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In the examined part of central Poland, there are numerous kettle-hole basins filled with mineral and biogenic sediments of the Eemian Interglacial and Early Weichselian. These basins are located in varied geological and geomorphological locations with variable thicknesses of the sediments and deposits. The infillings were investigated by lithological and palaeobotanic methods. Lithology of the biogenic sediments is diverse, primarily gyttja and peat, but also organic silt. A number of the documented sites contain a record of environmental changes throughout the glacial-interglacial cycle from the end of the Warta Stadial (Saalian) to Early Weichselian. Local geological, geomorphological and hydrological conditions influenced the possibility of continuous peat-lake accumulation and the timing of the completion of this accumulation. Biogenic sediments are covered with the Middle and Late Weichselian mineral sediments which indicate climatic changes and are the main reason for rapid and synchronic degradation of kettle-hole infillings.

The diversity of origins of peatland basins in Central Poland allowed the peatlands to be distinguished by location (in valleys or upland mires) and by the processes forming their basins (e.g. glacigenic, aeolian, fluvial or thermokarst processes). Peats prevail in the structure of the sediments in the analysed basins of peatlands; among them the most predominant are fens, whereas the amount of raised bogs is low. In parts of the analysed objects there are lake sediments, which usually form the bottom sections of the profiles of the biogenic sediments, and were usually deposited in the Late Vistulian. In the Holocene, peat series were accumulated. In the examined peatlands located on morainic uplands, lacustrine sediments of the Late Vistulian and Early Holocene covered by Late Holocene peats are documented. Peatlands located near aeolian forms do not show evidence of continuous accumulation of biogenic deposits. They are particularly sensitive to changes in humidity and they underwent frequent modifications during phases of aeolian activity. The sediments of valley peatlands are not suitable objects for stratigraphic analyses, but they are appropriate for reconstructions of short events that occurred in the river valleys.

This research is focused on a small kettle hole located within the Morąg moraines (Ilawa Lake District, NE Poland). The study objective was to determine the impact of palaeoenvironmental changes in sedimentation and properties of sediments filling the bottom of the kettle hole. Sedimentological, geochemical, and palaeobotanical studies enabled us to distinguish several development phases of the kettle hole, and cluster analysis performed on physicochemical data yielded seven local geochemical zones (Ju I/I to Ju I/VII ). The beginning of biogenic sedimentation in the conditions of a small water body, functioning in the Late Glacial period (4.20–4.10 m), was determined on the basis of palaeobotanical research. Sediments deposited in the lake during its further evolution were rich in microelements such as Ca, Na, Mg, and K, and to a smaller extent – Fe and Mn (Ju I/I–III local geochemical zones). The Late Glacial lacustrine period ended with the accumulation of very silty, pollen-free gyttja, with a stratigraphic hiatus (Ju I/IV , 3.40–3.20 m). The sediments were enriched with SiO2ter, which indicates an increased rate of slope erosion, and concretions of Fe-Mn occurring below this layer (Ju III ) provide evidence for lowering of the water level and even desiccation. In the Holocene, the lacustrine period ended with the accumulation of coarse detrital gyttja (3.20–2.60 m). Palaeobotanical data indicate that the next group of sediments were deposited in the Late Subboreal and Subatlantic periods (2.60–0.0 cm, Ju I/V–VII ; sedge peat). Their properties were varied and related to hydrologic conditions, limited denudation, and vegetation succession. There was also a significant change in the trophic conditions of the water and consequently in the sediments of the kettle hole, which changed during the lacustrine period from basic to acid, and strongly acid in the surface layer. This reaction may be related to a change in the water regime as well as to human impact in the environment, which led to the colonization of the peat bog by Sphagnum moss.

The first building blocks of life could be produced in ultramafic-hosted hydrothermal systems considering the large amounts of hydrogen and methane generated by serpentinisation and Fischer-Tropsch-Type synthesis, respectively, in those systems. The purpose of this study was to detect and characterise organic molecules in hydrothermal fluids from ultramafic-hosted hydrothermal systems in the Mid-Atlantic Ridge (MAR) region. During the EXOMAR cruise 2005, fluids from the Rainbow (36 degrees 14'N) and the Lost City (30 degrees N) hydrothermal fields were collected and treated by Stir Bar Sorptive Extraction (SBSE) and Solid Phase Extraction (SPE). The extracts were analysed by Thermal Desorption-Gas Chromatography-Mass Spectrometry (TD-GC-MS) and GC-MS, respectively. Compared to nearby deep seawater, hydrothermal fluids were clearly enriched in organic compounds, with a more diverse spectrum of molecules. We observed a very similar range of organic compounds in fluids from both sites, with a dominance of aliphatic hydrocarbons (C9-C14), aromatic compounds (C6-C16) and carboxylic acids (C8-C18). The occurrence of these compounds is supported by other field studies on serpentinites and sulfide deposits. Literature on thermodynamic data and experimental work has suggested the possible abiogenic origin of hydrocarbons and organic acids. In addition, it has been shown elsewhere that catalytic reactions producing hydrocarbons likely occur at both Lost City and Rainbow hydrothermal fields as suggested by the evolution of delta C-13 with increasing C number for methane, ethane, propane and butane. In order to investigate the origin of the organic molecules in the fluids, compound-specific carbon isotope ratio measurements were performed on n-alkanes and carboxylic acids, for which the delta C-13 values were in the range of -46 to -20 parts per thousand (vs. V-PDB). These preliminary data did not allow conclusive support or rejection of an abiogenic origin of the compounds. Indeed, predicting delta C-13 signatures in hydrothermal systems is likely to be complicated, due to differences in source delta C-13 signatures (i.e., of the C building blocks), and a variety of, mostly unknown. fractionation steps which may occur along the synthesis pathways. in addition, even though a fraction of the compounds detected in the fluids is likely abiotically produced, a dominance of biogenic sources and/or processes might hide their characteristic signature. (C) 2008 Elsevier B.V. All rights reserved. ispartof: Chemical geology vol:258 issue:3 pages:299-314 status: published

We studied the seasonal exchange of biogenic silica and dissolved silica between a freshwater and a saltwater tidal marsh and the nearby coastal waters. From both tidal marshes export of dissolved Si (DSi) was observed, while concurrently biogenic Si (BSi) was imported along with suspended solids. The export of DSi was highest (23.4 % and 123.8 % in the freshwater and saltwater marsh respectively) in summer when dissolved Si concentrations were low in the nearby coastal waters. Combined data from both marshes suggested a logarithmic decrease in DSi export with increasing DSi concentrations in the inundating waters. BSi import was observed year round in the freshwater marsh, but only in summer in the saltwater marsh. The results show that dissolved silica recycling from tidal marshes, both freshwater and saltwater, contributes significantly to estuarine Si availability in summer and provide new insight in the link between tidal marshes and secondary production in nearby coastal waters.