Evidence of high Sr/Ca in a Middle Jurassic murolith coccolith species.

International audiencePaleoceanographical reconstructions are often based on microfossil geochemical analyses. Coccoliths are the most ancient, abundant and continuous record of pelagic photic zone calcite producer organisms. Hence, they could be valuable substrates for geochemically based paleoenvironmental reconstructions but only Sr/Ca is exploited even if it remains poorly understood. For example, some murolith coccoliths species have very high Sr/Ca compared to the common 1-4 mmol/mol recorded in placolith coccoliths. In this study, we analyzed the elemental composition of the Middle Jurassic murolith Crepidolithus crassus by synchrotron-based nanoXRF (X-ray Fluorescence Spectroscopy) mapping focusing on Sr/Ca and compared the record to two placolith species, namely Watznaueria contracta and Discorhabdus striatus. InC. crassus, Sr/Ca is more than ten times higher than in both placoliths and seems higher in the proximal cycle. By comparison with the placoliths analyzed in the same analytical setup and from the same sample, we exclude the impact of the diagenesis and seawater Sr/Ca to explain the high Sr/Ca in C. crassus. Based on comparisons to Pontosphaera discopora and Scyphosphaera apsteinii which also have high Sr/Ca, it seems more likely that high Sr/Ca in C. crassus is either due to the vertical elongation of the R-units of the proximal cycle or related to the action of the special polysaccharide controlling the growth of those vertically elongated R-units that may have affinities to Sr2+. In order to apply the Sr/Ca proxy to muroliths, further investigations are needed on cultured coccoliths

NanoXRF elemental mapping of Middle Jurassic (~-170Ma) coccoliths

International audienceCoccolithophores algae produce micrometric calcite platelets called coccoliths. Coccoliths geological record is continuous from their appearance 220 Ma ago until today and are found in abundant marine environment in this time interval. Hence, coccoliths have huge potential for geochemical reconstruction of paleoclimate and paleoceanography through time. We have performed nanometric XRF analysis on 3 species of Early Bajocian (Middle Jurassic) coccoliths at European Synchrotron Radiation Facility (ESRF) on the beamline ID22NI, Grenoble, France. Based on this analysis, we endeavor to have a better understanding of the chemical composition of coccoliths and thus of marine waters where they were precipitated. Samples have been collected at Cabo Mondego, Portugal, the international reference section (GSSP) for the Early Bajocian interval and they were selected based on their preservation. Beforehand, coccoliths were separated from the matrix using a picking technique and deposited on 500 nm-thick silicon nitride membranes. With an excitation beam at 17 KeV and a resolution of 100 m, we have mapped 14 elements in coccoliths, i.e., S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb and Sr. The mapping allows the recognition of biological incorporation of elements from the diagenetic overprint. Calcium, Strontium and Manganese are biologically organized in coccoliths. Sulfur, Chlorine, Chromium, and Bromine are also homogenously incorporated without relation with the crystallographic organization of the coccolith. Conversely, Potassium, Iron, Copper, Zinc, Titanium and Rubidium are related to diagenetic processes and clays contamination. These results will (1) help in a better understanding of the chemical incorporation of elements, and (2) in the recognition of diagenetic effects on coccoliths chemistry, and finally (3) develop new paleoceanographic proxies, e.g. the Chlorine and Bromine incorporation in coccoliths for salinity reconstructions. Further analysis especially on living species will greatly help in the calibration of such a proxy

NanoXRF cartography of Middle Jurassic (~-170 Ma) coccoliths

International audienceCoccolithophores, golden-brown algae, produce micrometric calcite platelets called coccoliths. Coccoliths geological record is continuous from their appearance 220 Ma ago until today. Hence, coccoliths have huge potential for geochemical reconstruction of paleoclimate and paleoceanography through time. We have performed sub-micrometric XRF analysis on 3 species of Early Bajocian (Middle Jurassic) coccoliths at European Synchrotron Radiation Facility (ESRF) on the beamline ID22NI, Grenoble, France. Based on this analysis, which had never been applied on coccoliths before, we endeavor to have a better understanding of the chemical composition of coccoliths and thus of marine waters where they were precipitated. Samples have been collected at Cabo Mondego, Portugal, the international reference section (GSSP) for the Early Bajocian interval and they were selected based on their preservation. Beforehand, coccoliths were separated from the matrix using a picking technique and deposited on 500 nm-thick silicon nitride membranes. With an excitation beam at 17 KeV and a resolution of 100 m, we have mapped 14 elements in coccoliths, i.e., S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb and Sr. The mapping allows the recognition of biological incorporation of elements from the diagenetic overprint. Calcium, Strontium and Manganese are biologically organized in coccoliths. Sulfur, Chlorine, Chromium, and Bromine are also incorporated in coccoliths without suffering any diagenetic process. Conversely, Potassium, Iron, Copper, Zinc, Titanium and Rubidium are related to diagenetic processes and clays contamination.These results, namely the first record of sub-micrometric chemical organization documented for coccoliths, will (1) help in a better understanding of the chemical incorporation of elements, and (2) in the recognition of diagenetic effects on coccoliths chemistry, and finally (3) develop new paleoceanographic proxies, e.g. the Chlorine and Bromine incorporation in coccoliths for salinity reconstructions. Further analysis especially on living species will greatly help in the calibration of such a proxy

