Kennedy, E.M.; Alloway, B.V. 2004 Paleoclimate assessment, paleobotany and stratigraphy of a mid-Pleistocene lacustrine section, Ormond Valley, Gisborne . Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 2004/13 32 p.
Abstract: Fossil leaf assemblages retrieved from lake deposits in the Ormond Valley near Gisborne were investigated for paleoclimate methods assessment. A new collection of plant, fish and bivalve impressions was made. Richly fossiliferous horizons, from which earlier collections were made in the early 1900s, were not relocated during this study. The new leaf collections had insufficient diversity for quantitative paleoclimate analysis. In their place, preliminary paleoclimate analyses were undertaken on the existing collections studied by Oliver in the late 1920’s. Two different methods (Leaf Margin Analysis and CLAMP) were used and there were significant discrepancies between the resulting temperature estimates. Leaf Margin Analysis produced higher temperature estimates than the multivariate method CLAMP, which indicated a cool temperate climate. These data mirror discrepancies observed from analyses of modern New Zealand vegetation. However, because these data are from existing leaf collections of low diversity, the paleoclimate estimates reported here must be considered with some caution. The Ormond Valley sections are interbedded by seventeen silicic tephra layers and five thin silicic hyperconcentrated flow (hcf) deposits. These interbeds have been geochemically characterised and confirm a Taupo Volcanic Zone (TVZ) source. One tephra layer (OVRd-T1) can be correlated on the basis of its glass chemistry to an equivalent ODP-tephra layer within the marine record that has an astronomically-tuned age of 0.71 Ma. Further isothermal plateau fission-track dating on three Ormond Valley tephra beds is underway and will provide direct age control that allows for comparison with the marine paleoclimate record and enable more conclusive paleoclimate inferences to be made based on these terrestrial data. (auth)