Fossil datums of Late Neogene sediments from the Southwest Pacific Ocean

The assumption of synchrony of first and last occurrences of fossil taxa can be tested using graphic correlation procedures which, by allowing measured stratigraphic sections to be compared on a common depth scale, make it possible to develop a correlation model which integrates information from a number of cores. The strategy of the test presented here is to use a graphic correlation model that is based on data from the Atlantic (Deep Sea Drilling Project (DSDP) sites 502, 516A) and north Pacific (DSDP site 577A) as a basis for determining to what extent fossil datums in the southwest Pacific are synchronous. First and last occurrences of Pliocene calcareous nannofossils and planktonic foraminifers have been compared in five DSDP cores from the southwest Pacific ocean (sites 586, 587, 588, 590A, and 592). All cores were recovered using hydraulic piston coring technology, which assures the best recovery and minimal disturbance. Most of these cores contain abundant, well-preserved foraminifers and nannofossils, as well as a partial record of many of the expected magnetic polarity reversals in this part of the section. To assure taxonomic consistency, all taxonomic identifications were made by the author. Graphic correlation of this data set suggests that several important biostratigraphic markers are highly diachronous. For example, this study confirms that Globorotalia truncatulinoides first occurs at approximately 2.4 Ma between 20° and 35° south latitude in the southwest Pacific, approximately 0.5 m.y. earlier than it is found elsewhere in the Atlantic and Pacific. Other datums, such as the last occurrence of Discoaster brouweri, are essentially synchronous. These findings suggest that biostratigraphic models based on the assumption of synchrony of first and last occurrences of fossil taxa may be incorrect. Biostratigraphic models created with the Graphic Correlation method offer an opportunity to examine the biogeographic dimensions of origination, migration, and extinction of planktonic taxa.

Oxygen isotopes and Sr/Ca ratios of fossil corals from Bonaire

Explanations for the demise of the Classic Maya civilization on the Yucatán Peninsula during the Terminal Classic Period (TCP; CE 750-1050) are controversial. Multiyear droughts are one likely cause, but the role of the Caribbean Sea, the dominant moisture source for Mesoamerica, remains largely unknown. Here we present bimonthly resolved snapshots of reconstructed sea surface temperature (SST) and salinity (SSS) variability in the southern Caribbean from precisely dated fossil corals. Our fossil coral results from Bonaire indicate strong interannual to decadal SST and SSS variability in the southern Caribbean Sea during the TCP with multiyear extremes of high SSS and high SST that coincide with droughts on the Yucatán Peninsula. The results are best explained by changed Caribbean SST gradients affecting the Caribbean low-level atmospheric jet with consequences for Mesoamerican precipitation, possibly linked to changes in Atlantic Meridional Overturning Circulation strength. Our findings provide a new perspective on the anomalous hydrological changes on the Yucatán Peninsula during the TCP that complement the often-suggested southward displacement of the Intertropical Convergence Zone. We advocate for a strong role of ocean-atmosphere interactions in the Caribbean Sea related to the multiyear variations in Caribbean Sea surface conditions as an important driver of the spatially complex pattern of hydrological anomalies during the TCP.

Coccolithosphores and fossil organic compounds of sediment core MD01-2444

This study analyzes coccolithophore abundance fluctuations (e.g., Emiliania huxleyi, Gephyrocapsa specimens, and Florisphaera profunda) in core MD01-2444 sediment strata retrieved at the Iberian Margin, northeastern Atlantic Ocean. Coccolithophores are calcareous nannofossils, a major component of the oceanic phytoplankton, which provide information about past ecological and climatological variability. Results are supported by data on fossil organic compounds (sea surface temperatures, alkenones, and n-hexacosan-1-ol index) and geochemical analyses (benthic d13Ccc and planktonic d18Occ isotopes). Three scenarios are taken into account for this location at centennial-scale resolution over the last 70,000 years: the Holocene and the stadial and interstadial modes. The different alternatives are described by means of elements such as nutrients; upwelling phenomena; temperatures at surface and subsurface level; or the arrival of surface turbid, fresh, and cold waters due to icebergs, low sea level, increased aridity, and dust. During the Holocene, moderate primary productivity was observed (mainly concentrated in E. huxleyi specimens); surface temperatures were at maxima while the water column was highly ventilated by northern-sourced polar deep waters and warmer subsurface, nutrient-poor subtropical waters. Over most of the last glacial stadials, surface productivity weakened (higher F. profunda and reworked specimen percentages and lower diunsaturated and triunsaturated C37 alkenones); the arrival of cold Arctic surface waters traced by tetraunsaturated C37 peaks and large E. huxleyi, together with powerful ventilated southern-sourced polar deep waters, disturbed, in all likelihood, the delicate vertical equilibrium while preventing significant upwelling mixing. Finally, during the last glacial interstadials (lower F. profunda percentages, nonreworked material, and higher diunsaturated and triunsaturated C37 alkenones) a combined signal is observed: warm surface temperatures were concurrent with generally low oxygenation of the deep-sea floor, moderate arrival of northern-sourced deep waters, and subsurface cold, nutrient-rich, recently upwelled waters, probably of polar origin; these particular conditions may have promoted vertical mixing while enhancing surface primary productivity (mainly of Gephyrocapsa specimens).

