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    The middle Pleistocene extinction of bathyal benthic foraminifera in the South Atlantic (ODP sites 1082 and 1088) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science at Massey University
    (Massey University, 2005) O'Neill, Tanya Ann
    The youngest major turnover in deep-sea benthic foraminifera (termed the Stilostomella extinction) is documented in two ODP sites in the South Atlantic Ocean. This study is the first detailed investigation of its kind in this region, and reveals the pulsed decline and eventual extinction of 33 species of elongate, cylindrical benthic foraminifera belonging to the families Stilostomellidae, Pleurostomellidae, and part of the Nodosariidae during the mid-Pleistocene climatic transition (MPT, ~1200 - 600ka). Furthermore, the Stilostomella extinction is limited to elongate species with highly specific apertural characteristics (e.g. cribrate, slit lunate, and hooded with secondary teeth), such as Chrysalogonium, Ellipsoglandulina, and Pleurostomella species, respectively. Micropaleontological and sedimentological data from lower bathyal Sites 1082 and 1088 (1290 m and 2082 m water depth, respectively) provide a proxy record of oceanographic changes in the South Atlantic Ocean through the MPT. This study compares the timing and causes of the Stilostomella extinction between two highly contrasting environmental settings in relation to paleoceanographic history, sediment regime and paleoproductivity. In the South Atlantic, the abundance and accumulation rate of Extinction Group (EG) taxa began to decline between ~ 1070 and 1000 ka at both core sites. The rate of decline was pulsed, with major declines usually associated with cool periods, and partial recoveries during intervening warm periods. The timing of highest occurrences (HOs) was diachronous between sites, and the final Stilostomella extinction datum is marked by the uppermost occurrence of Myllostomella matanzana and Siphonodosaria sagrinensis at ~705 ka in Site 1082, and Myllostomella matanzana and Pleurostomella alternans at ~600 ka in Site 1088. This corresponds with the previously documented global Stilostomella extinction datum within the period of 700 and 570 ka. Detailed comparisons with North Atlantic and Southwest Pacific studies confirm the highly diachronous nature of HOs of EG species, and furthermore, reveal that there is a lead time of ~100 kyr between HOs of the same species in the North Atlantic, compared with the South Atlantic. This study suggests that declines and extinctions at Site 1082 were primarily driven by highly fluctuating food supply associated with increased productivity caused by intensified upwelling during MPT glacial periods. In contrast, extinctions at Site 1088 appear to have been a result of the MPT reorganisation of the global deep-water 'conveyor belt', with δ 13 C gradients revealing that high dissolved oxygen Glacial North Atlantic Intermediate Water (GNAIW) bathed the region during cool periods. Far from a simple response to change in a single parameter, numerous factors have interacted and appear to have caused the demise of the Stilostomella extinction taxa. These factors include encroachment by well-ventilated (high dissolved oxygen) GNAIW, fluctuations in food supply, and possibly winnowing (of the phytodetritus layer) by vigorous bottom currents during MPT glacial periods.
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    High-precision tephrostratigraphy : tracking the time-varying eruption pulse of Mt. Taranaki, North Island, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science, Massey University, Palmerston North, New Zealand
    (Massey University, 2017) Damaschke, Magret
    In this research it was proposed that a more robust record of volcanic activity for Mt. Taranaki (New Zealand) could be derived from tephras (pyroclastic fall deposits) within cores from several lakes and peatlands across a 120o arc, NE-SE of the volcano, covering a range of prevailing down-wind directions. These data were integrated with previous tephrochronology studies to construct one of the longest and most complete volcanic eruption history records ever developed for an andesitic stratovolcano. Using 44 new radiocarbon dates, electron microprobe analysis of glass shard and ttitanomagnetite chemical composition, along with whole-rock chemistry, a chrono- and chemostratigraphy was established. The new record identifies at least 272 tephraproducing eruptions over the last 30 cal ka BP. Six chemo-stratigraphic groups were identified: A (0.5 – 3 cal ka BP), B (3 – 4 cal ka BP), C (4 – 9.5 cal ka BP), D (9.5 – 14 cal ka BP), E (14 – 17.5 cal ka BP), and F (23.5 – 30 cal ka BP). These were used to resolve previous stratigraphic uncertainties at upper-flank (proximal) and ring-plain (medial) sites. Several well-known “marker tephras” are now recognized as being ~2000 years older than previously determined (e.g., Waipuku, Tariki, and Mangatoki Tephra units) with the prominent Korito Tephra stratigraphically positioned above the Taupo-derived Stent Tephra. Further, new markers were identified, including the Kokowai Tephra unit (~4.7 cal ka BP), at a beach-cliff exposure, 40-km north-east of the volcano. Once age-models were established for each tephra, units were matched between sites using statistical methods. Initial statistical integration showed that the immediate past high-resolution tephrochronological record suffered from a distinctive “old-carbon” effect on its ages (Lake Rotokare). This had biased the most recent probabilistic forecasting and generated artificially high probability estimates (52-59% eruption chance over the next 50 years). Once the Rotokare record was excluded and chemostratigraphy constraints were applied, a reliable multi-site tephra record could be built only for the last ~14 ka BP. The new data confirms a highly skewed distribution of mainly (98% of cases) short intervals between eruptions (mode of ~9 years and average interval ~65 years). Long intervals (up to 580 years) as seen in earlier records were reduced to 2% of the record, but can now be considered real, rather than missing data. The new data confirm a cyclic pattern of varying eruption frequency (with a five-fold range in annual frequency) on a period of ~1000-1500 years. The new time-varying frequency estimates suggest a lower probability for a new eruption at Mt. Taranaki over the next 50 years of 33-42%. The newly established chemostratigraphy was further used to investigate time-related compositional changes. Whole-lapilli analyses highlighted that a specific very evolved Ca-rich and Fe-poor composition was only found within the easterly and south-easterly depositional sites. This was explained by eruption of a stratified magma reservoir, which holds greater modal proportions of plagioclase and lower proportions of pyroxene within low-density, gas-rich upper conduit regions. During the most explosive phases of eruptions, when plumes reach the stratospheric jetstream, the lowest-density pumice is thus dispersed by high-level stable westerly winds. Further, two distinct evolutional trends were seen in the long and new tephrochronological record; from 17.5 to 3 cal ka BP and <3 cal ka BP; with wholelapilli, glass, and titanomagnetite compositions overall evolving over time. The former compositional trend indicates a crystallising and cooling magma source in the deep crust, with multiple, spatially separated magma source regions forming, each generating magmas (i.e., magma batches) with unique titanomagnetite compositions. This trend is interrupted by a distinct shift towards less-evolved compositions and the initiation of a second parasitic vent (Fanthams Peak at the southern flank of Mt. Taranaki).