. In the mid–Late Cretaceous, the gap was probably punctuated by land on two intervening physiographical highs, the northern Madagascar Plateau and Conrad Rise, the latter of which, although probably large, was still separated from Antarctica’s Riiser‐Larsen Peninsula by c. 1600 km. Recent, stratigraphically calibrated phylogenies including large, terrestrial end‐Cretaceous vertebrate taxa of Madagascar and the Indian subcontinent reveal long ghost lineages that extended into the Early Cretaceous. Main conclusions The view that Antarctica and Madagascar were connected by a long causeway between the Gunnerus Ridge and southern Madagascar in the Late Cretaceous, and that terrestrial vertebrates were able to colonize new frontiers using this physiographical feature, is almost certainly incorrect, as was previously demonstrated for the purported causeway between Antarctica and the Indian subcontinent across the Kerguelen Plateau. Connection across mainland Africa to account for the close relationships of several fossil and extant vertebrate taxa of Indo‐Madagascar and South America is another option, although this too lacks credibility. We conclude that (1) throughout the Late Cretaceous there was no intervening, continuous causeway through Antarctica and associated land bridges between South America to the west and Indo‐Madagascar to the east; and (2) mid‐ to large‐sized, obligate terrestrial forms (e.g. abelisauroid theropod and titanosaurian sauropod dinosaurs and notosuchian crocodyliforms) gained broad distribution across Gondwanan land masses prior to fragmentation and were isolated on Indo‐Madagascar before the end of the Early Cretaceous.     

A major change in monsoon-driven productivity in the tropical Indian Ocean during ca 1.2–0.9 Myr: Foraminiferal faunal and stable isotope data

Tropical climate is variable on astronomical time scale, driving changes in surface and deep-sea fauna during the Pliocene–Pleistocene. To understand these changes in the tropical Indian Ocean over the past 2.36 Myr, we quantitatively analyzed deep-sea benthic foraminifera and selected planktic foraminifera from > 125 μm size fraction from Deep Sea Drilling Project Site 219. The data from Site 219 was combined with published foraminiferal and isotope data from Site 214, eastern Indian Ocean to determine the nature of changes. Factor and cluster analyses of the 28 highest-ranked species distinguished four biofacies, characterizing distinct deep-sea environmental settings. These biofacies have been named after their most dominant species such as Stilostomella lepidula–Pleurostomella alternans (Sl–Pa), Nuttallides umbonifer–Globocassidulina subglobosa (Nu–Gs), Oridorsalis umbonatus–Gavelinopsis lobatulus (Ou–Gl) and Epistominella exigua–Uvigerina hispido-costata (Ee–Uh) biofacies. Biofacies Sl–Pa ranges from ~ 2.36 to 0.55 Myr, biofacies Nu–Gs ranges from ~ 1.9 to 0.65 Myr, biofacies Ou–Gl ranges from ~ 1 to 0.35 Myr and biofacies Ee–Uh ranges from 1.1 to 0.25 Myr. The proxy record indicates fluctuating tropical environmental conditions such as oxygenation, surface productivity and organic food supply. These changes appear to have been driven by changes in monsoonal wind intensity related to glacial–interglacial cycles. A shift at ~ 1.2–0.9 Myr is observed in both the faunal and isotope records at Site 219, indicating a major increase in monsoon-induced productivity. This coincides with increased amplitude of glacial cycles, which appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the tropical Indian Ocean.     

Revision of the Zone 13 graptolite biostratigraphy in the Marathon, Texas, standard succession and its bearing on Upper Ordovician graptolite biogeography