Calcareous nannofossils from ODP Leg 105 holes

Neogene calcareous nannofossils were examined from 10 holes at three sites cored during ODP Leg 105. Sediment recovered in Baffin Bay at Site 645 is virtually barren of calcareous nannofossils, with the exception of a sparse lower Miocene assemblage. Sites 646 and 647 in the Labrador Sea contain upper Miocene to Holocene sediments having numerous barren intervals. Upper Pleistocene fossil coccolithophorid floras in the Labrador Sea indicate alternations of cold subpolar with transitional (subpolar/subtropical) assemblages. Extreme variations in the abundance of Coccolithus pelagicus were observed at Sites 646 and 647. These variations are correlated with stable isotopic data to interpret oceanographic responses to warming and cooling trends. The climatic history indicated by the changes of these assemblages closely approximates the past climatic fluctuations recorded in other North Atlantic cores. One new taxon, Discoaster bergenii, is described.

Measurements of gastropods shell sizes from 23 fossil and extant long-lived lakes

Aim: To investigate shell size variation among gastropod faunas of fossil and recent long-lived European lakes and discuss potential underlying processes. Location: 23 long-lived lakes of the Miocene to Recent of Europe. Methods: Based on a dataset of 1412 species of both fossil and extant lacustrine gastropods, we assessed differences in shell size in terms of characteristics of the faunas (species richness, degree of endemism, differences in family composition) and the lakes (surface area, latitude and longitude of lake centroid, distance to closest neighbouring lake) using multiple and linear regression models. Because of a strong species-area relationship, we used resampling to determine whether any observed correlation is driven by that relationship. Results: The regression models indicated size range expansion rather than unidirectional increase or decrease as the dominant pattern of size evolution. The multiple regression models for size range and maximum and minimum size were statistically significant, while the model with mean size was not. Individual contributions and linear regressions indicated species richness and lake surface area as best predictors for size changes. Resampling analysis revealed no significant effects of species richness on the observed patterns. The correlations are comparable across families of different size classes, suggesting a general pattern. Main conclusions: Among the chosen variables, species richness and lake surface area are the most robust predictors of shell size in long-lived lake gastropods. Although the most outstanding and attractive examples for size evolution in lacustrine gastropods derive from lakes with extensive durations, shell size appears to be independent of the duration of the lake as well as longevity of a species. The analogue of long-lived lakes as 'evolutionary islands' does not hold for developments of shell size because different sets of parameters predict size changes.

Benthic foraminiferal assemblages in surface sediments of the Elbe estuary

Two foraminiferal assemblages are observed in surface sediments of the Elbe estuarv. an Elphidium excavatum assemblaae and an Ahmonia/Protelphidium assemblage. They are the result of test-size sorting in accordance to the grain size of the sediments. These assemblages of mainly empty tests differ basically from the living population, which is dominated exclusively by E. excavatum. The average test size is decreasing when advancing from the Open sea into the estuary and the living fauna disappears near the entrance of the Kiel Canal. In the dead assemblage the diversity is distinctively higher and the average test size varies with the grain size of the sediment. The assemblages found in plankton tows are nearly identical with those in corresponding bottom samples. This indicates the distribution pattern to be caused by transport in currents (mainly in suspension). This type of foraminiferal assemblages characterize macro- and mesotidal estuaries and might indicate a high tidal range when observed in sediments of fossil estuaries.

Phenotypic evolution in a fossil gastropod species lineage: evidence for adaptive radiation?

Detecting speciation in the fossil record is a particularly challenging matter. Palaeontologists are usually confronted with poor preservation and limited knowledge on the palaeoenvironment. Even in the contrary case of adequate preservation and information, the linkage of pattern to process is often obscured by insufficient temporal resolution. Consequently, reliable documentations of speciation in fossils with discussions on underlying mechanisms are rare. Here we present a well-resolved pattern of morphological evolution in a fossil species lineage of the gastropod Melanopsis in the long-lived Lake Pannon. These developments are related to environmental changes, documented by isotope and stratigraphical data. After a long period of stasis, the ancestral species experiences a phenotypic change expressed as shift and expansion of the morphospace. The appearance of several new phenotypes along with changes in the environment is interpreted as adaptive radiation. Lake-level high stands affect distribution and availability of habitats and, as a result of varied functional demands on shell geometry, the distribution of phenotypes. The on-going divergence of the morphospace into two branches argues for increasing reproductive isolation, consistent with the model of ecological speciation. In the latest phase, however, progressively unstable conditions restrict availability of niches, allowing survival of one branch only.

