Brad Pillans

Reconciliation of late Quaternary sea levels derived from coral terraces at Huon Peninsula with deep sea oxygen isotope records

A major discrepancy between the Late Quaternary sea level changes derived from raised coral reef terraces at the Huon Peninsula in Papua New Guinea and from oxygen isotopes in deep sea cores is resolved. The two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka (ka = 1000 yr before present), but between 70 and 30 ka the isotopic sea levels are 20–40 m lower than the Huon Peninsula sea levels derived in earlier studies. New, high precision U-series age measurements and revised stratigraphic data for Huon Peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic δ18O data. Using the sea level and deep sea isotopic data, oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from Greenland ice cores. The record of ice volume changes through the last glacial cycle now appears to be reasonably complete.

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.

Upper Quaternary marine terrace chronology and deformation, South Taranaki, New Zealand

An extensive flight of late Quaternary marine terraces, in the South Taranaki region of the North Island of New Zealand, is dated using fission track, radiocarbon, and amino acid racemization methods. A simple model of terrace deformation based on a doming-type uplift pattern allows terrace strandline ages to be estimated. Twelve strandlines are recognized and are estimated to have formed during high sea-level stands at 60,000, 80,000, 100,000, 120,000–135,000, 210,000, 310,000, 340,000, 400,000, 450,000, 520,000, 600,000 and 680,000 yr B.P.

A review of the Milankovitch climatic beat: template for Plio–Pleistocene sea-level changes and sequence stratigraphy

The Milankovitch theory of climate change predicts that global ice volume, and hence sea-level changes, were controlled by long-term quasi-periodic variations in the earth’s orbital parameters (obliquity, precession and eccentricity). d 18 O records from deep-sea cores are a proxy for sea-level changes and have an orbitally tuned chronology covering the last 5 Ma. The sea-level signal in d 18 O data from east equatorial Pacific core V19-30 is well calibrated with sea-level data from coral terraces on Huon Peninsula, New Guinea, over the last 140 ka, and with less certainty back to 340 ka. Over the last 140 ka, the sea-level contribution to benthic glacial‐interglacial isotopic variation is about 1.2‐1.3‰ or 0.011‰ m 1 , and for core V19-30 the glacial-age temperature contribution from deep ocean cooling of 1.7oC is 0.4‰. Independent constraints on Late Pliocene sea-level changes interpreted from shallow marine continental margin records indicate that the sea-level d 18 O calibration may not have been the same over the last 2.6 Ma, and the temperature correction is unlikely to have been the same in all glacial periods and all ocean settings. Nevertheless, the astronomically tuned isotopic records from deep-sea cores provide an accurate chronology and approximate the magnitudes of sea-level changes over the last 2.6 Ma, against which the facies architecture of stratigraphic sequences can be analysed and the concepts of sequence stratigraphy properly evaluated.

High resolution windows into early Holocene climate: SrCa coral records from the Huon Peninsula

High-precision measurements of SrCa ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ234U(t) values of 145 ± 2, similar to modern seawater. The SrCa coral records provide 5–6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Nino-Southern Oscillation) events. Mean annual SrCa temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ∼ 2–3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (∼ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ∼ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ∼ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

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.

An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia

How well the ecology, zoogeography and evolution of modern biotas is understood depends substantially on knowledge of the Pleistocene. Australia has one of the most distinctive, but least understood, Pleistocene faunas. Records from the western half of the continent are especially rare. Here we report on a diverse and exceptionally well preserved middle Pleistocene vertebrate assemblage from caves beneath the arid, treeless Nullarbor plain of south-central Australia. Many taxa are represented by whole skeletons, which together serve as a template for identifying fragmentary, hitherto indeterminate, remains collected previously from Pleistocene sites across southern Australia. A remarkable eight of the 23 Nullarbor kangaroos are new, including two tree-kangaroos. The diverse herbivore assemblage implies substantially greater floristic diversity than that of the modern shrub steppe, but all other faunal and stable-isotope data indicate that the climate was very similar to today. Because the 21 Nullarbor species that did not survive the Pleistocene were well adapted to dry conditions, climate change (specifically, increased aridity) is unlikely to have been significant in their extinction.

