Tindaria kretensis n. sp., a new deep water protobranch (Bivalvia) from the Early Pliocene of Crete (Southern Greece)

Tindaria kretensis n. sp., a minute deep-water protobranch, is described from Early Pliocene marls cropping out in the Voutes section, northern Crete Island. This is one of the few fossil records of Tindaria from the Mediterranean area, the first well documented for the Neogene. Tindaria is an almost cosmopolitan deep-water genus, absent from the modern Mediterranean. Its occurrence in the Early Pliocene is in agreement with what is known about the past psychrospheric conditions in the Mediterranean.     

Size analyses of the coccolith species Biscutum constans and Watznaueria barnesiae from the Late Albian “Niveau Breistroffer” (SE France): taxonomic and palaeoecological implications

The size variability of the coccolith species Biscutum constans and Watznaueria barnesiae has been studied in 50 samples of the Late Albian “Niveau Breistroffer” black shales (Col de Palluel section, SE France). For each species, length and width of the total coccolith and the central unit have been measured in 60 specimens per sample. In addition, ellipticity and central unit length/total coccolith length ratio have been calculated. This study aims to improve our understanding of the taxonomic concepts of B. constans and W. barnesiae, and to test whether the size changes correspond to palaeoceanographic changes interpreted from other proxies. Two morphotypes (varieties) were differentiated for each of the two taxa studied. B. constans includes morphotypes with a narrow (B. constans var. constans) and a wide central unit (B. constans var. ellipticum). Between these two morphotypes no significant size differentiation has been observed. They seem to represent end members of a size continuum, relating to both the total coccolith- and central unit size distribution. The two morphotypes of W. barnesiae differ only in the absence (W. barnesiae var. barnesiae) and the presence of a narrow central opening (W. barnesiae var. fossacincta). No significant size differences have been observed between these two morphotypes, and both show similar distributions of the measured characteristics. We recommend that the studied morphotypes of both B. constans and W. barnesiae should not be assigned to different morphospecies. Throughout the studied black shale succession the measured parameters show mostly statistically insignificant, short-term fluctuations, but significant long-term trends have been observed for B. constans. These show a trend to smaller forms with a narrower central unit in the upper part of the succession. This change coincides with a cooling trend, as indicated by a nannofossil based temperature index. Therefore the two morphotypes of B. constans are interpreted to represent ecophenotypic varieties rather than two different morphospecies. No clear relationship has been recognized between the size of W. barnesiae and the palaeoenvironmental conditions.     

Palaeoceanographical changes recorded by Cenozoic deep-sea ostracod assemblages from the South Atlantic and the Southern Ocean (ODP Sites 1087 and 1088)

Cenozoic palaeoceanography of the SE Atlantic and Southern Oceans has been investigated using Late Eocene/Early Oligocene to Quaternary ostracod assemblages from 49 samples of ODP Sites 1087 and 1088. Although the overall abundance of ostracods is relatively low (means of 17 and 49 specimens per sample at Sites 1087 and 1088, respectively) and there is an apparently high level of endemism (ranging from 50% to 80% at Sites 1087 and 1088), three major changes in the faunal assemblages are identified at Site 1087 (denoted A, B and C) and two at Site 1088 (denoted B' and C'). The assemblage boundaries, detected on the basis of stepwise changes in the abundance, diversity, dominance, endemism, faunal turnover and relative abundance of common taxa, coincide broadly with previously identified, ostracod-based palaeoceanographical 'events' discussed by Benson and co-workers over the last two decades. The data do not extend sufficiently far back to record the initiation of Assemblage A, but the faunal change between Assemblages A and B, marked by a decline in abundance, species diversity and faunal turnover, occurs within the Middle Miocene (NN5-6). It coincides with a previously documented palaeoceanographical 'event' at 16-14 Ma which, we suggest, may be related to the initiation of North Atlantic Deep Water (NADW) production and/or an expansion of the East Antarctic ice sheet. Assemblage B' is subdivided into the two Sub-assemblages B'¹ and B'² mainly on the basis of an increase in diversity, a peak in faunal turnover and a drop in the relative abundance of the genus Krithe in early Late Miocene time (NN9, c. 10.5 Ma). The B'¹/B'² Sub-assemblage boundary cannot be related to any previously documented faunal change in deep-sea ostracods. Changes associated with the boundaries between Assemblages B and C, and B' and C', which we believe to be synchronous, both include a decrease in diversity and abundance. In addition, two strong turnover peaks occur near the B'/C' boundary at Site 1088. The B/C and B'/C' boundaries coincide with a previously documented midPliocene 'event' (3.5 Ma) (NN15-16) which may be linked to putative closure of the Straits of Panama and increased production of NADW, the latter in turn leading to increased production of Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Alternatively, fiuctuations in size of the Antarctic ice sheet during possible Pliocene warm periods could indirectly be responsible for the observed midPliocene faunal changes.     

