Post Gondwana breakup evolution of the SE Australia rifted margin revisited

Low‐temperature thermochronology (LTT) is commonly used to investigate onshore records of continental rifting and geomorphic evolution of passive continental margins. The SE Australian passive margin, like many others, has an elevated plateau separated from the coastal plain by an erosional escarpment, presumed to originate through Cretaceous rifting prior to Tasman Sea seafloor spreading. Previous LTT studies have focused on reconciling thermal histories with development of the present‐day topography. New apatite LTT data along an escarpment‐to‐coast transect define a classic “boomerang” (mean track length vs. fission‐track age), indicating variable overprinting of late‐Palaeozoic cooling ages by a younger, mid‐Cretaceous cooling event. Regionally, however, the boomerang trend diverges NNW away from the coast and crosses the escarpment, implying the underlying thermal history pre‐dates escarpment formation and is largely independent from post‐breakup landscape evolution. We suggest that Cretaceous cooling might relate to erosion of Permo‐Triassic sedimentary cover from a formerly more extensive Sydney Basin.     

Feeding dynamics of the invasive gastropod Tarebia granifera in coastal and estuarine lakes of northern KwaZulu-Natal,South Africa

Gut fluorescence and carbon budget techniques were applied to Tarebia granifera (shell height 10–12 mm) at the iSimangaliso Wetland Park, a UNESCO World Heritage Site. This snail has recently invaded a number of estuaries in northern KwaZulu-Natal, where it reaches densities of over 1000 ind. m^?2 and becomes a dominant component of the benthic community. Its rapid establishment and spread have raised concerns about potential top-down impacts on the ecosystem. This study shows that T. granifera can utilize large amounts of microphytobenthos (MPB) in addition to detritus. In situ total available MPB pigment concentrations ranged from 11.6 to 110.5 mg pigm. m^?2. T. granifera’s gut pigment content ranged from 54 to 1672 μg pigm. ind^?1. Gut evacuation rates (k) ranged from 0.36 to 0.62 h^?1 (R² range: 16.2–35.2, P < 0.05). Individual ingestion rates ranged from 6.6 to 30.4 μg pigm. ind.^?1 d^?1. T. granifera was estimated to consume from 0.5 to 35% of the total available MPB biomass per day, or 1.2–68% of the daily primary benthic production. The carbon component estimated from the gut fluorescence technique contributed 8.7–40.9% of the total gut organic carbon content. The average carbon daily ration contributed by microalgal biomass was ≈16% body carbon per day. Variability in the data was attributed to the complex feeding history of snails. Further studies are needed to validate these results and provide more information on the ecological impact of T. granifera on this wetland and other similar invaded ecosystems, both estuarine and freshwater.     

A detailed post‐IR IRSL dating study of the Niuyangzigou loess site in northeastern China

In this study, we report standard quartz SAR OSL and post‐IR infrared (IR) stimulated luminescence (post‐IR IRSL; pIRIR₂₉₀) measurements made on sand‐sized quartz and K‐feldspar extracts from the loess‐palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR_50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ~15 and ~80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ～800 Gy. Otherwise, the dose recovery ratio deviates from unity. The D_e values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR₂₉₀ results are compared with multiple elevated temperature ‐pIRIR (MET‐pIRIR) data. It appears that the low temperature MET‐pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR₂₉₀ results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ~10% signal loss occurs in pIRIR signals. Long‐term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR₂₉₀ signal is reached after ~300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR_50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol.     

El Niño–Southern Oscillation diversity and Southern Africa teleconnections during Austral Summer

Climate Dynamics - A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–Southern Oscillation events of 1950–2010, which have occurred...     

石榴石Lu-Hf、原位独居石U-Pb定年对多期变形的时代制约——以北祁连托勒牧场为例

多期变质变形事件的精确年代限定是造山构造年代学研究的热点问题之一。本文尝试运用面理弯切轴测量技术,结合石榴石Lu-Hf和原位独居石U-Pb定年,厘定北祁连托勒牧场地区石榴石和斜长石斑晶记录的两期构造变形事件:石榴石斑晶生长记录的早期构造变形事件年代为512.3±2.7Ma;斜长石斑晶生长记录的晚期构造变形事件年代不早于481.0±2.3Ma,并推断该期构造变形水平挤压主应力方向为北东-南西。斜长石斑晶内未发现独居石,用于年代学测试的独居石颗粒均位于斜长石斑晶外基质中。显微构造分析认为,独居石生长不早于斜长石斑晶。481.0±2.3Ma的独居石U-Pb年龄,应为斜长石斑晶所记录构造变形的时代下限。结合前人锆石U-Pb定年和Hf同位素研究结果分析认为,获得的512.3±2.7Ma石榴石-全岩Lu-Hf等时线年龄,代表了祁连洋俯冲过程中石榴石的生长时间,后期变质变形作用未对石榴石的Lu-Hf同位素体系产生明显影响。结合显微构造分析,石榴石Lu-Hf定年可为早期构造变形提供有效年代学制约。     

