Reconstructing the accumulation history of a saltmarsh sediment core: Which age-depth model is best?

Abstract. The systematic bioturbation of single particles (such as foraminifera) within deep-sea sediment archives leads to the apparent smoothing of any temporal signal as record by the downcore, discrete-depth mean signal. This smoothing is the result of the systematic mixing of particles from a wide range of depositional ages into the same discrete depth interval. Previous sediment models that simulate bioturbation have specifically produced an output in the form of a downcore, discrete-depth mean signal. Palaeoceanographers analysing the distribution of single foraminifera specimens from sediment core intervals would be assisted by a model that specifically evaluates the effect of bioturbation upon single specimen populations. Taking advantage of recent increases in computer memory, the single-specimen SEdiment AccuMUlation Simulator (SEAMUS) was created in Matlab, whereby large arrays of single specimens are simulated. This simulation allows researchers to analyse the post-bioturbation age heterogeneity of single specimens contained within discrete-depth sediment core intervals, and how this heterogeneity is influenced by changes in sediment accumulation rate (SAR), bioturbation depth (BD) and species abundance. The simulation also assigns a realistic 14C activity to each specimen, by considering the dynamic Δ14C history of the Earth and temporal changes in reservoir age. This approach allows for the quantification of possible significant artefacts arising when 14C dating multi-specimen samples with heterogeneous 14C activity. Users may also assign additional desired carrier signals to specimens (e.g., stable isotopes, trace elements, temperature, etc.) and consider a second species with an independent abundance. Finally, the model can simulate a virtual palaeoceanographer by randomly picking whole specimens (whereby the user can set the percentage of older, broken specimens) of a prescribed sample size from discrete depths, after which virtual laboratory 14C dating and 14C calibration is carried out within the model.

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Sediment core fossils in ancient Lake Ohrid: testing for faunal change in molluscs since the Last Interglacial period

Biogeosciences Discussions ◽

10.5194/bgd-7-3969-2010 ◽

2010 ◽

Vol 7 (3) ◽

pp. 3969-3999 ◽

Cited By ~ 3

Author(s):

C. Albrecht ◽

H. Vogel ◽

T. Hauffe ◽

T. Wilke

Keyword(s):

Sediment Core ◽

Fossil Record ◽

Interglacial Period ◽

Ancient Lake ◽

Last Interglacial ◽

Lake Ohrid ◽

Last Interglacial Period ◽

History Of ◽

Extinction Events ◽

Mollusc Shells

Abstract. Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harboring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130±28 ka. Lithofacies III sediments, i.e. a subdivision of the stratigraphic unit comprising the basal succession of core Co1200 between 181.5–263 cm appeared solid, grayish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO3>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated. The agreement between sediment and palaeontological proxies was tested. The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial period. We tested for major faunal changes since the Last Interglacial period and searched for signs of extinction events. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5–25 m) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future deep drilling projects. It can be hoped that a more far reaching mollusc fossil record will then be obtained, enabling insight into the early evolutionary history of Lake Ohrid.

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Penguin occupation in the Vestfold Hills

Antarctic Science ◽

10.1017/s095410200800165x ◽

2008 ◽

Vol 21 (2) ◽

pp. 131-134 ◽

Cited By ~ 11

Author(s):

Tao Huang ◽

Liguang Sun ◽

Yuhong Wang ◽

Renbin Zhu

Keyword(s):

Sediment Core ◽

Environmental Changes ◽

Sediment Cores ◽

East Antarctica ◽

Before Present ◽

The Holocene ◽

History Of ◽

Vestfold Hills ◽

Free Area ◽

Ornithogenic Sediment

AbstractDuring CHINARE-22 (December 2005–March 2006), we investigated six penguin colonies in the Vestfold Hills, East Antarctica, and collected several penguin ornithogenic sediment cores, samples of fresh guano and modern penguin bone and feather. We selected seven penguin bones and feathers and six sediments from the longest sediment core and performed AMS14C dating. The results indicate that penguins occupied the Vestfold Hills as early as 8500 calibrated years before present (cal. yrbp), following local deglaciation and the formation of the ice free area. This is the first report on the Holocene history of penguins in the Vestfold Hills. As in other areas of Antarctica, penguins occupied this area as soon as local ice retreated and the ice free area formed, and they are very sensitive to climatic and environmental changes. This work provides the foundation for understanding the history of penguins occupation in Vestfold Hills, East Antarctica.

