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。     

古地理和古地形三维再造的发展趋势

“模拟技术”是当今科学研究的主要手段之一,把它应用于地质学的某些方面,能取得很好的效果,如盆地模拟已经发展到了比较成熟的阶段。但在古地理和古地形再造方面,国内外在这方面的研究甚少,尤其是在三维模拟方面。根据Hay等(1989)提出的物质平衡理论,在给定时间间隔内,作用在研究区表面的构造、侵蚀和沉积过程所造成的沉积物的侵蚀总量与沉积总量之间物质守恒,与古地形再造和古地理重建相结合,用三维数值模型来模拟研究区域的变化过程,用GIS技术把这个变化过程的动态显示出来,是一项具有理论意义和实践意义的工作。     

Mesozoic and Cenozoic reconstructions of the South Atlantic

The movement of Antarctica with respect to South America has a number of implications for paleocirculation as well as for the reconstructions of Gondwanaland. Recent papers on the Southwest Indian Ridge have published new or revised poles of opening for Africa and Antarctica which can be combined with the poles of opening between South America and Africa to give resultant motions between South America and Antarctica.The first indication of a complete closure between South America and the Antarctic Peninsula is at anomaly 28 time (64 Ma) as the two continents are now configured. Between anomaly 28 time (64 Ma) and anomaly M0 time (119 Ma) the amount of closure does not change greatly, and the small computed overlap can be explained by minor uncertainties in the rotation poles used for the reconstructions or some slight extension between East and West Antarctica. By 135 Ma some rotation or translation of the Antarctic Peninsula with respect to East Antarctica must be postulated in addition to any presumed extension between East and West Antarctica in order to avoid an overlap of South America with the Antarctic Peninsula.Having determined what we feel to be a viable reconstruction of Western Gondwanaland and holding South America fixed, we rotated Africa and Antarctica, with respect to South America, for eight different times during the past. Africa moved away from South America in a more or less consistent manner throughout the time period, closure to present, while Antarctica moved away from Africa in a consistent manner only between 160 Ma and 64 Ma. At 64 Ma its motion changed abruptly: it slowed its north-south motion with respect to Africa and began slow east-west extension with respect to South America. This change supports the hypothesis that a major reorganization of the triple junction between Africa, Antarctica and South America occurred between 60 and 65 Ma. The triple junction changed from ridge-ridge-ridge to ridge-fault-fault at the time of the major westward jump of the Mid-Atlantic Ridge just south of the Falkland-Agulhas Fracture Zone.The Mesozoic opening of the Somali Basin moved Madagascar from its presumed original position with Africa in Gondwanaland. The closure of Sri Lanka with India produces a unique fit for India and Sri Lanka with respect to Africa, Madagascar and Antarctica. This fit juxtaposes geological localities in Southeast India against similar localities in Enderhy Land. East Antarctica. The late Jurassic opening in the Somali Basin is tied to opening of the same age in the Mozambique Basin. Since this late Jurassic movement represents the initial break-up of Gondwanaland, it is assumed that similar movement must have occurred in what is now the western Weddell Sea and may also explain the opening evidenced by the Rocas Verdes region of southern South America.     

Analysis of kames for palaeogeographical reconstructions

A well-pronounced order in the vertical and horizontal arrangement of sediments was observed in the kames ridges occurring within the compass of the Middle Polish (Riss) glaciation on the Lódź Upland in Central Poland. The order was also noticed in the distribution of the kamc sediments and in the directions of dips of layers. Palaeogeographical conclusions could be drawn concerning the mechanism of waning of the dead-ice cover, the directions of outflow of the ablation waters, the relief of surface underlying the glacier and its influence upon the present-day relief. Analysis of the Pleistocene kames brings new elements into the discussion on the course and extension of postglacial, mainly periglacial, denudation of the kamc landscape.     

The emergence of multiplex dynamics between information provision ties and rescue collaboration ties: a longitudinal network analytic approach to flooding cases in Myanmar

Natural Hazards - In disaster response processes, collaborations among multiple organizations are vital for effective disaster management. This study examined how multiplex ties concerning...     

