Hydrodynamic behavior of empty larger foraminiferal tests

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New methods for ichnofabric analysis and correlation with orbital cycles exemplified by the Baden-Sooss section (Middle Miocene, Vienna Basin)

A two step cluster analysis based on log-likelihood measures for categorial variables using "Schwarz's Bayesian Criterion" for grouping allows the automatic detection of ichnofabric categories from a large data set. Preferred successions of these ichnofabrics were tested by "Embedded Markov Chains". This leads to the following ichnofacies interpretation: Alternating periods of higher/lower accumulation rates with higher/lower inputs of particulate food and higher/ lower oxygen contents in pore waters led to sequential colonization of the substrate. The trace fossils Phycosiphon and Nereites represent opportunistic colonization of oxygenated sediments rich in particulate organic matter (POM) by deposit-feeding animals, quickly after an increased sediment input. A further stage of colonization caused by the decrease of POM induced by consumption and oxidation forced the animals to search for food on sediment surfaces and from the water column. The open burrows Thalassinoides, Chondrites, Trichichnus and Zoophycos indicate stable-bottom conditions in periods of low accumulation rates. Zoophycos, Phycosiphon, Nereites and Teichichnus suggest the Zoophycos ichnofacies for the lower section of the core; a transition to the distal part of the Cruziana ichnofacies is suggested for the upper section of the core with the appearance of Thalassinoides. The changes between stable and unstable bottom conditions significantly correlate with periods in magnetic susceptibility and calcium carbonate content, both forced by orbital cycles

Nannofossil biostratigraphy, strontium and carbon isotope stratigraphy, cyclostratigraphy and an astronomically calibrated duration of the Late Campanian Radotruncana calcarata Zone

AbstractA section from the southern (Austro-Alpine Northern Calcareous Alps) margin of the Penninic Ocean in the NW Tethys realm of Late Campanian age is investigated stratigraphically. Plankton foraminifer and nannofossil biostratigraphy designate the presence of the Globotruncana ventricosa Zone and the Radotruncana (Globotruncanita) calcarata Zone, and standard nannofossil zones CC21–UC15cTP and CC22ab–UC15deTP. The combination of carbon isotope stratigraphy, strontium isotopes, and cyclostratigraphy allows a detailed chronostratigraphic correlation. Periodicity was obtained by power spectral analysis, sinusoidal regression, and Morlet wavelets. The duration of the calcarata Total Range Zone is calculated by orbital cyclicity expressed in thickness data of limestone–marl rhythmites and stable carbon isotope data. Precessional, obliquity, and short and long eccentricity cycles are identified and give an extent of c. 806kyr for the zone. Mean sediment accumulation rates are as low as 1.99cm/kyr and correspond well to sediment accumulation rates in similar settings. We further discuss chronostratigraphic implications of our data

Growth oscillation in larger foraminifera

This work shows the potential for applying three-dimensional biometry to studying cell growth in larger benthic foraminifera. The volume of each test chamber was measured from the three-dimensional model obtained by means of computed tomography. Analyses of cell growth based on the sequence of chamber volumes revealed constant and significant oscillations for all investigated specimens, characterized by periods of approximately 15, 30, 90, and 360 days. Possible explanations for these periods are connected to tides, lunar cycles, and seasonality. The potential to record environmental oscillations or fluctuations during the lifetime of larger foraminifera is pivotal for reconstructing short-term paleoenvironmental variations or for gaining insight into the influence of tides or tidal current on the shallow-water benthic fauna in both recent and fossil environments. \uc2\ua9 2014 The Paleontological Society

Lunar cycles and rainy seasons drive growth and reproduction in nummulitid foraminifera, important producers of carbonate buildups

Representatives of the foraminifer Nummulites are important in Earth history for timing Cenozoic shallow-water carbonates. Taphonomic complexity explains the construction of carbonate buildups, but reproduction and life span of the constructing individuals are unknown. During the 15-month investigation period, asexually reproduced schizonts and gamonts showed equal proportions in the first half of this period, whereas gamonts predominated in the second half. Oscillations in cell growth are mainly caused by light intensities during chamber construction when minor differences in water depth increase the photosynthetic rate of endosymbiotic diatoms during neap tides. The continuous reproduction rate of N. venosus throughout the year is increased in subtropical calms by higher summer temperatures and the marginal input of inorganic nutrients during rainy seasons. The expected life span of both gamonts and schizonts are 18 month

Growth Rate Biometric Quantification by X-ray Microtomography on Larger Benthic Foraminifera: Three-dimensional Measurements Push Nummulitids into the Fourth Dimension

