一张相图引发的奇迹——论活动论构造—古地理

构造-古地理在地学基础研究与能源矿产勘查中具有重要的指导意义,国内外学者与勘探家进行了长期卓有成效的探索。本文以四川盆地东北部二叠、三叠系礁滩天然气勘探为例,探讨了沉积相图在油气勘探发现中的重要作用,以及活动论思想在相图编制中的指导意义。结果表明,40余年对四川盆地晚二叠世-早三叠世沉积相的研究,引发了长兴组生物礁、飞仙关组鲕滩天然气勘探的突破与普光、龙岗、元坝等大气田的持续发现,相图的创新与发展带来了油气田大发现的奇迹;将盆地与周缘造山带相结合,探索晚二叠世-早三叠世的原型盆地,表明四川盆地内部及周缘在该时期内构造-古地理环境发生了巨大变迁,台地边缘是礁、滩发育的有利场所,台地内凹陷则是烃源岩分布的有利地区;对沉积盆地的复位与复原有助于矿产资源的预测。新一轮活动论"构造-古地理"研究将基于海量地质调查与油、气、煤勘探等资料,大数据时代下的活动论古地理重建必将带来地学的进步与资源勘查的系列发现。     

Paleofloods and ancient fishing weirs in NW Iberian rivers

A 15-m-thick, fluvial sedimentary record of the NW Iberian lower Miño River was studied. Grain-size analyses were performed and twelve samples were dated using optically stimulated luminescence dating techniques, documenting a 1300-yr-old reconstructed fluvial record that does not match with known climate fluctuations in the area, but is linked instead to the construction of a series of ancient fishing weirs (pesqueiras). The sedimentation phases are in agreement with known episodes of increased population density, which suggests active use of the pesqueiras. A number of sedimentation hiatuses in the fluvial record point towards damage to the pesqueiras during large-scale flooding in the Miño River basin, and a sudden drop in population probably due to the arrival of the plague in the 13th century AD. The oldest sedimentation phases started just after 700 AD, and we infer that the first pesqueiras were constructed around this time. This timing coincides with the transition of the NW Iberian landscape towards a more intensively used agricultural landscape, as evidenced from other geo-archeological investigations. The results demonstrate that the pesqueiras are several hundreds of years older than known from historical records, but not so old as to date back to the Roman occupation.     

Border carbon adjustments and the potential for protectionism

Balancing a legitimate fear that carbon leakage could undermine the impact of any global climate change agreement is a countervailing fear that leakage could be the excuse for protectionism in the guise of ‘border carbon adjustments’. This would be dangerous for the world trading system, risking disputes due to ambiguities in the details of World Trade Organization rules over what types of border measures are potentially and actually admissible. Even with good-quality data, there is considerable potential for judgemental discretion, and hence opportunistic manipulation, in estimating the carbon charges to levy on an imported product. This is true even given agreement on whether to use importer or exporter coefficients. A clear distinction needs to be made between environmental and competitiveness motives for border adjustments. The key argument is that the traditional symmetry, between origin (production)-based taxes and other charges (e.g. due to a cap-and-trade scheme) and those based on the destination (consumption) principle, breaks down in the case of carbon charges. The potential is explored for regional agreements to ensure origin as the basis for carbon levies, while recognizing the challenges this poses for the mutual recognition of emissions regimes in particular.     

Changes in the Level of Proteins,Free Amino Acids and Protease Activities of Clarias batrachus in Response to Sodium meta‐arsenite Intoxication

Increased hazard of arsenic toxicity at many provinces of India causing extensive contamination of their wetlands. To illustrate the consequences of the arsenic menace on the aquatic fauna, a nutritionally important freshwater catfish Clarias batrachus (Linn.) was subjected to the stress of sublethal concentration (1 mg/L; 5% of 96‐h LC₅₀ value) of sodium meta‐arsenite. The alterations induced by the arsenic salt on certain biomolecules (proteins, free amino acids (FAA), and protease activities) in five tissue components (muscle, liver, brain skin, and gills) of the fish using biochemical techniques were estimated. Significant (p < 0.01) decrease in the concentration of proteins in all the tissues (19.74–44.84% in muscles; 3.17–49.39% in liver; 10.05–36.16% in brain; 12.62–52.01% in skin and 7.34–61.69% in gills), and significant (p < 0.01) increase in FAA (6.84–269.89% in muscles; 125.89–358.03% in liver; 1.07–152.90% in brain; 29.31–401.62% in skin and 38.53–165.07% in gills), and protease activities (43.59–183.33% in muscles; 19.52–131.90% in liver; 8.85–46.72% in brain; 33.33–261.53% in skin and 25.39–50.79% in gills) of the exposed fish were observed. This increase in amino acids and enzyme activity point out toward breakdown of protein leading to their depletion.     

Cross‐shelf colour zonation in northern Great Barrier Reef lagoon surficial sediments

A cross‐shelf colour zonation is observed in Great Barrier Reef lagoon surficial sediments from 12 to 18°S, with colours tending to lighten from inner to outer shelf. The phenomenon is particularly well defined south of Cairns where four zones occur. The colour zonation appears to reflect the abrupt facies changes that occur in the lagoon. Visual estimates of relative optical lightness for the zones are strongly related to carbonate content, and lightness class boundaries broadly follow carbonate contours, indicating that the mechanisms leading to the colour zones are related to those governing carbonate distribution.     

