Alan S. Palmer

Soil quality and financial performance of biodynamic and conventional farms in new zealand.

Biodynamic farming practices and systems show promise in mitigating some of the detrimental effects of chemical-dependent, conventional agriculture on the environment. The physical, biological, and chemical soil properties and economic profitability of adjacent, commercial biodynamic and conventional farms (16 total) in New Zealand were compared. The biodynamic farms in the study had better soil quality than the neighboring conventional farms and were just as financially viable on a per hectare basis.

The last glacial maximum in central and southern North Island, New Zealand: a paleoenvironmental reconstruction using the Kawakawa Tephra Formation as a chronostratigraphic marker

Abstract Kawakawa Tephra Formation, comprising Oruanui Ignimbrite flow member and Aokautere Ash airfall member, represents the products of an exceptionally large and widespread volcanic eruption from Taupo Volcanic Centre in the North Island of New Zealand. The eruption occurred during the Last Glacial Maximum, and is radiocarbon dated at c. 22.6 ka B.P. Thermoluminescence ages are in broad agreement with the radiocarbon age. The presence of Aokautere Ash in loess deposits, in alluvial gully-fills, on river terraces, and its absence from unstable sites, permits a detailed assessment of geomorphic activity during the Last Glacial Maximum. Widespread erosion of regolith, aggradation of river valleys, and deposition of loess, particularly in the period following eruption of the Kawakawa, point to a cold, dry, variable climate. A collation of pollen data for sediments containing Aokautere Ash, and those 14C dated in the range 17–23 ka, shows that tall forest was highly restricted in the central and southern parts of the North Island. An apparently subalpine grassland/shrubland was present at sites from present sea level to over 800 m elevation, suggesting that factors other than lower temperatures, such as exposure to wind and frost, fire and reduced rainfall, were important in controlling vegetation patterns. We conclude that the interval 23-13 ka B.P., broadly equivalent to oxygen isotope stage 2, represents the period of greatest environmental change in the North Island.

Dating loess up to 800 ka by thermoluminescence

Thermoluminescence (TL) ages agreeing with expected ages have been obtained for 13 loess samples spanning the age range from 20 to 800 ka. Our samples are from Alaska and North Island, New Zealand, and are unusual in TL dating studies of loess older than 80-100 ka by having independent age assignments that are generally well constrained, from ages of associated tephra beds. With the polymineral fine-silt-sized (4-11 μm) grains, the partial-bleach TL technique yielded expected ages up to about 350 ka, whereas the total-bleach method gave accurate ages in the range 100 to 800 ka. Thus, the much disputed upper age limit of 100-150 ka for the TL dating of loess now appears to be sample and worker dependent, rather than a global property of the TL signals in the TL-dominant feldspars.

Changes in Whangaehu river lahar characteristics during the 1995 eruption sequence, Ruapehu volcano, New Zealand

Abstract During the 1995 Ruapehu eruptive sequence multiple lahars occurred in the Whangaehu river, which drains Ruapehus Crater Lake. During the earlier phreatic and phreatomagmatic eruptions, lahars were generated by expulsion of waters from the Lake, but once the lake had emptied, lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra. Four types of lahars occurred during the eruptive sequence: (1) Initial snow-slurry lahars, composed of granular snow and ice incorporated by eruptively expelled Crater Lake waters which left behind frozen deposits with 2.5–20% clastic sediment. (2) Large dilute lahars, generated as the volumes of ejected lake water increased and removed much of the readily available snow. At least one third of the pre-eruption Crater Lake volume was expelled during one day producing the largest lahars of the series. These lahars were hyperconcentrated flows for up to 84 km from source, leaving extensive deposits along the channel margins. (3) Concentrated lahars; smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined. These lahars were able to maintain high sediment concentrations, measured at 46–52% by volume suspended sediment at 42 km from source. Their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins. (4) Remobilised tephra lahars, generated following the two largest tephra eruptions of the sequence. Seasonal snowpack was covered by water-saturated tephra. Warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra, producing several lahars in catchments draining eastern Ruapehu.

Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand

A stratigraphy and chronology of andesitic tephras erupted from Mt Ruapehu, and other volcanoes of Tongariro Volcanic Centre, is constructed from the tephra record preserved on the southeastern Mt Ruapehu ring plain. Here, tephras of late Quaternary age (c. 22,500 years B.P. to present) are found interbedded with local laharic and fluvial deposits, and with distal rhyolitic tephras from Taupo and Okataina Volcanic Centres. Tephras are identified from their field characteristics and stratigraphic positions relative to dated rhyolitic tephra marker beds. The radiocarbon ages of these rhyolitic tephras provide a chronology for the andesitic tephras, dating back to 22,500 years B.P. All tephras erupted from Tongariro Volcanic Centre are grouped into two subgroups: the Tongariro Subgroup (redefined) and the newly defined Tukino Subgroup. Tephras identified on the southeastern Mt Ruapehu ring plain are grouped into seven formations on the basis of lithology: Ngauruhoe Formation [dated c. 1,850 years B.P. ‐ pres...

El Niño–Southern Oscillation signal associated with middle Holocene climate change in intercorrelated terrestrial and marine sediment cores, North Island, New Zealand

A synchronous textural variation in intercorrelated, high-resolution sediment records from floodplain, continental-shelf, and continental-slope settings of the eastern North Island, New Zealand, provides evidence of increased storminess after ca. 4 ka. An upcore change in sediment texture reflects the transition to landsliding, which supplanted fluvial incision as the dominant mode of sediment production in the middle Holocene. This signal, which appears in all three records, indicates a regional response to external forcing and records the impact of an intensified atmospheric circulation marking the establishment of the contemporary climate that is strongly influenced by the El Nino–Southern Oscillation. The change in climate was a hemispheric event, and in the Southern Hemisphere its timing is confirmed by independent proxy records from elsewhere in New Zealand and the circum–South Pacific region.

Dating the culmination of river aggradation at the end of the last glaciation using distal tephra compositions, eastern North Island, New Zealand

An extensive terrace (Waipaoa-1) that can be traced for about 29 km in the Waipaoa valley, eastern North Island, New Zealand, is underlain by at least 10 m of coarse, aggradational, river gravels. Terrace cover beds contain tephras erupted from central North Island volcanoes and these provide minimum ages for the underlying gravels. Tephra or tephric layers occurring in the lower cover beds were investigated at five sites using a combination of stratigraphy, mineralogy, and the major element composition of glass shards together with discriminant function analysis (DFA). The basal tephra is identified as the ca. 14,700 14C years old (ca. 17,700 cal. years B.P.) Rerewhakaaitu Tephra, erupted from Okataina Volcanic Centre. Using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca. 15,000 14C years (ca. 18,000 cal. years). Correlation with aggradational terraces elsewhere in North Island and northern South Island indicates that aggradation ended at the same time over a wide area and confirms a climatic origin for the terraces. Subsequent downcutting was apparently rapid because Rerewhakaaitu Tephra also occurs at the base of cover beds on a ca. 15 m lower terrace. The downcutting represents a major change in river dynamics and is most likely the response to climatic change and the resultant upper catchment landscape stability.

Silicic tephras in Pleistocene shallow‐marine sediments of Wanganui Basin, New Zealand

Abstract Vitric‐rich volcaniclastic horizons are important for correlation of glacio‐eustatic sedimentary cycles, both within the well known shallow‐marine record of Wanganui Basin, and other New Zealand terrestrial and deep marine records. They also record distal major rhyolitic eruptions from the Taupo (TVZ) and Coromandel (CVZ) Volcanic Zones that are lacking in proximal source areas. Twenty‐eight volcaniclastic horizons are recognised in the Castlecliffian and late Nukumaruan strata of Wanganui Basin from glass shard major element geochemistry and stratigraphic position, and are dated using magnetostratigraphy, orbitally tuned cyclostratigraphy and isothermal plateau fission track (ITPFT) ages. The major named volcaniclastic horizons (with ITPFT and/or astronomical ages, respectively) are: Onepuhi (0.57 Ma), Kupe (0.63 ± 0.08 Ma; 0.65 Ma), Kaukatea (0.86 ± 0.08 Ma; 0.90 Ma), Potaka (1.00 ± 0.03 Ma; 0.99 Ma), Rewa (1.20 ± 0.14 Ma; 1.19 Ma), Mangapipi (1.51 ± 0.16 Ma, 1.54 Ma), Ridge (1.56 Ma), Pakihikura (1.58 ± 0.08 Ma; 1.58 Ma), Birdgrove (1.60 Ma), Mangahou (1.63 Ma), Maranoa (1.63 Ma), Ototoka (1.72 ± 0.32 Ma; 1.64 Ma), Table Flat (1.71 ± 0.12 Ma; 1.65 Ma), Vinegar Hill (1.75 ± 0.20 Ma; 1.75 Ma), and Waipuru (1.79 ± 0.15 Ma; 1.83 Ma). The ITPFT ages are consistent with the astronomically tuned Geomagnetic Polarity Timescale. Volcaniclastic horizons in Wanganui Basin have been emplaced through a variety of primary and secondary processes, including direct tephra‐fall as well as transitional water supported mass flow through to hyperconcentrated flow. No gas supported flow deposits have yet been recognised. Only some horizons from Wanganui Basin can be chemically and chronologically linked to known TVZ eruptions, while others remain uncorrelated owing to proximal source area erosion and/or burial as well as vapour phase alteration and devitrification within near‐source welded ignimbrites. Nevertheless, many volcaniclastic deposits in Wanganui Basin can be reliably correlated to distal sedimentary successions in Auckland Region, Hawkes Bay and in Ocean Drilling Program (ODP) cores 1123 and 1124, to the east of New Zealand. The orbitally tuned chronology for ODP cores, which is calibrated by numeric ages on tephras and magnetostratigraphy, enhances inter‐regional correlation, providing an important framework for future pal‐aeoenvironmental reconstructions.