This work demonstrates the potential of three-dimensional biometric quantification using microtomography on larger benthic foraminifera. We compare traditional linear and area measures used for calculating three-dimensional characters with actual 3D measurements made from volume images obtained using X-ray microtomography (microCT). Two specimens of recent larger benthic foraminifera, i.e., Palaeonummulites venosus and Operculina ammonoides, were imaged with a high-resolution microCT scanner. This method enables three-dimensional imaging and calculation of measurements like 3D distances, surfaces and volumes. The quantitative high-resolution images enabled the extraction of the lumina from the proloculus to the last complete scanned chamber and of the canal system spreading into marginal chord and septa. External surfaces and volumes were calculated on the extracted parts. These measurements allowed the calculation of porosity and microporosity to obtain the test density, which is the basis for many inferences about foraminifera, e.g., reconstructions of transport and deposition. Volume and surface measurements of the proloculus allow the calculation of sphericity deviation, which is useful for determining evolutionary trends in species based on individuals resulting from asexual reproduction (A forms). The three-dimensional data presented here show the actual growth of the foraminiferal cell and the development of the test. Measurements made on an equatorial section cannot be considered representative of a three-dimensional test, unless a correspondence between 2D data with 3D data shows significant correlation. Chamber height, septal distance, spiral growth and chamber area were measured on the equatorial section and correlated with the volume measurements from 3D images to determine the predictive value of the 1D and 2D measures for estimating the 3D morphological parameters. In particular, we show that the equatorial section area of chambers correlates significantly with the chamber volume and can be used to differentiate between nummulitid genera according to their different growth patterns. \uc2\ua9T\uc3\u9cB\uc4\ub0TAK

Growth of Heterostegina depressa under natural and laboratory conditions

The use of micro-computed tomography (\uce\ubcCT) provides a unique opportunity to look inside the shells of larger benthic foraminifera to investigate their structure by measuring linear and volumetric parameters. For this study, gamonts/schizonts and agamonts of the species Heterostegina depressa d'Orbigny were examined by \uce\ubcCT; each single chamber's volume was digitally measured. This approach enables cell growth to be recognised in terms of chamber volume sequence, which progressively increases until reproduction occurs. This sequence represents the ontogeny of the foraminiferal cell and has been used here to investigate controlling factors potentially affecting the process of chamber formation. This is manifested as instantaneous or periodic deviations of the realised chamber volumes derived from modelled growth functions. The results obtained on naturally grown specimens show oscillations in chamber volumes which can be modelled by sums of sinusoidal functions. A set of functions with similar periods in all investigated specimens points to lunar and tidal cycles.To determine whether such cyclic signals are genuine and not the effects of a theoretical model, the same analysis was conducted on specimens held in a closed laboratory facility, as they should not be affected by natural environmental effects. Surprisingly, similar cyclicities were observed in such samples. However, a solely genetic origin of these cycles couldn't be verified either. Therefore, detailed analysis on the phase equality of these growth oscillations have been done. This approach is pivotal for proving that the oscillatory patterns discovered in LBF are indeed genuine signals, and on how chamber growth might be influenced by tidal currents or lunar months

Morphological variations in Cycloclypeus carpenteri: Multiple embryos and multiple equatorial layers

In this work, 17 specimens of Cycloclypeus carpenteri have been analysed by means of microCT scanning. It has been observed that many specimens possess multiple embryos, multiple nepionts and some tests show more than one equatorial layer. The diameter of each proloculus has been measured, and it seems that they are very variable even within the same specimen, therefore questioning the long known theory that schizonts have smaller proloculi than gamonts and also questioning the fact that proloculi in the same species should all have comparable size. Whenever the nepionts are positioned on different planes, thus creating an angle between them, this angle has a significant correlation to the angle connecting different equatorial layers. T-shaped connections are located at the junction between two equatorial layers; these junctions are made by a chamberlet, which possesses an unusually higher number of apertures, resembling the chamberlet structure of the genus Spiroclypeus

Dissimilarity between living and dead benthic foraminiferal assemblages in the Aveiro Continental Shelf (Portugal)

This study compares living (LA) and dead (DA) benthic foraminiferal assemblages and identifies different factors that possibly cause differences in the distribution of both assemblages in the Aveiro Continental Shelf (Portugal). A total of 44 sediment samples was collected during summers of 1994 and 1995 along transects (east-west direction) and between 10 and 200 m water depth. Complex statistical analyses allow us to compare the abundance and composition of the LAs and DAs in function of depth, grain-size and total organic matter in all studied stations even in those where the numbers of individuals were rare in one or both assemblages. The highest densities and diversities of the LAs are found in the middle continental shelf on gravel deposits (coarse and very coarse sands) mostly due to the substrate stability, reduced deposition of fine sedimentary particles, availability of organic matter with high quality related to oceanic primary productivity likely induced by upwelling events, and oxygenated porewaters conditions. The DAs have, in general, higher densities and diversities than the LAs. In the outer continental shelf, the dissimilarity between both assemblages is higher due to the accumulation of tests, low dilution by sedimentary particles and scarcity of living foraminifera. Based on the comparison of LAs and DAs and considering the characteristics of the study area and the species ecology, it has been possible to understand the cause of temporal deviation between the LAs and DAs of benthic foraminifera. This deviation is much more pronounced in the inner shelf where the energy of the waves and the currents induce very dynamic sedimentary processes preventing the development of large LAs and the preservation of DAs. Some deviation also occurs in the middle shelf due to the seasonal loss of empty tests. The most well-preserved time-averaged DAs were found in the outer continental shelf.Universidade de Aveiro Fundação para a Ciência e a Tecnologia (FCT, Portugal) Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, CnPQ, Brazil 301588/2016-3info:eu-repo/semantics/publishedVersio