1 University of Canterbury, Department of Geological Sciences, Christchurch, New Zealand. 2 Oberlin College, Department of Geology, Oberlin, Ohio

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1 Phytoliths reconstruction of the environment surrounding the Kawakawa tephra in Banks Peninsula, South Island Margaret Rubin 1,2, Josh Borella 1, Samuel Hampton 1, and Chris Grimshaw 1 1 University of Canterbury, Department of Geological Sciences, Christchurch, New Zealand 2 Oberlin College, Department of Geology, Oberlin, Ohio Abstract The use of phytoliths in paleoenvironmental reconstructive research is well documented in New Zealand with a wide variety of identification resources available. This in combination with phytoliths relative indestructibility, in situ deposition, and distinctive morphologies makes phytoliths the ideal for reconstruction the paleoenvironment of Pa Bay, Banks Peninsula. An extensive methodology was developed, drawing from multiple sources, and the count results gave an idea of the environment during the last glacial maximum, although it showed little change over time. Additionally, the tentative identification of the diatom Cyclostephanos novazeelandiae confirms the identity of the tephra layer as the Kawakawa tephra which chronostratigraphically marks the layer as deposited 25.4 ka. Introduction The use of phytoliths in paleoenvironmental reconstruction is an emerging field. The biogenic silica is virtually impervious to most forms of decomposition and degradation, morphologically distinct, and are usually deposited directly into the soil where the plant of origin decays, allowing an accurate picture of local vegetation to be painted. Due to the specificity of the morphologies plants can be identified through their phytoliths, sometimes down the species level, and general morphologies and abundances can be used to reconstruct the environment in which they were deposited. They have been utilized in conjunction with diatoms and palynological (pollen) studies, but include several distinct advantages in that they are found in a wider range of sediments and are less likely to have been carried long distances, thereby providing a more accurate picture of an area where they might be found. Additionally, unlike phytoliths, pollen is not well preserved in the loess. Banks Peninsula is a Miocene-era volcanic complex Due to the last glacial maximum, dated as lasting from ka by Barrell et al. (2013), the bulk of the peninsula is covered in

2 loess which means that pollen is not well preserved. This presents a unique opportunity for phytoliths to be used to reconstruct and track paleovegetation and paleoclimate trends and changes, similar to Shulmeister et al. (1999) who did a reconstructive study of Hawkes Bay. The sequence being examined, sampled from Pa Bay on Banks Peninsula, is chronostratigraphically identified by an ash layer that has been compositionally matched to the Oruanui eruption 25.4 ka (Barrell et al. 2013, Vandergoes et al. 2013). This puts the sequence firmly in the center of the last glacial maximum, although the top and bottom of the sequence (470mm and 400mm from the ash layer respectively) have not been dated and it is uncertain how much time had passed in the deposition of the sequence. The Kawakawa ash includes tephra glass and diatoms from the lake through which the Oruanui eruption exploded; these will be extracted with the phytoliths and their presence in layers above or below the ash could have implications about reworking of the sediment which could in turn call into question the results. Methods Field The Kawakawa tephra is a 10cm thick, cream-white tephra horizon embedded within an 8m-high coastal exposure of interbedded silt to very fine loessic sediments with sporadic volcanic and mudstone clasts. The tephra is comprised of well sorted, fine-grained, finely bedded silt-sized sandstone and contains burrows along its upper contact. Directly beneath the tephra is a 12cm-thick mottled yellowish grey, moderately sorted, highly burrowed, massive, very fine sandstone. Overlying and infilling the burrows into the tephra is a 17cm-thick, mottled yellowish gray and pale orange crenulated, clast rich very fine sandstone unit. A transect was selected through the 8m high section, with 33 samples systematically collected at individual layers ranging from 20 to 300mm. At a range of one meter below and one meter above the tephra unit, 22 samples were taken below and 5 above. 6 samples were taken of the tephra unit itself including sample PB21, a bulk sample taken in the same vertical sequence as the 22 loess samples. Layers were defined by distinctive contacts, differences in coloration, and varying lineation thicknesses. Detailed field notes were taken, describing structure, texture, and composition of the sampled subunits. PB21 was used for phytolith extraction as well as two samples each from the loess below and above the tephra layer, PB19 and 20 and PB22 and 23 respectively.