NanoXRF cartography of Middle Jurassic (~-170 Ma) coccoliths

International audienceCoccolithophores, golden-brown algae, produce micrometric calcite platelets called coccoliths. Coccoliths geological record is continuous from their appearance 220 Ma ago until today. Hence, coccoliths have huge potential for geochemical reconstruction of paleoclimate and paleoceanography through time. We have performed sub-micrometric XRF analysis on 3 species of Early Bajocian (Middle Jurassic) coccoliths at European Synchrotron Radiation Facility (ESRF) on the beamline ID22NI, Grenoble, France. Based on this analysis, which had never been applied on coccoliths before, we endeavor to have a better understanding of the chemical composition of coccoliths and thus of marine waters where they were precipitated. Samples have been collected at Cabo Mondego, Portugal, the international reference section (GSSP) for the Early Bajocian interval and they were selected based on their preservation. Beforehand, coccoliths were separated from the matrix using a picking technique and deposited on 500 nm-thick silicon nitride membranes. With an excitation beam at 17 KeV and a resolution of 100 m, we have mapped 14 elements in coccoliths, i.e., S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb and Sr. The mapping allows the recognition of biological incorporation of elements from the diagenetic overprint. Calcium, Strontium and Manganese are biologically organized in coccoliths. Sulfur, Chlorine, Chromium, and Bromine are also incorporated in coccoliths without suffering any diagenetic process. Conversely, Potassium, Iron, Copper, Zinc, Titanium and Rubidium are related to diagenetic processes and clays contamination.These results, namely the first record of sub-micrometric chemical organization documented for coccoliths, will (1) help in a better understanding of the chemical incorporation of elements, and (2) in the recognition of diagenetic effects on coccoliths chemistry, and finally (3) develop new paleoceanographic proxies, e.g. the Chlorine and Bromine incorporation in coccoliths for salinity reconstructions. Further analysis especially on living species will greatly help in the calibration of such a proxy

NanoXRF elemental mapping of Middle Jurassic (~-170Ma) coccoliths

International audienceCoccolithophores algae produce micrometric calcite platelets called coccoliths. Coccoliths geological record is continuous from their appearance 220 Ma ago until today and are found in abundant marine environment in this time interval. Hence, coccoliths have huge potential for geochemical reconstruction of paleoclimate and paleoceanography through time. We have performed nanometric XRF analysis on 3 species of Early Bajocian (Middle Jurassic) coccoliths at European Synchrotron Radiation Facility (ESRF) on the beamline ID22NI, Grenoble, France. Based on this analysis, we endeavor to have a better understanding of the chemical composition of coccoliths and thus of marine waters where they were precipitated. Samples have been collected at Cabo Mondego, Portugal, the international reference section (GSSP) for the Early Bajocian interval and they were selected based on their preservation. Beforehand, coccoliths were separated from the matrix using a picking technique and deposited on 500 nm-thick silicon nitride membranes. With an excitation beam at 17 KeV and a resolution of 100 m, we have mapped 14 elements in coccoliths, i.e., S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb and Sr. The mapping allows the recognition of biological incorporation of elements from the diagenetic overprint. Calcium, Strontium and Manganese are biologically organized in coccoliths. Sulfur, Chlorine, Chromium, and Bromine are also homogenously incorporated without relation with the crystallographic organization of the coccolith. Conversely, Potassium, Iron, Copper, Zinc, Titanium and Rubidium are related to diagenetic processes and clays contamination. These results will (1) help in a better understanding of the chemical incorporation of elements, and (2) in the recognition of diagenetic effects on coccoliths chemistry, and finally (3) develop new paleoceanographic proxies, e.g. the Chlorine and Bromine incorporation in coccoliths for salinity reconstructions. Further analysis especially on living species will greatly help in the calibration of such a proxy

NanoXRF cartography of Middle Jurassic (~-170 Ma) coccoliths

International audienceCoccolithophores, golden-brown algae, produce micrometric calcite platelets called coccoliths. Coccoliths geological record is continuous from their appearance 220 Ma ago until today. Hence, coccoliths have huge potential for geochemical reconstruction of paleoclimate and paleoceanography through time. We have performed sub-micrometric XRF analysis on 3 species of Early Bajocian (Middle Jurassic) coccoliths at European Synchrotron Radiation Facility (ESRF) on the beamline ID22NI, Grenoble, France. Based on this analysis, which had never been applied on coccoliths before, we endeavor to have a better understanding of the chemical composition of coccoliths and thus of marine waters where they were precipitated. Samples have been collected at Cabo Mondego, Portugal, the international reference section (GSSP) for the Early Bajocian interval and they were selected based on their preservation. Beforehand, coccoliths were separated from the matrix using a picking technique and deposited on 500 nm-thick silicon nitride membranes. With an excitation beam at 17 KeV and a resolution of 100 m, we have mapped 14 elements in coccoliths, i.e., S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Br, Rb and Sr. The mapping allows the recognition of biological incorporation of elements from the diagenetic overprint. Calcium, Strontium and Manganese are biologically organized in coccoliths. Sulfur, Chlorine, Chromium, and Bromine are also incorporated in coccoliths without suffering any diagenetic process. Conversely, Potassium, Iron, Copper, Zinc, Titanium and Rubidium are related to diagenetic processes and clays contamination.These results, namely the first record of sub-micrometric chemical organization documented for coccoliths, will (1) help in a better understanding of the chemical incorporation of elements, and (2) in the recognition of diagenetic effects on coccoliths chemistry, and finally (3) develop new paleoceanographic proxies, e.g. the Chlorine and Bromine incorporation in coccoliths for salinity reconstructions. Further analysis especially on living species will greatly help in the calibration of such a proxy