Long-period variations of sea-level in Australasia

Summary. The ability of the Australian sea-level monitoring network is assessed in the investigation of long-period sea-level signals. Through the character of coastal long waves, seasonal variations in level and inter-annual level anomalies, the importance of the south coast of the Continent is identified as a coherent indicator of large-scale marine and atmospheric teleconnections. The source of the sea-level signal is investigated by the tracing of progressive features, by the numerical modelling of wind stress over the Southern Ocean, by the modelling of the effect of monsoonal rains over the Indian Ocean and the mass transport through the Indonesian Strait. These features are related to the ENSO cycle which for the first time is linked, inter alia , with Southern Ocean mechanisms.     

陕西段家坡黄土剖面中布容／松山古地磁界线附近铱异常的发现及其启示

利用高灵敏度放射化学中子活化分析方法,对我国陕西段家坡黄土剖面早－中更新统（约０．７３Ｍａ）沉积界线附近铱和其它元素的丰度进行了测定。结果表明,在布容／松山（Ｂ／Ｍ）古地磁界线附近铱的含量明显增大,最大值为４６．３ｐｇ／ｇ。相对于整个剖面的平均背景值（约１５ｐｇ／ｇ）大约富集了３倍。用地壳元素钪进行标准化之后,铱异常十分明显,而其它元素在界线附近则没有变化。黄土剖面上铱异常的赋存层位与西南太平洋钻     

High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary

High-precision ⁴⁰Ar/³⁹Ar ages for a series of proximal tuffs from the Toba super-volcano in Indonesia, and the Bishop Tuff and Lava Creek Tuff B in North America have been obtained. Core from Ocean Drilling Project Site 758 in the eastern equatorial Indian Ocean contains discrete tephra layers that we have geochemically correlated to the Young Toba Tuff (73.7 ± 0.3 ka), Middle Toba Tuff (502 ± 0.7 ka) and two eruptions (OTTA and OTTB) related to the Old Toba Tuff (792.4 ± 0.5 and 785.6 ± 0.7 ka, respectively) (⁴⁰Ar/³⁹Ar data reported as full external precision, 1 sigma). Within ODP 758 Termination IX is coincident with OTTB and hence this age tightly constrains the transition from Marine Isotope Stage 19–20 for the Indian Ocean. The core also preserves the location of the Australasian tektites, and the Matuyama-Brunhes boundary with Bayesian age-depth models used to determine the ages of these events, c. 786 and c. 784 ka, respectively. In North America, the Bishop Tuff (766.6 ± 0.4 ka) and Lava Creek Tuff B (627.0 ± 1.5 ka) have quantifiable stratigraphic relationships to the Matuyama-Brunhes boundary. Linear age-depth extrapolation, allowing for uncertainties associated with potential hiatuses in five different terrestrial sections, defines a geomagnetic reversal age of 789 ± 6 ka. Considering our data with respect to the previously published age data for the Matuyama-Brunhes boundary of Sagnotti et al. (2014), we suggest at the level of temporal resolution currently attainable using radioisotopic dating the last reversal of Earths geomagnetic field was isochronous. An overall Matuyama-Brunhes reversal age of 783.4 ± 0.6 ka is calculated, which allowing for inherent uncertainties in the astronomical dating approach, is indistinguishable from the LR04 stack age (780 ± 5 ka) for the geomagnetic boundary. Our high-precision age is 10 ± 2 ka older than the Matuyama-Brunhes boundary age of 773 ± 1 ka, as reported previously by Channell et al. (2010) for Atlantic Ocean records. As ODP 758 features in the LR04 marine stack, the high-precision ⁴⁰Ar/³⁹Ar ages determined here, as well as the Matuyama-Brunhes boundary age, can be used as temporally accurate and precise anchors for the Pleistocene time scale.     

青藏高原末次快速隆升与“亚澳”陨击事件

黄土、山前磨拉石年代学最新研究成果表明青藏高原及其相邻山脉最晚一期,也是最强烈的隆升事件发生在早更新世晚期(0.9～0.8MaB.P.)。这是一次由于印度板块脉冲式陆内俯冲(A型)引起的“挤压隆升”,而不是重力均衡引起的“伸展隆升”。它对中亚及我国西部广袤区域盆-岭地貌的形成、盆地中-新生界构造变形和大范围的干旱与沙漠化起了决定性的影响。0.9～0.8MaB.P.期间发生在印度洋洋中脊三联点附近(67°E,20°S)的“亚澳”陨击事件,很可能是引起印度洋快速扩张、导致印度板块在锡瓦利克带强烈俯冲(A型),并引起了青藏高原0.9～0.8MaB.P.快速隆升的大陆动力学背景。其影响不止于印度洋周边,而且还涉及西南太平洋。0.9MaB.P.前后引起全球气候变化的“中更新世革命”(MPR)、“西太平洋暖池”的形成以及0.78MaB.P.布容期与松山期地磁极性倒转(BM界限)的发生都可能与此有关。     

Emission and flux of DMS from the Australian Antarctic and Subantarctic Oceans during the 1988/89 summer

DMS emissions and fluxes from the Australasian sector of the Antarctic and Subantarctic Oceans, bound by 46–68° S and 65.5–142.6° E, were determined from a limited number of samples (n=32) collected during three summer resupply voyages to Australian Antarctic continental research bases between November 1988 and January 1989 (a 92 day period). The maximum DMS emission from this sector of the Antarctic Ocean was in an area near the Antarctic Divergence (60–63° S) and the minimum DMS emission was from the Antarctic coastal and offshelf waters. The greatest emission of DMS from this sector of the Southern Ocean was from the Subantarctic waters. DMS flux from the Australasian Antarctic Ocean was 64.3×10⁶ (±115) mol d^–1 or 5.9 (±10.6)×10⁹ mol based on an emission of 10.9 (±19.5) µmol m^–2 d^–1 (n=26). The flux of DMS from the Australasian sector of the Subantarctic Ocean was probably twice the flux of DMS from the adjacent Antarctic Ocean.     