Tectonostratigraphy as a basis for paleotectonic reconstructions

Tectonostratigraphy deals with distinguishing megasequences and their interpretation in terms of tectonic settings. It is closely related to sequence stratigraphy and regional tectonics. Tectonosratigraphic units are distinctly displayed on seismic profiles. Examination of megasequences is a reliable tool for regional-scale research. We discuss, using several specific examples, the process of identifying tectonostratigraphic units in various types of sedimentary basins, as well as their relations to chronostratigraphic units.     

Identification of paleosol types and their applicability for paleoclimatic reconstructions

Genetic diagnostics of paleosols are based on the morphology of soil profiles, on the combination of the stable properties of microstructure and on the mineral composition of soils (taking into account diagenetic transformations). As a result of spatial paleopedological reconstructions performed both at a level of the structure of soil cover (study of paleosols in the catena) and at the zonal-provincial level allowed to compile soil maps of Eastern Europe for the Mikulino Interglacial (125 ka BP), the Bryansk Interstadial (32 to 24 ka) and the Holocene climatic optimum (5.5 ka). These data can be used for paleoclimatic reconstructions.     

Early Cretaceous sedimentary provenance and structural evolution of the central Sanandaj–Sirjan Zone,Iran: implications for palaeogeographic reconstructions of the northern Neo-Tethyan margin

ABSTRACT

The Early Cretaceous was an important epoch in the evolution of the Earth system in which major tectonic episodes occurred, especially along the Alpine–Himalayan belt. The paucity of reliable palaeogeographic data from the central segment of this geological puzzle, however, hampers the reconstruction of a panoramic view of its Early Cretaceous palaeogeography and geodynamic setting. Here we present multidisciplinary provenance data from Lower Cretaceous strata of the overriding plate of the Neo-Tethyan subduction zone (the Sanandaj–Sirjan Zone; SSZ, of central Iran), including structural, basin-fill evolution, petrographic and geochemical analyses. Sandstone provenance analysis of Lower Cretaceous red beds suggests the occurrence of sub-mature litho-quartzose sandstones attributed to an active continental arc margin in convergent setting predominantly derived from plutonic, quartzose sedimentary and metamorphic rocks exposed in the central SSZ. Weathering indices indicate moderate chemical weathering in the source area which may be related to close source-to-sink relationships or arid climate. Our palaeogeographic reconstructions and original geological mapping indicate that the erosion of uplifted basement rocks exposed in horst blocks provided the sediment sources for the syn-extensional deposition of uppermost Jurassic–lowermost Cretaceous conglomerates and Lower Cretaceous siliciclastic red beds within a continental retro-arc basin during initiation of the ‘Neo-Tethys 2?. The polyphase tectonic reactivation along the principal fault of the study area controlled the syn- and post-extensional tectonostratigraphic evolution that reflect the corresponding mechanical decoupling/coupling along the northern Neo-Tethyan plate margin.     

Gabbro-granite intrusive series and their indicator importance for geodynamic reconstructions

One of the problems faced by researchers when paleogeodynamic reconstructions are carried out for deeply eroded orogenic terranes is the limited usage of geological and isotopic geochemical data on volcanic associations. The utilization of information on gabbroids and granitoids considered separately also fails to resolve this problem. The convergence of features of arc, collisional, and within-plate magmatic processes leads the researcher to search for indicator plutonic associations, such as paired gabbrogranite intrusive series. The latter were distinguished using geoinformation databases (including those compiled by the authors of this paper), which were composed for the Early Caledonides in the Altai-Sayan folded area and adjacent territories. This makes it possible to characterize mantle-crustal magmatism in suprasubductional and collisional environments and the conditions under which these geodynamic regimes (plate- and plume-tectonic factors) interact. This paper presents estimates of the composition of the parental basic magmas, distinctive features of their differentiation, and the compositional specifics of the accompanying extensive granite-forming processes. The example of the Altai-Sayan folded area and adjacent territories is employed to correlate the composition of the basic-ultrabasic and granitoid magmas and, on this basis, distinguish (a) differentiated gabbro-tonalite-plagiogranite intrusive series corresponding to accretionary-collisional geodynamic environments, and (b) gabbro-monzonite-granosyenite-potassic granite intrusive series, which were produced when the accretionary-collisional system was affected by a plume.     