Chert petrology and geochemistry at DSDP Leg 62 Holes

Sixty-five chert, porcellanite, and siliceous-chalk samples from Deep Sea Drilling Project Leg 62 were analyzed by petrography, scanning electron microscopy, analysis by energy-dispersive X-rays, X-ray diffraction, X-ray spectroscopy, and semiquantitative emission spectroscopy. Siliceous rocks occur mainly in chalks, but also in pelagic clay and marlstone at Site 464. Overall, chert probably constitutes less than 5% of the sections and occurs in deposits of Eocene to Barremian ages at sub-bottom depths of 10 to 820 meters. Chert nodules and beds are commonly rimmed by quartz porcellanite; opal-CT-rich rocks are minor in Leg 62 sediments 65 to 108 m.y. old and at sub-bottom depths of 65 to 520 meters. Chert ranges from white to black, shades of gray and brown being most common; yellow-brown and red-brown jaspers occur at Site 464. Seventy-eight percent of the studied cherts contain easily recognizable burrow structures. The youngest chert at Site 463 is a quartz cast of a burrow. Burrow silica maturation is always one step ahead of host-rock silicification. Burrows are commonly loci for initial silicification of the host carbonate. Silicification takes place by volume-f or-volume replacement of carbonate sediment, and more-clay-rich sediment at Site 464. Nannofossils are commonly pseudomorphically replaced by quartz near the edges of chert beds and nodules. Other microfossils, mostly radiolarians and foraminifers, whether in chalk or chert, can be either filled with or replaced by calcite, opal-CT, and (or) quartz. Chemical micro-environments ultimately control the removal, transport, and precipitation of calcite and silica. Two cherts from Site 465 contain sulfate minerals replaced by quartz. Site 465 was never subaerially exposed after sedimentation began, and the formation of the sulfate minerals and their subsequent replacement probably occurred in the marine environment. Several other cherts with odd textures are described in this paper, including (1) a chert breccia cemented by colloform opal-CT and chalcedony, (2) a transition zone between white porcellanite containing opal-CT and quartz and a burrowed brown chert, consisting of radial aggregates of opal-CT with hollow centers, and (3) a chert that consists of silica-replaced calcite pseudospherules interspersed with streaks and circular masses of dense quartz. X-ray-diffraction analyses show that when data from all sites are considered there are poorly defined trends indicating that older cherts have better quartz crystallinity than younger ones, and that opal-CT crystallite size increases and opal-CT cf-spacings decrease with depth of occurrence in the sections. In a general way, depth of burial and the presence of calcite promote the ordering in the opal-CT crystal structure which allows its eventual conversion to quartz. Opal-CT in porcellanites converts to quartz after reaching a minimum d-spacing of 4.07 Å. Quartz/opal-CT ratios and quartz crystallinity vary randomly on a fine scale across four chert beds, but quartz crystallinity increases from the edge to the center of a fifth chert bed; this may indicate maturation of the silica. Twenty-four rocks were analyzed for their major- and minor-element compositions. Many elements in cherts are closely related to major mineral components. The carbonate component is distinguished by high values of CaO, MgO, Mn, Ba, Sr, and (for unknown reasons) Zr. Tuffaceous cherts have high values of K and Al, and commonly Zn, Mo, and Cr. Pure cherts are characterized by high SiO2 and B. High B may be a good indicator of formation of chert in an open marine environment, isolated from volcanic and terrigenous materials.

Occurrence of mammalia relicts at site Nörre-Lyngby

Investigations at a Late Weichselian freshwater basin in northwestern Jutland, Denmark, yielded a fairly rich assemblage of vertebrate remains, mostly bones and teeth of small mammals. The remains are primarily allochthonous and the bones have been subjected to different taphonomic pathways and agents. AMS 14C-dates on terrestrial organic remains provided ages of Middle to Late Allerød time. Identifications revealed the first fossil record in Scandinavia of Rana arvalis, Sorex minutus, Ochotona cf. pusilla, Microtus gregalis, Microtus oeconomus, and Sicista cf. betulinu. Spermophilus cf. major and Desmana moschata, previously found only once and twice respectively, were retrieved, and Sorex araneus and Arvicola terrestris were recovered for the first time beyond the Atlantic chronozone. Ecologically, the Nørre Lyngby small mammal fauna can be characterized by its very high and almost equal proportions of boreal forest and steppe elements followed by a relatively high proportion of tundra elements. The fossil species share a modern area of sympatry north of the Caspian Sea from the river Volga in the west to the southern and western slopes of the Urals. If, however, the large Allerød mammals are added, the fauna is without modern analogues. The Nørre Lyngby fauna can be seen as a last expansion of the North European glacial fauna. Provided that an absolute chronology and a differentiated sea-level curve for the area can be established, the Nørre Lyngby fauna could become important for studies in mammalian dispersal and migration rates.