U-Th stratigraphy of a cold seep carbonate crust

摘要: On continental margins, oxidation of methane-rich fluids from the sediment often leads to formation authigenic carbonate pavements on seafloor. The biogeochemical processes involved during this precipitation are increasingly understood, but little is known about duration or mode crust formation. Here, we report uranium and thorium concentrations isotope compositions for a set 14 samples drilled across an pavement, which provide first stratigraphy cold-seep crust. 5.5-cm thick (NL7-CC2) was collected by submersible Nile deep-sea fan in area active fluid venting. U-Th analyses must be corrected initial Th measurement co-existing sediments indicates presence both scavenged detrital 230Th, considered correction. calculated 230Th/U age-depth profile NL7-CC2 provides evidence continuous downward at studied location over last ~ 5000 years. Three distinct phases can distinguished top bottom with average growth rates 0.4, 5 0.8 cm/kyr, respectively, corresponding ranging 7 92 µmol m2 h− 1 (rates consistent previous estimates). High-resolution δ13C profiles [Gontharet, S., Pierre, C., Blanc-Valleron, M.-M., Rouchy, J.M., Fouquet, Y., Bayon, G., Foucher, J.P., Woodside, J., Mascle, Nautinil Scientific Party, 2007. Nature origin diagenetic crusts concretions mud volcanoes pockmarks (eastern Mediterranean Sea). Deep Sea Res. II 54, 1292-1311] major elements show that variations were also accompanied changes mineralogy composition. We suggest these primarily reflect modification environment, i.e. progressive depletion dissolved sulphate through anaerobic methane, caused resulting reduction bioirrigation. Overall, dating cold seep carbonates offers promising tool bring new insights into seeps assess timing venting margins.