Merging chironomid training sets: implications for palaeoclimate reconstructions

Icelandic and Norwegian chironomid calibration or training sets were merged to investigate whether a larger combined training set would be useful to apply to subfossil chironomid data from Iceland for periods such as the early Holocene, the Holocene Thermal Maximum and the Little Ice Age, when temperatures can be expected to be outside the current temperature range of the Icelandic training set. Following taxonomic harmonisation, the Icelandic and Norwegian data sets were compared before being merged to form a combined Norwegian-Icelandic training set. Analyses showed that it was biologically and statistically valid to merge the two data sets. The resulting combined inference model for mean July air temperature had improved performance statistics (r²_jack = 0.87; RMSEP_jack = 1.13) when compared to the best performing Icelandic model (r²_jack = 0.61; RMSEP_jack = 0.83), due to the longer environmental gradient covered (Icelandic 6–11 °C; combined 3.5–16 °C), and to the increased number of samples (Icelandic = 53 lakes; combined = 207 lakes) and taxa (Icelandic = 47 taxa; combined = 133 taxa) present within the combined training set. The inference models were applied to an early Holocene chironomid sequence from Vatnamýri, north Iceland, and a 450-year recent record from Myfluguvatn, north-west Iceland, to compare the reconstructions produced. The various inference models produced similar trends and patterns of temperature reconstruction, but the inference model based on the combined training set produced a larger range of reconstructed temperatures than the Icelandic model. It was found that different inference models produced more variation in the reconstruction than when different training sets were used. A comparison of the Myfluguvatn reconstructions with meteorological observations showed that the combined Norwegian–Icelandic inference model produced more reliable results than the Icelandic or Norwegian inference models alone.     

过去千年ENSO演化历史重建再分析

厄尔尼诺-南方涛动（El Niño-Southern Oscillation,简称ENSO）作为气候系统内部变率的最显著模态,对全球气候变化起到重要影响。利用珊瑚、树轮等气候代用记录对ENSO进行重建研究能够帮助我们认识气象仪器观测之前历史时期ENSO的变化规律,但由于气候代用记录和重建方法的不确定性导致目前对过去千年ENSO变化特征及其机理仍不明确。文章从气候代用记录和重建方法两方面对目前已公开发表的21条ENSO重建序列进行了评估。结果发现：在1146~1335年和1627~1757年,已有ENSO重建序列之间存在明显不一致现象,1146~1335年相关性差,可能与北美低纬树轮对ENSO响应不一致有关,而1627~1757年相关性差,可能与热带西太平洋珊瑚对ENSO的记录能力下降有关;同时,在过去千年,ENSO年际振幅变化在现代暖期呈显著上升趋势,而年代际振幅变化在中世纪暖期呈显著下降趋势,并且ENSO振幅存在多年代际周期振荡,其振幅的年际-年代际变化可能均与热带太平洋气候平均态有关。讨论和评估现有的ENSO重建结果有助于更好地了解不同重建之间的异同性,对进一步准确认识ENSO变化规律提供集成证据。

     

Late Pleistocene equilibrium-line reconstructions in the northern Peruvian Andes

Equilibrium-line-altitude (ELA) reconstructions using the toe-to-headwall-altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes (7–10°S; 77°20'–77°35'W), indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2) were c . 4300 m in the Cordillera Blanca, c . 3900–3600 m on the west side of the Cordillera Oriental, and c . 3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged from c . 700 m in the Cordillera Blanca to c . 1200 m on the east side of the Cordillera Oriental. This augments data from many mountain ranges in middle- and low-latitude regions that indicate that ELAs during the LGM were depressed by c . 1000 m. Published palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (> 5–6°C) that greatly exceeded the tropical sea-surface temperature depression estimates of CLIMAP (< 2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have been even steeper during the LGM.     

Carbon and oxygen isotopic composition of the Vendian-Cambrian carbonate rocks and paleoecological reconstructions

The carbon isotopic composition of carbonate rocks is widely used for the reconstruction of sedimentation paleoenvironment. Of special interest is the study of the Upper Proterozoic-Cambrian interval—the turning point in the Earth’s geological evolution. Rocks of this age show the widest variations in the carbon isotopic composition of carbonates typically correlated with epochs of global glaciations and change in the CO₂ regime. In this paper, we attempted to show that carbon isotopic variations often indicate postsedimentary alterations of carbonates and reflect the specific geochemical transformations of the rocks. Study of variations of carbon and oxygen isotopic compositions in the Vendian-Cambrian rocks provide insight into lithogenetic processes.     

Effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals

The integrity of coral-based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post-depositional alteration on coral skeletal geochemistry. Here we combine millimeter-scale and micro-scale coral Sr/Ca data, scanning electron microscopy (SEM) images, and X-ray diffraction with previously published δ¹⁸O records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub-fossil corals from the central tropical Pacific. In a 40-year-old modern coral, we find secondary aragonite is associated with relatively high coral δ¹⁸O and Sr/Ca, equivalent to sea-surface temperature (SST) artifacts as large as −3 and −5 °C, respectively. Secondary aragonite observed in a 350-year-old fossil coral is associated with relatively high δ¹⁸O and Sr/Ca, resulting in apparent paleo-SST offsets of up to −2 and −4 °C, respectively. Secondary Ion Mass Spectrometry (SIMS) analyses of secondary aragonite yield Sr/Ca ratios ranging from 10.78 to 12.39 mmol/mol, significantly higher compared to 9.15 ± 0.37 mmol/mol measured in more pristine sections of the same fossil coral. Widespread dissolution and secondary calcite observed in a 750-year-old fossil coral is associated with relatively low δ¹⁸O and Sr/Ca. SIMS Sr/Ca measurements of the secondary calcite (1.96-9.74 mmol/mol) are significantly lower and more variable than Sr/Ca values from more pristine portions of the same fossil coral (8.22 ± 0.13 mmol/mol). Our results indicate that while diagenesis has a much larger impact on Sr/Ca-based paleoclimate reconstructions than δ¹⁸O-based reconstructions at our site, SIMS analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of Sr/Ca which can be used to derive paleo-SSTs.     

Late Quaternary ice age climates of tropical Australasia: Interpretations and reconstructions

Paleoecological and paleogeographical evidence is used to mold a framework from which the basic parameters of the late Quaternary glacial-age climate of tropical Australasia can be inferred. The theory of physical circulations, a knowledge of present tropical circulation patterns, and a study of anomalous and extreme events in the present era are used to reemphasize the view of a less pluvial tropical and subtropical zone at that time. Cooler sea-surface temperature, cooler trades, and the effect of the then exposed land areas are indicated as instrumental in producing drier conditions. Tropical areas west of Cape York Peninsula and Torres Strait were subject to fewer tropical disturbances and were similar to the present tropical savannah of the northern interior of Australia. Such effects would exist even without shifts in major climatic zones, although they are shown to be consistent with an equatorward shift of the westerlies brought about by the increased pole to equator temperature gradient. Paleoenvironmental evidence from the New Guinea Highlands and southeastern Australia suggests that their climates were anomalous. Substantial data of the glacial period in New Guinea show snow lines to be 1000 to 1500 m lower than at present which matches a 6 to 8°C lowering of temperature in highland New Guinea. The deep-sea cores of the CLIMAP Project suggest a mere 2°C cooling of the surrounding tropical oceans. It is shown that it is highly unlikely that an upper-level decrease in temperature of 6 to 8°C could be maintained while the surface cools by only 2°C. It is suggested that either the temperature of the tropical oceans of the western Pacific were overestimated by CLIMAP or that cold air incursions from higher latitudes (for which some analogs exist today) were sufficiently frequent to allow the maintenance of a snow line well below the freezing level of the ancient ambient tropical atmosphere. It is shown that in southeastern Australia considerable evidence of aridity cannot be explained by merely displacing the westerlies more equatorward. To account for the aridity, a new circulation pattern is proposed. Noting that there is CLIMAP evidence of preferred equatorward extension of sea ice, a pattern is postulated that displays only small seasonal change and is characterized by an enhanced Indian Ocean trough, marked ridging at eastern Australian longitudes, and a further trough in the western Tasman. Such a basic flow is consistent with (i) a low rainfall over southeastern Australia, (ii) frequent cold outbreak conditions favorable for the maintenance of the New Guinea glaciers, and (iii) considerable precipitation to nourish the ice caps of Tasmania and the Australian and New Zeland Alps.