Showing papers by "Lionel Carter published in 2004"

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

Abstract: 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.

Thermal isolation of Campbell Plateau, New Zealand, by the Antarctic Circumpolar Current over the past 130 kyr

Abstract: [1] Campbell Plateau occupies a key position in the southwest Pacific sector of the Southern Ocean The plateau confines and steers the Antarctic Circumpolar Current (ACC) along its flanks, isolating the Subantarctic plateau from cold polar waters Oxygen and carbon isotope records from Campbell Plateau cores provide new records of water mass stratification for the past 130 kyr During glacial climes, strengthening of the Subantarctic Front (SAF) caused waters over the plateau flanks to be deeply mixed and ∼3°C cooler Waters of the plateau interior remained stratified and isolated from the cold southern waters In the west, waters cooled markedly (∼4°C) owing to reduced entrainment of Tasman Sea water Marked cooling also occurred north of Campbell Plateau under increased entrainment of polar water by a branch of the SAF The ACC remained along the flanks of Campbell Plateau during the last interglacial, when interior waters were stratified and warmer by ∼1°C than now

Collapse in a Quaternary shelf basin off East Cape, New Zealand: Evidence for passage of a subducted seamount inboard of the Ruatoria giant avalanche

Abstract: The Ruatoria margin indentation and its associated giant avalanche off East Cape, New Zealand, have been inferred to result from margin instability following oblique subduction of a large seamount. The earlier studies hypothesise that a diachronous seamount‐wake trough formed the northern part of the indentation, and collapse between the oblique trough and an oversteepened margin front formed the southern indentation and giant avalanche. If correct, then the impacting seamount must now be landward of the indentation. New seismic profiles, supported by multibeam bathymetry and core samples, from landward of the Ruatoria Indentation, provide support for the passage of a large seamount deep beneath the continental shelf. The continental margin around the head of the indentation is underlain by Quaternary basins that are inferred to result from transpression associated with oblique plate convergence. One basin underlies the shelf landward of the indentation, its seaward edge having collapsed into the...

Deep‐ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

Abstract: A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123. Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6–1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary—a trend that probably reflected (1) more frequent and intense volcanism...

Leg 181 synthesis: fronts, flows, drifts, volcanoes, and the evolution of the southwestern gateway to the Pacific Ocean, Eastern New Zealand

Abstract: The Late Cretaceous-Cenozoic geology of New Zealand represents the evolution of a post-Gondwana, Pacific-facing passive margin which interacted, first, with the mid-Cenozoic development of the Australian/Antarctic and Australian/Pacific plate boundaries and, second, with the subsequent development of the oceanic thermohaline circulation system. Situated between the Tasmanian and southwest Pacific oceanic current gateways, the stratigraphy of the New Zealand region provides our best record of the evolution of the Pacific Ocean's largest deep cold-water inflow, the Deep Western Boundary Current (DWBC), and also possesses an important record of Antarctic Intermediate Water flow. Prior to Leg 181, our knowledge of southwest Pacific Ocean history and, in particular, the development of the DWBC and its local partner, the Antarctic Circumpolar Current (ACC), was poor. Seven holes were therefore drilled east of New Zealand to determine the stratigraphy, sedimentary systems, and paleoceanography of the DWBC, ACC, and related water masses and fronts. The sites comprised a transect of water depths from 396 to 4488 m and spanned a latitudinal range from 39° to 51°S. Leg 181 drilling provided the data needed to study a wide range of problems in the Southern Ocean Neogene. Driven by rifting and a new cycle of seafloor spreading along the Mid-Pacific Rise, New Zealand's youngest (Kaikoura) stratigraphic cycle begins with Late Cretaceous rift fill followed by subsidence and marine transgression until the late Eocene. Biopelagic oozes accumulated throughout as an abyssal apron around the Pacific perimeter of the New Zealand Plateau, seen as Paleocene siliceous nannofossil chalk, chert, and clay at Site 1121 (water depth = 4488 m) and nannofossil chalk at Site 1124 (water depth = 3967 m). At the Eocene/Oligocene boundary (~33.7 Ma), the spreading ridge between Australia and Antarctica broke through south of the Tasman Rise, linking for the first time the Indian and Pacific Oceans into a continuous Southern Ocean. Powerful wind-forced currents, predecessors to the modern ACC, were funneled through the Tasmanian Gateway and into the Pacific, where their path, combined with that of the thermohaline DWBC, was impeded by the shallowly submergent New Zealand Plateau, centered then at latitude ~55°S. All drill sites within or east of the Tasmanian Gateway and all onland sections in New Zealand record this event as a regional unconformity, the Marshall Paraconformity, across which a there is a time gap of ~3-10 m.y., a result of a combination of corrosion, erosion, and nondeposition. Above the paraconformity, sedimentation in both shallow and deep water resumed as late Oligocene (~27-29 Ma) sediment drifts (Site 1124; water depth = 3967 m). Younger deepwater drifts at Sites 1123 (water depth = 3290 m) and 1124 comprise alternating nannofossil chalks containing greater or lesser amounts of terrigenous clay. At Site 1123 on the North Chatham Drift, sediment accumulated essentially continuously from ~20.5 Ma onward. Analysis of this record shows that the stratigraphic rhythms there correspond to 41-k.y. Milankovitch climatic cycles, with faster DWBC flow during colder or glacial intervals. Site 1123 is globally unique. It provides an essentially complete, richly microfossiliferous Miocene to Quaternary record of uniform ~4-cm/k.y. sedimentation that has been astronomically tuned. It also contains an almost complete paleomagnetic record since Chron C6r at 20.5 Ma, including the first record of new magnetic subchron C5ADn1r. Shallower-water Sites 1125 (water depth = 1366 m), 1120 (water depth = 546 m), and 1119 (water depth = 396 m) reveal, respectively, a major productivity bloom between 5.6 and 4.8 Ma on the north side of the Subtropical Front (STF) (Site 1125), foraminiferal nannofossil chalk accumulation punctuated by paraconformities at 16.7-15.8, 5.6-1.9, and 0.9-0.24 Ma (Site 1120), and enhanced frontal flows along a seaward-relocated STF during glaciations (Site 1119). The late Quaternary climatic record at Site 1119 also closely matches that of air temperature in the Vostok ice core, indicating close links between climate change in southern middle and polar latitudes. From ~24 Ma onward, abundant terrigenous material was shed into the southwest Pacific from rising mountains along the South Island Alpine Fault plate boundary. Gradually changing clay mineral assemblages in DWBC drifts, with chlorite + illite replacing smectite + kaolinite, reflect the increasing influence of newly unroofed basement (Rangitata) graywackes and schists through the Miocene-Quaternary. From 12 Ma onward, sediments were augmented by an influx of mainly rhyolitic tephra from the North Island volcanic arc. Site 1122 (water depth = 4432 m), on the left bank levee of the abyssal Bounty Fan, records a marked increase in the input of terrigenous turbidites and fan building starting at ~1.7 Ma and peaking at average rates >50 cm/k.y. after 0.7 Ma. Site 1124, on the Rekohu Drift near the Hikurangi Channel, records the start of overbank turbidite deposition, and therefore avulsion of the Hikurangi Channel from the Hikurangi Trough following channel deflection by a large submarine landslide from the North Island continental margin at ~1.65 Ma. Geological and oceanographic events that have occurred in the southwest Pacific since the Eocene/Oligocene boundary (~33.7 Ma) together compose the Eastern New Zealand Sedimentary System (ENZOSS), studies of which are contributing to our understanding of the history of global ocean circulation and climate change.