3 Extraction The samples were placed in 250ml beakers, dried, and weighed before being mixed with Calgon (50 g/l) in order to deflocculate the sediments. 30% H 2 O 2 was mixed in and heated to 40 C to digest any organic sediments, bubbling indicating that a reaction was taking place. The samples were moved to 50ml centrifuge tubes and diluted with deionized H 2 O before being centrifuged and rinsed at 3000 rpm for 3 minutes. This was done 3 times with the sample being vortexed in between each centrifugation. The sediments were washed back into clean 250ml beakers with deionized water and 100ml each of Na-citrate and Na-carbonate were added. When the samples had been heated to 80 C, 1-2 scoops of Na-dithionate were stirred in until the solution turned brown and the sediments turned gray. The solutions were left overnight to cool and settle before the samples were transferred back to 50ml centrifuge tubes and re-centrifuged 3 times at 3000 rpm for 3 minutes. Once the samples had been cleaned they were washed through a 250µm sieve with deionized H 2 O. The >250µm portion was transferred to 50ml centrifuge tubes and dried at 50 C for two days. When they were dry of all other liquids, 30ml of LST heavy liquid with a specific gravity of 2.36(?) were added and the sample was vortexed to suspend the sediments in the liquid. The samples were then centrifuged at 1000 rpm for 10 minutes, pushing the sediments to the bottom and leaving the phytoliths suspended. The phytoliths could then be pipetted off the top and diluted with deionized H 2 O so that the phytoliths could be pushed to the bottom, rinsed, and transferred to slides. The slides were heated to evaporate the water and a drop of Naphrax was placed on each of them to make the phytoliths more visible(?) before they were sealed. Identification 200 phytoliths were counted and identified for each sample, except PB21 (see results). Phytoliths were identified using Kondo (2004) and Carter (1994) and photographed using *specifications of microscope and camera*. Results A count of the phytoliths shows a vast proportion of them to be grass phytoliths, particularly elongate morphologies which comprised between 50 and 70% of the samples (Fig.

4 1). Other grass morphologies included point-shapes, panicoids, chloridoids, chionochloids, and truncated cones (Fig. 2). Chionochloids (spools), and chloridoids (saddles) are associated with tussock grasses, panicoids (dumb-bells) with warm weather grasses (Shulmeister et al. 1999), while elongates, truncated cones, and points are more general grass signifiers. Possible spherical morphologies were also present, specifically spherical verrucose which indicates the presence of occasional undifferentiated trees and/or shrubs. Additionally, multiple diatom morphologies were found, some of which have been tentatively identified as Diploneis subovalis (Shulmeister et al. 1999) and Cyclostephanos novazeelandiae (Van Eaton et al. 2013) (Fig. 3). Some difficulty was had with differentiating phytoliths from the large amount of tephra and the occasional diatoms of sample PB21. As such, only ~25 phytoliths were identified and the results were not included in analysis of trends. It is also worth noting that inexperience may have played a significant part in what morphologies were or were not identified, as some (ex. elongates) were easier to pick out than others. Discussion Nearly all the phytoliths identified were grass phytoliths, with ~60% being elongate and another 25% being truncated cones. Other grass morphologies pointed specifically to tussock grasses and warm weather grasses. A very small percentage (2-4%) of phytoliths were identified as spherical verrucose which indicates trees and shrubs. Looking at trends in the phytolith abundances (Fig. 1) shows that except for PB23, elongate phytoliths were decreasing in abundance while truncated cones were increasing apart from PB19. Warm weather grasses, represented by panicoid dumb-bell shapes, show a spike immediately after the Oruanui eruption (PB22). Saddles were at their maximum at the same time while spools, also associated with tussock grasses, show their peak immediately before the eruption in PB20. Point-shapes show a general decrease. The phytolith distribution indicates a grassy plain dotted by the occasional tree or shrub, like much of Banks Peninsula today. There are no clear trends among the differentiated grasses to indicate a shift in climate or environment. This indicates that the tephra fallout from the Oruanui eruption had little effect on the vegetation of Pa Bay. One of the difficulties of determining changes over time is that except for the chronostratigraphic marker of the Kawakawa tephra it is unknown how much time has passed. The Oruanui eruption occurred