Geological interpretation of the Cootamundra gravity high,New South Wales

An intense Bouguer anomaly ‘high’ of about 30 milligals amplitude has been delineated to the east of Cootamundra, New South Wales. It is correlated with a north‐trending belt of basic metamorphic rocks of probable Upper Silurian age. The subsurface shape of the belt is deduced by qualitative and quantitative analytical techniques applied to the gravity data; it is inferred that the boundary on the western side is near‐vertical, while that on the eastern side is believed to have been overthrust by the Middle Devonian Young Granite. It appears also that there are no horizontal density variations below a depth of 6–7 km, implying that the base of the Young Granite lies at about this depth.     

Late Holocene island reef development on the inner zone of the northern Great Barrier Reef: insights from Low Isles Reef

A sedimentological and stratigraphic study of Low Isles Reef off northern Queensland, Australia was carried out to improve understanding of factors that have governed Late Holocene carbonate deposition and reef development on the inner to middle shelf of the northern Great Barrier Reef. Low Isles Reef is one of 46 low wooded island-reefs unique to the northern Great Barrier Reef, which are situated in areas that lie in reach of river flood plumes and where inter-reef sediments are dominated by terrigenous mud. Radiocarbon ages from surface and subsurface sediment samples indicate that Low Isles Reef began to form at ca 3000 y BP, several thousand years after the Holocene sea-level stillstand, and reached sea-level soon after (within ～500 years). Maximum reef productivity, marked by the development of mature reef flats that contributed sediment to a central lagoon, was restricted to a narrow window of time, between 3000 and 2000 y BP. This interval corresponds to: (i) a fall in relative sea-level, from ～1 m above present at ca 5500 y BP to the current datum between 3000 and 2000 y BP; and (ii) a regional climate transition from pluvial (wetter) to the more arid conditions of today. The most recent stage of development (ca 2000–0 y BP) is characterised by extremely low rates of carbonate production and a dominance of destructive reef processes, namely storm-driven remobilisation of reef-top sediments and transport of broken coral debris from the reef front and margins to the reef top. Results of the present study enhance existing models of reef development for the Great Barrier Reef that are based on regional variations in reef-surface morphology and highlight the role of climate in controlling the timing and regional distribution of carbonate production in this classic mixed carbonate–siliciclastic environment.     

明代朝贡贸易体制下澳门的兴起及其与广州的关系

明中后期澳门的兴起既是历史选择的一次偶然,也是明代特殊海外贸易政策下的必然结果。文章从明代朝贡贸易和市舶司制度的兴衰入手,探讨澳门兴起的动力机制和主要影响因素,特别是在澳门兴起过程中广州所起的作用以及两者的经济互动。同时,基于明代全国视角下的海外贸易与港口分布的总体格局,综合分析澳门、广州以及隆庆以后的月港这3个在明代后期开放的港口,探讨三者在功能、性质、贸易对象等方面的异同点,进一步论证澳门的兴起在很大程度上受益于明代朝贡贸易体制对海外贸易和港口发展的束缚。正是由于广州在明代后期对外通商的垄断性和不完整性,澳门才能以广州外港的性质互补,从而成为当时最大的东西方国际贸易体系之枢纽。     

Sediment source changes over the last 250 years in a dry-tropical catchment, central Queensland, Australia

Rivers draining to the Great Barrier Reef are receiving increased attention with the realisation that European land use changes over the last  150 years may have increased river sediment yields, and that these may have adversely affected the reef environment. Mitigation of the effects associated with such changes is only possible if information on the spatial provenance and dominant types of erosion is known. To date, very few field-based studies have attempted to provide this information. This study uses fallout radionuclide (¹³⁷Cs and ²¹⁰Pb_ex) and geochemical tracing of river bed and floodplain sediments to examine sources over the last  250 years for Theresa Creek, a subcatchment of the Fitzroy River basin, central Queensland, Australia. A Monte Carlo style mixing model is used to predict the relative contribution of both the spatial (geological) sources and erosion types. The results indicate that sheetwash and rill erosion from cultivated basaltic land and channel erosion from non-basaltic parts of the catchment are currently contributing most sediment to the river system. Evidence indicates that the dominant form of channel erosion is gully headcut and sidewall erosion. Sheetwash and rill erosion from uncultivated land (i.e., grazed pasture/woodland) is a comparatively minor contributor of sediment to the river network. Analysis of the spatial provenance of floodplain core sediments, in conjunction with optical dating and ¹³⁷Cs depth profile data, suggests that a phase of channel erosion was initiated in the late nineteenth century. With the development of land underlain by basalt in the mid-twentieth century the dominant source of erosion shifted to cultivated land, although improvements in land management practices have probably resulted in a decrease in sediment yield from cultivated areas in the later half of the twentieth century. On a basin-wide scale, because of the limited spatial extent of cultivation, channel sources are likely to be the largest contributor of sediment to the Fitzroy River. Accordingly, catchment management measures focused on reducing sediment delivery to the Great Barrier Reef should focus primarily on decreasing erosion from channel sources.