Origin of Carboniferous sandstones fringing the northern margin of the Wales‐Brabant Massif: insights from detrital zircon ages

A study of detrital zircon age populations in Namurian–Westphalian (Carboniferous) sandstones in the southern Central Pennine Basin of the UK has revealed considerable complexity in their provenance history. The Pendleian–Marsdenian Morridge Formation, which is known to have been derived from the Wales‐Brabant Massif to the south on the basis of palaeocurrent and petrographic information, is dominated by zircons ultimately derived from the Caledonian belt to the north. These zircons were recycled from sandstones of northern origin that had been previously deposited over the massif during Middle to Late Devonian times. The Morridge Formation also includes Late Neoproterozoic zircons of local Wales‐Brabant Massif origin. The south lobe of the Yeadonian Rough Rock has been previously interpreted as having a complex provenance including sediment of northern origin interbedded with sediment ascribed to a Wales‐Brabant Massif source. However, the zircon spectrum lacks a Late Neoproterozoic component that would have been diagnostic of input from the Wales‐Brabant Massif, and the provenance history of the Rough Rock south lobe therefore remains enigmatic. The Langsettian Ludgbridge Conglomerate is dominated by Late Neoproterozoic zircons of Wales‐Brabant Massif origin, but even in this evidently proximal deposit, the provenance is complex since the main zircon group (ca. 640 Ma) cannot be matched with known local Neoproterozoic basement sources. The data either indicate the presence of hitherto‐unknown magmatic rocks of this age adjacent to the South Staffordshire coalfield or indicate that the zircons were recycled from sediment with a more distal origin. Finally, the Duckmantian Top Hard Rock contains zircons that can be reconciled with a source in the Irish Caledonides, consistent with the palaeocurrent evidence, supplemented by zircons derived from the Wales‐Brabant Massif, possibly including the Monian Composite Terrane of Anglesey. The study reinforces the important message that failure to recognize the presence of recycled zircon could lead to erroneous reconstructions of sediment provenance and transport history. Copyright © 2014 John Wiley & Sons, Ltd.     

David Mark’s contribution to ethnophysiography research

This article describes Professor David Mark’s considerable contributions over the last 11 years to research in Ethnophysiography, the study of terms used for landscape features in different languages, and toponyms (place-names). His preceding research is briefly discussed to provide a summary of the foundation from which ethnophysiography emerged. This article describes the key stages of development of this new field, including David Mark’s collaborations with Andrew Turk, David Stea, and others. It briefly summarizes the key theories used and the two ethnophysiography case studies undertaken thus far. This article provides an overview of how this collaborative transdisciplinary area of research has developed. It highlights the importance of David Mark’s scholarship in this process and indicates some of the impacts of the research.     

The regional forcing of Northern hemisphere drought during recent warm tropical west Pacific Ocean La Niña events

Northern Hemisphere circulations differ considerably between individual El Niño-Southern Oscillation events due to internal atmospheric variability and variation in the zonal location of sea surface temperature forcing over the tropical Pacific Ocean. This study examines the similarities between recent Northern Hemisphere droughts associated with La Niña events and anomalously warm tropical west Pacific sea surface temperatures during 1988–1989, 1998–2000, 2007–2008 and 2010–2011 in terms of the hemispheric-scale circulations and the regional forcing of precipitation over North America and Asia during the cold season of November through April. The continental precipitation reductions associated with recent central Pacific La Niña events were most severe over North America, eastern Africa, the Middle East and southwest Asia. High pressure dominated the entire Northern Hemisphere mid-latitudes and weakened and displaced storm tracks northward over North America into central Canada. Regionally over North America and Asia, the position of anomalous circulations within the zonal band of mid-latitude high pressure varied between each La Niña event. Over the northwestern and southeastern United States and southern Asia, the interactions of anomalous circulations resulted in consistent regional temperature advection, which was subsequently balanced by similar precipitation-modifying vertical motions. Over the central and northeastern United States, the spatial variation of anomalous circulations resulted in modest inter-seasonal temperature advection variations, which were balanced by varying vertical motion and precipitation patterns. Over the Middle East and eastern Africa, the divergence of moisture and the advection of dry air due to anomalous circulations enhanced each of the droughts.