The Cenomanian of northern Germany: facies analysis of a transgressive biosedimentary system

A facies analysis of the epicontinental marine Cenomanian sediments of northern Germany shows the presence of 17 facies types (FTs, including several subtypes) which can be assigned to three facies associations: 1) an inner shelf facies association (FT 1–8) with high amounts of terrigenous material and/or high-energy depositional features, 2) a middle shelf facies association (FT 9–15) of predominantly calcareous sediments with moderate amounts of generally fine siliciclastics, and 3) an outer shelf facies association (FT 16–17) of low-energy, fine-grained, pure limestones. These three facies associations roughly correspond to the well-known lithological units of the Cenomanian of northern Germany, i.e., the Essen Greensand/Cenomanian Marls complex, the Pläner Limestones, and the Poor rhotomagense Limestones. The sediments were deposited on a northward-dipping homoclinal ramp with more-or-less shoreline-parallel facies belts. The sediment composition on this ramp-like shelf was a function of the varying importance of three different sediment sources: 1) terrigenous input from the south (Rhenobohemia), generally fining/decreasing in a proximal–distal (i.e., S–N) direction; 2) production of skeletal grains, mainly by macrobenthic organisms; and 3) settling of planktic carbonate (mainly calcispheres and calcareous nannofossils). In response to decreasing water energy with increasing water depth, the seaward decreasing terrigenous influence, and increasing planktic carbonate production, increasingly finer and more calcareous sediments were deposited in a proximal–distal transect. This rather straightforward picture was slightly modified by highest carbonate accumulation rates (planktic and benthic) on the middle shelf, forming a mid-shelf depocenter (fossiliferous, calcisphere-rich Pläner Limestones). Time-transgressive, southward-directed onlap of this biosedimentary system during the Cenomanian caused a significant retreat of the coastline towards the south and a retrogradational stacking of facies belts, explaining the broadly similar facies development and lithology of Cenomanian successions across northern Germany. The boundaries of the lithological units, however, tend to be considerably diachronous in a distal–proximal transect. In the late Middle and early Late Cenomanian, a final drowning and facies levelling (“oceanization”) is indicated by the widespread deposition of uniform calcareous nannofossil mudstones (Poor rhotomagense Limestones).     

Calcareous nannofossil surface sediment assemblages from the Sicily Channel (central Mediterranean Sea): Palaeoceanographic implications

Quantitative analysis of 67 calcareous nannofossil assemblages from surface sediments recovered in a wide area across the Sicily Channel has been carried out in order to improve the interpretation of palaeontological data based on this planktonic group in a key area for Mediterranean palaeoceanographic studies. The investigation focused on three case studies that demonstrate the high potentiality of such a combined approach, taking into account the recent distribution of taxa or groups of taxa on the sea floor and the palaeontological record. The distribution of reworked specimens over the northern Sicily Channel sea floor validates the role of southern Sicily as a source region for reworked nannofossils and the role of rivers as their carrier. Eustatic sea-level fluctuations can be considered to be the main factor that influenced the abundance variations in sedimentary sequences of this area. The distribution of Florisphaera profunda can be explained in terms of topography (positive correlation) and mesoscale oceanographic circulation. In particular, its significant anti-correlation to the amount of chlorophyll-A deduced by satellite imagery validates the use of this species as a proxy for palaeoproductivity reconstructions. Finally, high abundance values of G. oceanica are confined to the westernmost part of the Sicily Channel, coinciding with a water mass salinity minimum. In particular, abundances of up to about 10% were observed in the westernmost part of the African Margin, suggesting the importance of the Atlantic Tunisian Current, whose activity is more pronounced in winter. The comparison of data of this species between 135 and 110 kyr BP, inside and outside the Channel, led us to deduce that the physical transport in almost unmodified waters of Atlantic origin might be the most important factor for its significant occurrence.     