Australasian asphaltite strandings: Their origin reviewed in light of the effects of weathering and biodegradation on their biomarker and isotopic profiles

Asphaltites, long known to strand along the coastline of southern Australia and as distantly as New Zealand and Macquarie Island, are widely regarded as artefacts of submarine oil seepage. Their remarkably uniform composition suggests a common source: marine shale containing sulphur-rich Type II kerogen, probably deposited during an Early Cretaceous oceanic anoxic event (OAE). Suitable hydrocarbon kitchens may exist in the offshore Bight and Otway basins. The physical character of the asphaltites, including laminations and flow structures, and their degree of alteration, which is not the result of biodegradation or extensive water washing, suggest an origin from subsurface tar mats subsequently exposed by the incision of submarine canyons, with the possible formation of asphaltic volcanoes. API gravities of 4–18° impart quasi-neutral buoyancy, implying many asphaltites were submerged drifters prior to stranding, their degree of weathering reflecting, at least in part, the residence time in the marine environment. For any individual asphaltite specimen, this will depend on the proximity of the seafloor seep to the stranding site, an important consideration when attempting to locate their point of origin.This study investigates the hydrocarbon biomarker signatures and n-alkane δ¹³C profiles of asphaltite specimens from stranding sites on the Eyre Peninsula (n = 2), Kangaroo Island (n = 4) and the Limestone Coast (n = 3), South Australia, and the south island of New Zealand (n = 2). Sub-samples of the interior and weathered surface of each specimen were analysed. No distinction could be made between strandings based on their source-dependent molecular and isotopic signatures, confirming their common origin. Comparison of the interior and exterior sub-samples revealed subtle although consistent differences. Given their degree of degradation and isotopic variance, these Australasian asphaltites seem to be products of low intensity seeps in the Ceduna Sub-basin of the Bight Basin and/or Morum Sub-basin of the Otway Basin.     

泰国东北部猜也奔府Noen Sa-nga地区Yasothon土壤剖面中的澳大拉西亚玻陨石

A sedimentary profile exposed in soil quarries a few kilometers north of Noen Sa-nga district, Chaiyaphum province, NE Thailand, reveals a Quaternary geological history. The lower part of the soil profile is a gravel deposit characterized by sub-angular to well-rounded pebbles representing an abandoned river sedimentary deposit. The gravel bed in some places is coated by iron oxide as a thin layer of ferricrete at the uppermost part. The upper part of the soil profile is a bright reddish brown structureless sand deposit with fining upward sedimentary structure at the basal portion, the Yasothon soil series. A piece of tektite was discovered at the contact boundary between the two sedimentary units. It is characterized by an irregular shape with a smooth concaved surface regarding as an external mold of a piece of well-rounded pebble. This piece of tektite indicates that a solidified tektite had fallen from high sky then was remelted into a plastic form prior to reach and partly cover a piece of well-rounded pebble. These evidences suggest that there was a meteoritic or cometary impact on our earth surface somewhere in the region then catapulted numbers of melted silica ejecta with vast volume of dust into the sky. The melted silica ejecta were solidified into splash-form tektites with various shapes while they were in the high sky. After that the tektites had fallen down and remelted into a plastic form prior to reach the ground surface and then solidified as a tektite deposit followed by larger-sized sediments and angular quartz fragments forming a fining upward sedimentary structure. The finer sediments were gradually settled down forming a bright reddish brown structureless sand deposit, the Yasothon soil series. This meteoritic impact event occurred at about 0.77 Ma ago as the evidence of the previous tektite radiometric dating.     

青藏高原隆升动力学与阿尔金断裂

青藏高原最晚一期也是最强烈的一期隆升发生在1-0.8Ma,与印度洋中脊三联点附近的“亚澳”陨击事件有关,陨击事件引起印度洋的快速扩张并导致印度板块在锡瓦利克带的强烈（A型）俯冲,正是这次俯冲引起了青藏高原及其外围山脉的快速隆升,中国西北的盆-山地貌因此而形成,其中东昆仑山推覆隆升近3000m,向北推挤近400km,是柴达木盆地,河西走廊新生界构造变形的主因,因此,“亚澳”陨击事件的影响,提供了青藏高原最晚一期隆升和中亚与中国西部大陆构造形成的大陆动力学背景;根据近年对阿尔金断裂带内同变形期新生矿（102-85Ma)近于同步,其累积错距达350-400km,晚白垩世一新生代同步错移了两侧原有的构造带和原型盆地。这为中国西部找矿,找油气的战略评估提供了一个新的思路。