Microfossils and geochemistry of some modern, Holocene and Pleistocene travertines from North Yorkshire and Derbyshire

The geochemistry of some modern, Holocene (4-4.5 ka) and Pleistocene (>100 ka) travertines from the UK is described. Four facies were recognized: one bryophyte, two algal and one clastic. In the Holocene travertine, from Gordale, Yorkshire, concentrations of Fe, Mn, Sr, Zn and the travertine porosity showed significant differences between facies that were related to the content of acid-insoluble residues and differences in meteoric diagenesis. The modern active travertines, also from Gordale, similarly showed significant geochemical differences between facies types. All geochemical determinants in the modern travertines were higher by a factor of about two compared with the Holocene travertine. This is believed to be due to increased catchment erosion over the past few centuries and travertine deposits may therefore provide information on rates of soil erosion. The stable isotopic compositions of the travertine averaged -5.9 ppm for delta (super 18) O and -9.6 ppm for delta (super 13) C, but there were no significant differences between the facies. Seventeen diatom taxa were found in the Holocene deposits but numbers were low when compared with the modern deposits, which were higher by a factor of about 1000. Dissolution of diatoms after burial would be sufficient to account for all of the authigenic quartz observed in these deposits. Four classes of organic matter were identified in the Holocene and Pleistocene samples: filaments, perforated plates, spores and amorphous forms. Their abundance differed little between facies. Some of the filamentous structures were probably post-depositional fungal hyphae utilizing carbon resources within the deposits.