Test of thermoluminescence dating of loess from New Zealand and Alaska

Abstract The accuracy of thermoluminescence (TL) ages for loess (and sediments in general) greater than ∼100 ka is disputed. We tested the accuracy of three common TL sediment-dating techniques applied to 4–11 μm sized polymineral grains from known-age loess, using 16 samples from North Island and South Island, New Zealand, and 2 samples from central Alaska. Estimated sample ages range from 20–26 to ∼800 ka. We varied the optical bleaching spectrum, the selected window of the emission spectra (ultraviolet or uv, blue and green wavelengths), the pre-readout heat treatment, and the TL equivalent-dose measurement technique. Most of the 20–26 ka samples gave TL age underestimates of 3–6 ka that may be attributed to post-burial open system behavior. For the older samples, the partial-bleach TL method gave expected ages up to ∼300 ka, and the total-bleach TL method produced expected ages above ∼100 ka. The partial-bleach regeneration TL method gave significant age underestimates for samples older than ∼100 ka, with a maximum TL age of ∼250 ka for samples having expected ages up to ∼350 ka. Two 300–360 ka,samples which gave total-bleach age underestimates with use of uv TL and green TL, gave expected ages with use of blue TL. These results demonstrate that reliable TL ages for loess from New Zealand and Alaska up to ∼800 ka can be obtained if uv (and green?) emissions and the various regeneration methods are avoided. This age range is well above the former putative 80–100 ka upper age limit for TL dating of loess from other regions, which was thought to be a global limit. Application of our successful procedures to such loess is encouraged.

The Rangipo fault, Taupo rift, New Zealand: An example of temporal slip-rate and single-event displacement variability in a volcanic environment

Geomorphic mapping and paleoseismic studies reveal that the Rangipo fault, the eastern boundary of the southern section of the Taupo rift, New Zealand, has highly variable single-event displacement and slip rate in time. Variability in single-event displacement (0.1–1.2 m since 14 cal. ka) is possibly the result of different fault rupture modes: primary (unsegmented and segmented) and secondary. Variability in fault-slip rate is attributed to interactions with volcanic activity of the nearby Ruapehu volcano (11 km distant), the southernmost and largest andesitic volcanic edifice within the southern Taupo volcanic zone. The Rangipo fault has had a mean slip rate of ∼1.4 mm/yr since ca. 25 cal. ka (calibrated radiocarbon age in thousands of years before present), and a mean slip rate of only ∼0.2 mm/yr since 14 cal. ka. This implies that during the period between 14 and 17–25 cal. ka, the fault had a slip rate of 2–9 mm/yr. This period of increased slip rate coincided with the most voluminous eruptions from Ruapehu volcano in the past 100 k.y. We infer that there is an interaction between the Rangipo fault and Ruapehu volcano, although we cannot confirm the sense of the interaction (i.e., volcano→fault or fault→volcano). The interaction could be related to pulsed rifting, where major rifting occurs in periods of accelerated faulting that coincide with extensive eruptions.