One of the long-standing problems in North American graptolite biostratigraphy is the distinct differences in assemblages of post-Climacograptus bicornis age between the classical graptolite sequences in the New York - Quebec and Marathon, west Texas, regions. These have been attributed either to faunal provincialism or to the presence of a major hiatus between the Woods Hollow and Maravillas formations in Texas. New collections from the key Marathon Picnic Grounds section contain diagnostic Late Ordovician graptolites that confirm the existence of a major stratigraphic gap below the Maravillas Formation. The lower Maravillas Formation (Zone 13) has a Late Ordovician, low-diversity Pacific Province graptolite fauna that includes the biostratigraphically diagnostic species Climacograptus nevadensis, C. tubuliferus, Orthograptus fastigatus and Dicellograptus ornatus. Zone 13 graptolite assemblages from the Marathon region correlate with the C. tubuliferus to D. ornatus zones in the Trail Creek, Idaho, succession, the Ea4-Bo2 interval in Victoria, the O. fastigatus Zone in the Canadian Arctic Islands, the O. quadrimucronatus to D. ornatus zones of the Canadian Cordillera, and the D. complanatus to D. anceps zones in Scotland. The hiatus between the Woods Hollow and Maravillas formations spans an interval corresponding to at least the Eal Ea3 interval in Australia, the C. americanus to upper A. manitoulinensis zones in the New York - Quebec succession, and the D. clingani and P. linearis zones in Scotland. These results agree with the magnitude of the hiatus previously indicated by conodont biostratigraphy. Late Ordovician graptolite distribution patterns in North America can be explained by an extension of Cooper, Fortey & Lindholm's (1991; Lethaia 24) Lower Ordovician graptolite biofacies model into the Upper Ordovician, which incorporates both lateral water-mass specificity and depth stratification. Using this model, we recognize in Laurentia two separate biofacies among tropical-zone Late Ordovician Pacific Province graptolite faunas, a cosmopolitan Oceanic biofacies, and a cratonic Laurentian biofacies. The lower Maravillas Formation graptolite fauna is clearly part of the Oceanic biofacies, whereas the coeval Appalachian faunas represent the Laurentian biofacies. □Graptolites, Ordovician, biostratigraphy, Texas, biofacies, biogeography.     

Tasman Front shifts and associated paleoceanographic changes during the last 250,000 years: foraminiferal evidence from the Lord Howe Rise

The paleoceanography of the Tasman Sea over the past 250,000 years was studied using benthic (>75 μm size fraction) and planktonic foraminifera (>149 μm size fraction) from three cores collected along 162°E traverse between 25°S and 30°S on the Lord Howe Rise. Planktonic foraminiferal oxygen isotope stratigraphy dates the cores between OIS 1 and 11. R-mode cluster and Q-mode factor analyses were carried out on benthic foraminiferal faunas, and Q-mode factor analysis and the modern analog technique (MAT) were used in analyzing planktonic foraminiferal faunas. Distinct benthic faunas across latitude from north (25°S) to south (30°S and 35°S) reflects the difference in primary productivity level in the overlying surface water. The MAT result is thought to express latitudinal shifts of the Tasman Front over the last 250,000 years with: (1) the Tasman Front at 35°S during the oxygen isotope stage (OIS) 1 (post-glacial period); (2) migration of the front nearby 25°S during the last glacial period (OIS 2–OIS 4) and slightly northward of its present position during the penultimate glacial period (OIS 6); and (3) a return of the front to near 35°S during OIS 5 and OIS 7. Based on time-series and spatial variations of benthic foraminiferal factor typified by Pseudoparrella exigua and Uvigerina peregrina and one variety, southern-winter mixing and convection along the Tasman Front may have strengthened during the interglacial OIS 7 in particular.     

Ostracod and conodont faunal changes across the Frasnian-Famennian (Devonian) boundary at Els Castells,Spanish central Pyrenees

Diverse conodont and silicified ostracod assemblages were found in the Spanish Pyrenees (Els Castells section), in the Frasnian/Famennian boundary beds (late rhenana and/or linguiformis to late triangularis zones), in strata below and above the well-known Kellwasser Extinction Event. Many of the ostracods studied here are conspicuous elements of the “Thuringian Mega-Assemblage”, and show maximum affinities with faunas from the southeastern Cantabrian Mountains (Spain), eastern Thuringia and the Harz (Germany). The composition of the faunas, however, is not uniform through the Els Castells section. A rather sharp break exists, roughly coinciding with the Frasnian/Famennian boundary. The break is characterized by the disappearance of many ostracods typical of the “Thuringian Mega-Assemblage”. This correlates with an important change in the conodont faunas related to the Kellwasser Event. The Frasnian (late rhenana and/or linguiformis zones) palmatolepid-polygnathid biofacies is followed in Famennian strata (middle and late triangularis zones) by a palmatolepid-icriodid biofacies. The icriodid maximum in the earliest Famennian rocks of the Pyrenees correlates with the “Icriodid Peak” described elsewhere. These changes depend on the age and palaeoenvironmental conditions.     

