Pollen, phytoliths, arthropods and high-resolution 14C sampling from Rano Kau, Easter Island: evidence for late Quaternary environments, ant (Formicidae) distributions and human activity

A 20-m sediment core from Rano Kau, Easter Island provides plant microfossil, arthropod fossil and high-resolution ¹⁴C sampling evidence for late Quaternary environments, ant (Formicidae) distributions and human activity. The record commences prior to or during the LGM, providing the two oldest dates for Rano Kau thus far, 20,340 ± 160 and 34,260 ± 440 BP. The vegetation at the time was mostly Arecaceae (palm)-dominated grassland-woodland, suggesting cooler/drier conditions than present. Near the start of the Holocene c. 12,500 cal BP, climate alleviation is indicated by Asteraceae shrubland increasing at the expense of grassland. There is an early to mid-Holocene sediment hiatus. The record recommences c. 3,500 cal BP, with in-washed clayey soils bearing charcoal and phytoliths of Polynesian-introduced Musa (banana) and mixed with wetland detritus, reflecting slumping as a result of forest clearance and gardening. Dates of material of other plants from the clay/detritus layers containing the Musa phytoliths are older than expected, within the range 3,680–2,750 cal BP, well before settlement of Eastern Polynesia. This could reflect horticultural material settling in an older part of the sediment column or age increase by reservoir effects. A long section of overlying unconsolidated detritus provides a progressively younger upward sequence from 2,840–2,870 to 930–810 cal BP, but dates are variable after 1,290–1,180 cal BP, where charcoal, disturbance-related pollen and older than expected ant exoskeletons demonstrate the inclusion of pre-aged material from the floating vegetation mat or upslope erosion in the sediment column. Arecaceae pollen declines sharply after 930–810 cal BP. Arthropod analysis reveals two new weevil species for Easter Island, and two ant taxa, Tetramorium bicarinatum and Pheidole sp., the latter of which is also new for the island. Three of the four age determinations on ant remains suggest that ants were present prior to c. 2,500 cal BP, and probably associated with the period following the resumption of sediment accumulation c. 3,500 cal BP. Unless the apparent ant ¹⁴C ages have been increased by reservoir effects, these results question the long-accepted assumption that all Eastern Polynesia’s ant species have been introduced.     

Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island

Previous wetland vegetation records from Easter Island showing deforestation and Polynesian agriculture are limited to cores that rely on pollen, with a single cultigen pollen type identified: Urticaceae/Moraceae, possibly Broussonetia payrifera (paper mulberry). Here we redress this by also using phytolith and starch analyses on four lake sediment cores on a ~350-m transect along the southwest edge of Rano Kau, focusing on in-washed basal clayey layers. We also use a new method, Fourier transform infrared spectroscopy, to positively identify degraded starch collected from sedimentary deposits. The cores are the first samples recovered from an area in the lake that (a) lies below the relict village of Orongo, (b) is near a section of the crater believed to be most accessible from the Pacific coast, and (c) is far from the northern crater rim and receives high solar radiation, a likely benefit for crops of tropical origin. Pollen and phytoliths are abundant in the clayey layers and sparse in overlying layers of organic lake detritus and living rhizomes. Mixing of core deposits as a result of human activity has disordered the radiocarbon sequence, precluding development of an reliable chronology. Containing microfossils of several introduced cultigens, the clayey layers represent gardened terraces that have slumped into the lake. The data indicate large-scale deforestation and a mixed-crop production system including Broussonetia papyrifera, Colocasia esculenta (taro), Dioscorea alata (greater yam), Ipomoea batatas (sweet potato), Lagenaria siceraria (bottle gourd) and Musa (banana) sp. The data show (a) the potential for using the combined analyses to provide direct evidence of Polynesian horticulture on Easter Island and (b) that the island’s wetlands potentially hold extensive horticultural records. The study highlights the concept of ‘transported landscapes,’ whereby colonising people replace indigenous forests with artificial, imported agricultural landscapes.     

Biological and Geochemical Record of Anthropogenic Impacts in Recent Sediments from Lake Pupuke, Auckland City, New Zealand

Frozen sediment cores from Lake Pupuke in Auckland City, New Zealand, contain a high resolution decadal to annual scale record of changing lake paleoenvironments and geochemistry that reflects changing landuse and hydrology in the catchment over the past c. 190 years. A reliable chronology is available from AMS ¹⁴C and ²¹⁰Pb dating of the sediments, with the timing of the older part of the record supported by the first appearance of pollen of introduced Pinus and Plantago lanceolata associated with European settlement of Auckland in the early 1840s. Diatom stratigraphy, sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions commensurate with European development of the Lake Pupuke catchment, in particular enhanced algal productivity controlled by the influx of nutrients after c. 1920 AD. Attempts to prevent nuisance algal blooms in 1933, 1934 and 1939 using CuSO₄ addition produced Cu spikes in the sediment that allowed confirmation of the accuracy of the ²¹⁰Pb chronology. Hence, the elemental and isotopic composition of the Lake Pupuke sediments reflect the timing of significant anthropogenic activities, rather than climatic variations, that have occurred within the watershed over the past c. 190 years. The comparison of records of land use change in the catchment with the multi-proxy record of changes in the sediments usually allowed unambiguous identification of the signatures of change and their causes.     