5 during the last glacial maximum so the presence of warm weather grasses is ambiguous. This could mean that the identification of the panicoid phytoliths is erroneous, the presence of a microclimate, or that the glacial maximum was not as cold as was previously thought. However, the identification of the diatom found in PB21 as Cyclostephanos novazeelandiae confirms the idenfitication of the Kawakawa tephra as it is endemic to the north island and is considered a unique identifier of the source region. (Van Eaton et al. 2013) Additionally, that particular diatom was only found in PB21, indicating that there was no reworking of PB21 either up or down. Moving forwards, more time should be spent with the slides, gathering larger counts of phytoliths and learning to identify the less obvious morphologies. This would help make more specific conclusions about the paleoenvironment. In addition, Identification of the diatoms and determining whether they are in situ, deposited, or reworked from the tephra layer could answer further questions about the legitimacy of the results. References 1. Barrell, D. J., Almond, P. C., Vandergoes, M. J., Lowe, D. J., Newnham, R. M., INTIMATE members (2013). A composite pollen-based stratotype for inter-regional evaluation of climatic events in New Zealand over the past 30,000 years (NZ-INTIMATE project). Quaternary Science Reviews, 74, Carter, J. A. (1994). Phytolith analysis in paleoenvironmental reconstruction. Department of Geography, Victoria University of Wellington, New Zealand. 3. Carter, J. A. (2000). Phytoliths from loess in Southland, New Zealand. New Zealand Journal of Botany, 38, Carter, J. A., Lian, O. B. (2000). Paleoenvironmental reconstruction from the last interglacial using phytolith analysis, southeastern North Island, New Zealand. Journal of Quaternary Science, 15, Kondo, R., Childs, C., Atkinson, I. (1994). Opal Phytoliths of New Zealand. Lincoln, New Zealand. 6. Schulmeister, J., Soons, J. M., Berger, G. W., Harper, M., Holt, S., Moar, N., Carter, J. A. (1999). Environmental and sea-level changes on Banks peninsula (Canterbury, New

6 Zealand) through three glaciation interglaciation cycles. Palaeogeography, Palaeoclimatology, Palaeoecology, 152, Van Eaton, A. R., Harper, M. A., Wilson C. J. N. (2013). High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption. GEOLOGY, 41, Vandergoes, M. J., Hogg, A. G., Lowe, D. J., Newnham, R. M., Denton, G. H., Southon, J., Barrell, D. J.A., Wilson, C. J.N., McGlone, M. S., Allan, A. S.R., Almond, P. C., Petchey, F., Dabell, K., Deiffenbacher-Krall, A. C., Blaauw, M. (2013). A revised age for the Kawakawa/Oruanui tephra, a key marker for the Last Glacial Maximum in New Zealand. Quaternary Science Reviews, 74,

7 Figure 1: Summary of phytolith abundances, showing percent abundances of identified morphologies

8 Figure 2: Shows key phytolith morphologies under 40x magnification. a-b. truncated cone; c-d. panicoid; e-f. spherical verrucose; g-i. elongate

9 Figure 3: Major diatom morphologies under 40x magnification. a. Diploneis subovali(?); b. unknown; c. Cyclostephanos novazeelandiae(?)