Extinction pattern of marine Ostracoda across the Pliensbachian-Toarcian boundary in the Cordillera Ibérica, NE Spain: Causes and consequences

This paper discusses the extinction pattern of the Pliensbachian-Toarcian boundary (PTB) ostracod assemblages at the Almonacid de la Cuba section (Cordillera Ibérica, NE Spain), which has been recently proposed as auxiliary boundary stratotype for the PTB. The ostracod record shows that the main Early Jurassic ostracod extinction event occurred not at the end of the Pliensbachian, but near the top of the Mirabile ammonite Subzone, Tenuicostatum ammonite Zone (Early Toarcian). On the basis of the evaluation of PTB ostracod record, a new causal explanation for the Early Toarcian ostracod turnover is proposed. This paper suggests that a reorganization of surface and deep-water circulations caused by the opening of the Hispanic Corridor could have generated a mild cooling episode, finally affecting the survival of healdioid ostracods.     

Development of facies and C/O-isotopes in transects through the Ludlow of Gotland: Evidence for global and local influences on a shallow-marine environment

Summary The Silurian of Gotland is characterized by repeated changes in depositional facies development. The deposition of uniform sequences of micritic limestones and marls was interrupted four times by the growth of reef complexes and the formation of expanded carbonate platforms. Coinciding with these, often abrupt, facies changes extinction events occurred which predominantly affected nektonic and planktonic organisms. Ratios of carbon- and oxygen-isotopes covary with the facies development. Periods in which the deposition of limestonemarl alternations prevailed are characterized by relatively low C- and O-isotope values. During periods of enhanced reef growth isotope values are high. For these changes,Bickert et al. (1997) assume climatic changes between humid “H-periods”, with estuarine circulation systems and cutrophic surface waters with decreased salinity in marginal seas, and arid “A-periods”, with an antiestuarine circulation and oligotrophic, stronger saline surface waters. In order to separate local and regional influences on the isotopic development from the global trend, the interactions between facies formation and isotope record have to be clarified. For this purpose, the patterns of isotope values in the upper part of the Silurian sequence on Gotland (upper Wenlock —upper Ludlow) has been determined and stratigraphically correlated along four transects through different facies areas. Facies formation during this time interval was investigated by differentiation and mapping of twelve facies complexes in the southern part of Gotland. These include shelf areas, reef complexes with patch reefs and biostromes, backreef facies, and marginal-marine deposits. The good correspondence between the carbon-isotope records of the four transects suggests that local environmental conditions in the different facies areas did not influence the δ¹³C values. Therefore, a supra-regional or even global mechanism for the C-isotope variations is likely. In contrast to carbon istopes, the oxygen-isotope values of the four transects generally show parallel trends, but higher variabilities and in parts distinctly deviating developments with a trend to more negative values. These are interpreted as an effect of local warming in small shallow-water areas which developed during arid periods in reef complexes and backreef areas. The boundaries between A-periods and H-periods, as defined by δ¹³C values, which are interpreted as isochrones, can be mapped. From the upper Homerian to the Pridolian six parastratigraphic isotope zones are defined which only partly match the stratigraphic division ofHede (1942, 1960). The isotope stratigraphy results in an improved correlation between the shallow and marginal-marine areas in the eastern part of Gotland and the uniform shelf areas at the west coast of the island. Furthermore, a detailed relationship between the development of carbon and oxygen isotope ratios, the carbonate facies formation, and the succession of palaeontological events could be observed. At the transition from H-periods to A-periods, major extinction events occurred prior to the first increase of δ¹³C and δ¹⁸O values. Extinction events affected conodonts, graptolites, acritarchs, chitinozoans, and vertebrates and resulted in impoverished nektonic and planktonic communities. The reef-building benthos was less affected. Parallel to a first slight increase of isotope values, facies began to change, and reefs developed in suitable locations. The subsequent rapid increase of C- and O-isotope values occurred contemporarily with strong facies changes and a short-term drop of sea-level. Oligotrophic conditions in the later stages of A-periods led to strong reef growth and to an expansion of carbonate platforms. The transitions from A-periods to H-periods were more gradual. The δ¹³C values decreased slowly, but reef growth continued. Later the reefs retreated and were covered by the prograding depositional facies of shelf areas. The diversity of planktonic and nektonic communities increased again. The close relationship between facies formation, palaeontological events and isotope records in the Silurian suggests common steering mechanisms but gives no indication of the causes for the repeated extincion events related to H-period/A-period transitions. Especially the observation, that strong extinctions occurred prior to changes of isotope values and facies, points to causes that left no signals in the geological record. Hypothetical causes like collapse of trophical nets, anoxias, or cooling events are not evident in the sediment record or do not fit into the regular succession of period transitions.     