Onshore-Offshore Correlation of Pleistocene Rhyolitic Eruptions from New Zealand: Implications for TVZ Eruptive History and Paleoenvironmental Construction

Abstract: Taupo Volcanic Zone (TVZ), in the North Island, New Zealand, is arguably the most active Quaternary rhyolitic system in the world. Numerous and widespread rhyolitic tephra layers, sourced from the TVZ, form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences. In deep-sea cores from Ocean Drilling Program (ODP) Leg 181 Sites 1125, 1124, 1123 and 1122, located east of New Zealand, ca 100 tephra beds are recognised post-dating the Plio-Pleistocene boundary at 1.81 Ma. These tephras have been dated by a combination of magnetostratigraphy, orbitally tuned stable-isotope data and isothermal plateau fission track ages. The widespread occurrence of ash offshore to the east of New Zealand is favoured by the small size of New Zealand, the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field. Although some tephras can be directly attributed to known TVZ eruptions, there are many more tephras represented within ODP-cores that have yet to be recognised in near-source on-land sequences. This is due to proximal source area erosion and/or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near-source welded ignimbrites. Despite these difficulties, a number of key deep-sea tephras can be reliably correlated to equivalent-aged tephra exposed in uplifted marine back-arc successions of Wanganui Basin where an excellent chronology has been developed based on magnetostratigraphy, orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra. Significant Pleistocene tephra markers include: the Kawakawa, Omataroa, Rangitawa/Onepuhi, Kaukatea, Kidnappers-B, Potaka, Unit D/Ahuroa, Ongatiti, Rewa, Sub-Rewa, Pakihikura, Ototoka and Table Flat Tephras. Six other tephra layers are correlated between ODP-core sites but have yet to be recognised within onshore records. The identification of Pleistocene TVZ-sourced tephras within the ODP record, and their correlation to Wanganui Basin and other onshore sites is a significant advance as it provides: (1) an even more detailed history of the TVZ than can be currently achieved from the near-source record, (2) a high-resolution tephrochronologic framework for future onshore-offshore paleoenvironmental reconstructions, and (3) well-dated tephra beds correlated from the offshore ODP sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore Plio-Pleistocene sedimentary sequences (e.g. Wanganui Basin, cf. Naish et al. [1998. Quaternary Science Reviews 17 695–710].

Zinc/silicon ratios of sponges: A proxy for carbon export to the seafloor

Abstract: [1] Reconstruction of past carbon export events is difficult. Most proxies for carbon export suffer from problems related to remineralisation and diagenetic effects above, at and below the sediment-water interface. Here we demonstrate that deep-sea hexactinellid sponges incorporate zinc (Zn) into their silica skeletons in a direct relationship with the amount of particulate organic carbon (POC) accumulating in sediments. Such a relationship suggests that Zn incorporation into siliceous sponge spicules is from Zn associated with particulate organic matter (POM) ‘raining down’ from overhead waters. The dissolved Zn pool does not appear to be a major Zn source to deep-ocean sponges. Likewise, water temperature and pressure do not appear to strongly influence Zn incorporation into sponge silica. These results suggest that the Zn to silicon (Si) ratio of deep ocean sponges could serve as a useful proxy for reconstructing past POC burial events.