南沙群岛永暑礁晚全新世软体动物记录与古环境变化

对南沙群岛永暑礁南永3井软体动物的丰度、营养结构、化学元素和堆积速率的定量分析表明,晚全新世永暑礁漏湖经历了数次相对开放与封闭、与外海交流时强时弱以及盐度多次显著变化的过程。与氧同位素和北半球晚全新世快速气候事件的进一步对比表明,晚全新世快速变化的气候事件也波及到南海,由此造成的溺湖水动力环境、古盐度和沉积速率的变化深刻地影响着软体动物的发育。基于软体动物的替代指标和氧同位素变化的综合分析,初步划分了晚全新世永暑礁漏湖7个变化阶段。     

HYDROLOGY AND MICROCLIMATE OF A PARTLY RESTORED CUTOVER BOG,QUÉBEC

Peatlands do not readily return to functional wetland ecosystems after harvesting (cutting), because the harsh hydrological and microclimatic conditions are unsuitable for Sphagnum regeneration. In this study, drainage ditches blocked after harvesting restored the water balance to a condition similar to a nearby natural bog. Evaporation averaged 2.9 and 2.7 mm day⁻¹ on the cutover and natural bog, respectively. Evaporation consumed most of the rainfall input (86 and 80%, respectively), whereas runoff was minor at both sites (6 and 4%, respectively). However, the water table position was markedly different at these sites. Median water table depth was 0.05 m below the surface in the natural bog, compared with 0.44 m in the cutover bog (ditches blocked). Changes to the peak soil matrix owing to drainage and cutting reduced the specific yield (Sy) of the peat to 0.04–0.06 from 0.35–0.55, causing exaggerated water table changes in the cutover site. Nevertheless, volumetric soil moisture in the cutover site (0.67 ± .08) had low variability, and was maintained above moisture contents found in Sphagnum hummocks in the natural bog (0.48 ± .10), although less than on Sphagnum lawn (0.84 ± .11). Poor Sphagnum regeneration on cutover surfaces can therefore be attributed to its inability to extract water from the underlying peat, which retains water at matric suction greater than the non-vascular Sphagnum can generate. The corrupted iron pan under main ditches has permitted partial recharge of the underlying aquifer, reducing local hydraulic gradients, thereby decreasing vertical seepage loss.     

QUANTIFYING UNCERTAINTY IN USING MULTIPLE DATASETS TO DETERMINE SPATIOTEMPORAL ICE MASS LOSS OVER 101 YEARS AT KÅRSAGLACIÄREN,SUB‐ARCTIC SWEDEN

Glacier mass balance and mass balance gradient are fundamentally affected by changes in glacier 3D geometry. Few studies have quantified changing mountain glacier 3D geometry, not least because of a dearth of suitable spatiotemporally distributed topographical information. Additionally, there can be significant uncertainty in georeferencing of historical data and subsequent calculations of the difference between successive surveys. This study presents multiple 3D glacier reconstructions and the associated mass balance response of Kårsaglaciären, which is a 0.89 ± 0.01 km² mountain glacier in sub‐arctic Sweden. Reconstructions spanning 101 years were enabled by historical map digitisation and contemporary elevation and thickness surveys. By considering displacements between digitised maps via the identification of common tie‐points, uncertainty in both vertical and horizontal planes were estimated. Results demonstrate a long‐term trend of negative mass balance with an increase in mean elevation, total glacier retreat (1909–2008) of 1311 ± 12 m, and for the period 1926–2010 a volume decrease of 1.0 ± 0.3 × 10^–3 km³ yr^–1. Synthesising measurements of the glaciers’ past 3D geometry and ice thickness with theoretically calculated basal stress profiles explains the present thermal regime. The glacier is identified as being disproportionately fast in its rate of mass loss and relative to area, is the fastest retreating glacier in Sweden. Our long‐term dataset of glacier 3D geometry changes will be useful for testing models of the evolution of glacier characteristics and behaviour, and ultimately for improving predictions of meltwater production with climate change.     

Regional Geobarometry in the Contact Aureoles of the Anorthositic Nain Complex, Labrador

The 1.4 Gyr anorthositic Nain complex was emplaced by multipleintrusion into Archean and Aphebian rocks whose metamorphicgrades range regionally from greenschist to granulite and whosetemperature at the time of emplacement was probably no higherthan 200–300 °C. Using experimental data on Ga-Cdand Hy-Ol-Qz equilibria, compositional studies allow the determinationof contact metamorphic pressures and temperatures for samplesover an area > 10,000 km². The results indicate that forthese specimens temperatures ranged from 645° to 915 °Cand pressures ranged from about 3.7 to 6.6 kbar. Locally, originalgarnet porphyroblasts have partially reacted to produce symplectitesof cordierite+hypersthene, resulting in a corona-like texture.These textures and associated mineral zoning indicate that someof the specimens have experienced a polymetamorphic history.This poly metamorphism presumably resulted from the multipleintrusions of magmas of the Nain complex. The regional distributionof pressures appears systematic and suggests an arch in theancient pressure surfaces (paleo-isobars). This postulated arch,which trends WNW-ESE, roughly coincides with a proposed grabenstructure in the Conrad discontinuity based on gravity studies(Stephenson, 1974). The association of these two features canbe rationalized with a mechanism of incipient continental rifting.The emplacement of the unmetamorphosed northern Labrador anorthositemassifs in a non-orogenic environment of low temperature andmoderate depth suggests that the metamorphosed anorthositessouth of the Grenville Front may have been accidental participantsin a post-anorthosite Grenville orogeny and metamorphism.     

Imbricate thrust stack model for the formation of glaciotectonic rafts: an example from the Middle Pleistocene of north Norfolk, UK

In this article, we present a glaciotectonic model for raft emplacement based on a study of large-scale and small-scale deformation structures associated with the accretion of chalk rafts at three Middle Pleistocene sites on the north Norfolk coast, eastern England. Detailed structural measurements taken from the three localities indicate an overall sense of ice movement and raft emplacement towards the south/southeast, suggesting a source area for the rafts located to the north of the present Norfolk coast in the offshore area of the North Sea. Provenancing of the chalk rafts, based on analysis of the foraminifera, also indicates a northern nearshore provenance for the chalk. Mechanisms for the detachment, transport and accretion of the rafts are explored, and it is concluded that pressurized pore water played an important role in all three phases. An imbricate thrust stack model of glaciotectonic raft generation is presented, with the structural history of raft emplacement explained by the geometric relationships between the large-scale basal shear planes and associated deformation structures within adjacent preglacial and glacial sediments.     

Patterns in the crust: a key to ore discovery

Modern exploration geologists are confronted by a mass of information on the characteristics and localization of mineral deposits. Even so, the search for new economic deposits can be expensive and unrewarding. A theory developed by Tim O'Driscoll, consultant to the Australian mining giant Western Mining Corporation, attempts to explain the distribution of mineral deposits in terms of major crustal lineaments. The theory poses questions regarding the evolution of the Earth and planets, and creates problems for current plate tectonic theory.     

Olympic Dam: a giant Australian ore deposit

Events leading to the discovery of one of the world's largest accumulations of metals show that original thinking coupled with geological persistence can pay big dividends for mineral explorers. Ideas on the origin and method of emplacement of this orebody have changed since exploration began in the 1970s, but available ore resources are sufficient to support a major mining operation well into the next century.