Revision of the marine chronology in the Wanganui Basin, New Zealand, based on the isothermal plateau fission-track dating of tephra horizons

Abstract The occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies. In this study, three widespread and stratigraphically important rhyolitic tephra horizons interbedded in Plio/Pleistocene strata of the Wanganui Basin, New Zealand, are dated by application of the isothermal plateau fission-track (ITPFT) technique to hydrated glass shards. All glass samples were corrected for annealing and consequently yield reliable ages. Rangitawa Tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission-track age estimates of ca. 0.35 Ma. ITPFT ages of 1.05 ± 0.05 and 1.63 ± 0.15 Ma for Potaka Pumice and Pakihikura Pumice, respectively, are considerably older than previous FT estimates but consistent with new magnetostratigraphic data that places the Potaka within the Jaramillo Subchron, and Pakihikura within the Matuyama Chron between the Cobb Mountain and Olduvai Subchrons. Combining our fission-track ages with the magnetostratigraphy, the true age of sediments within the Wanganui Basin is found to be significantly underestimated. Sedimentation rates of between ca. 680-630 m/Ma from 1.63 Ma to 0.35 Ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous FT chronology. This new ITPFT-age data demonstrates that the existing Plio/Pleistocene marine chronology in New Zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern North Island that contain the same ITPFT-dated tephra horizons.

New Zealand Quaternary stratigraphy: An overview

Abstract New Zealand Quaternary strata, including marine sediments, loess, volcanic and glacial deposits, offer detailed records of Quaternary environmental change from a geographically significant location. Time-stratigraphic subdivision of New Zealand Quaternary strata, based on marine biostratigraphy and climatostratigraphy, has resulted in a series of locally defined stages and substages. The Plio/Pleistocene boundary as defined at Vrica in Italy, and dated at ca. 1.63 Ma, lies near the top of the Nukumaruan Stage in New Zealand. The first faunal evidence of cooling in New Zealand Plio/Pleistocene sequences occurs much earlier, at the base of the Nukumaruan Stage ca. 2.4 Ma, with the appearance in central New Zealand of the subantarctic taxa Chlamys delicatula and Jacquinotia edwardsii . Although glacial deposits of the South Island have long been central to New Zealand Quaternary stratigraphy, they are poorly dated and lack continuity. More complete records of Quaternary events are found within uplifted marine strata and associated terrestrial deposits of the North Island, such as in Wanganui Basin. The use of widespread rhyolite tephra for precise correlation and dating in North Island offers much for improved land-sea correlations. Direct correlation of on-land sequences, using tephra, with Oxygen Isotope Stages of deep sea cores may negate the need for further local time-stratigraphic subdivision in the New Zealand Quaternary. However, there will still be scope for regional comparisons highlighting climatic changes not apparent in deep sea cores.

Radiocarbon evidence for the timing and rate of Island development, beach-rock formation and phosphatization at Lady Elliot Island, Queensland, Australia

Abstract Lady Elliot Island (Great Barrier Reef) is a coral cay constructed from near-concentric shingle ridges composed of coral, Tridacna shells and bioclastic sand bound by guano-derived phosphatic cement. Radiocarbon dating of individual Tridacna samples is used to investigate the evolution of the island and place constraints on the variations in storminess of the last 3200 years. A shallow platform reef existed at Lady Elliot since at least 6500 yrs B.P. Shortly before 3200 yrs B.P. island growth by shingle progradation commenced and proceeded to the present at a rather uniform lateral rate (60 m ka −1 to leeward and 90 m ka −1 windward). Phosphatization may have occurred continuously or episodically at any time throughout the last 3200 years. The youngest cemented ridge top is less than 770 years, whereas at the base of uncemented ridges, phosphatization is a modern (∼1950 A.D.) process. Similarly, low-level beach rock has continued to form within the last 25 years. A significant period of instability occurred less than 500 years ago during which marine erosion truncated the southwestern extremity of Lady Elliot Island, formed an eastern “spit” and stranded high-level beach rock. However, the radiocarbon ages of Tridacna samples from shingle ridges from Lady Elliot and Curacoa Islands are uniformly distributed (Kolmogorov-Smirnov test) throughout the last 4000 years. We interpret this to indicate no significant variation in ridge-forming processes or fluctuation in average storminess during this interval.