Cenomanian–Turonian carbonate and organic-carbon isotope records, biostratigraphy and provenance of a key section in NE Sicily, Italy: Palaeoceanographic and palaeogeographic implications

In eastern Sicily, a series of highly organic-rich black shales occur as exotic blocks (~ 100 m across) floating in tectonized sediments (Argille Varicolori Unit containing olistoliths of Cretaceous–Palaeogene age). A 19-metre section, through one of these blocks near the town of Novara di Sicilia, includes cyclically bedded black shales, marlstones and claystones, which have been dated using planktonic foraminiferal and nannofossil biostratigraphy. On this basis, the section is assigned to the latest Cenomanian and clearly represents a manifestation of the Oceanic Anoxic Event characteristic of that interval. Total organic-carbon values range up to 23% and the relatively high hydrogen indices record the presence of marine organic matter of low thermal maturity. High-resolution carbonate and organic-carbon isotope curves are comparable with those recorded elsewhere in indicating a significant positive excursion and confirm that, in the Novara di Sicilia section, the black shales are latest Cenomanian in age. By comparison with Cenomanian–Turonian black shales exposed elsewhere in Italy (Calabianca section, western Sicily; Livello Bonarelli, Bottaccione Gorge, Gubbio, Marche–Umbria), the section of Novara di Sicilia is different in being more stratigraphically expanded. However, this section from eastern Sicily does resemble extremely closely coeval sediments cropping out in Tunisia and Morocco. This association is taken as evidence that the Argille Varicolori Unit includes elements that were initially deposited on the north African shelf during Cretaceous time.     

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.     

Late Holocene paleofish populations in Effingham Inlet, British Columbia, Canada

Paleontological studies of fish remains in laminated sediments provide a proxy relationship between fish populations and ocean climate. This study examines climate variability from approximately 500 y B.P. to 4000 y B.P. as recorded in fish remain abundances (primarily scales) collected from laminated sediments within Effingham Inlet on the west coast of Vancouver Island, British Columbia. The study also discusses technical issues involving fish remains from laminated sediments, including sampling resolution, sediment volume, identification of remains and appropriate abundance considerations.The dominant species in the assemblage include Northern anchovy and Pacific herring, with lesser percentage-abundances from rockfish, hake, elasmobranches and surfperch. The data indicate that Northern anchovy experienced a shift in scale deposition abundance at approximately 2800 y B.P. with not only a greater total abundance but also a greater consistency of deposition with time. Pacific herring underwent cyclical deposition that changed little through time. Statistical analysis reveals that none of these species is directly responding to climatic signals as indicated in the lithological and palynological record, but that this could have been partially due to the sampling resolution of the piston core. Analysis indicates a lack of correlation between the two dominant species, as might be expected on the basis of their opposing lifestyle strategies with respect to sea surface temperatures.With appropriate sampling strategies, paleohistorical fish remains from laminated sediments reflect changes in population structure and behaviour for some species, illustrate basic secondary trophic information, and provide potential clues to basin-scale oceanographic/climatological variability.