Discovery of an oak gall wasp (Hymenoptera: Cynipidae) inducing galls on deciduous oak trees in India

We report for the first time the occurrence of an oak gall wasp Andricus mukaigawae (Mukaigawa) (Hymenoptera: Cynipidae) on the deciduous oak Quercus griffithii Hook. F & Thomson ex Miq. in India. Andricus mukaigawae is the only cynipid species that has been observed to induce galls on deciduous oak species in India to date. In addition, this is the first record of a gall wasp species with a distribution extending all the way from the eastern Palearctic region to the Indian subcontinent, suggesting the existence of a close relationship between cynipid faunas on deciduous oak trees in the two regions.     

Benthos of Lake Mikri Prespa (North Greece)

An extensive sampling of Lake Mikri Prespa was carried out in summer 1990, aimed at evaluating benthic abundance, recording the species involved and detecting their response to some environmental variables. Three oligochaete species are endemic to the region,Potamothrix prespaensis, Psammoryctides ochridanus variabilis andPsammoryctides ochridanus typica. The bathymetric curve of the benthos resembles that of eutrophic lakes. A great abundance ofChironomus plumosus andChaoborus flavicans occurred. Four community patterns were revealed by TWINSPAN analysis, division level two, explicitly discriminated by the influence of substrate type, depth, C/N ratio and pH. Species richness and diversity was minimal in the profundal and maximal in the shallows, whilst the equitability index was high in all site groups. Depth and bottom type were the most important variables in defining species distribution. More precisely,Chironomus plumosus, Chaoborus flavicans andPotamothix hammoniensis were ubiquitous, preferring mostly deep waters.Tanytarsus sp.,Einfeldia dissidens, Cladopelma lateralis, Tanypus punctipennis andPotamothrix prespaensis favoured shallower and less productive waters with a bottom rich in decaying plant fragments, and thePsammoryctides species showed a littoral origin and regular occurrence on gravel beds. A few species displayed a particular distribution with changes of depth, C/N ratio and pH.     

Do Rapoport's rule,the mid‐domain effect or the source–sink hypotheses predict bathymetric patterns of polychaete richness on the Pacific coast of South America?

Aim We evaluated the bathymetric gradient of benthic polychaete species richness from the Chilean coast, as well as its possible underlying causes. We tested three possible hypotheses to explain the richness gradient: (1) Rapoport's effect; (2) the mid‐domain effect (MDE); and (c) the source–sink hypothesis. Location South‐eastern Pacific coast of Chile. Methods The bathymetric gradient in richness was evaluated using the reported ranges of bathymetric distribution of 498 polychaete species, from the intertidal to abyssal zone (c. 4700 m). Rapoport's effect was evaluated by examining the relationship between bathymetric mid‐point and bathymetric range extent, and species richness and depth. The MDE was tested using the Monte Carlo simulation program. The source–sink hypothesis was tested through nestedness analysis. Results Species richness shows significant exponential decay across the bathymetric gradient. The pattern is characterized by a high presence of short‐ranged species on the continental shelf area; while only a few species reach abyssal depths, and they tend to show extremely wide bathymetric ranges. Our simulation analyses showed that, in general, the pattern is robust to sampling artefacts. This pattern cannot be reproduced by the MDE, which predicts a parabolic richness gradient. Rather, results agree with the predictions of Rapoport's effect. Additionally, the data set is significantly nested at species, genus and family levels, supporting the source–sink hypothesis. Main conclusions The sharp exponential decay in benthic polychaete richness across the bathymetric gradient supports the general idea that abyssal environments should harbour fewer species than shallower zones. This pattern may be the result of colonization–extinction dynamics, characterized by abyssal assemblages acting as ‘sinks’ maintained mainly by shallower ‘sources’. The source–sink hypothesis provides a conceptual and methodological framework that may shed light on the search for general patterns of diversity across large spatial scales.     

