10 research outputs found
Fluid flow through the sedimentary cover in northern Switzerland recorded by calcite-celestite veins (Oftringen borehole, Olten)
Abundant veins filled by calcite, celestite and pyrite were found in the
core of a 719 m deep borehole drilled in Oftringen near Olten, located
in the north-western Molasse basin, close to the thrust of the Folded
Jura. Host rocks are calcareous marl, argillaceous limestone and
limestone of the Dogger and Malm. The delta O-18 values of vein calcite
are lower than in host rock carbonate and, together with
microthermometric data from fluid inclusions in vein calcite, indicate
precipitation from a seawater-dominated fluid at average temperatures of
56-68A degrees C. Such temperatures were reached at the time of maximum
burial of the sedimentary pile in the late Miocene. The depth profile of
delta C-13 and Sr-87/Sr-86 values and Sr content of both whole-rock
carbonate and vein calcite show marked trends towards negative delta
C-13, high Sr-87/Sr-86, and low Sr content in the uppermost 50-150 m of
the Jurassic profile (upper Oxfordian). The Sr-87/Sr-86 of vein minerals
is generally higher than that of host rock carbonate, up to very high
values corresponding to Burdigalian seawater (Upper Marine Molasse,
Miocene), which represents the last marine incursion in the region. No
evidence for internally derived radiogenic Sr (clay minerals) has been
found and so an external source is required. S and O isotope composition
of vein celestite and pyrite can be explained by bacterial reduction of
Miocene seawater sulphate. The available data set suggests the vein
mineralization precipitated from descending Burdigalian seawater and not
from a fluid originating in the underlying Triassic evaporites
The Palaeoproterozoic perturbation of the Global Carbon Cycle : the Lomagundi-Jatuli Isotopic Event
On Earth, carbon cycles through the land, ocean, atmosphere, living and dead biomass and the planet’s interior. The global carbon cycle can be divided into the tectonically driven geological cycle and the biological/physicochemical cycles. The former operates over millions of years, whereas the latter operate over much shorter time scales (days to thousands of years). Within the geological cycle, atmospheric carbon dioxide concentration is controlled by the balance between weathering, biological drawdown, size of sedimentary reservoir, subduction, metamorphism and volcanism over time periods of hundreds of millions of year
Trace element geochemistry as a tool for interpreting microbialites
Microbialites are critical for documenting early life on earth and-possibly elsewhere in the solar system. However, criteria for microbialite identification are controversial. Trace element geochemistry provides two types of information that aid interpretation of putative microbialites. Firstly, because most microbialites-consist of hydrogenous precipitates, trace elements can be used to investigate the fluids in which the structures formed, thus aiding identification of environments of formation. For example, rare earth elements preserved in microbialites have proven very useful in discriminating depositional environments. Secondly, microbes utilize and concentrate a wide range of elements, including many metals. Preservation of such elemental enrichments may provide a valuable biosignature. Although research in this field is relatively young, high precision, in situ measurement of metals in microbialites using techniques such as laser ablation-inductively coupled plasma-mass spectrometry, now with spatial mapping, have identified consistent enrichments in biologically important metals in microbialites. Hence, trace element studies are finding increasing utility in studying microbialites, and so long as diagenesis and the degree to which specific precipitates represent microenvironments are taken into account, trace element inventories may provide important information about depositional settings and, potentially, metabolic processes within biofilms