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Chronology and dust mass accumulation history of the Wenchuan loess on eastern Tibetan Plateau since the last glacial

Aeolian Research ◽

10.1016/j.aeolia.2021.100748 ◽

2021 ◽

Vol 53 ◽

pp. 100748

Author(s):

Li Liu ◽

Shengli Yang ◽

Ting Cheng ◽

Xiaojing Liu ◽

Yuanlong Luo ◽

...

Keyword(s):

Tibetan Plateau ◽

Eastern Tibetan Plateau ◽

Last Glacial ◽

Dust Mass ◽

History Of ◽

Mass Accumulation ◽

The Last Glacial ◽

Accumulation History

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Petroleum accumulation history of Nanbaxian belt — Study of gas generation and fluid phase, northern margin of Qaidam Basin, West of China

Journal of Petroleum Science and Engineering ◽

10.1016/j.petrol.2019.03.060 ◽

2019 ◽

Vol 178 ◽

pp. 449-458 ◽

Cited By ~ 1

Author(s):

Deliang Fu ◽

Shixin Zhou ◽

Yu Ma ◽

Jing Li ◽

Guosheng Xu ◽

...

Keyword(s):

Qaidam Basin ◽

Fluid Phase ◽

Gas Generation ◽

Northern Margin ◽

History Of ◽

Petroleum Accumulation ◽

Accumulation History

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Accumulation History of Uranium in Boulders - New Support for Postglacial Matrix Diffusion

MRS Proceedings ◽

10.1557/proc-506-1073 ◽

1997 ◽

Vol 506 ◽

Author(s):

Kari Rasilainen ◽

Juhani Suksi ◽

Antero Lindberg

Keyword(s):

Time Scale ◽

Early Stage ◽

Matrix Diffusion ◽

Natural Analogue ◽

Land Uplift ◽

Decay Stage ◽

History Of ◽

End Stage ◽

Chain Decay ◽

Accumulation History

Extended AbstractGeological formations are being considered as host media for nuclear waste disposal. The occurrence of natural U in rocks provides a possibility to test the radionuclide migration models used in safety studies of the disposal over comparable time periods. Here we study U accumulation into boulders as a process analogue for matrix diffusion; the boulders were found in glacial till in Hämeenlinna, southern Finland. Based on the glacial history of the site, matrix diffusion simulations, and independent U-series disequilibria (USD) dating, the U accumulation was interpreted to originate from the end stage of the latest glaciation, i.e. the system age is about 10 000 years1,2. The known time scale offers a rare opportunity for quantitative model testing; normally the time scale is difficult to determine for a single process in a natural analogue.The U accumulation was earlier1,2 interpreted to be due to matrix diffusion and sorption. The postulated accumulation history consists of short in-diffusion and out-diffusion stages, as well as a longer chain decay stage. The in-diffusion was caused by U-rich waters discharging on the boulders at the end stage of the glaciation. The subsequent partial out-diffusion represents the period the boulders were temporarily submerged in the Yoldia sea during the early stage of the Baltic Sea. The final isolated radioactive chain decay stage began when the boulders, and their surroundings, rose above the sea level due to land uplift.In this paper we report the first radiochemical results of a new larger boulder from the same area as the one studied earlier1; qualitatively, also the U distribution appears to be the same. Due to the larger dimensions, we can sample the inner zone of the boulder which matrix diffusion can not have reached within the postulated time, i.e. the state of the boulder before the U accumulation. The large amount of sample material containing almost only the recently accumulated U provides an opportunity to experimentally approach the kinetics of U fixation in situ. Understanding the long-term U fixation is essential in natural analogue studies, because the matrix diffusion model only has fast reversible adsorption (based on Kd) as the fixation process. Attempts to separate and quantify sorbed U in natural analogues have been reported elsewhere3.

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