Early Miocene reef- and mudflat-associated gastropods from Makran (SE-Iran)

A new gastropod fauna of Burdigalian (early Miocene) age is described from the Iranian part of Makran. The fauna comprises 19 species and represents three distinct assemblages from turbid water coral reef, shallow subtidal soft-bottom and mangrove-fringed mudflat environments in the northern Indian Ocean. Especially the reef-associated assemblage comprises largely new species. This is explained by the rare occurrence of reefs along the northern margin of the Miocene Indian Ocean and the low number of scientific studies dealing with the region. In terms of paleobiogeography, the fauna corresponds well to coeval faunas from the Pakistani Balochistan and Sindh provinces and the Indian Kathiawar, Kutch and Kerala provinces. During the early Miocene, these constituted a discrete biogeographic unit, the Western Indian Province, which documents the near complete biogeographic isolation from the Proto-Mediterranean Sea. Some mudflat taxa might represent examples of vicariance following the Tethys closure. The fauna also displays little connection with coeval faunas from Indonesia, documenting a strong provincialism within the Indo-West Pacific Region during early Miocene times. Neritopsis gedrosiana sp. nov., Calliostoma irerense sp. nov., Calliostoma mohtatae sp. nov. and Trivellona makranica sp. nov. are described as new species.     

Aptian to Maastrichtian paleobathymetric reconstruction of the Eastern Venezuelan Basin

The objective of this study is a paleobathymetric reconstruction of the depositional environment during the Cretaceous (Aptian-Maastrichtian) on the northern flank of the Eastern Venezuelan Basin. The model is based on the presence of benthic foraminifera in 17 well sections, spread across the paleoslope in a passive margin. Cluster analysis separates five distinct assemblages of foraminifers. The analysis is based on the assumption that the species must occur in 10% or in at least two wells of the area. The R-mode for each well provides clusters of species that are similar in distribution and abundance trends. These clusters together with the diversity and abundance of planktic foraminifers, dinoflagellates, pollen, spores, calcareous nannofossils, and sedimentological data help to delineate the biofacies. The biofacies are distributed in a pattern from the updip position (southwest) to the downdip position (northeast). The shallowest biofacies (0–50 m) is represented by Ammobaculites sp., Haplophragmoides sp., Lituolidae, with abundant terrestrial palynomorphs and dinoflagellates. Abundant species in depths greater than 100 m are Praebulimina carseyae, Epistomina lacunosa, Gavelinella sp., Buliminella sp., and Pullenia cretacea. This biofacies interpretation allows us to establish a paleocoast orientation during the Aptian-Maastrichtian.The establishment of the age-paleobathymetry relationships in this area provides the basis for the stratigraphic reconstruction of the Cretaceous in the Eastern Venezuelan Basin, thus reducing the risk for oil exploration.     

Structure of the extraembryonic matrices around the benthic embryos of Patiriella exigua (Asteroidea) and their roles in benthic development: Comparison with the planktonic embryos of Patiriella regularis

The extracellular matrices (ECMs) surrounding the benthic embryos and larvae of the seastar Patiriella exigua and the planktonic embryos of Patiriella regularis were examined by transmission and scanning electron microscopy. Three ECMs surround unhatched embryos: An outer jelly coat, a fertilization envelope, and an inner hyaline layer. The ECMs of P. exigua are modified for supporting benthic development. The dense jelly coat attaches the embryo to the substratum, and the fertilization envelope forms a though protective case. In comparison, P. regularis has a less dense jelly coat and a thinner fertilization envelope. The hyaline layer of both species is comprised of three main regions: An intervillous layer overlying the epithelium, a supporting layer, and a coarse meshwork layer. Unhatched P. exigua have an additional outer amorphous layer that adheres to the fertilization envelope. As a result, the hyaline layer forms a continuous ECM that unites the embryonic surface with the fertilization envelope. Embryos of P. exigua removed from their fertilization envelopes lack the outer amorphous region, have a poorly developed hyaline layer, and do not develop beyond gastrulation. It appears that the substantial hyaline layer of P. exigua and its attachment to the fertilization envelope are essential for early development and that this ECM may function as a gelatinous cushioning layer around the benthic embryos. At hatching, the amorphous layer is discarded with the envelope. In contrast, an amorphous layer is absent from the hyaline layer of P. regularis. The demembranated embryos of this species have an ECM similar to that of controls and develop normally to the larval stage. © 1995 Wiley-Liss, Inc.