Late Quaternary environments,vegetation and agriculture in northern New Zealand

A sedimentological and plant microfossil history of the Late Quaternary is preserved in two sediment cores from early Polynesian ditch systems on southern Aupouri Peninsula. The study places human activities into a geomorphological and ecological context and allows comparison of natural and anthropogenic effects on two different geological settings: a floodplain and a relatively closed peat swamp. The data fill part of the current gap in the environmental record from northern New Zealand, namely MIS 3 (57k–26k yr BP). There is evidence for an increase in fire frequency in the region after 40k ¹⁴C yr BP, suggesting a shift to drier (and cooler) conditions. Pollen records show that conifer‐hardwood forest dominated by podocarps (especially Dacrydium) prevailed prior to Polynesian arrival and deforestation within the last millennium, with Fuscopsora insignificant throughout. Both cores show sections with gaps in deposition or preservation, possible flood‐stripping of peat during the pre‐Holocene and mechanical disturbance by early Polynesians. The identification of prehistoric starch grains and other microremains of introduced Colocasia esculenta (taro) in both cores supports indirect evidence that the ditch systems of far northern New Zealand were used for the extensive cultivation of this crop. Copyright © 2006 John Wiley & Sons, Ltd.     

Fossil plant remains at Rano Raraku, Easter Island’s statue quarry: evidence for past elevated lake level and ancient Polynesian agriculture

Previous paleoenvironmental records from the lake of Rano Raraku crater, Easter Island??s statue quarry, showed evidence of two major environmental changes, fluctuating lake levels and Polynesian forest clearance. There have been no reports, however, of former shorelines and it is not known if deforestation of the crater was for quarrying alone, or also for agriculture. We shed light on this by examining macrofossil casts of plants found in dryland iron pan deposits, and using combined analyses of pollen, phytoliths and starch in a lake sediment core and dryland soil profile. Casts of wetland taxa, namely Scirpus californicus and fern rhizomes, were identified in the iron pan deposits up to ~10?m above the current lake level, providing evidence of higher lake level during the last Glacial period. This height is near the level of the col on the western side of the crater, indicating that the lake was at its maximum possible elevation at the time, with overflow via the col. Microfossils of introduced Colocasia esculenta (taro), Ipomoea batatas (sweet potato), Musa (banana sp.) and possibly Lagenaria siceraria (bottle gourd) were identified in the core and soil profile, providing evidence of ancient Polynesian agriculture. Earliest evidence of gardening occurs at ~627?C513?cal BP, immediately after large-scale forest clearance. The core and soil profile were located on opposite sides of the catchment, suggesting that the crater was intensively multi-cropped and that widespread irrigated gardens co-existed with statue-quarrying activity.     

The Mk II sampler: a device to collect sediment cores for analysis of uncontaminated DNA

We describe an improved piston corer, the Mk II, for sampling soft sediments for ancient DNA analysis. The original Mk I model, designed to minimize contamination and successfully used in New Zealand, was subsequently deployed on Easter Island where three problems arose. Two of these problems related to sediment and water entering the core barrel and contaminating samples. The other difficulty was that plant material accumulated ahead of the piston and blocked the corer aperture. Design improvements were made to the prototype model and eliminated these problems.     

High-magnesium staurolite in a sapphirine-garnet rock from the Limpopo Belt,Southern Africa

Unusually Mg-rich staurolite with F=Fe/(Fe+ Mg) = 0.51 occurs in a peraluminous silica-deficient sapphirine-garnet-gedrite-spinel-corundum-phlogopite rock as relic inclusions within pyrope-almandine garnet (F=0.43–0.48), from which it is generally separated by sapphirine (F=0.19). Gedrite has F=0.24–0.27, phlogopite 0.19, and spinel 0.43. The gradual disappearance of staurolite is due to a shift of the 3-phase AFM assemblage staurolite-garnetsapphirine to more Fe-rich compositions according to probably prograde reactions between staurolite and garnet to form sapphirine together with either quartz or gedrite. Thus still more Mg-rich staurolite seems to have existed in the rock at earlier stages of metamorphism characterized by lower temperatures and perhaps higher pressures. The local equilibria now frozen in indicate minimum pressures of 7–8 kbar and temperatures in excess of about 800° C.Staurolite is free from Zn, very low in Si, and richer in Ti than any other staurolite found thus far. Most notable is the unique Mg/Fe fraction between staurolite and garnet with staurolite being the more Fe-rich phase (K_D=1.32).     

3-D geochemical interpolation guided by geophysical inversion models

3-D geochemical subsurface models, as constructed by spatial interpolation of drill-core assays, are valuable assets across multiple stages of the mineral industry's workflow.However, the accuracy of such models is limited by the spatial sparsity of the underlying drill-core, which samples only a small fraction of the subsurface.This limitation can be alleviated by integrating collocated 3-D models into the interpolation process, such as the 3-D rock property models produced by modern geophysical inversion procedures, provided that they are sufficiently resolved and correlated with the interpolation target.While standard machine learning algorithms are capable of predicting the target property given these data, incorporating spatial autocorrelation and anisotropy in these models is often not possible.We propose a Gaussian process regression model for 3-D geochemical interpolation, where custom kernels are introduced to integrate collocated 3-D rock property models while addressing the trade-off between the spatial proximity of drill-cores and the similarities in their collocated rock properties, as well as the relative degree to which each supporting 3-D model contributes to interpolation.The proposed model was evaluated for 3-D modelling of Mg content in the Kevitsa Ni-Cu-PGE deposit based on drill-core analyses and four 3-D geophysical inversion models.Incorporating the inversion models improved the regression model's likelihood(relative to a purely spatial Gaussian process regression model) when evaluated at held-out test holes, but only for moderate spatial scales(100 m).